Nanoparticle Emissions From Combustion Engines [1 ed.] 978-3-319-15927-0, 978-3-319-15928-7

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Springer Tracts on Transportation and Traffic STTT

Jerzy Merkisz Jacek Pielecha

Nanoparticle Emissions from Combustion Engines 123

Springer Tracts on Transportation and Traffic Volume 8

Series editor Roger P. Roess, New York University Polytechnic School of Engineering, New York, USA e-mail: [email protected]

About this Series The book series “Springer Tracts on Transportation and Traffic” (STTT) publishes current and historical insights and new developments in the fields of Transportation and Traffic research. The intent is to cover all the technical contents, applications, and multidisciplinary aspects of Transportation and Traffic, as well as the methodologies behind them. The objective of the book series is to publish monographs, handbooks, selected contributions from specialized conferences and workshops, and textbooks, rapidly and informally but with a high quality. The STTT book series is intended to cover both the state-of-the-art and recent developments, hence leading to deeper insight and understanding in Transportation and Traffic Engineering. The series provides valuable references for researchers, engineering practitioners, graduate students and communicates new findings to a large interdisciplinary audience. More information about this series at http://www.springer.com/series/11059

Jerzy Merkisz · Jacek Pielecha

Nanoparticle Emissions from Combustion Engines

ABC

Jerzy Merkisz Institute of Combustion Engines and Transport Poznan University of Technology Poznan Poland

Jacek Pielecha Institute of Combustion Engines and Transport Poznan University of Technology Poznan Poland

ISSN 2194-8119 ISSN 2194-8127 (electronic) Springer Tracts on Transportation and Traffic ISBN 978-3-319-15927-0 ISBN 978-3-319-15928-7 (eBook) DOI 10.1007/978-3-319-15928-7 Library of Congress Control Number: 2015932788 Springer Cham Heidelberg New York Dordrecht London c Springer International Publishing Switzerland 2015  This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. Printed on acid-free paper Springer International Publishing AG Switzerland is part of Springer Science+Business Media (www.springer.com)

Contents

1

Introduction ............................................................................................ References ................................................................................................

1 7

2

Characteristics of Particulate Matter Considering Particle Mass and Particle Number ............................................................................. References ................................................................................................

9 16

The Process of Formation of Particulate Matter in Combustion Engines .................................................................................................... References ................................................................................................

19 24

3

4

Methods of Measuring Particulate Matter Emissions ......................... 4.1 Type-Approval Testing Methods of Particle Mass and Particle Number............................................................................................ 4.2 Integrated Systems for Measuring Particle Mass ............................ 4.3 Systems for Measurement of Particle Number ................................ References ................................................................................................

27 27 37 41 44

5

Particulate Matter Emissions during Engine Start-Up ....................... References ................................................................................................

47 60

6

Determination of Particulate Matter Equivalents ............................... References ................................................................................................

61 67

7

Measurements of Particle Mass and Particle Number in Real Traffic Conditions .................................................................................. 7.1 Determination of Road Emissions of Particulate Matter from Light-Duty Vehicles ........................................................................ 7.2 Tests of Particulate Matter Emissions from Heavy-Duty Vehicles ........................................................................................... References ................................................................................................

69 69 84 90

VI

Contents

8

The Relationship between Particle Mass and Particle Number ......... 8.1 Measurements during Stationary Tests ........................................... 8.2 Measurements in Dynamic Test ...................................................... References ................................................................................................

93 93 105 108

9

Methods of Decreasing Emissions of Particulate Matter in Exhaust Gas ........................................................................................................... References ................................................................................................

109 128

10 Conclusions ............................................................................................. References ................................................................................................

131 137

Key Acronyms

a A A/F ANR ASC B20 B50 B100 b c C CAA CAFE CARB CDPF CEE CIMAC CNG COP CRT CSF D DCS DEP DEPM DEPN DOC DPF e E5 E85 EEA EGR EPA

acceleration surface area air-fuel ratio all new registrations ammonia slip catalyst fuel which is a mixture of rapeseed oil esters (20% v/v) and diesel (80% v/v) fuel which is a mixture of rapeseed oil esters (50% v/v) and diesel (50% v/v) fuel consisting of 100% rapeseed oil esters road emissions concentration coal Clean Air Act Cleaner Air for Europe California Air Resources Board catalysed diesel particulate filter Communauté Economique Européenne Congrés International des Moteurs á Combustion Interne compressed natural gas conformity of production continuously regenerating trap catalysed soot filter the diameter of a solid particle diffusion charge sensor diesel emission particle diesel emission particle (mass) diesel emission particle (number) diesel oxidation catalyst diesel particulate filter specific emission gasoline containing 5% vol. bioethanol gasoline containing 75–85% vol. bioethanol European Environment Agency exhaust gas recirculation Environmental Protection Agency

Key Acronyms

VIII

E ESC ETC EU FAME FBC FFF GDI ge Ge GPF HDV HEV IDI IUPR kj LEV LPG m Mo MPI n NC Ne NEDC NTA OBD OTR p PAC PAH PC PEMS PFF PM PM PMP PM2.5 PM10 PN POC RME RPM SAE SCR SCRF

emission rate European Stationary Cycle European Transient Cycle European Union fatty acid methyl esters fuel borne catalyst full flow filter gasoline direct injection specific fuel consumption fuel flow rate gasoline particulate filter heavy duty vehicles hybrid electric vehicle indirect injection INSOL in use performance emission index low emission vehicles liquid petroleum gas mass engine torque multi point injection engine speed standardized number concentration of particulates effective power New European Driving Cycle new type approval on-board diagnostics on the road opacimeter pressure polycyclic aromatic compounds polycyclic aromatic hydrocarbons passenger car portable emissions measurement system partial flow filter particulate matter particle mass particle measurement programme particles of diameter less than 2.5 µm particles of diameter less than 10 µm particle number particle oxidation catalyst rapeseed methyl esters residual particulate mass Society of Automotive Engineers selective catalyst reduction selective catalyst reduction and filter

Key Acronyms

SOF SOL St t T TPM u W We WHSC WHTC WLTC WLTP v V Z

IX

soluble organic fraction insoluble fraction Stokes number time temperature total particulate matter operating time share volume emission index operation World Harmonized Stationary Cycle World Harmonized Transient Cycle World harmonised Light duty vehicle Test Cycle World harmonised Light duty vehicle Test Procedure speed volume engine load factor (defined as Mo actual/Mo max for a given engine speed)

Chapter 1

Introduction 1 Intro ductio n

Technological development in all fields of industry makes it necessary to reduce its negative impact on the environment. The use of advanced techniques and their developments make it necessary to continuously verify the working conditions of machinery and equipment and to analyse their impact on the environment and civilization. The automotive industry is recognized as a very dynamically developing branch; for this reason it is necessary to reduce, above all, emissions of harmful exhaust gas components. The emission of solid particles is a major threat to humans, and is a barrier to the development of modern internal combustion engines, especially engines with direct fuel injection (both diesel engines and gasoline engines). An important challenge for car manufacturers consists of subsequent projects on toxicity standards, according to which the emissions of particulate matter should be a few times lower than current levels. Apart from introducing improvements to classic propulsion systems (i.e. the internal combustion engine) research is also carried out aimed at searching for nonconventional propulsion systems. Based on the former analysis, however, it can be concluded that by 2050 internal combustion engines will still dominate (Fig. 1.1). Due to the more and more frequent introduction of diesel engines in passenger cars, their total domination among heavy-duty vehicles (HDV) and their use away from roads (off-road), attention should be paid to the issue of particulate emissions

Fig. 1.1 Predicted share of passenger cars in the world by 2050 [11] © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_1

1

2

1 Introduction

from that engine type . In Europe, the share of cars with diesel engines increased to 52% in 2010 [5], which is equivalent to approximately 35 million vehicles (Fig. 1.2). In Germany alone, the sales of passenger cars equipped with diesel engines increased by almost 40% in 2010, in relation to the previous year, while the number of newly registered cars increased by only 10%. The reason for this is, first and foremost, the placing on the market of diesel engines with direct fuel injection (at the beginning of the last decade, these engines represented a few percent of all diesel engines; currently, in some Member States of the European Union they account for more than 75% of total production of diesel engines – Fig. 1.3). The concept of particulate matter (PM) was introduced in the 1970s; usually in measurements on internal combustion engines it means the whole matter, solid or liquid, organic or inorganic, which collects on a filter (of 99% efficiency, which traps particles of dimensions bigger than 300 nm) after the passage of the exhaust stream diluted with air at a temperature of 52 ±3°C [8, 10].

Fig. 1.2 Share of diesel engines in newly registered vehicles in the European Union in years 1994–2010 [7]

Fig. 1.3 Share of diesel engines among newly registered vehicles in selected European Union countries in 2010 [7]

1 Introduction

3

The road and specific emissions of gaseous compounds and particulate matter are determined for diesel engines during a toxicity measurement. Up to 1992, the measurements of particulate matter were limited to passenger cars in Europe and to passenger cars and trucks in the USA. Currently, determination of specific emissions of particulate matter for truck engines is also required for their typeapproval in Europe, and extended to all uses of diesel engines. A gradual reduction of road and specific emission limits of particulate matter, for passenger cars and trucks, respectively, has led to very low emissions (about 99% less than in 1999 – Fig. 1.4).

Fig. 1.4 Changes in European regulations on road and specific emissions of particulate matter [13]

For a long time, vehicles and engines have played an important role in the people’s daily lives. Currently, increased usage of combustion engines for various applications has been observed; the growing number of vehicles and engines is not only a factor for development, but also a threat – burning fuels has a negative impact on human health and also causes environmental pollution, the formation of smog and the greenhouse effect. At the end of the 1990s there was an increase in the worldwide interest in the negative impact of particulate matter on human health [6, 12]. The first document claiming increased mortality due to the toxic impact of particulate matter was published in 1993, as a result of research carried out under the direction of Dockery et al. [2]. The results of these tests were also confirmed in other studies [9]. Previous studies, for example those conducted by the Georgius Agricola and published in ‘De Re Metallica’ (circa 1556), focused on the impact of dust in coal mining on the health of miners.

4

1 Introduction

Particulate matter emissions are a phenomenon occurring mainly in diesel engines. On the basis of the analysis of these engines so far produced and prospects for their development, it can be concluded that there are no problems with the fulfilment of the limiting standards for CO and HC, while it seems to be harder to comply with the requirements limiting the emission of NOx. The particulate matter emission limit is a critical requirement for these engines (Figs 1.5 and 1.6), and therefore the focus of research on the reduction of diesel engine toxicity shifted to an explanation of phenomena related to the formation of particulate matter and reduction of those emissions [4].

Fig. 1.5 Emissions of PM and NOx from diesel engines against the provisions in force provisions in Europe and the USA [14]

Fig. 1.6 Changes in road and specific emissions of particulate matter and nitrogen oxides (in g/kWh) in Europe, the USA and Japan for the years 2004–2014 [15]

1 Introduction

5

The limits for particulaate emissions, as a wider concept, replaced the standardds for smoke (soot in the ex xhaust gas), which are still used in the preliminary annd complementary tests. The concept of particullate matter is ambiguous, because of the following: • • • • •

it cannot be unambigu uously defined, neither physically nor chemically, it is larger than gaseou us molecules, it is not identical in terrms of dimensions and shapes, it is an irregular mixtu ure of chemical compounds, it can be separated (fiiltered; not screened) by using a filter (with pores largeer than the size of the PM M).

Vehicles are the cause of the formation of combustion products and also of paarticulate matter as a resultt of abrasive wear of tires and the friction lining of thhe clutch, brake pads and braake shoes. The current approval regulations prohibit prooduction of these rapidly-w wearing elements from dangerous asbestos, and materiaals contributing to an increasse in the risk of cancer. In this way, the problem of paarticulate emissions was lim mited just to those originating from engine. The harmful effects off solid particles on the environment and living organism ms are due to the fact that beecause of their small dimensions, the particles stay in thhe air for a long time and arre easily absorbed through the respiratory systems of huumans and animals. This enables penetration of the body by heavy metals, nitrogeen a various hydrocarbons (PAC – polycyclic aromattic and sulfur compounds and compounds, PAH – poly ycyclic aromatic hydrocarbons), among which can bbe found substances, which, directly or indirectly, are carcinogens. Increasing awareness of o environmental risks is the reason that many countriees have been issued provisio ons regulating the emission values of toxic compoundds, which has largely contrib buted to the development of studies on the physical annd chemical nature of emissiions and to the search for means of limiting those emiissions. The immediate con nsequence of environmental pollution caused by particlees with a diameter of 2.5 μm m is a reduction in air transparency. For example, a conn3 centration of less than 5 μg/m μ of the aforementioned particulate matter in the aair does not cause significan nt effects, while a concentration of 35 μg/m3 causes thhe phenomenon of smog (Fig g. 1.7).

Fig. 1.7 The impact of particulate matter on air quality (Chicago, summer 2000): a) a concentration of the particles wiith a diameter of up to 2.5 µm of less than 5 μg/m3, b) a concentration of particles with a diaameter of up to 2.5 μm of about 35 μg/m3 [1]

6

1 Introduction

During the measurements of emissions of toxic compounds emitted by combustion engines particular measuring procedures are implemented. This applies to research and development, type-approval tests, as well as to control and approval measurements. However, each type of test to be carried out requires apparatus with different parameters. Tests carried out nowadays on the reduction of combustion engines’ toxicity aim to provide an explanation of phenomena related to the formation of particulate matter and possibilities for reductions of both particle number and particle mass. There is still a need for intense research on the improvement of the operational processes of these engines, and on fuel properties. In this respect, agents improving control over the formation of the combustion mixture and improving combustion itself are particularly promising [3].

References [1] Damberg, R., Wallace, L., Vasu, A.: PM2.5 Implementation Program. EPA Office of Air Quality Planning and Standards, New Orleans (May 18, 2005) [2] Dockery, D.W., Pope, C.A., Xu, X., Spengler, J.D., Ware, J.H., Fay, M.E., Ferris, B.G., Speizer, F.E.: An Association Between Air Pollution and Mortality in Six U.S. Cities. N. Engl. J. Med. 329(24) (1993) [3] Kowalewicz, A.: Systemy spalania szybkoobrotowych silników spalinowych. WKŁ, Warszawa (1990) [4] Merkisz, J., Pielecha, J., Radzimirski, S.: New Trends in Emission Control in the European Union. STTT, vol. 4. Springer, Heidelberg (2014) [5] Schöppe, D., Greff, A., Zhang, H., Frenzel, H., Rösel, G., Achleitner, E., Kapphan, F.: Requirements for Future Gasoline DI Systems and Respective Platform Solutions. In: 34 Internationales Wiener Motorensymposium, Wiena (2011) [6] Schwela, D., Morawska, L., Kotzias, D.: Guidelines for Concentration and exposureResponse Measurement of Fine and Ultrafine Particulate Matter for Use in Epidemiological Studies. European Commission, World Health Organization (2002) [7] The Automobile Industry Pocket Guide. European Automobile Manufacturers Association ACEA, Brussels (2011) [8] United Nations. Agreement concerning the adoption of uniform conditions of approval and re-ciprocal recognition of approval for motor vehicle equipment and parts. Addendum 23: Regulation No. 24 to be annexed to the Agreement. Uniform provisions concerning the approval of vehicles equipped with diesel engines with regard to the emission of pollutants by the engine. E/ECE/324 ECE/TRANS/505 Rev. 1/Add. 23 (August 23, 1971) [9] Vedal, S.: Ambient Particles and Health: Lines that Divide. Journal of the Air and Waste Management Association 47 (1997) [10] Vuk, C.T., Jones, M.A., Johnson, J.H.: The Measurement and Analysis of the Physical Character of Diesel Particulate Emissions. SAE Technical Paper Series 760113 (1976) [11] Warnecke, W., Lueke, W., Clarke, L., Louis, J., Kempsel, S.: Fuels of the Future. In: 27th International Vienna Motor Symposium, Viena (2006)

References

7

[12] World Health Organization (WHO). Health Effects of Transport-Related Air Pollution, Geneva (2005) [13] Worldwide Emissions Standards, Passenger Cars & Light Duty Trucks, Heavy Duty & Off-Road Vehicles, Delphi (2013/2014) [14] Zelenka, B., Zelenka, P.: Meeting EU 4/5 PM Emission Standards: Comparison of Different Par-ticulate Filter Types. In: 10th ETH Conference on Combustion Generated Nanoparticles, Zurich (2006) [15] Zikoridse, G.: Perspektiven der Abgasmestechnik. In: 6 FAD-Konferenz, Dresden, November 5-6 (2008)

Chapter 2

Characteristics of Particulate Matter Considering Particle Mass and Particle Number 2 Characteristics of Particulate Matter Considering Particle Mass

The form, size and composition of particulate matter depend to a large extent on location and temperature within the system: the cylinder – the exhaust system – the surroundings, where, depending on type of tests conducted, the particles are captured for measurements. For this reason, the most widely accepted way of defining particulate matter contains in its formula an element defining the conditions in which the emission measurements were carried out [19]. The solid particles emitted can be divided into two main fractions, which are generally demonstrated in Fig. 2.1: • PMSOF – soluble organic fraction (SOF), which is the part of the particulate matter which is extracted with the use of dichloromethane CH2Cl2, • PMSOL – insoluble fraction (SOL), whose fundamental part is solid carbon (‘solid’, PMC), in a form similar to graphite.

Fig. 2.1 Diagram of the structure of a particle [2] © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_2

9

10

2 Characteristics of Particulate Matter Considering Particle Mass

The other components of PMSOL include: • • • • •

water-soluble sulfates, water associated with sulfates, nitrates, metals, other carbon-containing particles – RPM (residual particulate mass) [2].

Particulate matter contained in exhaust gas is a polydisperse system, consisting of particles of different size, shape and composition. Due to the difficulty in describing particulate matter, as it is an irregular mixture of various chemical compounds and is inhomogeneous in terms of size and shape, it cannot be unequivocally defined physically or chemically [16, 19]. The nature of particles, mainly the distribution of geometric dimensions, the number of particles and their morphology are all important factors when estimating their impact on the environment and the human body. Characteristics of particulate matter formed in a combustion engine can be considered from two points of view: in relation to the fractional composition or to the nature of the particles. The fractional composition of particles, mainly in terms of the soluble and insoluble organic fractions, sulfates, water and soluble organic fractions divided into particles originating from the fuel and the oil, is the object of interest mainly in research and development departments, therefore fractional analysis is performed in many engine laboratories. The term ‘physical properties’ means: dimension, shape and composition of particulate matter. The dimensional distribution of particles emitted by combustion engines is similar to a normal distribution. In numerous publications it is presented in a slightly different form, namely using logarithmic coordinates as a function of the mass or the percentage share of the particles with dimensions smaller than the specified particle diameter. The dimensional distribution is characterized by determining the mean diameter of the particles (the average value of the distribution), or by the median of the distribution, which is such a particle size below which lie 50% of the particles in the sample analyzed [5]. Individual particles that occur separately and those included in aggregates or agglomerates have dimensions of approximately 0.01–0.12 μm [21], with an average particle diameter from 0.025 μm [14] to about 0.05 μm [23]. The dimensions of the particles, as well as their average size, increase with decreasing exhaust gas temperature [6]. At high exhaust gas temperatures, particles with dimensions less than 1 μm account for approximately 96% of the mass of the total emissions, while at low temperatures this quantity is approximately 80% [15]. It is difficult to accept a particular value as a temperature limit, below which there would be a rapid increase in the dimensions of the particles, however, it is believed that the increase appears at temperatures below 160–120°C [13, 16]. The particulate matter emitted by all internal combustion engines (Fig. 2.2) includes solid and liquid particles that, depending on physical conditions (temperature, pressure), are subject to condensation. Individual particles aggregate,

2 Characteristics of Particulate Matter Considering Particle Mass

11

forming agglomerates; the properties of agglomerates (e.g. density, total surface area, size distribution, chemical composition) are different from the properties of individual particles (Fig. 2.3). The presence of sulfur in this fraction is associated mainly with its presence in the fuel (nowadays it amounts to 10 ppm). Sulfur in exhaust gas may occur as SO2 and SO3, creating sulfurous acid and sulfates in the particles emitted. The share of SOF in the particle mass can range from 10% to 90% and it usually increases with a reduction in engine load, when the temperature decreases [3, 19].

Fig. 2.2 The size and the presence of particles in the environment [9]

Fig. 2.3 Parameters characterizing particle agglomerates and single solid particles [8]

Particle size distributions indicate three different formation mechanisms, depending on the stipulated size of the diameter. The greatest population of particles is formed in accordance with the so-called accumulative mechanism (the size of

12

2 Characteristics of Particulate Matter Considering Particle Mass

the surface area under the curve on the diagram), and includes particles with diameters from 80 to 1000 nm (0.08–1.0 μm). These are agglomerates of soot with adsorbed SOF substances. The second, but many times smaller, accumulation of masses of particles is formed according to the nucleation mechanism during dilution and cooling of exhaust gas (after emission of the exhaust gas into the environment). Then the smallest particles are formed, of diameter of 1–80 nm, consisting of substances included in the composition of the volatile fraction of SOF, a small amount of carbon and metal compounds. The third, accumulation of particle masses, also small, is formed by the coarse mechanism and includes particles of large diameters (2.5–40 μm). These are probably the particles created in the course of the accumulative mechanism, which settled on the walls of the exhaust system and then were broken up by the gas flow. Liquid particles with diameters of about 1 µm are usually spherical, while solid particles have complex shapes. In an estimation analysis, the particles’ shapes might be omitted, however, in most situations the equivalent diameters expressing the physical property of a non-spherical particle should be taken into account. Here, equivalent diameter [9] and aerodynamic diameter are widely used. The equivalent diameter in relation to the density is the diameter of a particle which has the same density and speed as the non-spherical particle; the aerodynamic diameter is the diameter of a sphere with a density of 1 g/cm3, with the same settling velocity as the given particle (of any shape and density) in a laminar air flow. Among the many parameters of particulate matter the most important is the diameter; particles are qualified as a given type depending on this value (Figs 2.4 and 2.5) [11, 12]. The current rapid development of research techniques has made it possible to identify and classify solid particles of different sizes (the aerodynamic diameter was assumed as characteristic): D < 10 μm – large particles (designated as PM10), D < 2.5 μm – fine particles (PM2.5), D < 100 nm – very fine particles and D < 50 nm – nanoparticles. Internal combustion engines emit particles of diameter greater than 10 nm. In the exhaust gas from diesel engines, mostly particles of diameter from 60 to 100 nm appear, and from gasoline engines – mostly particles of diameter 50–80 nm; their mass comprises approximately 20% of the estimated mass of all particles [11].

Fig. 2.4 Classification of solid particle sizes

2 Characteristics of Particulate Matter Considering Particle Mass

13

Fig. 2.5 Classification of solid particles on the basis of their dimensions [4]

The PM10 symbol means theoretically solid particles of diameter less than 10 μm; however, in practice the impactors (or other classifiers) do not reach the efficiency enabling only the transmission of particles of diameter of up to 10 μm (usually they enable the transmission of particles of diameter of up to 15 μm). It is assumed that PM10 (or, respectively, PM5, PM2.5) is achieved at 50% collection efficiency of particles of diameter of 10 μm (or, respectively, 5 μm and 2.5 μm). To describe the efficiency of particle transmission the Stokes characteristic number (St) is used, which can be represented as (Fig. 2.6) [7]:

St =

τv rd

(2.1)

where: τ – relaxation time, v – particle speed, rd – nozzle radius. The Stokes number is defined as the ratio of the time required to collect the particle and the radius of the nozzle. The relaxation time is the time needed to adjust the particle speed to the new flow conditions (the new force system); it is defined by the following dependency [20]: τ=

ρD 2 9μ

where: ρ –particle density D –particle diameter µ – viscosity of the medium (air, exhaust gas).

(2.2)

14

2 Characteristics of Particulate Matter Considering Particle Mass

On the basis of equations (2.1) and (2.2), it is possible to calculate the diameter D50 of the particle, which will be transmitted with 50% efficiency of the impactor (assuming that Reynolds numbers range from 500–3000 and the distance of the plate on which the particles are deposited is at least 1.5–times the diameter of the nozzle) [20]: 9 μrd St 50 4 ρv

D50 =

(2.3)

The actual curve of the particle collection efficiency slightly differs from the theoretical curve (too small or too large particles can be collected). Using this value to characterize particulates its physical sense should be kept in mind. The efficiency curve divides all the particle diameters into two equal parts: one half consists of particles of diameter less than D50 and the other of particles of greater diameter. The diameter D50 is therefore a statistical value and it is possible that in the sample analyzed there are no particles of diameter exactly equal to this value (Fig. 2.7).

Fig. 2.6 Construction of a single impactor

Fig. 2.7 Curve of the impactor efficiency for diameter D50 (in this example PM10) [20]

Knowing the dependence between the number of solid particles (PN) and their diameter (D) (Fig. 2.8), the dependence PN = f(D) (or, more briefly: PN(D)), it is possible to characterize the basic numerical parameters for solid particles (for the i-th measuring ranges of diameters):

• particle number (the zero-order moment):

∫

∞

∫

∞

PN = PN( D)dD = N (ln D)d ln D ≈ 0

0

∑ PN i

i

(2.4)

2 Characteristics of Particulate Matter Considering Particle Mass

15

• the diameter of solid particles (the first-order moment):

∫

∫

∞

∞

1 1 D= D ⋅ PN( D)dD = D ⋅ PN(ln D)d ln D ≈ PN PN 0

∑ D PN i

i

i

(2.5)

PN

0

• the surface area of particulate matter (the second-order moment):

∫

∫

∞

∞

A = πD 2 ⋅ PN ( D )dD = πD 2 ⋅ PN (ln D)d ln D ≈ 0

∫

∞

0

• and particle mass:

∫

∞

m= ρ 0

∫6D

∞

π 3 D ⋅ PN( D)dD = 6

2 i

π

3

⋅ PN(ln D)d ln D ≈

π

0

π

3 i

(2.7)

i

i

0

∫ρ6D

∑ 6 D PN

∞

π 3 D ⋅ PN( D)dD = 6

(2.6)

i

i

0

• the volume of particulate matter (third-order moment): V=

∑ πD PN

3

⋅ PN (ln D )d ln D ≈

∑ ρ 6 D PN π

3 i

i

(2.8)

i

Fig. 2.8 Size distribution of particles formed as a result of nucleation and aggregation in the exhaust gas of a combustion engine [10]

16

2 Characteristics of Particulate Matter Considering Particle Mass

Fig. 2.9 Particulate emissions from different types of combustion engines: a) the road emission of particle mass bPM, b) road emission of particle number bPN [1]

The processes taking place during the measurement can result in considerable variation of dimensions and masses of the particles mixed with air after leaving the exhaust system of the engine. What is characteristic is that both particle sizes and their mass distribution are good approximations to the log-normal distribution, which is of great importance when considering the process of comminution of solids. From the character of the particle dimensions, depending on their diameter, it appears that nanoparticles comprise more than 90% of the total number of particles emitted by a diesel engine, but only 10–20% [22] of the total mass of particles emitted with the exhaust gas (Fig. 2.9).

References [1] Aakko, P., Nylund, N.O.: Particle Emissions at Moderate and Cold Temperatures Using Different Fuels. SAE Technical Paper Series 2003-01-3285 (2003) [2] AVL Partikelseminar. Graz (Nonember 10-12, 1993) [3] Bischof, O.F., Horn, H.-G.: Zwei Online-Messkonzepte zur physikalischen Charakterisierung ultrafeiner Partikel in Motorabgasen am Beispiel von Diesel-emissionen. Motortechnische Zeitschrift 4 (1999) [4] Brook, R.D., Franklin, B., Cascio, W., Hong, Y., Howard, G., Lipsett, M., Luepker, R., Mittleman, M., Samet, J., Smith, S.C., Tager, I.: Air Pollution and Cardiovascular Disease. Circulation 109 (2004)

References

17

[5] Carpenter, K., Johnson, J.H.: Analysis of the Physical Characteristics of Diesel Particulate Matter Using Transmission Electron Microscope Techniques. SAE Technical Paper Series 79081 (1979) [6] Dolan, D.F., Kittelson, D.B.: Diesel Exhaust Aerosol Particle Size Distributions – Comparison of Theory and Experiment. SAE Technical Paper Series 780110 (1978) [7] Foreman, R.J.: Mass Loading and Stokes Number Effects in Steady and Unsteady Particle-Laden Jets. University of Adelaide, School of Mechanical Engineering, Adelaide (2008) [8] Franke, H.U., Tschöke, H., Veit, P.: 3D – Morphology of Particles of Soot of Different Fuels Depending on the Combustion Process. In: World Automotive Congress FISITA, Paris (1998) [9] Gruber, M., Klawatsch, D.: Influence of Motor Parameters and Fuel Quality on Particulate Emissions. Vehicle Systems Technology for the Next Century. European Automotive Congress, Barcelona (1999) [10] Kittelson, D.B., Arnold, M., Watts, W.F.: Review of Diesel Particulate Matter Sampling Methods. Mineapolis (1999) [11] Kittelson, D.B.: Engines and Nanoparticles: A Review. J. Aerosol. Sci. 29 (1998) [12] Kittelson, D.B., McMurry, P., Park, K., Sakurai, H., Tobias, H., Ziemann, P.: Chemical and Physical Characteristics of Diesel Aerosol. In: Cambridge Particle Conference (2002) [13] Kowalewicz, A.: Systemy spalania szybkoobrotowych silników spalinowych. WKŁ, Warszawa (1990) [14] Lange, W., Regllitzky, A., Krumm, H., Cowley, L.: The Influence of Diesel Fuel on Exhaust Emission. Motortechnische Zeitschrift 10 (1993) [15] MAN – B&W, Emission Control of Two Stroke Low Speed Diesel Engines. SAE Technical Paper Series 890925 (1989) [16] Merkisz, J.: Ekologiczne aspekty stosowania silników spalinowych. Wydawnictwo Politechniki Poznańskiej, Poznań (1995) [17] Merkisz, J.: Pewne uwagi o emisji cząstek stałych w silnikach ZS. Ekonomiczne i ekologiczne aspekty rozwoju pojazdów samochodowych i silników spalinowych. KONMOT, tom 3. Silniki spalinowe. Ekologia, paliwa alternatywne, eksploatacja, Kraków–Raba Niżna (1994) [18] Merkisz, J.: Wpływ motoryzacji na skażenie środowiska naturalnego. Wydawnictwo Politechniki Poznańskiej, Poznań (1993) [19] Merkisz, J., Pielecha, J.: Emisja cząstek stałych ze źródeł motoryzacyjnych. Wydawnictwo Politechniki Poznańskiej, Poznań (2014) [20] Park, J.-H.: Impactors and Particle Size Distribution. National Institute for Occupational Safety and Health Division of Respiratory Disease Studies Field Studies Branch, Washington (2004) [21] Szlachta, Z.: Metodyka pomiaru emisji cząstek ze spalinami silników wysokoprężnych. Ekonomiczne i ekologiczne aspekty rozwoju pojazdów samochodowych i silników spalinowych. KONMOT, tom 3. Silniki spalinowe. Ekologia, paliwa alternatywne, eksploatacja, Kraków–Raba Niżna (1994) [22] Zabłocki, M., Ekert, K.: Emisja nanocząstek nowym wyzwaniem dla silników z zapłonem samoczynnym. In: Sympozjum EKODIESEL, Warszawa (1998) [23] Zikoridse, G.: Perspektiven der Abgasmestechnik. 6 FAD-Konferenz, Dresden, November 5-6 (2008)

Chapter 3

The Process of Formation of Particulate Matter in Combustion Engines 3 The Process of Format ion of Particulate Matter in Co mbustion Engines

Solid particles are created as a result of complex chemical and physical processes, often occurring time, though the time and place of their occurrence are very different. The form, size and composition of PM depends to a large extent on the temperature and location within the system: the cylinder – the exhaust system – the surroundings, where the particles are collected [19, 20]. The final form of the emissions is affected by all intermediate stages, but in a particular cases different phases can be decisive [5]. However, typically the processes that occur in the engine cylinder shortly after fuel injection are most important. Their nature and characteristics are different for different engines, their operational conditions and fuels burned. Formation mechanisms of the individual components of emissions are also different. The formation of soot (including carbon) in the flame is a complex process, in which, within a few microseconds, solid particles are formed from fuel droplets. The combustion process in diesel engines has a different course than in gasoline engines; in diesel engines there is a more significant concentration of soot. In the diesel engine ignition of the sprayed liquid takes place, and the combustible mixture has a combustion air factor of less than one (λ < 1); such conditions promote the formation of soot. The soot formation rate is greater during the combustion of diesel fuel than during the combustion of gasoline. This is the result of the greater content of polycyclic aromatic hydrocarbons and the higher value of the ignition point of diesel fuel. Soot formation proceeds in combustion chamber areas rich in fuel at a temperature of 1400 to 2800 K (the bold line in Fig. 3.1) [17]. Recent research by Akihama et al. [24] on the formation of soot suggests that the temperature range from 1700 to 2600 K should be considered (Fig. 3.1). This is a narrower range than the one given in the results of other studies (e.g. Kmimoto [17]). In diesel engines soot formation starts as a result of the oxidation of fuel molecules and/or thermal decomposition of unsaturated hydrocarbons, including acetylene and its derivatives (C2nH2) and polycyclic aromatic hydrocarbons. It is believed that the oxidation and products of thermal decomposition of fuel molecules can be important intermediate stages in the formation of particulate matter [24]. When particle condensation takes place, the first identifiable soot particles with a diameter of about 2 nm occur (Fig. 3.2). These particles, called nuclei, are © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_3

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3 The Process of Formation of Particulate Matter in Combustion Engines

involved in the process of nucleation [12]. Dehydrogenation of particles takes place within the range of high-temperature ignition [3]. Particles with a diameter of 2 nm are very mobile (Brownian motion) and collide with each other; as a result large structures with the number of atoms higher than 105 are formed. Their aerodynamic diameter ranges from 10 nm to 80 nm, but particles with dimensions of 15–30 nm are most common. In these particles there are ten times more carbon than hydrogen atoms [3]. Factors affecting the formation of soot are, among others: fuel parameters, the fuel injection process, combustion pressure and combustion chamber shape.

Fig. 3.1 Relative soot formation in an engine as a function of T–1/λ [24]

After the formation of the particles, an increase of their surface area and agglomeration take place. The increase of the surface area ensues from the combination of particles with those already existing through nucleation and condensation. The process of the increase in surface area depends, to a large extent, on the pressure of the mixtures of vapors and their temperature. Agglomeration (coagulation and aggregation) is the process of colliding particles, due to which a smaller number of larger particles is created. Both of these processes (surface area increase and agglomeration) depend on the number concentration of the particles. In order to take steps to restrict the emission of particulate matter it is necessary to identify and describe the mechanisms leading to PM formation and, at least approximately, to determine the PM mass formed during engine operation. Changes in the physical properties of solid particles depends on the processes to which they are subjected (Tab. 3.1). Nucleation occurs in the engine’s combustion chamber ; ignition and combustion parameters have significant impacts on this process. Nucleation of hydrocarbons with other compounds (including fuel additives and, to a very small degree, sulfur) takes place as a result of cooling (i.e. diluting) of the exhaust gas in the engine exhaust system. The increase in the size of the particles depends mainly on their degree agglomeration, which is affected by the initial number concentration of the particles and the coagulation time. The coagulation rate is proportional to the square of the initial number concentration of solid particles (t = 0) and the coagulation index K [13]:

cPN (t = 0) dcPN = K ⋅ (cPN ) 2 ⇒ cPN (t ) = dt 1 + cPN (t = 0) ⋅ K ⋅ t

(3.1)

3 The Process of Formation n of Particulate Matter in Combustion Engines

221

Fig. 3.2 Soot formation phasses (based on [2, 4, 18])

Table 3.1 Changes in the ph hysical properties of solid particles [6] Physical effect Nucleation Agglomeration/coagulation n Diffusion/penetration Adsorption/condensation

Parameter change particle number

Occurrence engine combustion chamber

surface area of particles

engine exhaust system

change of mass

engine exhaust system, collection of exhaust gas sample

mass increase

dilution tunnel

Schematicc

From the formula (3.1)) it follows that after some time of coagulation, the initiial number concentration of the t particles will be reduced. Measurement of the numbeer concentration of particulaate matter shall be carried out so that it does not take intto account the impact of coaagulation: in the flame it should take place within the firrst

22

3 The Process of Formation of Particulate Matter in Combustion Engines

few milliseconds (approx. 1012 1/cm3), and in the exhaust gases (approx. 108 1/cm3) – within 10 s (Fig. 3.3).

Fig. 3.3 The number concentration of particulate matter cPN as a function of time, assuming a coagulation factor of K = 5·10–10 cm3/s [9]

The composition of the emitted particles, as well as their number and size depends on the location and method of the exhaust gas sampling. In accordance with the standards in force in Europe and the United States, samples for analysis of particulate matter shall be taken after dilution of the exhaust gases in air and cooling the mixture to a temperature of 52°C. Then, the volatile components of the SOF are submitted to adsorption, condensation and nucleation. This transformation changes the share of SOF in the already existing particles and results in the creation of new solid or liquid particles. Agglomeration does not change the particle mass or chemical composition, however, through its impacts the particle number, size distribution and fractional composition are changed. The agglomeration mechanism does not affect the particles’ mass, but it has a significant impact on their number and size distribution. As a result of the diffusion mechanism, the particle mass changes (increases or decreases); this is the result of the presence of concentration gradients of particular fractions of particulate matter. However, as a result of adsorption and condensation, the particle mass increases – which is the effect of reducing the exhaust gas temperature in the engine’s exhaust system. The particulate matter emitted from diesel engines consists mostly of carbon with absorbed hydrocarbons in liquid form (hydrocarbon condensate – Fig. 3.4). In the literature, (e.g. Kittelson [16]), a view prevails based on tests results from diesel engines that the carbon part of the particle (its ‘skeleton’) can range from 20 to 45% of the total mass of a solid particle. The remaining part is uncombusted lubricating oil (25%), fuel (up to 10%), sulfur compounds and water (altogether at very low sulfur content – less than 10 ppm), and other substances.

3 The Process of Formation of Particulate Matter in Combustion Engines

23

Increased requirements associated with the protection of atmospheric air make it necessary to pay attention to the large number of particles with dimensions smaller than 100 nm emitted by diesel engines (and by gasoline direct injection engines – particles with dimensions of 60–80 nm), which are very dangerous for human health. Therefore, it can be expected that additional limits on emissions of particles of nano sizes will be introduced. Since 2011, for a road emission limit for particulate matter of 5 mg/km has been in force for passenger vehicles with gasoline DI engines; and since September 2011, measurements of particle number have been conducted during the type-approval tests of passenger vehicles with diesel engines.

Fig. 3.4 The structure of solid particles (and their diameter) directly downstream of the outlet valve and at the end of the exhaust system and the thermodynamic parameters of the exhaust gases [14]

Nanoparticles comprise the majority of the total number of particles emitted by engines, but a very small part of their total mass. The current mass method of determining particulate emissions is not sufficient to assess the emission of nanoparticles [21]. The introduction of emission restrictions will certainly require other measurement methods, which are currently being intensively studied [1, 7, 8, 10, 11, 15, 22, 23].

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3 The Process of Formation of Particulate Matter in Combustion Engines

References [1] Ahlvik, P., Ntziachristos, L., Keskinen, J., Virtanen, A.: Real Time Measurement of Diesel Size Distribution with an Electrical Low Pressure Impactor. SAE Technical Paper Series 980410 (1998) [2] Appel, J.: Numerische Simulation der Russbildung bei der Verbrennung von Kohlenwasserstoffen: Teilchengrössenverteilungen und deren statistische Momente. Fortschritt Berichte VDI, Düsseldorf (2000) [3] Baron, P.A., Willeke, K.: Aerosol Measurement – Principles, Techniques and Applications. John Wiley and Sons, New York (2001) [4] Bockhorn, H.: Soot Formation in Combustion. Springer, Berlin (1994) [5] Broome, D., Khan, I.M.: The Mechanism of Soot Release from Combustion of Hydrocarbon Fuels. In: Conference on Air Pollution Control in Transport Engines. Inst. of Mech. Eng., London (1971) [6] Fritz, O.: GDI Engine Development According EU 6. AVL Seminar, Graz (2012) [7] Fukushima, H., Asano, A., Nakamura, S., Ishida, K., Gregory, D.: Signal Processing and Prac-tical Performance of a Real-Time Particulate Analyzer Using Fast Fids. SAE Technical Paper Series 2000-01-1135 (2000) [8] Fukushima, H.: Continuous Measurement of Soot and Soluble Organic Fraction Emission from Advanced Powertrains. In: World Automotive Congress FISITA, Seoul (2000) [9] Gruber, M., Klawatsch, D.: Influence of Motor Parameters and Fuel Quality on Particulate Emissions. Vehicle Systems Technology for the Next Century. In: European Automotive Congress, Barcelona (1999) [10] Guenther, M., Sherman, M.T., Vaillancourt, M., Carpenter, D., Rooney, R., Porter, S.: Advanced Emissions Test Site for Confident PZEV Measurements. SAE Technical Paper Series 2002-01-0046 (2002) [11] Hall, D.E., Dickens, C.J., Measurement of the Number and Size Distribution of Particles Emitted from a Gasoline Direct Injection Vehicle. SAE Technical Paper Series 1999-01-3530 (1999) [12] Heywood, J.B.: Internal Combustion Engine Fundamentals. McGraw Hill, New York (1988) [13] Hinds, W.C.: Aerosol Technology. John Wiley and Sons, New York (1998) [14] Johnson, J.H., Bagley, S.T., Gratz, L.D., Leddy, D.G.: A Review of Diesel Particulate Control Technology and Emissions Effects. SAE Technical Paper Series 940233 (1994) [15] Khalek, I.S., Kittelson, D.B., Graskow, B.R., Wei, Q., Brear, F.: Diesel Exhaust Particle Size: Measurement Issues and Trends. SAE Technical Paper Series 980525 (1998) [16] Kittelson, D.B., McMurry, P., Park, K., Sakurai, H., Tobias, H., Ziemann, P.: Chemical and Physical Characteristics of Diesel Aerosol. In: Cambridge Particle Conference (2002) [17] Kmimoto, T., Bae, M.: High Combustion Temperature for the Reduction of Particulate in Diesel Engines. SAE Technical Paper Series 880423 (1988) [18] Mayer, K.: Pyrometrische Untersuchung der Verbrennung in Motoren mit CommonRail-Direkteinspritzung mittels einer erweiterten Zwei-Farben-Methode. Forschungsberichte aus dem Institut für Kolbenmaschinen der Uni Karlsruhe, Karlsruhe (2000)

References

25

[19] Merkisz, J.: Ekologiczne aspekty stosowania silników spalinowych. Wydawnictwo Politechniki Poznańskiej, Poznań (1995) [20] Merkisz, J.: Wpływ motoryzacji na skażenie środowiska naturalnego. Wydawnictwo Politechniki Poznańskiej, Poznań (1993) [21] Pielecha, J.: Analysis of Particle Emission and Smoke Measurements in Stationary Cycles. In: PTNSS Kongres 2007; The Development of Combustion Engines, Cracow, May 20-23 (2007) [22] Pungs, A., Pischinger, S., Backer, H.: Analysis of the Particle Distribution in the Cylinder of a Common Rail DI Diesel Engine during Combustion and Expansion. SAE Technical Paper Series 2000-01-1999 (2000) [23] Transient Particulate Analysis using Tapered Element Oscillating Microbalance TEOM. Engine Measurement Division, HORIBA Ltd. (1999) [24] Turns, S.R.: An Introduction to Combustion Concepts and Applications. McGrawHill, New York (1996)

Chapter 4

Methods of Measuring Particulate Matter Emissions

4.1

Type-Approval Testing Methods of Particle Mass and Particle Number

Measurement of Particle Mass According to the definition of particles, testing them requires dilution of the exhaust gas in the dilution tunnel at full or partial flow. Additional considerations to be taken into account when measuring are the degree of dilution, the mass of the filter before and after the measurement, the air humidity and the sample collection time. Tests of particle mass are therefore carried out in several stages; it is a longterm process, requiring that the filters be kept for 8 h in air at constant humidity and temperature, both before and after the measurement. This means that the results cannot be obtained directly during engine operation. Thus, the mass of particles collected on the measuring filter is an average value resulting from the collection time of the exhaust gas sample. This method is most commonly used to determine the mass of particulate matter at a certain time, e.g. for regular, repetitive operational conditions of the engine. The mass method for determining the mass of particulate matter does not guarantee obtaining data on the emission rate under variable conditions, e.g. while increasing the engine load; it is possible, however, to obtain the total mass of particles in these conditions over the selected time interval. The particle mass can be determined by a mass method involving a very precise weighing – with an accuracy of 0.001–0.005 mg – of the collected sample of particles (usually together with the filter paper on which particulate matter is deposited), at a strictly defined and constant temperature and at constant relative air humidity. This method is widely believed to be the most accurate and therefore is the only one allowed in type-approval tests; the results obtained from this method are used to calibrate other measuring devices. Now, in the European Union all type-approval measurements require dilution of exhaust gas with air at a temperature of 20–30°C; however, water should not condense, and the particulate matter sampling should be carried out at a temperature of © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_4

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4 Methods of Measuring Particulate Matter Emissions

52°C. The mixing of exhaust gas with air, at varying degrees of dilution, depending on the engine working conditions and the dilution factor, takes place in devices called dilution tunnels. The concentration of the individual harmful components in the exhaust gas in modern cars is decreasing, which is why it is necessary to develop methods providing measurement of their emissions subject to errors which are as small as possible. Currently used measuring methods recommended by European ECE/EC and American provisions (requirements of the EPA and CARB), based on an analysis of the exhaust gas diluted with air in devices called exhaust gas sampling systems, do not guarantee that excessive errors of measurement will be avoided [20]. CVS type exhaust gas sampling systems (constant volume sample – system with constant sample collection) have been used for measuring exhaust emissions from car engines since 1971. In this system, the exhaust gas is diluted with air to prevent condensation of water vapour contained in the exhaust gas in the exhaust lines and in the sample bags. The amount of air used for this purpose must ensure that a mixture temperature greater than the dew point is achieved. However, the degree of dilution should also be as small as possible, in order to ensure the ability to measure small concentrations of harmful exhaust gas components, for example in vehicles of Euro V class. In vehicles which comply with the requirements of the Euro 5 standards, the concentrations of harmful components in the diluted exhaust gas are similar to their concentrations in ambient air. The concentration of harmful components in the exhaust gas (where undiluted) and for a warmed up engine with an efficient catalytic system is also often close to their concentration in the air (or lower), which means that in such a situation the harmful components are not emitted into the atmosphere. This situation confirms the need to develop technical advances in particulate matter emission tests (Fig. 4.1), as well as the need for thorough preparation of the diluted exhaust gas. Neglecting the effect of the background level during a test of emissions of particles above 0.1 g/(kW·h) (emissions from heavy duty vehicles of Euro III class), does not cause a significant error (less than 1%). During the tests of the particulate emissions from heavy-duty vehicles of Euro IV class, the error in determining the specific emission of this component is approximately 10% (not taking into consideration the background measurement), while determination of specific emissions of particulate matter from heavy goods vehicles of Euro V class may cause an error of about 50% [26]. Currently, it is required to use air-conditioned engine test benches for typeapproval tests, to provide constant values of temperature and relative humidity of the air. Type-approval tests require the use of fibreglass membrane filters. Other filters may be used for special purpose measurements. In cases where the correlation between the results of the tests is determined, filters of the same quality must be used. Filters should show a particle collection efficiency of 95% (for a single filter). The velocity of gas flow through the measuring cuvette should be 0.35– 0.40 m/s; the pressure drop during the test shall not exceed 25 kPa. The minimum

4.1

Type-Approval Testing Methods of Particle Mass and Particle Number

29

Fig. 4.1 The impact of the specific emission of particulate matter on the value of the error of its determination (assumed concentration of particulate matter in the air = 0.026 mg/m3) [25]

Fig. 4.2 Determining the smallest particle mass on the filter according to filter diameter [25]

diameter of the filters is 47 mm (37 mm effective diameter). Filters with a larger diameter are also acceptable. The recommended minimum filter loading shall be 0.5 mg/1075 mm2 of the effective surface area if one pair of filters is used [32]. The above data indicate that according to the Euro III standard, during testing on an engine test bench it was possible to use filters of diameter 90 mm for measuring the particulate emissions, and for testing engines that meet the Euro IV (and subsequent) standards, only filters of diameter 47 mm should be used (Fig. 4.2). The diluted exhaust gas should be sampled by a pair of filters arranged in series (one primary and one auxiliary filter) during each phase of the test. The auxiliary filter should be located no further than 0.1 m from the primary filter, and so that there is no contact between them. The filters should be weighed separately or as a pair, joined together with colored signs. The temperature of the chamber in which the filters are stored and weighted should be kept within limits of 295 ±3 K

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4 Methods of Measuring Particulate Matter Emissions

(22 ±3°C). The relative humidity should be controlled and kept within limits of 45 ±8%. Stabilization of filters takes at least one hour, but no longer than 8 h [5]. Filters or filter pairs shall be weighed twice at an interval of 4 hours. If the change in their weight is more than ± 5% (±7.5% for the filter pair), filters should be rejected and the measurement should be repeated. The analytical balance used to determine the mass of the filters must be of an accuracy 20 μg (1 graduation = 10 μg), and for weighing filters with a diameter of at least 70 mm and smaller these figures must be 2 μg and 1 μg, respectively. The results of repeated measurements of particulate emissions by means of the gravimetric method are not identical. Two concepts are used to evaluate the range of variation of the measurements (i.e. tests): repeatability and reproducibility. Repeatability defines the range of variability of the results of repeat measurements of one object in a given test on one test bench. The range of variation is taken as the measure of repeatability, or in the case of many measurements – the ratio of the standard deviation of the results to the mean of the results. Unrepeatability of the results of tests carried out many times on the same test bench ensues from the difference in actual emissions during individual tests (including the tolerance of operating cycle and ambient conditions) as well as from random errors in measurements of the parameters defining the emissions (Fig. 4.3).

Fig. 4.3 The principle of determining the value of road emissions of particulate matter for a vehicle [29]

Reproducibility characterizes the range of variation of the results of tests of emission of pollutants carried out on various test benches in different laboratories, or on different test benches in a single laboratory. In order to assess the reproducibility, comparative studies are carried out in different laboratories or on different test benches in one laboratory.

4.1

Type-Approval Testing Methods of Particle Mass and Particle Number

31

If the number of measurements is large enough, the unrepeatability of a particular engine’s emissions does not affect the mean value of the emissions result. Different emission values determined on particular test benches depend on the engine operating conditions resulting from the tolerances of the operating cycle, the method of its reproduction, resistance to motion, ambient conditions, fuel properties, etc. permitted by the test procedure. In the measurement of road emissions of particulate matter via the gravimetric method, in the dilution tunnel with full flow of exhaust gas, the standard deviation of the measurement is 0.3–0.5 mg/km [29] and the minimum measurable value (at least three times the standard deviation) is equal to 0.9–1.5 mg/km. As a result, the maximum acceptable value for road emissions of particulate matter shall not be less than 2.7–4.5 mg/km (a value at least three times larger than the minimum measurable value). The result obtained of 4.5 mg/km is the value corresponding to the limit defined in the Euro 5 and Euro 6 standards. Introduction of lower acceptable values in subsequent provisions means that the mass method would not provide the required accuracy. Assuming that the repeatability and reproducibility cause an error of 2 mg/km while determining road emissions of particulate matter, then the value corresponding to road emissions of 2.7–4.5 mg/km should be increased to the range from 4.7 to 6.5 mg/km. Additionally, the measurement of the production and in–service conformity values shows an uncertainty of about 3 mg/km. As a result, an accuracy range of 7.7–9.5 mg/km is obtained in determining road emissions of particulate matter. Taking this value into account, together with the emission deterioration factor of 1.2 (for passenger vehicles with a mileage of 160,000 km), the procedures of the on-board diagnostics systems (OBD) should detect road emissions of particulate matter at a minimum value of 9.27–11.4 mg/km. This value is more than 100% higher than the acceptable value specified in the Euro 5 and Euro 6 standards (4.5 mg/km). In publications the significant unrepeatability of the tests of road emission of particulate matter has been highlighted, which is reflected in defining the decision-making thresholds of diagnostic systems, whose values in the measurement of particle mass are equal to 10 times the limit for the type-approval test. To increase the accuracy of the particle mass measurements, the method utilizing a dilution tunnel with partial gas flow is used more and more often (Fig. 4.4). Due to the lower dilution of the exhaust gas, this method also requires adjustment for measurements of smaller particle mass. It is anticipated that the following modifications will be introduced [11]: • in relation to the engine exhaust system: – length of not more than 10 m, – diameter of not less than 0.15 m, – exhaust gas temperature higher than 56°C; for lower temperatures a heated line will be required;

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4 Methods of Measuring Particulate Matter Emissions

• in relation to the tunnel with full exhaust gas flow: – dilution air temperature higher than 15°C; up to now a temperature range of 20–30°C has been used, – diluted exhaust gas flow rate through the full–flow dilution tunnel of 1.33 m3/s, – flow with a Reynolds number higher than 4000, – inner diameter of the tunnel of more than 0.2 m, – temperature of the diluted exhaust gas of less than 191°C, – degree of dilution greater than 3.3; • in relation to the particulate matter measuring probe: – length of less than 0.91 m, – inner diameter of the probe not less than 0.085 m, • in relation to the secondary dilution tunnel: – the intensity of the flow proportional to the full-flow dilution tunnel (5% of that value), – rate of the air flow through the secondary dilution tunnel of 1.5 m3/h, with the temperature of the dilution air not less than 15°C, – the required degree of dilution equal to 5.5, in order to reduce the temperature of the diluted exhaust gas from 191°C to 47°C; • in relation to the pre-classifier: – transmission of 99% (by mass) of particles of diameter 1 mm, – retention of 50% of particles of diameters 2.5 µm and 10 µm;

Fig. 4.4 Diagram of the recommended system for measuring particle mass – collecting samples from the dilution system with partial flow of exhaust gas; 1 – engine exhaust system, 2 – air filter, 3 – full-flow dilution tunnel, 4 – dilution air filter, 5 –secondary dilution tunnel, 6 – pre-classifier, 7 – particulate filter [5, 6]

4.1

Type-Approval Testing Methods of Particle Mass and Particle Number

33

• in relation to the particulate matter filters: – diameter of the measuring filters 46.5 ±0.6 mm, – temperature of the heated line and measuring filters of 47 ±5°C (up to now 52 ±3°C), – increase of the flow rate of the exhaust gas sample through a measuring filter from 0.55 m/s to 0.9 m/s. Measurement of Particle Number The size distribution of particulate matter in exhaust gas is bimodal [7]. Particulates emitted having been created in the nucleation phase have a diameter of 30 nm, and those created in the accumulation phase – about 50 nm. Occurrence of the nucleation phase depends on the technology of which the engines are made up, the type of fuel, systems used for exhaust gas cleaning and the sampling conditions. In the nucleation phase 0.1 to 10% of particle mass is formed, but at the same time this represents over 90% of the total particle number [16]. In accordance with the measurement requirements (regulation no. 692/2008) [6] only the solid fraction of particles should be measured, i.e. particles from the accumulation phase. The reason for this is that tests on those particles are repeatable, and the particles formed in the nucleation phase are sensitive to the sampling conditions (their number varies depending on where the sample exhaust gas is collected) [14, 19]. In addition, particles created in the nucleation phase transform quickly in the atmosphere, so it would be difficult to determine repeatable measurement conditions. However, recent research shows that the volatile part of particulate is more toxic than the solid part [2, 4, 33]. The sampling system for the measurement of particle number (Fig. 4.5) consists of the tip of the sampling probe (or from the sampling point in the dilution system), a line for particulate transfer, a particulate matter pre-classifier (4) and a device to remove the volatile particles before the particle counter (Fig. 4.5 and 4.6). The system removing volatile particles must cover the devices for dilution of samples (diluents of particulate matter 6 and 8) and for vaporizing solid particles (vaporizing line – 7). The sampling probe or sampling point should be placed in the dilution tunnel during on testing the gas flow, thereby making it possible to collect the sample from a homogeneous mixture of diluted exhaust gas. The mixture residence time in the sampling system and the measuring time should not exceed 20 seconds. The gas sample collected by the system for particulate transfer must meet the following requirements: the Reynolds number should be less than 1700, and the sample’s residence time in the sampling system should not exceed 3 s. The heated outlet, through which the diluted sample passes from the device retaining volatile particles to the outlet inlet of the particle counter must have an internal diameter of at least 4 mm, and the transfer time of the samples gas shall be 0.8 s, maximum.

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4 Methods of Measuring Particulate Matter Emissions

Fig. 4.5 Diagram of the recommended system for particulate sampling – sampling in the full-flow exhaust gas dilution system: 1 – engine exhaust system, 2 – air filter, 3 – dilution tunnel, 4 – pre-classifier, 5 – heated gas line for connection of additional devices (e.g. classifier of particulate matter), 6 – the first particulate matter diluter, 7 – vaporizing line, 8 – the second particulate matter diluter, 9 – device retaining volatile particles, 10 – particle counter, 11 – dilution air inlet [5, 6]

Fig. 4.6 Diagram of the recommended system for particulate sampling – collecting samples in the partial-flow exhaust gas dilution system; designation as in Fig. 4.5 [5, 6]

The particulate matter pre-classifier shall be placed before the device retaining particles and should assure 50% efficiency in retention of solid particles of diameters 2.5–10 µm. In systems with partial dilution of exhaust gas it is acceptable to use the same pre–classifier for the particle mass and particle number measurement samples. The device retaining the volatile particles must consist of one diluter for the particulate matter (6), a vaporizing line (7) and a second diluter (8), all connected in series. Diluting involves reducing the number of solid particles in the sample introduced into the particle counter to a value less than the upper limit of counting for individual particles, and eliminating the nucleation process within the sample.

4.1

Type-Approval Testing Methods of Particle Mass and Particle Number

35

The first device for diluting particulate matter must have a wall operating temperature of 150°C to 400°C. The wall temperature should be maintained at a constant, nominal level with a tolerance of ±10ºC. The diluter should be supplied with filtered dilution air and should be capable of achieving dilution factors from 10 to 200. Along the entire length of the vaporization line (7), walls should be kept at a temperature equal to that of the temperature of the first particulate matter dilution device (from 300°C to 400°C with a tolerance of ±10°C), or higher. The second particulate matter diluter (8) should be supplied with filtered dilution air and should keep the dilution factor within the range from 10 to 30, in order to ensure that the number of solid particles downstream of the second diluter is smaller than the upper particle counting limit of the counter, and so that prior to entering the counter the temperature of the gas is less than 35°C. Volatile compounds can be eliminated by means of dilution and thermal conditioning (Fig. 4.7) [13]. During the collection of samples from the CVS tunnel, both the concentration and the temperature of the sample are reduced (A → B curve). During dilution, volatile compounds condense after passing through the dew point. Subsequent dilution (B → D curve) leads to a reduction of the concentration of volatile fractions, but does not allow them to evaporate, due to the hysteresis between the particle nucleation process and vaporization of the exhaust gas sample. One option to avoid condensation is preparation of the exhaust gas sample using a hot diluter (curve A → C) and a diluter head (Fig. 4.8). Taking into consideration the significant degree of dilution during cooling (curve C → D), it can be concluded that there is no nucleation of volatile compounds, despite the fact that the same final state as when sampling in the CVS tunnel has been achieved (curve A → B → D).

Fig. 4.7 Block diagram of the principle of thermodilution [13]

36

4 Methods of Measuring Particulate Matter Emissions

Fig. 4.8 The diluter head block diagram [13]

The particle counter should: • provide a counting accuracy of ±10% within the range from 1 particle per 1 cm3 up to the upper counting limit of the single solid particles, • provide measurement of at least 0.1 solid particles per 1 cm3 at a number concentration of less than 100 particles per 1 cm3, • have a linear response throughout the entire measuring range in individual particle counting mode, • have a data transfer frequency of at least 0.5 Hz, • have a response time t90 of less than 5 s, • provide a counting efficiency of solid particles of diameters 23 nm (±1 nm) and 41 nm (±1 nm) of 50% (±2%) and at least 90%, respectively. Systems for measurement of particle number are effective in relation to particles of diameter greater than 23 nm. However, this condition is not applicable to all vehicles. Gidney et al. [10] found that using gasoline with the addition of iron and manganese as fuel; it is possible to obtain a significant concentration of particles of diameter lower than 23 nm. A similar conclusion was drawn by Kirchner et al. [15], who observed a significant concentration of particles of diameter less than 23 nm at low engine loads. Many studies suggest that engines intended for use in heavy-duty vehicles may emit a large concentration of particles of diameter less than 23 nm [12, 17, 27]. This suggestion also applies to motorcycle and scooter engines (studies by Czerwiński et al. [8]), and at the same time a similar relationship for aviation engines has been demonstrated in the studies of Petzold et al. [24].

4.2

Integrated Systems for Measuring Particle Mass

37

4.2

Integrated Systems for Measuring Particle Mass

Photoacoustic Measurement Method – AVL, Micro Soot Sensor For determination of particle mass an AVL Micro Soot Sensor analyser may be also used, incoorporating a sample conditioning system – the exhaust gas dilution system [30]. The system utilizes a partial flow of the diluted exhaust gas; it maintains a temperature of up to 60°C. The principle of operation of this system is based on photoacoustic measurement (Fig. 4.9) in a so–called ‘resonant’ measuring cell. The measuring cell enables detection of solid particles from concentrations of 5 mg/m3 upwards. The exhaust gas is delivered directly into the measuring cell (at a temperature of 47 ±5°C) and heated with modulated laser light of wavelength 808 nm (such a wavelength minimizes interference from other components). This leads to a periodic pressure fluctuation, which is received by the detector – a microphone – as a sound wave. The signal is then amplified and filtered (basic data about the device are shown in Table 4.1).

Fig. 4.9 Operating diagram of the [30] Table 4.1 Technical specification of AVL 483 Micro Soot Sensor analyzer [30] Parameter

Value

Measurement range

0–50 mg/m3

Resolution

0.001 mg/m3

Degree of dilution

5000

Sample gas flow rate

0.12 m3/h

Operating conditions

5–45°C, humidity 0–95%

38

4 Methods of Measuring Particulate Matter Emissionns

Measurements with the Frequency Method – Sensors, PPMD This system for measuriing particulate matter is equipped with a proportionnal exhaust gas sampling sysstem and quartz crystals (oscillating microbalance). Thhe exhaust gas sample is tak ken from the exhaust system and diluted with air, in order to increase the relaxation time. The dilution air flow is controlled with the use oof electromagnetic valves an nd allows for further dilution during tests on exhaust gaas with a high concentration of solid particles.

Fig. 4.10 Quartz crystals of the t analyzer [3]

Fig. 4.11 Diagram showing supply s of the charge and deposition of particulate matter on thhe crystals [3]

4.2

Integrated Systemss for Measuring Particle Mass

339

The measuring system for particle mass consists of 8 quartz crystals (Fig. 4.100), each of which is heated and a equipped with a vibration frequency meter. The cryystal chosen by the user is the reference crystal, while the others are used for thhe measurement of particulaate matter contained in the diluted exhaust gas. The measuring time for each crysttal is specified within the range from 1 to 2 min., a sam mple is taken at a flow ratee of 4 dm3/min. The vibration frequency of the crystals is determined with the use of o an oscillator placed on either side of the quartz. Depoosition of electrically ch harged particles (Fig. 4.11) reduces the frequency oof vibration of quartz crystalls and, on this basis, the mass of the solid particles is determined (after a specifieed period of sampling and for a given number of quarrtz crystals used in the tests) [18]. Measurements with the Gravimetric Method and with a Diffusion Sensor – Horiba OBS The analyzer produced by y Horiba (OBS-TRPM – on-board transient response paarticulate measurement) con nsists of two measurement systems: an exhaust gas diluution system (proportionaal partial flow) and a diffusion charge sensor (DCS S). Figure 4.12 shows the diaagram and principle of operation of the analyzer. On thhe left side there is the exhau ust gas dilution system and measurement of particle mass with the gravimetric meth hod. The dilution air is supplied from the probe before thhe heated dilution tunnel. After mixing the exhaust gas with air (the temperature oof the mixture is maintained d at 47°C) part of the exhaust gas passes through the cycclotron (where particles off diameter greater than 6 µm are retained) and is directeed to the filter with a diametter of 47 mm. The remaining part of the diluted exhauust gas is directed to the diffu usion charge sensor (right side of Fig. 4.12). In this moddule, the change of the con ncentration of particulate matter is measured on ongoinng continuous basis. The corrrelation between the total mass of the particulates (gravimetric method), and thee course of cumulative concentrations of particulate maatter makes it possible to deetermine changes of the particle mass during testing [21]].

Fig. 4.12 Diagram and the prrinciple of operation of the Horiba OBS analyzer [21]

40

4 Methods of Measuring Particulate Matter Emissionns

Particulate Matter Senso or – Pegasor PPS-M This instrument produced d by Pegasor Ltd [31] is a compact device, which does noot require any exhaust gas diilution system (Fig. 4.13) [23]. It utilizes raw exhaust gaas and can be installed on th he engine exhaust system of the vehicle, or on an enginne test bench. The principle of operation of the sensor is similar to the ‘Faraday cupp’, inside which solid particles acquire an electric charge, and are then transported tto an electrode included in the structure of the sensor. Clean air flows through thhe first part of the sensor, which w is ionized (by applying a voltage of 2 kV). Positivve air ions are pushed out through t the ejector of the nozzle generating pressure tto suck in the exhaust gas sample. s This jet pump generates a constant flow of thhe sample through the senso or, which is not affected by a change of flow inside thhe exhaust system. After the turbulent mixing of air, ions and solid particles, partiallly charged solid particles arre obtained. Positive air ions (not deposited on the soliid particles) are removed fro om the flow of the sample by a positively charged centrral electrode. The electric fieeld generated pushes them towards the wall of the sensoor body, where only ionized d particles are collected. The electrometer measures thhe difference between the degree d of charge on the input and output of the devicce. This difference is proporttional to the particle number (where the central electrodde is powered with a voltagee of 50 V) or to the total mass (where the central electrodde voltage is 500 V) in the ex xhaust gas sample. The current loss is proportional to thhe concentration of particulaate matter [23]. The advantage of this sensor is the abilitty to measure the particulatee number and particulate mass in undiluted exhaust gas iin real time at high resolution (1 Hz) and a response time of less than 0.3 s. Addditionally, the readout from m the sensor is independent of the measuring conditionns (pressure changes, flow raate, exhaust gas temperature), because it is determined bby the air flow rate and exhau ust gas suction (Fig. 4.14). The device can be used to teest the concentration of partiiculate matter before or after the particulate matter filteer. The measuring range of particulate p matter is the readout of concentration withiin the range from 0.01 to 250 0 mg/m3.

Fig. 4.13 Pegasor PSS-M sen nsor diagram [31]

4.3

Systems for Measu urement of Particle Number

441

Fig. 4.14 Pegasor sensor witth the values of the exhaust gas flow [31]

4.3

Systems for Measurement M of Particle Number

AVL Particle Counter For measuring the numbeer concentration of particulate matter, an AVL 489 paarticle counter complying with w the requirements of PMP can be used. This device is equipped with a measuriing probe and a system for dilution of the exhaust gaas sample with clean air (Fig. 4.15). The total number of particulates in the exhauust b of the measurement of the number concentration oof gas is determined on the basis particulate matter (basic data d presented in Table 4.2), including the measuremennt of mass flow rate of exhau ust gas.

Fig. 4.15 Exhaust gas dilutio on system used in the particle counter [9] Table 4.2 Technical specificcation of the AVL 489 particle counter [9] Parameter Operating range Lower measuring limit Response time Sample flow Air flow rate Operating conditions of thee device Exhaust gas temperature

Value 0–10,000 1/cm3 ≤ 0.1 1/cm3 5s 0.06–0.3 m3/h 1.8 m3/h 0–40°C < 200°C

42

4 Methods of Measuring Particulate Matter Emissions

Solid particles are directed from the dilution system, which maintains the sample at a constant temperature, to the heated saturator (39°C), where the particles are saturated with n-butanol. In the condensation line the n-butanol vapour is cooled to a temperature of 22°C (whereupon then vapour becomes oversaturated and can condense on solid particles). As a result of enclosing the particles within n-butanol, droplets of diameter 11.3–12.3 µm are formed (in the latest designs of counters, instead of n-butanol, water is used and the droplets generated have a diameter of about 2 µm). These droplets are directed to the laser counting system (the passage of droplets through the measurement system results in the dispersion of radiation). The counting system has a temperature of 40°C, which prevents condensation of n–butanol on the lenses and any resulting reduction of the accuracy of the measurement. Mass Spectrometer – TSI EEPS 3090 For measurements of solid particles diameters the EEPS 3090 mass spectrometer (engine exhaust particle sizer™ spectrometer) by TSI Incorporated [22] is used. It enables measurement of the discrete range of particle diameters (from 5.6 nm to 560 nm) on the basis of their varying speed (Fig. 4.16). The electric range of the mobility of solid particles changes exponentially, and the measurement of their size is executed at a frequency of 10 Hz (the basic data are presented in Table 4.3). The exhaust gas is directed to the mass spectrometer through the dilution system and the system maintaining the required temperature. The pre-filter retains particles with a diameter bigger than 1 µm, which exceed the measuring range of the device. After passing through the neutralizer, the particles are directed to the charging electrode;

Fig. 4.16 Operational diagram of the analyser of the distribution of solid particle diameters [22]

4.3

Systems for Measurement of Particle Number

43

after obtaining an electrical charge they can be classified according to their size. Particles deflected by the high-voltage electrode are directed to the ring gap, which is the gap between the two cylinders. The gap is surrounded by a stream of clean air supplied from outside the instrument. The outlet cylinder has the structure of a stack of sensitive electrodes isolated from each other and arranged in the form of a ring. The electric field between the cylinders repels the particles from the positively charged electrode; these particles then accumulate on the external electrodes. Hitting the electrode, particles produce electricity, which is read by the processing system. Table 4.3 Technical data of the mass spectrometer EEPS 3090 by TSI [22] Parameter

Value

Particle size range

5.6–560 nm

Available characteristics of particles depending on their diameter Particle size resolution

cPN = f(D), A = f(D), V = f(D), m = f(D) (for ρ = 1 g/cm3) 16 channels per decade (32 total)

Frequency resolution

10 Hz 0.6 m3/h

Flow rate: sample flow The range of pressure required inside the column

(700–1034)·102 Pa

Inlet sample temperature

10–52°C

Operating temperature

0–40°C

In studies on the measurements of particle parameters concepts of number concentration of particles (cPN), surface area (A), volume (V) and particle mass (m) are used. The definition of concentrations of these parameters is more universal as their values are given as the number of particles per unit of volume (1/cm3). The same rules apply to determining the surface area, volume and particle mass. The way of describing the number concentration of particles while using devices with different numbers of measuring channels (different resolution) might be misleading (Fig. 4.17), thereby causing the need for standardization of measurement results. Standardization involves submitting the results as the quotient of the number concentration of particles in each channel and the standardized width of the measuring channel:

NC =

c PN ( D ± ∆D) log[( D + ∆D ) / ( D − ∆D )]

(4.1)

where: cPN(D ±∆D) – the number concentration of particles of diameter (D ±∆D) [1/cm3], D + ∆D – upper value for the range of measured particle diameter [nm], D – ∆D – lower value for the range of measured particle diameter [nm].

44 a)

4 Methods of Measuring Particulate Matter Emissions b)

Fig. 4.17 Comparison of standardized number distribution of particles depending on the diameter (D) with the use of: a) an analyzer with 16 measuring channels, b) an analyzer with 32 measuring channels [1]

The given value of standardized number concentration (NC) is several hundred times greater than the non-standardized number concentration, which is associated with a large number – and thus small width – of the measuring channels. From this point in the text onwards, the standardized number concentration is used for determination of number concentration dependent on the particle size.

References [1] Aerosol Statistics Lognormal Distributions and dN/dlogDp. Particle Instruments, TSI Incorporated (2010) [2] Biswas, S., Verma, V., Schauer, J.J., Cassee, F.R., Cho, A.K., Sioutas, C., Oxidative Potential of Semivolatile and Non-Volatile Particulate Matter (PM) from Heavy-Duty Vehicles Retrofit-ted with Emission Control Technologies. Environ. Sci. Technol. 43 (2009) [3] Booker, D.: Semtech PPMD. In: Semtech Users Network (SUN) Conference, Ann Arbor, September 21-22 (2010) [4] Cheung, K., Polidori, A., Ntziachristos, L., Tzamkiozis, T., Samaras, Z., Cassee, F.: Chemical Characteristics and Oxidative Potential of Particulate Matter Emissions from Gasoline, Diesel and Biodiesel Cars. Environ. Sci. Technol. 43 (2009) [5] Commission Regulation (EC) No. 582/2011 of 25 May 2011 implementing and amending Regulation (EC) No. 595/2009 of the European Parliament and of the Council with respect to emissions from heavy-duty vehicles (Euro VI) and amending Annexes I and III to Directive 2007/46/EC of the European Parliament and of the Council. OJ L 167/1 (June 25, 2011) [6] Commission Regulation (EC) No. 692/2008 of 18 July 2008 implementing and amending Regulation (EC) No 715/2007 of the European Parliament and of the Council on type-approval of motor vehicles with respect to emissions from light passenger and commercial vehicles (Euro 5 and Euro 6) and on access to vehicle repair and maintenance information. Official Journal of the European Union, L199, 1–136 (July 28, 2008)

References

45

[7] Directive 2004/ 26/EC of the European Parliament and of the Council of 21 April 2004 amend-ing Directive 97/68/EC on the approximation of the laws of the Member States relating to measures against the emission of gaseous and particulate pollutants from internal combustion engines to be installed in non-road mobile machinery (April 21, 2004) [8] Czerwinski, J., Comte, P., Larsen, B., Martini, G., Mayer, A.: Research on Particle Emissions of Modern 2-stroke Scooters. SAE Technical Paper Series 2006-01-1078 (2006) [9] Emission Instruments: AVL Particle Counter. AVL List GmbH, Graz (2010) [10] Gidney, J., Twigg, M., Kittelson, D.: Effect of Organometallic Fuel Additives on Nanoparticle Emissions from a Gasoline Passenger Car. Environ. Sci. Technol. 44 (2010) [11] Giechaskiel, B., Dilara, P., Sandbach, E., Andersson, J.: Particle Measurement Programme (PMP) Light-Duty Interlaboratory Exercise: Comparison of Different Particle Number Measurement Systems. Measurement Science and Technology 19 (2008) [12] Johnson, K.C., Durbin, T.D., Jung, H., Chaudhary, A., Cocker, D.R., Herner, J.D.: Evaluation of the European PMP Methodologies during On-Road and Chassis Dynamometer Testing for DPF Equipped Heavy-Duty Diesel Vehicles. Aerosol Sci. Technol. 43 (2009) [13] Kasper, M.: The Number Concentration of Non-Volatile Particles – Design Study for an Instrument According to the PMP Recommendations. SAE Technical Paper Series 2004-01-0960 (2004) [14] Khalek, I.A., Kittelson, D., Brear, F.: The Influence of Dilution Conditions on Diesel Exhaust Particle Size Distributions. SAE Technical Paper Series 1999-01-1142 (1999) [15] Kirchner, U., Scheer, V., Vogt, R., Kägi, R.: TEM Study on Volatility and Potential Presence of Solid Cores in Nucleation Mode Particles from Diesel Powered Passenger Cars. J. Aerosol. Sci. 40 (2009) [16] Kittelson, D.B.: Engines and Nanoparticles: A Review. J. Aerosol. Sci. 29 (1998) [17] Kittelson, D.B., Watts, W.F., Johnson, J.P.: On-road and Laboratory Evaluation of Combustion Aerosols. Part 1: Summary of Diesel Engine Results. J. Aerosol Sci. 37 (2006) [18] Mamakos, A., Carriero, M., Bonnel, P., Demircioglu, H., Douglas, K., Alessandrini, S., Forni, F., Montigny, F., Lesueur, D.: EU-PEMS PM Evaluation Program – Third Report – Further Study on Post DPF PM/PN Emissions. JRC Scientific and Technical Reports, European Union, Luxemburg (2011) [19] Maricq, M.M., Chase, R.E., Podsiadlik, D.H., Vogt, R.: Vehicle Exhaust Particle Size Distribu-tions: A Comparison of Tailpipe and Dilution Tunnel Measurements. SAE Technical Paper Series 1999-01-1461 (1999) [20] Merkisz, J., Pielecha, J., Lijewski, P., Bielaczyc, P.: Remarks about Particular Matter and Smoke Measurements in Stationary Cycles. In: International Conference EURO OIL&FUEL, Cracow (2006) [21] OBS-TRPM on Board System – Transient PM Mass Measurement. PEMS-PM Evaluation. Pro-gram Meeting Explore the Future (March 3, 2008) [22] Particle Instruments: Model 3090 Engine Exhaust Particle SizerTM Spectrometer. TSI Incorporated (2009) [23] Pegasor Particle Sensor, Pegasor Ltd., Tempere, Finland (2010), http://www.pegasor.fi

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4 Methods of Measuring Particulate Matter Emissions

[24] Petzold, A., Fiebig, M., Fritzsche, L., Stein, C., Schumann, U., Wilson, C., Vrchoticky, S.M., Wahl, C.: Particle Emissions from Aircraft Engines – A Survey of the European Project PartE-mis. Meteorol. 14 (2005) [25] Pielecha, J.: Analysis of Particle Emission and Smoke Measurements in Stationary Cycles. In: PTNSS Kongres 2007; The Development of Combustion Engines, Cracow, May 20-23 (2007) [26] Pielecha, J., Merkisz, J.: Reliability of Particle Emissions Measurement on Engine Test Stand. In: World Filtration Congress, Discover the Future of Filtration and Separation, Leipzig (2008) [27] Rönkkö, T., Virtanen, A., Kannosto, J., Keskinen, J., Lappi, M., Pirjola, L.: Nucleation Mode Particles with Nonvolatile Core in the Exhaust of a Heavy Duty Diesel Vehicle. Environ. Sci. Technol. 41 (2007) [28] Rozporządzenie Ministra Gospodarki i Pracy z dnia 19 sierpnia 2005 r. w sprawie szczegółowych wymagań dla silników spalinowych w zakresie ograniczenia emisji zanieczyszczeń gazowych i cząstek stałych przez te silniki (DzU nr 202, poz. 1681) [29] Schindler, P.K.: Feinstaub – Ein Beitrag zur Versachlichung. In: Partikelworkshop: Gravimetrie Und Feinstaub, Woflsburg (2005) [30] Schindler, W.: Haisch, Ch., Beck, H.A., Niessner, R., Jacob, E., Rothe, D.: A Photoacoustic Sen-sor System for Time Resolved Quantification of Diesel Soot Emissions. SAE Technical Paper Series 2004-01-0968 (2004) [31] Tikkanen, J.: Pegasor Particle Sensor (PPS-M) for Combustion PM Measurement. Pegasor Ltd., Finland, Ympäristömittauspäivät, Vantaa (May 5, 2011) [32] United Nations. Agreement concerning the adoption of uniform conditions of approval and recip-rocal recognition of approval for motor vehicle equipment and parts. Addendum 48: Regulation No. 49. Uniform provisions concerning the approval of diesel engines with regard to the emis-sion of gaseous pollutants. E/ECE/324 ECE/TRANS/505 Rev. 1/Add. 48 (April 5, 1982) [33] Vouitsis, E., Ntziachristos, N., Pistikopoulos, P., Samaras, Z., Chrysikou, L., Samara, K.: An In-vestigation on the Physical, Chemical and Ecotoxicological Characteristics of Particulate Matter Emitted from Light-Duty Vehicles. Environ. Pollut. 157 (2009)

Chapter 5

Particulate Matter Emissions during Engine Start-Up

Taking into account the continuous tightening of regulations limiting emissions of harmful compounds in the exhaust gas, it is essential to recognize the cause of such emissions and eliminate or reduce them [1, 2, 7, 8]. It is believed that one of these reasons is insufficient warm up of the engine, occurring primarily during cold start. Limits for emission of harmful compounds in the exhaust gas are forcing manufacturers to shorten the cold phase and at the same time to reduce the percentage share of emissions during cold start in the total emission of harmful substances emitted by the engine. Engine start-up and warm-up periods fall within the range of the tests currently in force, defining the amount of emissions of toxic compounds in exhaust gas. The amount of the emissions from these periods, due to the lack of the efficient operation of the exhaust gas purification systems (below 300°C), has a significant share in the final results of driving tests. It should be noted that physical, rather than chemical, processes have a significant impact on the emission of particular toxic substances in the exhaust gas, and that their emissions are closely co-related, and the possibility to reduce emissions of one component can result in increased emissions of another (Fig. 5.1). For this reason, any action undertaken to lower the content of toxins in the exhaust gas must rely on finding a compromise, where the negative impact of components on the environment will be the smallest [3, 9]. Many factors have an influence on the course of correct engine operation, the most important of which is the course of the combustion process and parameters related to it (such as the fuel injection system, the combustion chamber shape, swirl, injection and fuel spray characteristics). With a reduction of the ambient temperature below 0°C, the time of acceleration of the crankshaft to the speed required by the start-up conditions gets longer, as the thermal conditions necessary for the first spontaneous ignitions deteriorate. Other adverse changes are deterioration of the conditions for dose spraying and an increased resistance of fuel flow throughout the fuel system. For engine start-up at low ambient temperature, the most significant factor is the temperature of the air supplied to the engine which, at the same time, depends on the engine design and materials. © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_5

47

48

5 Particulate Matter Emissions during Engine Start-Up

An important factor increasing the emission of pollutants during cold start is the use of the so-called start-up dose, which is an increased fuel dose, administered in the initial cycles of engine operation in order to facilitate engine start-up. The startup dose contributes to a substantial reduction of the combustion air factor λ, resulting in incomplete combustion. However, the increased fuel dose is necessary, since it shortens the start-up time, results in more favorable distribution of the diameters of droplets and contributes to sealing the piston–cylinder assembly [10].

Fig. 5.1 Diagram of the mixing process and combustion in a diesel engine and their results [2]

Consumption of lubricating oil that results from many processes taking place in the cylinder has a significant impact on the value of the hydrocarbons emissions. The main causes of oil consumption are:

5 Particulate Matter Emissions during Engine Start-up

• • • •

49

oil entering the combustion chamber through the rings, absorption processes – desorption of oil and fuel vapor, absorption of oil vapors by soot particles, evaporation of oil as a result of cavitation occurring during the expansion stroke.

During cold start there is an increase in the amount of particles emitted and a change in their fractional composition. Individual particles join together, forming agglomerates, the properties of which might be characterized by total surface area, mass, size distribution, as well as chemical composition. During engine start-up the share of the solid particles originating from uncombusted fuel increases. This is associated with a significant amount of hydrocarbons formed under these conditions. The flame quenching effect (wall and crevice) has a crucial influence here. Low temperatures in the cylinder and the exhaust system promote the condensation of these compounds onto soot particles [2, 4]. Bench Testing During tests [5] starting at engine start-up, a continuous recording of exhaust gas emissions was conducted engine operation at idle. The tests were conducted for two variants of thermal conditions of a TDI engine: cold and hot start-up. During the cold start, at an ambient temperature of 20°C, the emission of particulate matter decreased as the engine warmed up. Hot start-up took place immediately after stopping the warmed engine. In this case, the oxidizing catalytic reactor was warm (maximum conversion efficiency), due to which the products of incomplete combustion were almost completely eliminated – the PM emissions were significantly reduced. The increasing tendency in the characteristics of PM concentration during hot start-up tests with a hot catalytic reactor ensued from the gradual reduction of the reactor temperature during idling. On the basis of the characteristics presented, it might be concluded that engine operation at idle does not permit quick warm up of the catalytic reactor, nor maintenance of the specific temperature for reactor operation. At cold start a momentary increase in particulate matter emissions is observed, occurring directly after engine start-up, while at hot start-up there is a constant (low) level of PM. An analysis of particular periods of engine operation shows that for cold start-up, the first 60 seconds of operation are crucial, during which 53% of solid particles are emitted. In the third minute of the test, the emission is far less: 16% of the PM. For hot start-up the share of specific periods of engine operation is more uniform (Fig. 5.2). The amount of harmful compounds emitted in the exhaust gas during cold start significantly exceeds the amount emitted by a warm engine. From an analysis of the emission of PM in the first 3 minutes of engine operation (Fig. 5.3) it ensues that the mass of particulate emissions is several times higher (8 times higher for 3 minutes of emission and 19 times higher for the first 30 seconds, respectively) for cold start compared to hot start.

50

5 Particulate Matter Emissions during Engine Start-Up

Fig. 5.2 Comparison of the share of individual periods of engine operation within the total emissions for an idling 1.9 TDI engine

Fig. 5.3 Comparison of emissions after 30 seconds and after 3 minutes of hot and cold phase – idling after start-up of a 1.9 TDI engine

Fig. 5.4 Comparison of the share of individual periods of engine operation within the total emissions for an idling SB3.1 engine

5 Particulate Matter Emissions during Engine Start-up

51

Tests of the particulate emissions ware also conducted for an SB3.1 engine at several start-up temperatures for both hot and cold start-up. The measurement of concentration of toxic compounds was performed from the engine start-up – during the first 3 minutes of engine operation. Results are presented for the cold start-up of the engine at a temperature of 20°C, and the results of measurements for, respectively, hot and forced hot start-up at 90°C (Fig. 5.4 and 5.5). Forced hot start-up at a temperature of 90°C is achieved by external heating of cooling liquid (using a device for stabilizing temperature) until the oil temperature reaches exactly 90°C.

Fig. 5.5 Comparison of emissions after 30 seconds and after 3 minutes of hot and cold phase – idling after start-up of a SB3.1 engine

Particulate Matter Emissions during Delayed Fuel Dosage A significant reduction in the emission of toxic compounds during cold start-up of an engine might be achieved by introducing a few seconds’ delay in dosing fuel into the combustion chamber, immediately after initiating the rotation of the engine crankshaft. Such a start-up strategy prevents accumulation of uncombusted fuel in the cylinder during the first cycles after starting the engine. The first dose of the injected fuel is dosed after several compression cycles, which provides much better conditions for evaporation and ignition, due to the initial heating of the combustion chamber as a result of the compression operation. Delayed fuel dosing helps to reduce the peak values of particulate emissions by 30% (Fig. 5.6). It might be presumed that at low ambient temperature start-up with delayed fuel dosing may contribute to a significant reduction of emissions of toxic compounds. With the use of electronic control systems, with which most of modern diesel engines are equipped, such a solution would cause neither any complications in the design, nor any increase in the costs of engine manufacture. In addition, it would be possible to adjust the delay time of fuel dosing to the conditions of start-up; that is, primarily to the current temperature of the engine cooling agent and the ambient temperature (of the intake air).

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Fig. 5.6 Particulate matter concentrations for different testing options for a 1.9 TDI engine

Studies on the impact of delayed fuel dosing were also repeated on the SB3.1 engine. The analysis was conducted only for the cold start at a temperature of 20°C. Delayed fuel dosing helps to reduce the peak values for particulate emissions by over 30%. On the basis of the modal analysis, it was found that in the first, second and third minute of the engine warm-up phase 63%, 19% and 18% of the particulate matter is emitted, respectively. For the cold start-up, the first 60 seconds of engine operation are crucial, during which 69% of solid particles are emitted – by weight this is approximately twice as much as for the hot start-up. After the analysis of the emission of PM in the first 3 minutes of engine operation (Fig. 5.7) it can be concluded that for start-up without the fuel dosing, a significant reduction in emissions (by 40%) of particulate matter was obtained. More significant differences in PM emissions relate to the first 30 seconds of engine operation. An analysis of this period of engine operation showed that during start-up with delayed fuel dosing, 58% of the particulate matter (compared to the standard start-up with immediate fuel dosing at the beginning of the start-up) is emitted.

Fig. 5.7 Comparison of particulate matter emissions after 30 seconds and 3 minutes of the warm-up phase for a SB 3.1 engine for the standard start-up and start-up with delayed fuel dosing (in relation to the cold start-up at temperature of 20°C with dosing fuel at the beginning of starter operation)

5 Particulate Matter Emissions during Engine Start-up

53

Particulate Matter Emissions during Engine Tests The effect of an engine’s thermal state on the emission of toxic compounds was determined in stationary tests carried out on an engine test bench. Two test procedures were carried out: measurements in compliance with the ECE R49 test conducted for cold and hot start-up, as well as measurements of emissions according to a new, 3-phase SEDT test (short engine diesel test). The test results are presented for all three engines tested. Analyzing the PM emission results from the ECE R49 test (Fig. 5.8), it can be concluded that the total emissions of PM in this test depend to a negligible degree on whether it is executed on a cold or hot engine, which is associated with the long duration of the test (78 min). The final difference is influenced only by the initial phases of the test, when the engine had not reached its nominal operating temperature.

Fig. 5.8 PM emission results during the ECE R49 test for various engines

A significant difference in PM emissions in relation to the engine’s thermal state is observed in the shortened 3-phase SEDT test (Fig. 5.9), for which the sequence of phases and the values of shares in the particular phases are shown in Fig. 5.10. More significant differences between the tests are associated with the duration of the test (the share of the first phase of engine start-up has a larger impact on the final, total emission in SEDT test compared to ECE R49 test). By comparing the emissions of the selected harmful components at idle (i.e. phases 1, 7 and 13 in the 13-phase ECE R49 test) during the cold start-up (Fig. 5.11), a conclusion may be drawn that the concentration of the compounds during the first (cold) phase of the measurement has the largest impact on the final emission value (the total of these three phases). Comparing the same phases for the hot start-up, it might be observed that the emission in the 1st phase of the test has only a slightly greater effect on total emissions during operation at idle.

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Fig. 5.9 PM emission results during the SEDT test

Fig. 5.10 Test diagram for the SEDT test for different engines

Fig. 5.11 Comparison of the PM emissions at idle; phases 1, 7 and 13 of the ECE R49 test

5 Particulate Matter Emissions during Engine Start-up

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On the basis of tests conducted, it was concluded that the main factors increasing particulate matter emissions in the exhaust gas during start-up and warm-up of a cold diesel engine are: • use of a start-up fuel dose in order to enrich the air-fuel mixture, which is necessary for proper engine start-up, its operation during warm-up and to achieve the required traction properties of the vehicle, • adverse temperature conditions at the engine intake system (and in the combustion chamber during the inlet stroke), resulting mainly in low temperature air reaching the cylinder, • global and local inconsistencies in the composition of a combustion mixture, leading to unrepeatability of the cycles, the existence of so-called wall and crevice effects and to increased consumption of lubricating oil. The values of exhaust emissions obtained in the ECE R49 test for various thermal conditions of the engines tested demonstrate an insignificant influence of the engine’s engine condition on the final emissions in the test. The reason for this is the long duration of the test and the small engine operation share of the cold phase. The methodology of investigating the issue of particulate matter emissions during the cold start-up of the engine, by calculating the emission results on the basis of the reduced 3-phase SEDT test, gives a ratio of the PM emissions results very close to the results obtained in the 13-phase test. Particle Mass and Particle Number Emission during Engine Start-up The aim of static studies presented in publication [6] was to compare the rate of particulate emissions EPM from passenger cars in use (differing, among other parameters, in date of production), which comply with subsequent standards of toxicity of exhaust gas. Particle parameters were measured during cold start-up of the vehicles (20 in total) equipped with diesel and gasoline engines. Gasoline engines were included in the study in order to compare them with diesel engines and to create classification of vehicles in terms of their particulate emissions. The vehicles selected for testing were equipped with gasoline engines with single point (Euro 1 emission standard) and multipoint (Euro 2–Euro 4 emission standard) injection systems. All vehicles were equipped with catalytic converters; vehicles with diesel engines were equipped with fuel injection system with an in-line pump (Euro 1), a common rail system (Euro 3, Euro 4) or an injector unit (Euro 4). Vehicles of Euro 4 class were also equipped with a particulate filter. The mileage of the vehicles also varied – from 20,000 km to 280,000 km. The tests were carried out in the morning, after a 12-hour period of engine stoppage at a room temperature ranging from 4 to 7oC. The measurement was started at the time of the engine cold start-up and it lasted for a 5-minute warm-up period. To carry on the assumed range of tests, apparatus was used to measure emissions of the major gaseous compounds, utilizing a heated gas line and allowing for measurement of the exhaust gas flow rate (Semtech DS by Sensors Inc.);

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the flow rate value was used during measurement of particle mass and particle number. In order to compare the values of the particulate emission rates, they were related to the measurement time (5 min) and to the engine displacement, determining the volumetric emission factor. In this way a reliable factor was obtained, the values of which can be compared independently of the engine type and displacement. The volumetric emission factor for particulate matter (Fig. 5.12a) determined for a diesel engines is approximately 50 times larger (the average value of the volumetric emission factor of particulate emissions WPM from vehicles complying with Euro 1 and Euro 2 standards is approximately 5 mg/dm3) than for gasoline engines (the average value of the factor is less than 0.1 mg/dm3). This shows that particulate matter emission from gasoline engines is low, even during cold startup of the engine. Considering the particle number emitted by different engines, it might be observed that that it is actually independent of the age (mileage) of the vehicle. In the case of gasoline engines, the value of the volumetric emission factor of particulate matter WPN is 1·109 1/dm3 over these 5 minutes, while for diesel engines it is 1–10·1010 1/dm3 for the same measuring time. Therefore, gasoline engines emit 10 to 100 times less particulate matter than diesel engines (Fig. 5.12b). a)

b)

Fig. 5.12 The volumetric emission factor during engine start-up and warm-up: a) in relation to particle mass, b) in relation to particle number; designation of emission class of the vehicles: E1 – Euro 1, E2 – Euro 2, E3 – Euro 3, E4 – Euro 4

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57

Determination of the average results of previous measurements made it possible to classify the vehicles considering their emissions. On the basis of the average emission values, the impact of the change of the exhaust gas toxicity standards on particulate matter emission and particle number during start-up and warm-up can be determined. The tests conducted made it possible to obtain qualitative and quantitative information on particulate emissions (on particle mass, particle number and particle size) during start-up of the vehicles from different emission classes. The data obtained on the rate of particulate emissions (Fig. 5.13a) with reference to the specific engine capacity indicate emissions 70 times larger from diesel engines compared to gasoline engines in the case of cars complying with the Euro 1 standard; and emissions 10 times higher in the case of cars complying with the Euro 4 standard (for engines without a DPF particulate filter). During start-up diesel engines emit approximately 200 times more particulate matter (quantitatively) than gasoline engines (Fig. 5.13b). a)

b)

Fig. 5.13 Volumetric emission factor of particulate matter (a) and particle number (b) for vehicles complying with Euro 1 – Euro 4 emission standards

With the use of a mass spectrometer, an analysis of particulate size distribution was conducted for the vehicles tested (Fig. 5.14). According to the analysis, the characteristic diameter of particles emitted by gasoline engines amounts to approx.

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40–60 nm, and for the particles emitted by diesel engines during start-up and warm-up – 80–100 nm. There is no straight answer to the question which of the engines emits more particles of a given diameter. This should be considered taking into account the category of the vehicle emission class: vehicles of category Euro 1 have much larger emission than the most recent vehicles. Vehicles with gasoline engines of Euro 4 category emit 4 to 5 times less particles during start-up than diesel engines belonging to the same category.

Fig. 5.14 Standardized particle number distribution of according to the diameters of particles emitted by vehicles complying with Euro 1 – Euro 4 emission standards

Comparing the particles emitted by the most recent vehicles and by vehicles complying with Euro 1 standard, independent of the engine type, a significant reduction in the number of particles with diameters from the same range can be observed. This is the result of the higher injection pressure and more efficient fuel fragmentation which, unfortunately, is also the reason for the significant emissions of nitrogen oxides. In order to classify the start-up emissions (during the start-up phase and in the five-minute engine warm-up phase), ranges of variation in emissions from vehicles with a specific mileage are presented, divided into diesel and gasoline engines. Apart from the ranges of variation of emissions, the correlation coefficient value is also given in Fig. 5.15. The values of particulate emissions depend strongly on the mileage of the vehicle: the bigger the mileage, the greater the emission of particulates. However, vehicles with diesel engines emit several times more particles than vehicles equipped with gasoline engines (Fig. 5.15a). There are two trends of changes in the emitted particle number (Fig. 5.15b): with regard to the vehicles with diesel engines, the increase in the emitted particle number is proportional to the vehicle mileage (vehicles complying with the Euro 1 standard

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59

emit approximately 10 times more particles than vehicles meeting the Euro 4 standard), while modern gasoline engines (complying with the Euro 4 standard) emit approximately 5 times fewer particles than engines meeting the Euro 1 standard, as a result of the increase in gasoline injection pressure. a)

b)

Fig. 5.15 The volumetric factor of particle emissions (a) and particle number (b) by vehicles with gasoline and diesel engines, as a function of their mileage

In order to classify vehicles according to particulate emissions depending on the standards met by the vehicles (Euro 1 – Euro 4), significant differences in emissions were indicated during start-up (in the engine start-up phase and in the 5minute engine warm-up phase) of the vehicles fitted with different engines. As a result the characteristics of the volumetric factor of emissions and the characteristics of particle number were obtained, as well as their size distribution, depending on the adopted standard for exhaust gas toxicity and the mileage of the vehicles fitted with different types of engines. A basis for the classification of vehicles in terms of emissions was created, proposing the research methodology and indices which can be used in further work. The tests can be extended to vehicles from the same emission category, but significantly differing in mileage. This would form the basis for conclusions on the durability of the engine and exhaust gas purification systems.

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References [1] Becker, U., Winter, M., Tschöke, H.: Efficient Reduction of Environmental Impacts from Transport. In: 6th International Exhaust Gas and Particulate Emissions Forum, “Forum am Schlosspark”, Ludwigsburg (2010) [2] Bielaczyc, P., Merkisz, J., Pielecha, J.: Stan cieplny silnika spalinowego a emisja związków szkodliwych. Wydawnictwo Politechniki Poznańskiej, Poznań (2001) [3] Dohle, U., Schneemann, A., Teetz, C., Wintruff, I.: Compliance with Future Emissions Regulations – Solutions Developed by MTU Friedrichshafen. In: 31st International Vienna Motor Symposium, Viena (2010) [4] Merkisz, J., Pielecha, I., Pielecha, J.: Remarks on Indirect Methods of Measurement of Particulate Matter Emission. The Archives of Automotive Engineering 1–2, Warsaw (1999) [5] Merkisz, J., Pielecha, J.: Some Remarks Particulate Matter Emission during Start Diesel Engine. Eksploatacja silników spalinowych, Wydawnictwo Politechniki Szczecińskiej, Szczecin (2002) [6] Merkisz, J., Pielecha, J.: Exhaust Emissions during Cold Start Gasoline and Diesel Engine from Passenger Cars. Combustion Engines 3 (2011) [7] Mori, K.: Contribution of the Diesel Engine to Sustainable Mobility. In: World Automotive Congress Fisita, Budapest (2010) [8] Mueller, W., Spurk, P., Franoschek, S.: Aftertreatment System Design for Euro VI Passenger Diesel. In: World Automotive Congress Fisita, Budapest (2010) [9] Neumann, D., Schrade, F., Basse, N., Schäffner, J., Tschiggfrei, W., Krämer, L.: CO – an Increasing Challenge for Lowest Emission Concepts. In: 6th International Exhaust Gas and Particulate Emissions Forum, Ludwigsburg (2010) [10] Pielecha, J.: Analiza wpływu fazy rozruchu i nagrzewania się silnika o zapłonie samoczynnym na poziom emisji toksycznych składników spalin. Praca doktorska, Politechnika Poznańska, Poznań (2000)

Chapter 6

Determination of Particulate Matter Equivalents 6 Determination of Particulate Matter Equiva lents

Thanks to continuous improvements, equivalent methods and techniques for measuring particulate matter in the real traffic conditions have been created [2–10, 14–19]. Despite the very small emissions of these compounds, it is possible to measure them in variable traffic conditions [11, 13]. In this chapter, on the basis of a verification of the optical method (measuring exhaust gas opacity) conducted for different types of motor vehicles, it is shown that such measurements are subject to significant error and do not provide conclusive results. It should be noted that the measured value of the opacity of the exhaust gas may correspond to value of particle concentration (not emission) in the exhaust gas, but only for large particles which, by absorbing light, reduce the energy reaching the detector of the device. Ambiguity of the results is caused by their insufficient resolution and the lack of a proportional relationship between the mass of a particle and its size. An evaluation of the possible use of exhaust gas opacity measurements in real traffic conditions was conducted [12] separately for light-duty vehicles (passenger cars) and heavy-duty vehicles (Fig. 6.1). The value of exhaust gas opacity was compared to the particle mass concentration measured in parallel. For the test, a portable OTR opacimeter (on the road opacimeter) by AVL was used [1], which enabled measuring the exhaust gas opacity Nz (with a resolution of 0.1%), and the extinction coefficient k (with a resolution of 0.01 1/m).

Fig. 6.1 Equipment for measurement of particulates and the opacimeter used during road tests of: a) light-duty vehicles, b) heavy-duty vehicles © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_6

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Simultaneous measurement of the mass concentration of particulate matter and the opacity of the exhaust gas was performed during a 60-minute drive in urban conditions, which forced dynamic movement of the vehicle and at the same time provided significant values of the recorded parameters (Fig. 6.2a). In order to observe the direct relationship between the particle mass concentration and the opacity of exhaust gas, a vehicle without an exhaust gas purification system was selected (Fig. 6.2b). Comparison of these two values does not allow for a direct interchangeable use of the measured values: the obtained dependency between the concentration of particulate matter cPM [mg/m3] and exhaust gas opacity Nz [%] exhibits a correlation coefficient R = 0.77 for this number of measurement points – 3600:

cPM = 4.37 Nz + 13.8

(6.1)

a)

b)

Fig. 6.2 A comparison of particle mass concentration cPM and exhaust gas opacity Nz during tests on light-duty vehicles: a) recorded mileage in urban conditions, b) the relationship between the measured values

6 Determination of Particulate Matter Equivalents

63

Analysis of the data obtained permits a statement to be made that values of the concentration of particulate matter of up to 200 mg/m3 do not correspond unequivocally to low values of exhaust gas opacity (range of opacity values from 0% to 40%). At higher values of opacity, the value of the mass concentration of par ticulate matter is more reliable (the range of variation of measurement values is much narrower). This allows for the formulation of the thesis that the measurement of exhaust gas opacity in real traffic conditions can be used as an alternative method for measurement of the mass concentration of particulate matter only for significant values of both parameters. When their values are low – the results obtained are excessively erroneous.

a)

b)

Fig. 6.3 Recorded values and an attempt to estimate the relationship between the values measured in the bus tests (driving in the very city centre)

This is also confirmed by the test results obtained for buses in driving test conditions simulating their speed in inner city areas (Fig. 6.3) and in urban (Fig. 6.4) and suburban conditions (Fig. 6.5). The registered parameters of the vehicle movement and engine operation did not confirm the possibility of interchangeable use of exhaust gas opacity values for the assessment of the particle mass concentration. Although the values of correlation coefficients obtained were satisfactory, such a large range of variation of results does not allow for precise substitution of the particle mass concentration measurements with measurements of exhaust gas

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opacity. The value of exhaust gas opacity do not unequivocally correspond to the value of particle mass concentration: it is influenced by the number of measurement points, limited because of short duration of tests – from 130 to 180 s, and equipping the buses with exhaust gas purification systems and relatively modern engines. The following dependencies between particle mass concentration cPM [mg/m3] and exhaust gas opacity Nz [%] were obtained: a)

b)

Fig. 6.4 Recorded values and an attempt to estimate the relationship between the values measured in the bus tests (urban driving conditions)

• in a test that simulates conditions in the inner city: cPM = 0.30 Nz – 0.02

(6.2)

• in a test that simulates the average urban traffic conditions: cPM = 0.28 Nz – 0.15

(6.3)

• in a test that simulates the suburban traffic conditions: cPM = 0.30 Nz – 0.055

(6.4)

In order to fully utilize the research potential, the road tests of buses in real traffic conditions were also conducted. As in the previous experiment, during this test parameters of the vehicle movement and of the engine operation were also recorded, and both the opacity of the exhaust gas and the particle mass concentration were

6 Determination of Particulate Matter Equivalents

65

a)

b)

Fig. 6.5 Recorded values and an attempt to estimate the relationship between the values measured in the bus tests (suburban driving conditions)

measured (Fig. 6.6a). The values obtained were significantly lower than those obtained for light vehicles; the range of maximum values was also lower. At the same time, most of the measurement results concentrated within the range of opacity values from 0% to 1.5% and values of the particle mass concentration from 0 mg/m3 to 0.4 mg/m3. A relation between particle mass concentration cPM [mg/m3] and exhaust gas opacity Nz [%] in real urban traffic conditions was obtained, defined as: cPM = 0.17 Nz + 0.11

(6.5)

The correlation coefficient obtained during the 50-minute recording was 0.5, which does not allow for a clear formulation of the conclusion about the possibility of the interchangeable use of the measurements of the considered parameters (Fig. 6.6b). When comparing the results of the measurements of exhaust gas opacity and particle mass concentration for light- and heavy-duty vehicles and presenting them as relative error values, related to the calculated value, a large discrepancy of the results is observed: for exhaust gas opacity less than 40%, the value of the error is approximately 100% (Fig. 6.7a). With the reduction of the obtained opacity values, the relative error increases reaching, 1000% for the lowest exhaust gas opacity values.

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b)

Fig. 6.6 A comparison of particle mass concentration cPM and exhaust gas opacity Nz for the bus: a) recorded characteristics of driving parameters and engine operation, b) the relationship between the measured values

The exact analysis of the values recorded also makes it possible to specify the most commonly occurring opacity of the exhaust gas from a light-duty vehicle (compliant with the Euro 2 standard) and heavy-duty vehicle (compliant with the Euro V standard). On the basis of the cumulative value of the exhaust gas opacity it is possible to determine a 50th percentile value that corresponds to the most commonly occurring value of exhaust gas opacity which, for light-duty vehicles is 6.8% (Fig. 6.7b), and for heavy-duty vehicles is 0.36% (Fig. 6.7c). There is approximately a 20-fold difference between these values, which results mainly from the engine design features (different values of particulate emissions) and from the use of exhaust gas purification systems. An estimation of the value of particle mass concentration on the basis of exhaust gas opacity is possible only in static tests, on the assumption that engines that emit particulate matter in high concentrations are tested. The received dependencies are subject to significant restrictions on the type of the engine and its working conditions, as well as the ranges of the considered values. The studies presented show that during dynamic tests, measures must be taken to eliminate such restrictions, e.g. by, among others, an attempt to estimate the road and specific emissions of particulate matter with the use of engine or vehicle operating parameters available from the on-board diagnostics system.

References

67

a)

b)

c)

Fig. 6.7 Comparison of the characteristic values of the particle mass concentration on the basis of exhaust gas opacity: a) relative error, b) determination of the 50th percentile relative cumulative value of the opacity for a light-duty vehicle, c) determination of the 50th percentile relative cumulative value of the opacity for a heavy-duty vehicle [12]

References [1] AVL On-Road Opacimeter, Maintenance Guide. AVL List GmbH, Graz (2008) [2] Bruneel, H.: Heavy Duty Testing Cycles Development: A New Methodology. SAE Technical Paper Series 2000-01-1860 (2000) [3] California Air Resources Board Exhaust Emission Standards and Test Procedures for 2001 and Subsequent Model Passenger Cars, Light-Duty Trucks, and Medium-Duty Vehicles, http://www.arb.ca.gov (last amended: December 2, 2009) [4] Fukushima, H., Uchihara, U., Asano, I., Adachi, M., Nakamura, S., Ikeda, M., Ishida, K.: An Alternative Technique for Low Particulate Measurement. SAE Technical Paper Series 2001-01-0218 (2001) [5] Khair, M.K.: An Integrated Control Approach for Future Heavy-Duty Diesels. In: International Symposium on Automotive Technology and Automation ISATA, Düsseldorf (1998)

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[6] Kittelson, D.B., Arnold, M., Watts, W.F.: Review of Diesel Particulate Matter Sampling Methods. Mineapolis (1999) [7] Lüders, H., Stommel, P.: Diesel Exhaust Treatment – New Approaches to Ultra Low Emission Diesel Vehicles. SAE Technical Paper Series 1999-01-0108 (1999) [8] Mayer, A.: Elimination of Engine Generated Nanoparticles. Haus der Technik Fachbuch. Expert Verlag, Renningen (2005) [9] Merkisz, J., Pielecha, J., Bajerlein, M., Bielaczyc, P.: Correlations between PM Emission and the Coefficient of Exhaust Gases Extinction in Engine Test Bed. In: International Conference EURO OIL&FUEL, Cracow, July 7-8 (2006) [10] Merkisz, J., Pielecha, J., Lijewski, P., Bielaczyc, P.: Remarks about Particular Matter and Smoke Measurements in Stationary Cycles. In: International Conference EURO OIL&FUEL, Cracow (2006) [11] Merkisz, J., Pielecha, J., Pielecha, I.: Road Test Emissions Using On-Board Measuring Method for Light Duty Diesel Vehicles. Jordan Journal of Mechanical and Industrial Engineering 5 (2011) [12] Pielecha, J.: Identyfikacja parametrów cząstek stałych z silników spalinowych. Seria Rozprawy nr 467, Wydawnictwo Politechniki Poznańskiej, Poznań (2012) [13] Pielecha, J.: The On-road Particle Emissions Characteristics of Vehicles Fitted with Diesel En-gines. In: 15th ETH-Conference on Combustion Generated Nanoparticles, Zurich, July 26-29 (2011) [14] Pielecha, J., Merkisz, J.: Reliability of Particle Emissions Measurement on Engine Test Stand. In: World Filtration Congress, Discover the Future of Filtration and Separation, Leipzig (2008) [15] Tao, F., Srinivas, S., Reitz, R.D., Foster, D.E.: Comparison of Tree Soot Models Applied to Multi-Dimensional Diesel Combustion Simulations. JSME International Journal 48 (2005) [16] Tritthart, P., Cartellieri, W.P.: Diesel Particulate Emissions – Experiences and Results. In: World Car Conference, California (1996) [17] Vouitsis, E., Ntziachristos, N., Pistikopoulos, P., Samaras, Z., Chrysikou, L., Samara, K.: An Investigation on the Physical, Chemical and Ecotoxicological Characteristics of Particulate Matter Emitted from Light-Duty Vehicles. Environ. Pollut. 157 (2009) [18] Vuk, C.T., Jones, M.A., Johnson, J.H.: The Measurement and Analysis of the Physical Character of Diesel Particulate Emissions. SAE Technical Paper Series 760113 (1976) [19] Yamazaki, H., et al.: A Study of Simplified Measurement Method for Diesel Particulate. Society of Automotive Engineers of Japan, Preliminary Staff Report 911 (1991)

Chapter 7

Measurements of Particle Mass and Particle Number in Real Traffic Conditions

7.1

Determination of Road Emissions of Particulate Matter from Light-Duty Vehicles

7.1

Determinatio n of Roa d Emiss ions of Particulate Matter

Tests on Vehicles with Diesel Engines The analysis of dynamic real traffic conditions of combustion engines can be reduced to the analysis of a given parameter with the following coordinates: vehicle speed – vehicle acceleration. Such a definition is similar to the analysis of the static characteristics of engines using coordinates of engine speed – engine load. If the whole vehicle with its drive unit is to be treated as a ‘closed object’ (a so-called black box), then the adoption of such an assumption allows for an analysis of the selected parameters of particulate matter, regardless of the internal changes taking place within the unit under consideration. This assumption does not preclude the simultaneous collection of data on the operation of the drive unit (such as engine speed and engine load from the OBD system [3, 4, 6, 11, 23, 36]). The description of any given parameter, e.g. road emissions of a given compound, in relation to coordinates, e.g. vehicle speed – acceleration, can be performed by the use of two-dimensional histograms of probability density which are a record of the duration of particular engine loads, or their shares. Although such characteristics do not take into account the dynamic properties of the engine defined on the basis of the control-torque dependence, published results of the optimisation of an approach using these characteristics show that such a simplification is acceptable [1, 2, 5, 13, 14, 16, 30]. The above may be used in the measurements of road emissions of particulate matter, e.g. to determine the environmental performance of a vehicle in real traffic conditions [7–12]. Such studies, in which passenger cars were tested, were conducted over a distance of approx. 150 km. The variability of traffic conditions was taken into consideration, by adopting three driving styles: in an urban area, a built-up area and on a motorway. The parameters measured were: the road emissions of particulate matter and the particle number emitted by vehicle “A” equipped with a particulate filter and those emitted by © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_7

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vehicle “B” without a filter. The results were compared using emission indices kPM (relating to the particle mass) and kPN (relating to the particle number), which can be calculated as the following types of value: • temporary (in Fig. 7.1 marked green) – it is characterized by high variability, as it is calculated for every second of the test, • increasing during the test (in Fig. 7.1 marked blue), calculated as the current road emission of a particular harmful compound (from the beginning of the test until the current moment) in relation to the standard value; • the value relating to the entire test as the ratio of the road emissions during the test in real traffic conditions to the standard value. The emission index (of a given harmful compound) of the vehicle is defined as [18, 29, 32]:

kj = where: j Ereal, j ENEDC, j

Ereal, j ENEDC(WHSC, WHTC), j

(7.1)

– the harmful compound for which the emission index is being determined, – the emission rate in real road conditions [g/s], – the emission rate measured over the NEDC test [g/s] or another test type concerning e.g. heavy-duty vehicles (WHSC, WHTC).

The exhaust emission flow rate in real traffic conditions can be calculated using the characteristics of the driving time distribution for the vehicle u(a,v) and the characteristics of the emission rate for the j-th harmful compound ej (a,v), expressed in grams per second [27–29]: Ereal, j = ∑ ∑ u ( a, v ) ⋅ e j ( a, v )

(7.2)

a v

If there is no information available on emissions of harmful compounds from a vehicle during the NEDC test, the allowable values can be accepted according to the applicable exhaust gas toxicity Euro standard. The limit values for road emission for a particular compound, given e.g. in g/km, can be converted into the average value of the emission rate (in g/s), knowing the duration (1180 s) and the distance travelled (11,007 m) in the NEDC type-approval test. The road emission index of a given harmful compound can take values in the range of [0, ∞). This means that if the road emissions of a vehicle do not exceed the standard values, the index has a value less than one; when they exceed the standard values, the index is greater than one, and when the actual emission is equal to the standard emission, the index is exactly 1. The characteristics of emission indices for the test vehicles are different: vehicle A (Fig. 7.1a) achieves the index kPM < 1 very fast (the limit for road

7.1

Determination of Road Emissions of Particulate Matter

71

emissions of particulate matter according to the Euro 4 standard is 25 mg/km), and for vehicle B (Fig. 7.1b) the index of less than one was achieved after travelling about 90 km, despite fitting the vehicle with particulate filter; this is due to the very low limit value for road emission of this compound adopted in the Euro 5 standard (5 mg/km). a)

b)

Fig. 7.1 The emission rate of particulate matter EPM during road tests of passenger vehicles depending on the travelled distance S: a) a vehicle without a particulate filter (Euro 4), b) a vehicle with a particulate filter (Euro 5); 1 – urban area, 2 – motorway, 3 – interurban road

The limit for particle number adopted in the Euro 5 standard refers only to vehicles with diesel engines; the planned limit for the Euro 6 standard is to be valid for all types of passenger vehicles. The characteristics of the particle number index value kPN is different for the test vehicles: for A vehicle (Fig. 7.2a) the index does not take a kPN value < 1 (this is the result of the compliance with the Euro 4 standard, according to which there is no road emission limit for particle number bPN; for comparison purposes only the limit value from the Euro 5 standard was used). For B vehicle equipped with a particulate filter (Fig. 7.2b), the index value complying with the Euro 5 standard in real traffic conditions (kPN < 1) is achieved after a distance of approximately 70 km (according to the Euro 5 standard the limit of particle number bPN in road emissions is 6·1011 1/km).

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7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions a)

b)

Fig. 7.2 The number concentration of particulate matter cPN during road tests of passenger vehicles depending on the distance travelled S: a) a vehicle without a particulate filter (Euro 4), b) a vehicle with a particulate filter (complying with the Euro 5 standard); 1 – urban area, 2 – motorway, 3 – interurban road

Considering the issue of the particle number concentration emitted by a vehicle with a particulate filter (currently, vehicles produced with diesel engines must be equipped with a particulate filter in order to comply with the provisions relating to road emission and limits on particle number, although it is not a legal requirement), against coordinates of speed – acceleration relating to the vehicle, it can be observed that the maximum mass concentration of particles (Fig. 7.3a) occurs within the range of large accelerations (from 0 m/s2 to 2 m/s2) over the whole range of vehicle speeds. In the other ranges the mass concentration of particulate matter takes values from within the range of 1–3 mg/m3, independent of the speed of the vehicle and its delay. Occurrence of the maximum values of concentration cPM results from a sudden increase in the fuel dose, which reduces the combustion air factor λ. The distribution of number concentrations of particulate matter is different (Fig. 7.3b); its maximum occurs at high vehicle speed and an average acceleration (the speed range from 24 m/s). This is associated directly with the change in the status of the engine: a rapid acceleration causes a delay in the operation of the particulate filter and an increase of the temporary number concentration of particles.

7.1

Determination of Road Emissions of Particulate Matter

73

a)

b)

Fig. 7.3 The mass concentration cPM (a) and the number concentration cPN (b) of particulate matter during road tests, taking into account the operating conditions of the vehicle

In the other ranges the concentration did not exceed a value of 15,000 1/cm3. A tendency was observed for the particle number concentration to increase with an increase in the vehicle speed. The presented values of the vehicle speeds and its acceleration can also be related to the engine’s working conditions. The data were averaged for particular engine speed and load ranges, and subsequently matrices of the particle mass and number concentrations were developed. The ranges of the maximum mass concentration of particles (Fig. 7.4a), dependent on the engine speed and equivalent load Z (expressed as Mo/Mo max at a given engine speed) occur for the engine operational range with maximum load (a small excess of air promotes increased formation of particulate matter). From the characteristics of the number concentration of particulate matter against coordinates of engine speed – engine load (Fig. 7.4b), it can be observed that the maximum value of the number concentration of particles occurs at low engine speed and low engine load. This is probably due to the relatively long time of injecting a small fuel dose into the combustion chamber with a high combustion air factor. Particulate matter will be formed from the partially evaporated drops of fuel.

74 a)

7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions b)

Fig. 7.4 The mass concentration cPM (a) and the number concentration cPN (b) of particulate matter during road tests related to the engine operating conditions (engine speed n and engine load coefficient Z)

The new rules on measuring particulate matter, introduced in the year 2011, took into account the measurement of particle number, but not within the entire range of particle diameters [28]. Only particles of diameter greater than 23 nm are counted. Particles of smaller diameters are not counted, though, which may lead to divergent results in simulations or modelling. The tests within this range confirmed that the differences between the number concentration of particles, measured taking into account the entire range of diameters with the use of a mass spectrometer (Fig. 7.5a), and taking into account the particles of diameter greater than 23 nm, can amount up to 80% (Fig. 7.5b) [30]. An analysis of the dimensions of particulate matter may be also carried out on the basis of the characteristics of the engine operation in real traffic conditions. The engine operational ranges, which are most commonly used during the operation of the vehicle, can also be included. They correspond to the following phases of operation (Fig. 7.6): 1 –engine idle, 2 – average engine speed at low load, 3 – average engine speed at medium load, 4 – high engine speed at high load. The test vehicles, equipped with different propulsion units, showed different ranges of operation (the relative engine speed and the relative engine load, related to the maximum value were selected as similarity criteria). For vehicle A without a DPF, the majority of the measuring points fall within the range of significant engine speeds and high engine loads (Fig. 7.6a, area no. 4). For vehicle B with a DPF, the measuring points are distributed in a different way: a significant number of points fall within the range of average engine speeds and average engine loads (Fig. 7.6b, area 2 and 3) and within the range of high engine speeds and high engine loads (Fig. 7.6b, area 4).

7.1

Determination of Road Emissions of Particulate Matter

75

a)

b)

Fig. 7.5 The number concentration of particulate matter cPN taking into account the entire range of diameters measured with the EEPS mass spectrometer by TSI (a) and the share of cPN PMP/cPN EEPS of particles of diameter larger than 23 nm (in accordance with the PMP program) within the total particle number (b) a)

b)

Fig. 7.6 Engine operating conditions against coordinates of engine speed – engine load during the road tests: a) vehicle A; b) vehicle B (the numbers denote the operational areas for which the particle size distribution was determined)

76

7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions 1

2

3

4

Fig. 7.7 The standardized number distribution of particulate matter NC in relation to the particle diameter in real traffic conditions for a vehicle without a DPF filter; numbers 1 – 4 define the operational areas from Fig. 7.6a: 1 – engine idle, 2 – average engine speed – low load, 3 – average engine speed – medium load, 4 – high engine speed – heavy load

7.1

Determination of Road Emissions of Particulate Matter

77

For these separate characteristic areas of engine operation a dimensional analysis of particles was conducted (for vehicle A without a DPF – Fig. 7.7): • range 1 (engine idle) – particles of diameter 10 to 100 nm are evenly distributed, with a number predominance of particles of larger diameter (approx. 50 nm); the number concentration of particles from every range of dimensions in the defined operational area is 4–5·106 1/cm3; this is due to the high combustion air factor and operating time sufficient to burn the minimum dose of fuel; • range 2 (average engine speed - low load) – particles of diameter 10 to 100 nm, with a number predominance of particles of approx. diameter 30 nm; their number concentration is 6–7·106 1/cm3; • range 3 (average engine speed – at average load) – particles of diameter between 15 to 140 nm with a number predominance of particles of approx. diameter 25–40 nm; their number concentration is 6–7·106 1/cm3; the distribution is close to values typical for engine idle; particles are formed as a result of the significant excess of air (supercharged engine) and the fuel injection pressure of approx. 50 MPa; • range 4 (high engine speed – high load) – particles of diameter 20–150 nm with a number predominance of particles of diameter 60–120 nm; their number concentration is 8–9·106 1/cm3; most particles emitted are of diameter larger than in the previous ranges, which is mainly due to the greater volume of fuel dose, the lower combustion air factor and shorter time available for burning the fuel dose. The dimensional analysis for vehicle B, equipped with a particulate filter DPF (Fig. 7.8) is different in terms of dimensions and in terms of the number concentration (there are lower values of particle size in most of the dimensional ranges): • range 1 (engine idle) – the biggest number of particles of approx. diameter 30 nm; their maximum number concentration is 1.5·105 1/cm3; • range 2 (average engine speed – low load) – particles of diameter in the range 10 to 30 nm; their number concentration is 1–1.5·105 1/cm3; • range 3 (average engine speed – average load) – particles of diameter between 10–60 nm, with a number predominance of particles of approx. diameter 25 nm; their number concentration is 1.5–2·105 1/cm3; • range 4 (high engine speed – high load) – particles of diameter 10–150 nm, with a number predominance of particles of diameter 30–50 nm; their number concentration is approx. 2.5–3·106 1/cm3. The particulate filter’s regeneration process can be observed during the road tests (driving on the motorway, at a vehicle speed of about 120 km/h – Fig. 7.9). As a result of a dimensional analysis carried out on data obtained during this process, a significant number concentration of emitted particles was found: initially, particles of diameter 20–30 nm (approx. 8·105 1/cm3), and in the final phase, particles of diameter of about 10 nm (about 1.3·106 1/cm3).

78

7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions 1

2

3

4

Fig. 7.8 The standardized number distribution of particulate matter NC in relation to the particle diameter in real traffic conditions for a vehicle with a DPF filter; numbers 1 – 4 define the operational areas from Fig. 7.6b: 1 –engine idle, 2 – average engine speed – low load, 3 – average engine speed – medium load, 4 – high engine speed – high engine load

7.1

Determination of Road Emissions of Particulate Matter

79

Fig. 7.9 The registered process of regeneration of the particulate filter and the associated change in the number distribution of particulates cPN and their diameter D

Moreover, in the initial phase of the regeneration (the first 4 min.) particles with significant range of diameters are formed: from 7–100 nm; in the last phase (the last 6 minutes of regeneration) – particles with a smaller range of diameter variability are formed: from 5 to 25 nm. It should be noted that no significant increase in the mass of particulate matter emitted during regeneration of the filter was observed. The standard values for road emission of particulate matter in the Euro 5 standard were defined taking into account the regeneration of a particulate filter, so the limit value cannot be exceeded, regardless of whether this process takes place on the vehicle or not. Tests on Vehicles with Gasoline Engines

Measurements of exhaust gas emissions were performed under urban conditions [20, 26]; two versions of the tests were performed: for vehicles fueled with gasoline and those fueled with CNG, with different mileages and of different emission classes. The characteristics of the route and the testing parameters are shown in Table 7.1. The measurements were taken 3 times – the values given are the mean values. Vehicles with dual fuel engines were tested (fueled with gasoline or compressed natural gas – CNG), equipped with a manual gearbox with mileages of 15,000, 75,000 and 500,000 km, complying with the Euro 4 and Euro 5 standards (four-cylinder engines with capacity of: 2.0 dm3, equipped with a three way catalytic converter, an EOBD diagnostic system– ISO 14230 or ISO 11888). The vehicle was factory-fitted for fueling with CNG and this is the basic fuel used by the vehicle; start-up at low temperature is assisted with gasoline (this type of fuel is also used as a reserve).

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7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions

Table 7.1 Characteristics of the test (fueled with gasoline or natural gas) Test parameter Test duration [s] Average speed during test [km/h] Test distance [km] Fuel consumption during test [dm3/100 km] [MJ/100 km]

Fueled with gasoline

Fueled with natural gas

994 9.56 11.82

1046 9.52 11.80

9.56

6980

322

268

There were significant similarities of the dynamic conditions of driving for the test runs (the ranges of occurrence of acceleration, constant driving speed, vehicle braking and stopping were compared). The percentage share of particular traffic conditions (shown in the lower right corner) indicate that for both fueling variants the constant speed occurred for 18% ±1% of the test duration, acceleration for 37% ±1%, and braking accounted for, altogether, about 33% ±1%, while stopping amounted to 12% ±1% of the test duration. Due to the significant repeatability of the test runs, it was possible to compare the emissions of harmful compounds for the vehicles tested. The determination of the road emissions of particulate matter with regard to their mass shows that their mass is several times lower for a CNG-fueled vehicle compared to the gasoline-fueled vehicle (Fig. 7.10). This is mainly associated with the type of fuel (liquid versus gaseous), but allows thesis to be posed that the longterm use of CNG- or gasoline-fueled vehicles has an adverse influence on the formation of particulate matter in their engines. However, these values should be compared with the current standards for diesel engines, for which the allowed emission of particulate matter is 5 mg/km. A comparison of the values obtained shows that they are as much as about 10 times lower for vehicles with a mileage of 500,000 km [35]. Configuration of the measuring apparatus also helped to determine the particle number in the exhaust gas of vehicles. The results obtained for the road emissions (Fig. 7.11), presented comparatively for vehicles of different emission classes and mileages, indicate insignificant differences in the values, however, correlating them with the particle mass makes it possible to state that the number of larger particles (of bigger mass) from vehicles with high mileages is much greater than for vehicles with low mileages.

7.1

Determination of Road Emissions of Particulate Matter

81

a)

b)

Fig. 7.10 Comparison of the road emissions of particle mass for vehicles with varying mileage and emission class: a) Euro 4, b) Euro 5 a)

b)

Fig. 7.11 Comparison of the road emissions of particle number for vehicles with varying mileages and emission classes: a) Euro 4, b) Euro 5

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7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions

To thoroughly explain this issue, size distributions of particles depending on their diameter for vehicles with different mileage (the value averaged for the whole measuring route) are presented in Figure 7.12 [34]. Analysis of the diagrams indicates that for a vehicle fuelled with gasoline, the characteristic particle diameter (the diameter of particles at which there is the largest particle number) falls within the range of 40 to 70 nm, whereas for CNG-fueled engines the range is smaller (30–40 nm).

a)

b)

Fig. 7.12 Comparison of the particle size distribution for the same vehicle with different fuel: a) gasoline, b) CNG (vehicle mileage 75,000 km)

A comparison of the same parameters for vehicles with mileage of 500,000 km shows insignificant changes in the presented characteristics of the particle number for gasoline-fueled vehicles (Fig. 7.13). This is associated mainly with the basic fuel of the CNG engine; comparing it with a vehicle of the Euro 4 emission class, increase in particle mass of half the size is observed. However, comparable particle number does not mean the same size distribution: particles for the gasolinefuelled vehicle with higher a mileage are of larger diameter, which is turn results in greater road emissions of particulate matter.

7.1

Determination of Road Emissions of Particulate Matter

83

By determining the road emissions of pollutants for a vehicle fuelled with gasoline and compressed natural gas, the relationship between the increase in the emissions of harmful components and vehicle mileage was obtained (for vehicles of the Euro 4 and Euro 5 classes). For vehicles with comparable mileages, the particulate matter emission for a gasoline-fueled vehicle is greater than for a vehicle fuelled with natural gas. In urban conditions, the emissions of particulate matter (in terms of particle mass) from a CNG-fueled vehicle compared to gasolinefueled vehicle are about 10 times lower (regardless of the vehicle’s mileage). In tests of the environmental performance of the vehicles considered, changes in the number and diameter of the particles emitted were also indicated [35]. An increase of the mileage of a gasoline-fueled vehicle causes a reduction in the number of particles of small diameter, and an increase in the number of particles of large diameter – as a consequence, the total particle number remains at the same level. This is different for CNG-fueled vehicles, as wear of the gas injectors causes the formation of slightly larger particles, but in larger quantities.

a)

b)

Fig. 7.13 Comparison of the particle distribution for the same vehicle with different fuel (mileage of vehicles: 500,000 km): a) gasoline, b) CNG

84

7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions

7.2

Tests of Particulate Matter Emissions from Heavy-Duty Vehicles

Commercial vehicles play a significant role in cargo transport. There are available many types of such vehicles with different carrying capacities, limited by gross vehicle weight rating (GVWR). The source of propulsion of vehicles carrying goods are mostly diesel engines characterized by large engine torque values. As for vehicles intended for the toughest applications (GVWR over 16,000 kg), their drive units are characterized by large engine displacement, with which is also associated with significant fuel consumption. This is an important issue from the point of view of the operational economy and the profitability and economic performance of business entities. It is therefore right to utilize the full carrying capacity of the vehicle (i.e. the maximum load without exceeding the GVWR) and to avoid so-called empty runs. Tests described in publications [21, 31, 33] were conducted in order to verify the impact of the vehicle load on particulate matter emissions. The influence of load on fuel consumption is easy to measure and commonly determined, while specialized testing apparatus described, among others, in [12, 15, 17, 19, 22, 24, 25, 31, 32] was used to determine emissions of particulate matter. Tests in real traffic conditions were conducted for two commercial vehicles of LDV type. The selected vehicles were characterized by similar external dimensions and authorized maximum total weight and were driven by 4-cylinder compression-ignition engines (Table 7.2). The main differences were associated with the type of gearbox and the operational parameters of the propulsion units. Table 7.2 Characteristics of the delivery trucks used for the test Parameter

Vehicle A

Vehicle B

Engine, number of cylinders Engine displacement Fuel injection system Maximum power Max. engine torque Supercharging Gearbox Volume emission factor Weight indicator Vehicle mileage

diesel, R4 1.9 dm3 rotary pump 68 kW at 4000 rpm 196 N·m at 2250 rpm yes 5, manual 36 kW/dm3 21 kg/kW 150,000 km

diesel, R4 2.2 dm3 common rail 90 kW at 3800 rpm 300 N·m at 1800–2500 rpm yes 4, automatic 41 kW/dm3 19 kg/kW 200,000 km

During road tests the particle concentration in the exhaust gas emitted by delivery trucks A and B was measured for individual measuring sections. On this basis it was possible to determine the intensity of emissions (in mg/s) of toxic

7.2

Tests of Particulate Matter Emissions from Heavy-Duty Vehicles

85

exhaust gas components of for the test run of the unloaded vehicle and for the loaded vehicle (Fig. 7.14–7.16). For both vehicles, during the entire route (three measuring sections) a significant increase in the emission rate of particulate matter was observed while transporting cargo. The most noticeable differences were observed for urban conditions (for vehicles A and B); this is mainly associated with the considerable dynamics of driving (frequent stopping and rapid acceleration) and a significant increase in the demand for energy. For the remaining measuring sections, the increase of the emission rate for the loaded vehicle amounted to about 10–50%. Variation in the number concentration of particles depending on their diameter is also noticeable during tests of loaded and unloaded delivery trucks, taking into account the diversity of engine designs. In real road operating conditions of such oi

Fig. 7.14 The particulate emissions rate in urban conditions: a) vehicle A, b) vehicle B, c) relative values

Fig. 7.15 The particulate emissions flow rate in rural conditions: a) vehicle A, b) vehicle B, c) relative values

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7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions

Fig. 7.16 The particulate emissions rate on a motorway: a) vehicle A, b) vehicle B, c) relative values

vehicles, the size distribution of particles can be calculated (defined as a dependency of their given parameter on the aerodynamic diameter) for various traffic conditions depending on the amount of load experienced. The resulting particle mass was determined on the assumption that the particulate matter density is independent of the particles’ aerodynamic diameter and amounts to 1 g/cm3. The highest number concentration of particles was reported for driving in urban conditions (Fig. 7.17a); an increase in the load results in a proportional increase in the number concentration of particles of all diameters, which is caused by a greater volume of fuel dose and a lower combustion air factor. The same pattern occurs while driving outside built-up areas (Fig. 7.17b) and on the motorway (Fig. 7.17c); however, the absolute values of the increase in the number of particles of particular diameters are lower. Taking into account the fact that increased vehicle loading requires a higher engine speed to balance the movement resistance of the vehicle, then the effect of the increased particle number will be intensified by the increase in the exhaust gas flow rate. Differences between vehicles A and B occur under all operating conditions: with regard to vehicle B, no particles of diameter of about 10 nm are observed at all. This is due to the use of a different fuel injection system and the greater mileage of the vehicle. Similar patterns were observed for measurements of the standardized surface area distributions of particles (Fig. 7.18). The basis for calculation of surface area of particles is the number of particles with a given diameter. Particles of very small diameter of up to 20 nm, formed in the nucleation phase, have a very small share in the overall surface area of all particles. Larger particles, of diameter from 50 nm to 150 nm, have the largest surface area distribution.

7.2

Tests of Particulate Matter Emissions from Heavy-Duty Vehicles Vehicle A

87

Vehicle B

a)

b)

c)

Fig. 7.17 Standardized number distribution of particles NC as a function of their diameter D recorded for different measuring sections for vehicles A and B: (a) urban area, (b) out-oftown area, c) motorway; ● – test run with load, ○ – test run without load

The concentration of particulate matter depended on the operating conditions of the vehicle. The load of the vehicle had a more significant influence on the measurement results than in the previous two cases (Fig. 7.19). While driving a loaded vehicle in urban conditions, an increase of the mass concentration of particles with diameters of 60–120 nm of over 100% was observed, where particles of larger diameter occurred in the largest concentration. This regularity – a larger mass concentration of particles of greater diameter – is observed in all operating conditions of the vehicle.

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7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions

Vehicle A

Vehicle B

a)

b)

c)

Fig. 7.18 Standardized surface area distribution of particles NCA as a function of their diameter D recorded for different measuring sections for vehicles A and B: a) urban area, b) rural area, c) motorway; ● – test run with load, ○ – test run without load

Comparing the relative cumulative values of particle mass and particle number (Fig. 7.20), it can be observed that for vehicle A 90% of the entire particle number comprises only 15–20% of the particle mass. About 90% of the particles contained in the exhaust gas have a diameter of less than 100 nm, and the increase in the particle mass is observed only above this diameter. As for vehicle B, about 90% of all particles account for 45–55% of the particle mass. About 90% of the particles contained in the exhaust gas have a diameter of less than 100 nm, and the increase of particle mass is observed only for diameters larger than 30 nm. By comparing the two vehicles, it was found that vehicle A emits particles of smaller sizes than vehicle B. At the same time, the lack of emission of small particles by vehicle B is the reason for the different shape of the cumulative characteristics compared (particle mass and particle number).

7.2

Tests of Particulate Matter Emissions from Heavy-Duty Vehicles

Vehicle A

89

Vehicle B

a)

b)

c)

Fig. 7.19 Standardized mass distribution of particles NCm as a function of their diameter D recorded for different measuring sections for vehicles A and B: a) urban area, b) out-oftown area, c) motorway; ● – test run with load, ○ – test run without load

The tests carried out on vehicles in real traffic conditions highlighted the significant impact of the load on the number and mass concentrations of particulate matter. The measurements carried out show that the characteristics of the number distribution of particles (as a function of their diameter) is dependent on the design of the fuel injection system, which in turn affects the share of the nucleation process in the formation of particulate matter within the cylinder of the combustion engine; an increase in vehicle load increases the number, surface and mass concentration of particulate matter, regardless of the conditions of use of the vehicle.

90

7 Measurements of Particle Mass and Particle Number in Real Traffic Conditions Vehicle A

Vehicle B

a)

b)

c)

Fig. 7.20 The relative cumulative value of particle number and particle mass as a function of their dimensions recorded for different measuring sections for vehicles A and B: a) urban area, b) out-of-town area, c) motorway; ● – test run with load, ○ – test run without load

References [1] Cadle, S.H., Mulawa, P., Groblicki, P., Laroo, C., Ragazzi, R.A, Nelson, K., Gallagher, G., Zielin-ska, B.: In-use Light-Duty Gasoline Vehicle Particulate Matter Emissions on Three Driving Cycles. Environmental Science & Technology 35 (2001) [2] Estwood, P.: Particle Emissions from Vehicles. John Wiley and Sons, Chichester (2008) [3] Florian, D., Giechaskiel, B., Bergmann, A., Linke, M.: 6 Years Experience with Particle Counting to Meet EU 6 Legislation Lessons Learned and Future Requirements. In: Exhaust Gas and Particulate Emission Forum, Shanghai, October 18-19 (2012) [4] Giechaskiel, B., Carriero, M., Martini, G., Andersson, J.: Heavy Duty Particle Measurement Programme (PMP): Exploratory Work for the Definition of the Test Protocol. SAE Technical Paper Series 2009-01-1767 (2009) [5] Gis, W., Merkisz, J., Pielecha, J.: Investigations of Vehicle Exhaust Emissions with use PEMS. In: Automobiles and Sustainable Mobility, FISITA 2010 World Automotive Congress, F2010-C-087, Budapeszt May 30-June 4 (2010)

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[6] Global Registry created on 18 November 2004, pursuant to Article 6 of the Agreement con-cerning the establishing of global technical regulations for wheeled vehicles, equipment and parts which can be fitted and/or be used on wheeled vehicles (ECE/TRANS/132 and Corr.1). GTR No. 5 – Technical requirements for on-board diagnostic systems (OBD) for road vehicles. ECE/TRANS/180/ Add. 5 (January 23, 2007) [7] Kayes, D., Hochgreb, S.: Mechanism of Particulate Matter Formation in SparkIgnition En-gines. Effect of Engine Operating Conditions. Environmental Science & Technology 33 (1999) [8] Khalek, I.S., Kittelson, D.B., Brear, F.: Nanoparticle Growth During Dilution and Cooling of Diesel Exhaust: Experimental Investigation and Theoretical Assessment. SAE Technical Paper Series 2000-01-0515 (2000) [9] Kittelson, D.B., Arnold, M., Watts, W.F.: Review of Diesel Particulate Matter Sampling Methods. Mineapolis (1999) [10] Lüders, H., Stommel, P.: Diesel Exhaust Treatment – New Approaches to Ultra Low Emission Diesel Vehicles. SAE Technical Paper Series 1999-01-0108 (1999) [11] Mayer, A.: Elimination of Engine Generated Nanoparticles. Haus der Technik Fachbuch. Expert Verlag, Renningen (2005) [12] Merkisz, J., Andrzejewski, M., Pielecha, J.: Comparison of Carbon Dioxide Emissions in Real Traffic Conditions of the Vehicle with the Values Obtained in the Certification Test on the Background of European Standards. Combustion Engines 3 (2011) [13] Merkisz, J., Jacyna, M., Merkisz-Guranowska, A., Pielecha, J.: Exhaust Emissions from Modes of Transport under Actual Traffic Conditions. In: Brebbia, C.A., Magaril, E.R., Khodorovsky, M.Y. (eds.) Energy Production and Management in the 21st Century, vol. 190. WIT Press, Southampton (2014) [14] Merkisz, J., Merkisz-Guranowska, A., Pielecha, J., Fuć, P., Jacyna, M.: On-Road Exhaust Emis-sions of Passenger Cars Using Portable Emission Measurement System (PEMS). In: 1st Annual International Conference on Architecture and Civil Engineering, Singapore, March 18-19 (2013) [15] Merkisz, J., Pielecha, I., Pielecha, J., Brudnicki, K.: On-Road Exhaust Emissions from Passenger Cars Fitted with a Start-Stop System. The Archives of Transport 23 (2011) [16] Merkisz, J., Molik, P., Pielecha, J.: Concept Test of Research Exhaust Emissions for Passenger Cars in Real Traffic Conditions. Combustion Engines 3 (2013) [17] Merkisz, J., Pielecha, J.: Comparative Investigations into Particulate Matter Cold Start Emissions from Euro 1–Euro 4 Passenger Cars. In: 14th ETH-Conference on Combustion Generated Nanoparticles, Zurich, August 1-4 (2010) [18] Merkisz, J., Pielecha, J.: On-Board Emissions from Light Duty Gasoline, Diesel and CNG Vehi-cles. In: THIESEL 2010 Conference on Thermo-and Fluid Dynamic Processes in Diesel Engines, Valencia, September 14-17 (2010) [19] Merkisz, J., Pielecha, J.: On-Board Particle Mass and Number Emissions Measurement from Light Duty Diesel Vehicles. In: PM Workshop on Particulate Matter Emissions from Engine and Automobile Source, Bielsko-Biała, July 2 (2012) [20] Merkisz, J., Pielecha, J.: Investigations into CNG Fuel Vehicle Emissions in Real Road Conditions. Combustion Engines 2 (2010) [21] Merkisz, J., Pielecha, J.: The Influence of Load Vehicles in Road Tests on the Particle Matter Parameters. Journal of KONES Powertrain and Transport 19 (2012)

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[22] Merkisz, J., Pielecha, J.: The On-Road Exhaust Emissions Characteristics of SUV Vehicles Fitted with Diesel Engines. Combustion Engines 2 (2011) [23] Merkisz, J., Pielecha, J., Fuć, P., Lijewski, P.: The Analysis of the PEMS Measurements of the Exhaust Emissions from City Buses Using Different Research Procedures. In: The 8th IEEE Vehicle Power and Propulsion Conference VPPC, Seul, October 9-12 (2012) [24] Merkisz, J., Pielecha, J., Gis W.: Exhaust Emission Results from Light Duty Diesel in a Road Tests. In Automobiles and Sustainable Mobility, FISITA 2010 World Automotive Congress, F2010-A-045, Budapest, May 30-June 4 (2010) [25] Merkisz, J., Pielecha, J., Lijewski, P., Merkisz-Guranowska, A., Nowak, M.: Exhaust Emissions from Vehicles in Real Traffic Conditions in the Poznan Agglomeration. In: Longhurst, J.W.S., Brebbia, C.A. (eds.) Air Pollution, WIT Transactions on Ecology and the Environment, vol. 174. WIT Press, Southampton (2013) [26] Merkisz, J., Pielecha, J., Łabędź, K.: Ekologiczna ocena pojazdów osobowych zasilanych dwupaliwowo w dużych aglomeracjach miejskich. Autobusy – Technika, Eksploatacja, Systemy Transportowe 3 (2013) [27] Merkisz J., Pielecha I., Pielecha J.: Gaseous and PM Emission from Combat Vehicle Engines during Start and Warm-Up. SAE Technical Paper Series 2010-01-2283 (2010) [28] Merkisz, J., Pielecha, J., Pielecha, I.: Road Test Emissions Using On-Board Measuring Method for Light Duty Diesel Vehicles. Jordan Journal of Mechanical and Industrial Engineering 5 (2011) [29] Merkisz, J., Pielecha, J., Radzimirski, S.: New Trends in Emission Control in the European Union. STTT, vol. 4. Springer, Heidelberg (2014) [30] Pielecha, J.: Identyfikacja parametrów cząstek stałych z silników spalinowych. Seria Rozprawy nr 467. Wydawnictwo Politechniki Poznańskiej, Poznań (2012) [31] Pielecha, J.: The Identification of PM Parameters in Compression Ignition Engines. In: Cleantech 2012: Energy, Renewables, Materials, Storage and Environment; Chapter 6: Nanomaterials for Clean & Sustainable Technology. CRC Press, Taylor & Francis Group, Boca Raton (2012) [32] Pielecha, J.: The On-Road Particle Emissions Characteristics of Vehicles Fitted with Diesel Engines. In: 15th ETH-Conference on Combustion Generated Nanoparticles, Zurich, July 26-29 (2011) [33] Pielecha, J., Merkisz, J.: Modeling of Particulate Matter Parameters for Passenger Cars Under Real Traffic Conditions. Combustion Engines 3 (2013) [34] Pielecha, J., Merkisz, J., Łabędź, K.: Particulate matter Emission from Bi-Fueled Vehicles Powered by Compressed Natural Gas and Gasoline. In: 17th ETH-Conference on Combustion Generated Nanoparticles, Zurich, June 23-26 (2013) [35] Pielecha, J., Merkisz, J., Łabędź, K.: The Effect of Mileage of the Vehicle Fueled with Natural Gas on the Vehicle’s Ecological Indices. Combustion Engines 3 (2013) [36] Voltz, M.: Potential of Fuels and Lubricants in Reducing Particle Emissions. In: Mayer, A. (ed.) Elimination of Engine Generated Nanoparticles. Haus der Technik. Expert Verlag, Renningen (2005)

Chapter 8

The Relationship between Particle Mass and Particle Number

8.1

Measurements during Stationary Tests

The possibility of establishing a correlation between the mass (or mass concentration) of particles and their number (or number concentration) seems to be interesting. This is a new research task, which due to the lack of clear regulations, has not been performed so far. Published results, e.g. in [5, 7, 8] differ substantially, different because of the different measuring methods and measurement conditions employed. This is associated mainly with the large range of particle diameters, as well as diversified particle number and the mass of a single particle (Table 8.1 and Fig. 8.1). The only constant parameter among the above parameters of particulate matter is particle density; this is accepted, as with establishing the aerodynamic diameter, as 1 g/cm3. This value is the adopted a priori, however it should be noted that it depends on the particle size and decreases with an increase in particle diameter (Fig. 8.2). Table 8.1 The range of variation of the particle mass, diameter and number Particle mass [g]

Particle diameter [μm]

Particle number [millions]

1

1000

0.002

1

100

2

1

10

2000

1

1

2,000,000

1

0.1

2,000,000,000

A study of the relation between particle mass and particle number in static conditions was performed, in accordance with the requirements of the standard [12, 13] (high repeatability of results with significant diversification of the comparable value was required). A particle counter was used to measure the particle number concentration, meeting the standard requirements – measurement of particles of © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_8

93

94

8 The Relationship between Particle Mass and Particle Numbber

oooo

Fig. 8.1 Variability of particlles: mass and number distributions as a function of aerodynam mic diameter

Fig. 8.2 Dependency of the particle p density on particle diameter (according to [9])

diameter greater than 23 nm; n for the measurement of particle mass an analyzer foor measuring the mass conccentration of particles was used. The values of particcle number and particle masss were obtained in each phase of the extended ESC teest for diesel, and then measu urements were repeated for other types of fuels [10, 111]. The summary of the resullts made it possible to compare the recorded values of thhe emission rate and specificc emissions for all types of fuels. The relations obtaineed permit estimation of the number n of particles contained in a specified unit of mass – i.e. 1 g. The values of the correlation coefficients for these tests, amounting tto more than 0.8, prove a strong relationship between particle number and particle mass (Fig. 8.3a). Where an a engine is fueled with diesel, 1 g of particulate matteer contains 2·1015 particles, and when an engine is fueled with a mixture of diesel and esters, or only esters, the particle number is greater – even twice as high. IIn general, it can be concluded that the mass emitted during one hour (1 g of paarticles) contains 2–4·1015 particles. p Comparing these parameters to the engine pow wer resulted in a non-reectilinear dependency. Most of the measurements oof specific emission of particculate matter ePM and specific particulate number ePN arre

8.1

Measurements during Stationary Tests

95

characterized by very similar values, thus the values recorded at engine idle (the largest values for specific emission and specific particulate number) were of key importance. The area of occurrence of the measuring points shows a characteristic relation: an increase in the specific emission of particulate matter above a certain value does not cause a significant increase in the specific particulate number (Fig. 8.3b). a)

b)

Fig. 8.3 Comparison of the particulate emissions rate EPN = f(EPM) (a) and the specific emission of particulate matter ePN = f(ePM) (b) for the different fuels tested [10]

The study of the relationship between the number concentration of particles and their diameter during the ESC test confirmed that the value of the number concentration of particles changes with a change in engine operating parameters (Fig. 8.4) [10, 11]. The particle number concentration characteristics obtained at the selected engine operating points show certain regularities: • the smallest particle number concentration occurs at engine idle: phase 1 of the ESC test, which is the lowest engine speed and the lowest engine load; this phase contains most particles of diameter of about 30–50 nm; • for low engine speed and light loads, e.g. phase 7, there is a lack of any characteristic particle diameter for engines fueled with the tested fuels; • at high engine speed and low load, e.g. phase 11, the characteristic diameter of particles emitted from the engine, for all types of fuels, is 30–50 nm; • operation of the engine at low speed and heavy load, e.g. phase 2 is characterized by a ‘flat’ distribution of particles of a characteristic diameter in the range from 10 to 100 nm; • average engine speed and average load – phases 3 and 4 – promote formation of the largest number of particles of diameter of about 10 nm; • for maximum engine speed and full load the largest number concentration of particles is observed, with a characteristic diameter of 50–70 nm.

96

8 The Relationship between Particle Mass and Particle Number

Fig. 8.4 Standardized particle number distribution related to particle diameter at selected engine operating points during the ESC test

A detailed relationship between engine operating parameters and particle parameters (number concentration-diameter) are noticeable in comparison of several characteristics of the selected engine operation parameters when using diesel as the test fuel. With increasing engine speed (Fig. 8.5a), an increased number concentration of particles is observed, along with a small increase in their characteristic diameters (i.e. a translation of the curve towards larger particle diameters). This is the effect of shortening the time of combustion, and at the same time of

8.1

Measurements during Stationary Tests

97

increasing the pressure of fuel injection into the combustion chamber. However, at constant engine speed and with load increased (Fig. 8.5b) up to a value of 75% of the nominal load, similar changes are observed in the number concentration of particles and their sizes – a slight increase in the concentration, while keeping a constant diameter. A further increase in the load causes a rapid reduction of the number concentration of particles with the smallest diameters, due to the maximum dose of fuel and the reduced combustion time, but an increase in the number concentration of particles of diameter 70–100 nm, and at the same time an increase of the characteristic diameter. a)

b)

Fig. 8.5 Standardized number distribution related to the particle diameter depending on: a) engine speed at constant load, b) engine load at a constant engine speed

The summary values obtained over the ESC test require an explanation. The particulate matter size distribution (Fig. 8.6a) for all phases shows the largest number concentration (more than 5·105 1/cm3) of the smallest particles with dimensions of about 10 nm for fuel marked with ‘B100’; the particle size distribution for diesel fuel is almost symmetrical – most of the particles are contained within the range from 80 to 100 nm; there are much fewer particles of other diameters. A larger number concentration of smaller particles when the engine is fueled with esters is the result of the smaller delay in self-ignition, compared to engines fueled with diesel, which results in earlier initiation of combustion and an increase in the maximum combustion pressure.

98 a)

8 The Relationship between Particle Mass and Particle Number b)

c)

Fig. 8.6 A summary of the results for particle parameters during the ESC test: a) average number distribution cPN for all phases, b) the specific number of particles ePN, c) specific emission of particulate matter ePM

However, these values do not directly match the ESC test results: the specific particle number is the largest for the engine fueled with diesel and the smallest for the engine fueled with B100 fuel. This is a result of the superposition of two factors: first, the final result is the weighted particle number average (i.e. the product of the particle number concentration and the exhaust gas flow rate) for each phase; as can be seen from Fig. 8.4, for large exhaust gas flow rate values (high engine speed and load) the number concentration of particles for the diesel-fueled engine is the highest. Secondly, a higher exhaust gas flow rate occurs for the engine fueled with B100 fuel: owing to the calorific value of esters of 37.4 MJ/kg, some 14% lower than the calorific value of diesel (42.87 MJ/kg), it is necessary to increase the dose of the fuel in order to achieve the same power output. The results of the specific emissions of particle mass obtained during the ESC test (Fig. 8.6c) are similar to the results of the specific particle number (Fig. 8.6b). The largest values of specific emissions were found for the engine fueled with diesel and the smallest for the engine fueled with B100 fuel. This is mainly associated with the fact that while running on B100 fuel an increased number of particles of smaller diameter and very low mass were observed, while during fueling with diesel particles with considerably bigger diameters were emitted. These results were verified by comparing them with the standards on exhaust gas toxicity (Fig. 8.7). The values obtained exceed by far the toxicity limits included in subsequent standards, but the engine tested met the standard in force in 2006. According to the new standards being introduced in Europe for trucks, e.g. Euro IV, the value of the specific emissions of particulate matter over the static (WHSC) and dynamic test (WHTC) should not exceed 10 mg/kWh. For these vehicles, for the static and dynamic tests, the maximum specific particle number is also determined: 8·1011 1/kWh and 6·1011 1/kWh, respectively.

8.1

Measurements during Stationary Tests

99

Fig. 8.7 A comparison of standard values (applicable from 2014) for particulate emissions from passenger vehicles and trucks

For passenger cars equipped with diesel and DI gasoline engines, according to the Euro 6 standard, a particulate matter road emission limit of 4.5 mg/km has been specified. This value may not be exceeded, regardless of whether regeneration of the particulate filter takes place during the type-approval test or not. However, for regeneration of particulate filter, no requirements were defined forbidding exceeding the particle number road emission limit (6·1011 1/km). In light of the authors’ test results and literature data on emissions of particulate matter in real traffic conditions (Fig. 8.8), it is not possible to comply with this limit during the particle filter regeneration process of (in the period of regeneration of about 10 minutes of, 1000 times more particles are formed than when there is no regeneration).

Fig. 8.8 Values of particle mass and particle number for light- and heavy-duty vehicles [5]

100

8 The Relationship between Particle Mass and Particle Number

For vehicles with emissions of less than 1 mg/km or 1 mg/kWh the correlation of particle mass and particle number is not possible [3]. The Euro 6 standard introduced, as well as ongoing monitoring of road emissions by the on-board diagnostic system (limit: 9 mg/km), also monitoring of the road emissions of particle number (1.2·1012 1/km). Relating the above information to the unit of mass, e.g. 1 mg of particulate matter, makes their comparison independent of the type of vehicle (passenger cars, trucks) and conditions of measurement (the type-approval test for passenger vehicles and trucks). The particle number corresponding to the mass of 1 mg varies in engine testing following European standard tests (values ranging from 0.6·1011 to 1.2·1011), as well as in US tests (values ranging from 1.8·1012 to 3·1012). In the latter tests there are approx. 10 times more particles in relation to the same mass (Fig. 8.9). It is believed that this is influenced by the measurement conditions, the lower range of particle diameters included in measurements and the sulfur content of the fuel (about 10 ppm). The results on particle number measurements obtained by the authors of this chapter are partially convergent with the results of the US study. This confirms the correspondence of the research methodology adopted and the correctness of the experiments carried out.

Fig. 8.9 The particle number corresponding to a mass of 1 mg for different vehicles and research tests

The data obtained during the experiment made it possible to determine the cumulative values of both particle mass and particle number, as well as their mass for each type of fuel tested. Determining the relative values with the use of the dependency PNsk/PNmax and PMsk/PMmax, increasing values of the particle number and mass were obtained (Fig. 8.10). On this basis, it can be concluded that when fueling the engine with diesel, 90% of all particles emitted comprise only about 30% of the total particle mass. About 90% of all particles contained in exhaust gas have a diameter of less than 80 nm, and the increase of particle mass is observed only for diameters larger than the average, for all fuels. When fueled with B100 fuel, 90% of the particles emitted constitute 20% of the total particle mass.

8.1

Measurements during Stationary Tests

101

Fig. 8.10 Cumulative values of particle number and mass obtained over the ESC test for different fuels and the corresponding shares of particle mass comprising 90% of particle number

On the basis of the cumulative particle number and mass, the particle density was evaluated for all fuel types used in the tests. After determining the 50th percentile cumulative volume of the particles (where the change in mass is equivalent to the change in volume), and knowing the 50th percentile value of PNsk/PNmax, the average particle density was calculated for the most common diameters. The values obtained were compared with the density of the fuels used (Fig. 8.11), giving a significant value of the correlation coefficient. This means that the particle density depends on the type of fuel. Assuming the density is equal to 1 g/cm3, in accordance with the definition of aerodynamic diameter, this gives a particle mass differing from the measured values.

Fig. 8.11 A comparison of particle density obtained depending on the density of fuel

102

8 The Relationship between Particle Mass and Particle Number

The density values obtained should be considered as an average for particles of diameter for which the value of PNsk/PNmax is 50%. However, obtaining such a dependence makes it possible to conclude that the density of the smaller particles that occur when fueling the engine with B100 fuel, is greater than the density of the larger particles found when fueling the engine with diesel. The relationship between the average particle density and the density of fuel obtained in this study is as follows:

ρPM = 0.022 ρfuel − 16.7

(8.1)

where: ρPM – particle density [g/cm3], ρfuel – fuel density [kg/m3]. This can be used to correct the particle mass in the diagnostic systems for vehicles, as well as to determine the particle mass on the basis of particle number data, without knowing the particle diameters. Confirmation of the relationship between particle mass and number prompted the authors of this chapter to look for alternative methods of estimating particle parameters for different fuels. The possibility of replacing the measurement of particle number with the measurement of exhaust gas opacity was evaluated. The measured values of the exhaust gas opacity and particle number for engine fueled with different fuels over the ESC test (Fig. 8.12) were quite well correlated with each other. The value of the correlation coefficient, ranging from 0.7 to 0.95, indicates that the interchangeable use of these measurements is possible to a limited extent. On the basis of the relationship between exhaust gas opacity and particle number, this number can be estimated for cognitive purposes, by specifying it in the diagnostic systems of vehicles, and – after additional research – in dynamic tests. The possibility to generalize the obtained relation to any operational conditions of engines is limited, because, due to the variety of particles, small particles – comprising up to 30–40% of the mass – do not cause any significant absorption of light (affecting the measurement result).

Fig. 8.12 The relationship between particulate emissions EPM and exhaust gas opacity Nz for

different fuels

8.1

Measurements during Stationary Tests

103

The particle density values obtained permitted determination of the particle mass concentration (not emission, as that is dependent on the exhaust gas flow rate), on the basis of the exhaust gas opacity. The values of the particle mass concentration obtained during the ESC test (Fig. 8.13) for the engine fueled with different fuels reflected the value of opacity well (the correlation coefficient ranged from 0.98 to 0.99). The maximum values of opacity for the engine fueled with diesel amounted to about 28%, and in the cases of fuels B50 and B100 they were 20% and 12%, respectively. This means that fueling the engine with diesel resulted in the largest particle mass concentration in the exhaust gas – up to a maximum of 130 mg/m3. Taking the exhaust gas opacity value into account instead of the particle mass concentration allows for a fairly accurate assessment of the particle mass per unit volume of the exhaust gas to be made, but does not allow prediction of the values of road or specific emissions of particulate matter (for these purposes the measurement of exhaust gas flow rate and engine power is required). The dependency determined, namely: cPM = (2.142 ±0.002) Nz(1.11 ±0.01)

(8.2)

refers to a fuel which is a mixture of diesel and esters in different proportions. The extreme values of particle mass concentration calculated from equation (8.2) differ insignificantly (Fig. 8.14a); the maximum difference is approx. 20%, assuming that the opacity value does not exceed 40%. However, analyzing the relative error, a relation between this error and the opacity value can be observed. The consequence of the equation determined (8.2) is a non-uniform nature of the relative error: for an opacity value Nz = 1%, the error is lowest, but it increases for other values of Nz. With a reduction of the exhaust gas opacity values, the relative error increases to infinity. The results of this analysis confirm the possibility of using formula (8.2) for values of exhaust gas opacity up to about 10%, for which the relative error does not exceed 15% (Fig. 8.14b).

Fig. 8.13 A comparison of the values of exhaust gas opacity Nz and particle mass concentration cPM for different types of fuel

104

8 The Relationship between Particle Mass and Particle Number a)

b)

Fig. 8.14 Particle mass concentration of the variable input parameters according to formula 8.2 (a) and the maximum relative error of determination of particle mass concentration (b)

The method presented here makes it possible to estimate the particle number for exhaust gas opacity ranging from 5 to 10%. For lower opacity values, the particle number cannot be unequivocally determined. Such an estimation can be useful, mainly in on-board diagnostic systems, where the particle number and mass emitted from the vehicle are assessed during actual operation. This method can also be used in measuring systems for testing engines emitting only particles of large diameter (older types of engines, fueled by diesel, where the emission of nanoparticles is small). Due to the high cost of testing equipment used for road tests and the limited possibility of its installation on a vehicle, and also because of the time-consuming nature of such measurements, this method could be used for the determination of particle mass and number emitted in real traffic conditions for all vehicles or equipment (machinery) types which are powered by combustion engines.

8.2

Measurements in Dynamic Test

8.2

Measurements in Dynamic Test

105

Measurements of particle mass and number were carried out on an air-conditioned chassis dynamometer over the NEDC test and its two phases (the UDC and the EUDC), on a chassis dyno as described elsewhere [3, 4]. During the test emissions of particulate matter (mass and sizes) from vehicles with emission class Euro 5 with diesel engine (with catalytic converter and particulate filter) and gasoline DI engine (with three way catalytic converter) were compared. The test vehicles were passenger cars of similar engine displacement and similar weight. The tests were carried out at an ambient temperature of 25°C, and comparatively – at a temperature of –7°C, after a 24-hour vehicle thermal stabilization period. A comparison of particulate emissions over the NEDC test carried out at a temperature of –7°C shows a two-fold increase in PM for the vehicle with the diesel engine and even a five-fold increase in the particle number for the gasoline DI engine, compared to the tests performed at a temperature of 25°C (Fig. 8.15). a)

b)

Fig. 8.15 The relative emission of particle mass (a) and particle number (b) over the NEDC test and two phases (the UDC and the EUDC) at different ambient temperatures for two different vehicles: diesel engine + DPF and gasoline DI [2]

During the test the PN/PM ratio was also determined, which amounted to 9·109 1/mg for a vehicle fitted with a diesel engine, regardless of the ambient temperature during the NEDC test. For the vehicle fitted with a gasoline DI engine, this

106

8 The Relationship between Particle Mass and Particle Number

indicator amounted to 1.2·1012 1/mg for the test at a temperature of 25°C, and for the NEDC test carried out at a temperature of –7°C the result obtained was 8·1011 1/mg. The difference between the vehicles resulted from their different combustion systems, despite their similar general concept, and from the lack of a particulate filter on the engine with direct gasoline injection (Fig. 8.16).

Fig. 8.16 The PM/PN index over the NEDC test and its two phases (the UDC and the EUDC) at different ambient temperatures for two different vehicles: diesel + DPF and gasoline DI [2]

Fig. 8.17 Differences in the sampling methodology for measuring particle mass and particle number [6]

8.2

Measurements in Dynamic Test

107

The particle mass and number results obtained prove that only one method of determining particulate matter should be used. It is believed [5], that it is possible to obtain such a correlation between these values, which would enable only particle number measurement to be used in type-approval tests, as the gravimetric method of determining the particle mass for values of about 1 mg/km is characterized by excessive measurement error and low repeatability. However, the differences in the research methodologies presented in Fig. 8.17 indicate that measurement of different parameters of particles do not give identical results. In order to more accurately compare particle number and particle mass, tests were conducted for vehicles equipped with diesel engines with particulate filters, of emission class Euro 5 and different mileages. Measurements were made with the use of a particle counter and the gravimetric method. The results obtained were characterized by considerable variability: values of particle mass varied by a factor of more than 15, while the particle number varied by a factor of 10,000 (Fig. 8.18a). a)

b)

Fig. 8.18 The relationship between particle mass and number over the NEDC test for vehicles equipped with diesel engines (a) and the correlational dependence between the determined values (b) [1]

108

8 The Relationship between Particle Mass and Particle Number

As a consequence of the comparison of all results obtained over the NEDC test and its UDC and EUDC phases, dependencies characterizing the particle number and mass were determined. The empirical dependence obtained for the whole NEDC test can be expressed by the following formula: PN [1/km] = 3·1012 PM [mg/km], and for the individual phases of the test: PN [1/km] = 2·1012 PM [mg/km] for the UDC and PN [1/km] = 4·1012 PM [mg/km] for the EUDC (Fig. 8.18b).

References [1] Bielaczyc, P.: Correlation between Particle Mass and Number for Euro 5 Compression Ignition Vehicles. In: 15th ETH-Conference on Combustion Generated Nanoparticles, Zurich (2011) [2] Bielaczyc, P., Klimkiewicz, D., Pajdowski, P., Szczotka, A., Woodburn, J.: A Quantitative Comparison of the Particulate Matter Emissions from Two Euro 5 Vehicles (Direct Injection Petrol & Diesel). In: 17th ETH-Conference on Combustion Generated Nanoparticles, Zurich (2013) [3] Bielaczyc, P., Pajdowski, P., Szczotka, A., Woodburn, J.: Development of Automotive Emissions Testing Equipment and Test Methods in Response to Legislative, Technical and Commercial Requirements. Combustion Engines 1 (2013) [4] Bielaczyc, P., Szczotka, A., Woodburn, J.: A Study of Gasoline-Ethanol Blends Influence on Performance and Exhaust Emissions from a Light-Duty Gasoline Engine. SAE Technical Paper Series 2012-01-1052 (2012) [5] Florian, D., Giechaskiel, B., Bergmann, A., Linke, M.: 6 Years Experience with Particle Counting to Meet EU 6 Legislation Lessons Learned and Future Requirements. In: Exhaust Gas and Particulate Emission Forum, Shanghai, October 18-19 (2012) [6] Fritz, O.: GDI Engine Development According EU 6. AVL Seminar, Graz (2012) [7] Giechaskiel, B., Carriero, M., Martini, G., Andersson, J.: Heavy Duty Particle Measurement Programme (PMP): Exploratory Work for the Definition of the Test Protocol. SAE Technical Paper Series 2009-01-1767 (2009) [8] Giechaskiel, B., Dilara, P., Sandbach, E., Andersson, J.: Particle Measurement Programme (PMP) Light-Duty Interlaboratory Exercise: Comparison of Different Particle Number Measurement Systems. Measurement Science and Technology 19 (2008) [9] Maricq, M.M., Podsiadlik, D.H., Chase, R.E.: Examination of the Size-Resolved and Transient Nature of Motor Vehicle Particle Emissions. Environ. Sci. Technol. 33 (1999) [10] Merkisz, J., Pielecha, J.: Emisja cząstek stałych ze źródeł motoryzacyjnych. Wydawnictwo Politechniki Poznańskiej, Poznań (2014) [11] Pielecha, J.: Identyfikacja parametrów cząstek stałych z silników spalinowych. Seria Rozprawy nr 467. Wydawnictwo Politechniki Poznańskiej, Poznań (2012) [12] Regulation (EC) No. 595/2009 of the European Parliament and of the Council of 20 June 2007 on type approval of motor vehicles with respect to emissions from heavy duty vehicles (Euro VI) and on access to vehicle repair and maintenance information and amending Regulation (EC) No 715/2007 and Directive 2007/46/EC and repealing Directives 80/1269/EEC, 2005/55/EC and 2005/78/EC. OJ L 188/1 (July 18, 2009) [13] Regulation (EC) No. 715/2007 of the European Parliament and of the Council of 20 June 2007 on type approval of motor vehicles with respect to emissions from light passenger and commercial vehicles (Euro 5 and Euro 6) and on access to vehicle repair and maintenance information. OJ L 171/1 (June 29, 2007)

Chapter 9

Methods of Decreasing Emissions of Particulate Matter in Exhaust Gas 9 Methods of Decreasing Emiss ions of Particulate Matter in Ex haust Gas

In order to remove insoluble particulate matter from the exhaust gas, particulate filters are necessary. Particle filters operate by retaining particles, and then burning them in order to clean the filtering elements. Problems that occur during the construction and operation of filters are: • the size of the particles (mostly less than 1 µm), • soot ignition temperature without a catalytic converter (in the filter and/or fuel) is about 550–600°C, the burn-out temperature of can exceed 1000°C, • very high hydrocarbon emissions during burn-out (regeneration of the filter), • increased flow resistance due to the deposition of particulate matter on the filter during engine operation. Soot combustion begins at a temperature of about 380°C, but the combustion rate reaches a significant value only at 550–600°C, and the complete combustion of soot requires temperatures exceeding 600°C [16]. In the case of diesel engines such high exhaust gas temperatures occur only for operation under conditions close to maximum power. Due to the low temperature of the exhaust gas in diesel engines, amounting under nominal conditions to about 500–700°C in the exhaust manifold (at the intake to the exhaust filter correspondingly less, depending on the distance and the intensity of cooling), and to 150–200°C for an idling engine, it becomes necessary to provide additional energy to heat up the filter. The filter cartridge must have good absorptive properties, low flow resistance and high resistance to high temperatures and significant thermal gradients. The most commonly used soot filters are ceramic wall-flow filters with a ceramic catalyst support (Fig. 9.1a) or steel wall-flow filters (Fig. 9.1b). Ceramic filter material is a porous ceramic foam, and a steel wall-flow filter consists of perforated steel tubes coated with a layer of ceramic fibre (Fig. 9.2). Due to the amount of exhaust purified in the particulate filter, filters can be divided into two types: • full-flow filters (FFF, Fig. 9.3a), • partial flow filters (PFF, Fig. 9.3b). © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_9

109

110

9 Method ds of Decreasing Emissions of Particulate Matter in Exhaust G Gas b)

a)

Fig. 9.1 Cross-sections of waall-flow filters made of: a), ceramic, b) steel a)

b)

Fig. 9.2 The channels of a particle filter: a) channels of the substrate have rectangular crooss sections, rounded by an interrmediate layer, b) longitudinal section [20] a)

b)

Fig. 9.3 Types of particulatee filters: a) full flow filters, b) partial flow filters [19]

Regardless of the typee of filter, three processes determine the retention of paarticles contained in the ex xhaust gas: diffusion, interception and inertial impactioon (Fig. 9.4). When the partiicle has a mass small enough to be moved by Browniaan motion, retention of the particle p results from contact with the surface of a fibre oor

9 Methods of Decreasing Emissions E of Particulate Matter in Exhaust Gas

1111

crevices within the wall-fflow filter. When the particle is still small enough so thhat its inertia is not significan nt, but too big to be influenced by the impact of gas paarticles, it moves along witth the gas stream and is retained when the stream hits a fibre or gets into a sufficciently narrow slit. When the particle is large enough sso that its inertia throws it ou ut of the stream, which rapidly changes direction, it is reetained by an obstacle whiich it encounters. For particles much larger than the filteer pores the phenomenon of sieving is utilized (Fig. 9.4d). a)

b)

c)

d)

Fig. 9.4 Particulate retention n processes: a) diffusion, b) interception, c) inertial impactioon, d) sieving [6]

The aforementioned PM P retention mechanisms work to different degrees, deepending on the dimension ns of the particles, the speed of the exhaust gas flow, thhe fibre diameter and the wid dth of the channels (pores). An increase in the number oof

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particles retained promotees retention of subsequent particles. However, very largge accumulation of the particcles in the filter can result in large agglomerations tearinng off, which can cause signiificant secondary emissions [15]. The volume of particu ulate filters is from 1.5 to 2.0 times the displacement oof the engine (Fig. 9.5) and depends d on the vehicle type – passenger car or truck [222].

Fig. 9.5 The dependence of the particulate filter volume on the displacement of the enginne of the vehicle [2]

Filters used up to now w allow for reductions of the emission of particle mass ranging from 70 to 99%. The critical aspects of utilization of previously used paarticulate filters are associaated with their need to be regenerated. One method of regeneration for particulate filters is the oxidation of soot (which is a component oof particulate matter), form ming carbon monoxide, and then carbon dioxide. T To achieve this, it is necessarry to increase the exhaust gas temperature, or to increasse the temperature of the filtter itself. This requires the use of an additional source oof energy, which involves additional a operational costs and there is also a danger oof damaging the filter. A mo ore economical and safer option is filter regeneration, innvolving the use of appro opriate catalysts in the exhaust gas purification system m which reduce the temperaature of soot oxidation. Passive regeneration (catalytic) involves lowering the temperature of soot iggnition with the use of cataalytic methods, to the temperature present during the opperation of a combustion engine [11]. Currently, three passive filter regeneratioon technologies are used (Fig. 9.6): coating the filter with a catalyst (referred to as a CDPF – catalyzed diesel particulate p filter, or CSF – catalyzed soot filter) or use oof the DOC before the basic filter, as well as the use of catalysts in the fuel, so-calleed FBC (fuel borne catalysts).

9 Methods of Decreasing Emissions E of Particulate Matter in Exhaust Gas a)

b)

1113

c)

Fig. 9.6 Types of DPF filterrs with passive regeneration: a) catalyzed soot filter, b) a DO OC with full flow filter system, c) c with FBC addition to fuel [8]

In technology based on n the continuous regeneration with the use of catalysts aas a coating for CRT filterrs (continuously regenerating trap) the regeneration innvolves the oxidation of a sufficient amount of NO contained in the exhaust gas tto NO2, which in turn reducces the temperature of oxidation of particulate matter tto ranges from 250–350°C. It is assumed that from the point of view of DPF regeneeration, the most beneficiaal ratio of NOx/PM in CRT filters is 25:1, which enablees correct and effective passiive regeneration of the DPF [7]. Filters coated with a catalyst shall be capable of fulfilling the following tasks [13]: • oxidizing CO and HC C in the exhaust gas, triggering the heat inside the filteer (no heat losses, which h is important in the case of regeneration), • oxidizing NO, formin ng NO2, which is used to react with soot; due to the faact that the volume of the stream of exhaust gas passing through a filter wall is small, there is a possiibility that a particle will move in the direction opposiite to the stream flow du ue to diffusion; this means that one NO molecule can bbe oxidized several timess and then reduced, improving the efficiency of the syystem and lowering the emission e of NOx, • oxidizing soot with NO O2, and at a higher temperature – with oxygen (Fig. 9.7)).

Fig. 9.7 Possibilities for paassive regeneration of particulate filters: a) standard solutioon, b) with an increased exhaustt gas temperature; * – the temperature of the exhaust gas [19]

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The FBC method, using catalysts in the fuel, (mainly Ce and Fe compounds, and precious metals, e.g. Pt), due to which the soot oxidation temperature is lowered from 600°C to 300°C (Fig. 9.8) does not lead to continuous regeneration of the filter. If the pressure in the filter reaches the limit value (specified by the manufacturer), additional fuel injection in the exhaust stroke is used, which provides additional energy and raises the temperature of the exhaust gas (Fig. 9.9). This leads to more efficient oxidation of soot. The addition of a catalyst to the fuel causes the formation of significant amounts of ash, which, depositing on the filter walls and its end, lowers the efficiency and durability of the filter.

Fig. 9.8 The dependence of soot burn-out on the regeneration time and the type of fuel additives [9]

Fig. 9.9 Start and duration of the particulate filter regeneration during passive regeneration (additive: 7 ppm Fe to diesel) [9]

9 Methods of Decreasing Emissions of Particulate Matter in Exhaust Gas

115

Wall-flow filters with a catalytic layer of transition metals with the optional addition of precious metals allow for a 30-fold reduction in soot emissions. At the same time, the temperature at the start of combustion is lowered to 480°C [3]. In filters with a catalytic layer, only the particles first deposited are in contact with the catalytic substance. Particles deposited subsequently are separated from the catalytic layer and this prevents any contact of the catalyst with the oxygen atoms flowing through the filter. Due to the addition of the catalyst to the fuel in such a form that it deposits on the filter along with the soot, there is continuous contact between the catalyst and both soot and oxygen, and the catalytic reaction can start when the reagents reach the right temperature. Then, a much higher combustion rate is observed than for the same catalyst put on the surface of the filter (Table 9.1). Table 9.1 The relative activity of mineral supplements added to fuel [3] Additive

Ignition temperature reduction [°C]

Relative combustion rate compared to pure graphite

Na Ca Zn Mn Fe NH4 Sn2+ Ni Pb Cu Ba Au V Ag Cs

92 124 130 130 131 137 153 162 180 284 – – – – –

230 4 – 86,000 – – – – 470,000 500 100 240 340 1340 64,000

The catalytic additives can be dissolved in the fuel, or fed to the filter during regeneration. The fuel additives used cannot have any harmful impact on the engine, or cause the formation and emission of additional harmful substances to the environment, such as heavy metals, halogen acids, etc. Considering fuel stability, it might be sensible to feed the additives just before injecting fuel into the engine’s cylinder. These additives can be supplied from a separate tank. It is necessary to prevent feeding the fuel not used by the engine back to the tank, as this would cause a continuous increase in the concentration of additives [3]. Active regeneration involves raising the temperature of the exhaust gas (e.g. by heating them up or appropriate control of engine operation) and does not

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use catalytic converters for regeneration, and the gas temperature required foor regeneration ranges from 600–700°C. The following methods are used to heat uup the exhaust gas (Fig. 9.10 0): • injection of additional fuel before the catalytic converter, or within the enginee, • electric heating, • heating with a burner. a)

b)

c)

Fig. 9.10 Types of DPF filteers with passive regeneration: a) with the injection of additionnal fuel before DOC, b) with eleectric heating, c) with a burner [8]

Active regeneration is controlled by the electronic controller of e.g. the enginne, after determining the leveel of the accumulated soot. Therefore, the active filterinng cycle involves long perio ods of soot accumulation punctuated by short, high regeeneration temperature valu ues. Such regeneration causes a drop of the pressure to a level comparable with a new n filter (Fig. 9.11).

Fig. 9.11 Characteristics of the pressure of exhaust gas flowing through the filter as wing the increase of the frequency of regeneration of the sooot a function of time and show filter during operation [16]

9 Methods of Decreasing Emissions E of Particulate Matter in Exhaust Gas

1117

Modern systems use caatalytic converters or fuel additives to reduce the ignitioon temperature of the soot. The T target temperature of the combustion gas in these syystems ranges from 350 to 450°C. 4 This temperature level can be achieved using thhe engine control system, in particular by means of: on into the combustion chamber, • secondary fuel injectio • delayed injection, • an increase of the intak ke air temperature. a)

b)

c)

d)

e)

f)

Fig. 9.12 Examples of typees of particulate filters: a) replaceable filter – no regeneratioon, b) filter with continuous reg generation (fuel additive), c) filter with continuous regeneratioon (a combination with catalyticc converter), d) filter with continuous regeneration, exhaust gas recirculation and catalytic converter, c e) filter with continuous regeneration (soot combuustion), f) filter with continuou us regeneration (fuel additive and changes in the fuel injectioon parameters) [15]

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Active regeneration caauses increased energy consumption – usually meaninng fuel consumption. This iss influenced by many adverse factors, the most importannt of which are: • additional fuel consum mption resulting from the production of electricity neceessary for the regeneration of a filter, he burners in case of heating-up filters by this means, • fuel consumption by th • the demand for energy y to power auxiliary equipment (such as fans), • the loss of heat energy y in the process of heat transfer to the particles. Cars equipped with dieesel engines have exhaust gas temperatures not exceedinng 300°C, particularly in urb ban driving conditions at low ambient temperature. Thhis phenomenon makes it imp possible to use only one method of regeneration of partticulate filters. For this reaason, the standard solution in modern vehicles equippeed with filtering systems is passive-active regeneration. Examples of currently useed particulate filters designs are shown in Fig. 9.12. The use of particulate filters that can be applied to engines already in use iin HDV vehicles, in order to o reduce the particle emissions, is called retrofitting, annd permits reductions particu ulate emissions by over 90%. In such systems, filter reegeneration takes place reg gardless of the exhaust gas temperature and engine opeerating parameters. Such fiilters can be built-in in vehicles with an SCR system, oor on those with no exhaust gas g purification systems. Combined exhaust gass treatment systems (DPF + SCR) are today the most eeffective technology for rad dical reduction of critical components of the exhaust gaas from diesel engines i.e. off particulate matter and nitrogen oxides (Figs 9.13–9.166). Selective catalytic reducttion is considered to be the most efficient system to reeduce NOx. Combined ex xhaust gas treatment systems for retrofitting heavy-dutty vehicles are already offeered by several manufacturers. The quality testing annd standards of those system ms are becoming essential. The following are the results oof the international VERT deePN project (deactivation, deposit prevention, removal oof particulate matter and niitrogen oxides), aimed at the introduction of the wideespread use of combined DPF D + SCR systems in vehicles already in use:

Fig. 9.13 Examples of the use of particulate filters in vehicles already in operation withoout exhaust gas purification systems [4]

9 Methods of Decreasing Emissions E of Particulate Matter in Exhaust Gas

1119

• combined DPF + SCR R systems designed for engines already in use which reeduce nitrogen oxides by 92% (while maintaining the appropriate temperaturre he quantitative particulate matter emission, the filtratioon range); in terms of th efficiency amounts to up to 99%, • inertia within the rang ge of alterations of required ammonia concentration caan be efficiently eliminatted with the use of an NH3 slip cat. a)

b)

Fig. 9.14 Exhaust gas trreatment systems: a) selective catalytic reduction system m, b) combined exhaust gas treaatment system (DOC + DPF + SCR + NH3 slip cat) [8]

Fig. 9.15 The mechanism off the reduction of pollutants in integrated exhaust gas purificcation systems [18]

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9 Method ds of Decreasing Emissions of Particulate Matter in Exhaust G Gas

Fig. 9.16 Integration of exh haust gas treatment systems; DOC – diesel oxidation catalysst, DPF – diesel particulate filtter, CSF – catalyzed soot filter (particulate filter with catalyttic coating), SCR – selective catalyst reduction (reactor of selective catalytic reductionn), yst (NH3 filter), SCRF – selective catalyst reduction and filtter ASC – ammonia slip cataly (SCR reactor with particulatee filter) [8]

Manufacturers of cataly ytic converters and research centres associated with thesse companies are currently considering two catalytic converter concepts for diessel engines: SCR reactor systtems and reactors absorbing NOx. In the United States thhe SCR system has many su upporters. This is partly due to the fact that an SCR syystem is well suited to larg ger engines. These systems are based on the presence oof NO2: absorbing catalysts obtain this component inside the reactor, and SCR syystem from an external sou urce. Exhaust gas purification systems are a response tto legislative requirements, but b at the same time, they move ahead of them. The Eurro 6 emissions standard for cars c fueled with diesel forces the use of exhaust gas purrification systems (a DOC together t with a DPF and an SCR system, Fig. 9.17). The studies published in i paper [9] relate to the analysis of exhaust gas temperature in the engine exhaustt system during the NEDC test, in which different relativve positions of DOC, SCR and DPF systems were investigated. An analysis of thhe SCR and DPF reactor systems’ location was conducted for two variants: • system A: DOC + DPF F + SCR, • system B: DOC + SCR R + DPF. Measurements carried out during the NEDC test indicate that higher exhauust gas temperatures occur when w system B is used (Fig. 9.18). This means the SC CR system can work over a wider w engine operation range, thus reducing emissions oof nitrogen oxides. In the caase of system B, the SCR system could be used for 83% % of the test duration, while in case of system A, only for 48% of the test.

9 Methods of Decreasing Emissions E of Particulate Matter in Exhaust Gas

1221

a)

b)

Fig. 9.17 Exhaust gas puriffication systems solutions in vehicles which comply with thhe Euro 6 emission standard: a)) a DOC system and integrated SCR + DPF systems, b) separaate DOC, NOx absorber and DPF F systems [21]

Fig. 9.18 The temperature of the exhaust gas during the NEDC test for different configurraF systems and the possibility of SCR system operation [9] tions of DOC, SCR and DPF

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9 Methods of Decreasing Emissions of Particulate Matter in Exhaust Gas

Particles not removed from the DPF system behave like a sponge and cause condensation [17]. An increase in the number of nanoparticles is caused by the nucleation process. As a result, filters have the ability to reduce agglomerated particles, but cause an increase in the number of liquid nuclei of nanoparticles, which is a process different from the use of oxidizing catalytic converters. The concentration of particulate matter before and after the oxidizing catalytic converter, depending on the diameter of the particles, is increased within the range of small diameters – and within the range of large particles it remains almost unchanged (Fig. 9.19). However, the concentration of the smallest particles increases when a particulate filter is used within the engine exhaust system (Fig. 9.20), and the concentration of large particles is reduced more than 3000 times.

Fig. 9.19 Particle size distribution for an engine with and without a catalytic converter (diesel DI engine, supercharged, chassis dynamometer V = 120 km/h) [12]

Fig. 9.20 Particle size distribution for an engine with and without a particulate filter diesel DI engine, supercharged, chassis dynamometer V = 120 km/h) [12]

9 Methods of Decreasing Emissions E of Particulate Matter in Exhaust Gas

1223

Studies of particulate filters f [5] were carried out over the NEDC test with thhe use of vehicles of Euro 4 and Euro 5 class. To determine the number of particlees according to their diameeter, particle counters and exhaust gas dilution system ms were used in accordance with w the requirements of PMP. The results prove the higgh efficiency of the DPF paarticulate filter (over 99.97%) and the particle numbeer emissions obtained compllied with the limits of the Euro 6 standard (6·1011 1/km m). It was also found that the efficiency during DPF regeneration is much smaller and, at the same time, the effiiciency of filtration increased as the filter filled up. Thhe number concentration off particulates with a particulate filter fitted is close tto background readings – th he particle concentration determined was smaller than oor equal to the concentration n of particles in ambient air (Fig. 9.21).

Fig. 9.21 Sample results off measurements of size distribution of particle number for a vehicle fitted with a particulaate filter [14]

The use of fuels with h different properties does not significantly change thhe quantity of particles acco ording to their measured diameter, regardless even of thhe sampling point (Fig. 9.22 2). This situation changes only during tests conducted foor the engine start-up and waarm-up phases, where for fuel B30 a larger number of thhe smallest particles might be observed. p mass emission over the FTP75 test for differennt The difference in the particle test vehicles were presen nted in the report [10]. The blackening of the measurinng filters occurring in all ph hases of the FTP75 test shows that vehicles of emissioon category LEV II equipped d with DI diesel engines emit similar particle mass durinng the first phase of the testt (a cold start-up + warm-up) to conventional diesel enngines without a particulatte filter. During the warm-up of the engine (phases 2 annd 3) the particle mass emittted from a DI gasoline engine is much smaller, but it exxceeds the particle mass emitted e from a diesel engine equipped with a particulaate filter. Emissions of particulate matter from a MPI gasoline engine are the smalleest – comparable to the masss of particles emitted from modern diesel engines with a particulate filter (Table 9.2).

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9 Method ds of Decreasing Emissions of Particulate Matter in Exhaust G Gas

a)

b)

Fig. 9.22 The distribution off the particle number and mass for different sampling points ffor different fuels: a) for fuel wiith a low sulfur content (less than 10 ppm), b) for fuel B30 wiith 30% methyl esters content [5 5] Table 9.2 Comparison of meeasuring particulate filters in phases of the FTP75 test [10] Phase 1

Conventional diesel

Gasoline GDI

Gasoline MPI

Diesel + DPF

Phase 2

hase 3

9 Methods of Decreasing Emissions E of Particulate Matter in Exhaust Gas

1225

A study commissioned d by the European Union according to the PMP schem me confirmed that particulatee filters are very effective at reducing the particle mass for light-duty vehicles (F Fig. 9.23). It was found that the use of particulate filteers not only ensures compliaance with the limits for particulate matter emissions set out in the Euro 4–Euro 6 standards, but also provides a significant reserve. a)

b)

Fig. 9.23 Road emissions of o particulate matter and the coefficient of variation over thhe NEDC test (a) and relative road r emissions of particulate matter in relation to the referencce vehicle (diesel with DPF) (b) [2]

Road emission values over the NEDC test (measurements repeated five timees) compared for different vehicles were as follows: • for vehicles with dieseel engines with a DPF: 0.3–1.0 mg/km (with an averagge value of 0.57 mg/km)), with a coefficient of variation of 26% (maximum vaalue); this value is closee to that obtained for the reference vehicle (Fig. 9.23b); • for the vehicle with an n MPI gasoline engine: 1.1 mg/km, with a coefficient oof variation of 40%; th his value is close to the values obtained for vehiclees equipped with a diesell engine with a DPF;

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9 Method ds of Decreasing Emissions of Particulate Matter in Exhaust G Gas

• for vehicles equipped with DI gasoline engines: 3–17 mg/km (with an averagge value of 10 mg/km) with w a coefficient of variation of 17%; the values obtaineed for this group of veh hicles are from 5 to 40 times greater than for vehiclees equipped with diesel engines e with a DPF; • for vehicles equipped with diesel engines without a DPF: 15–40 mg/km (witth 0 mg/km) with a coefficient of variation of 11%; the vaalan average value of 20 ues of particulate mattter emissions for this group of vehicles are 30–120 timees larger than for vehiclees equipped with a DPF. Simultaneous tests caarried out on the road emissions of particle numbeer (Fig. 9.24a and b) made itt possible to draw the following conclusions: • for vehicles with dieseel engines with a DPF: 2·1010–2·1012 1/km (with an aveerage value of 5·1010 1/k km), at a coefficient of variation of 35% (maximum vaalue); this value is close to that obtained for the reference vehicle – values foor the 3rd vehicle were omitted o (Fig. 9.24b); a)

b)

nd the coefficient of variation in the NEDC test (a) and relativve Fig. 9.24 Particle number an particle number in relation to o the reference vehicle (diesel with DPF) (b) [2]

9 Methods of Decreasing Emissions of Particulate Matter in Exhaust Gas

127

• for the vehicle with the MPI gasoline engine: 1·1011 1/km at a coefficient of variation of 25%; this value is close to the values obtained for vehicles equipped with diesel engine with DPF; • for vehicles equipped with DI gasoline engines: 4·1012–2·1013 1/km (the average value of 6·1012 1/km) at a coefficient of variation of 26%; the values obtained for this group of vehicles are from 40 to 140 times greater than for vehicles equipped with diesel engines with particulate filter; • for vehicles equipped with diesel engines without DPF: 4·1013–8·1013 1/km (average value of 6·1013 1/km) at a coefficient of variation of 7%; the values of particulate matter emissions for this group of vehicles are 300–700 times greater than for vehicles equipped with the particulate filter. The high efficiency of particulate matter filtration is confirmed in the tests performed for heavy-duty vehicles [1]. The efficiency of the filtration of particle number in the ETC test is more than 99.9%, and in the WHTC test – more than 99.8%. The particle number in the ETC test is 4·1014 1/kWh – before the filter, and 4·1011 1/kWh – behind the filter, and in the WHTC test it is, respectively, 3·1014 1/kWh and 5·10111/kWh (Fig. 9.25).

Fig. 9.25 The specific emission of particle number for engines of heavy-duty vehicles in ETC and WHTC tests [1]

The use of particulate filters in the off-road machinery also brings measurable results. In a report [14] it was found that the specific emission of particulate matter in the test of off-road machinery equipped with the DPF filters reached values several times smaller than the acceptable values specified in Stage IV standard (Fig. 9.26). The efficiency of the particulate mass filtration in the NRSC and NRTC C1 tests amounts to 96–97%, and the final value of the emissions is 1–2 mg/kWh. In dynamic NRTC tests, the specific particle number value is less than 1·1011 1/kWh, and in the static NRSC tests it is slightly more (Fig. 9.27). Determining the specific emissions of particle number before the filter (6·1013–3·1014 1/kWh), the efficiency of filtration of the particle number can be estimated as over 99.8%.

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9 Methods of Decreasing Emissions of Particulate Matter in Exhaust Gas

Fig. 9.26 The specific emission of particle mass before and after the particulate filter, and the particulate filter efficiency in various tests of the off-road machinery [14]

Fig. 9.27 Specific emissions of particulate matter before and after the particulate filter in

various tests of off-road machines [14]

References [1] Anderson, J.: Particle Results from the AECC Programme and their Relationship to PMP. In: AECC, Euro VI Heavy-Duty Symposium (2007) [2] Andersson, J., Giechaskiel, B., Muñoz-Bueno, R., Sandbach, E., Dilara, P.: Particle Measurement Programme (PMP) Light-Duty Inter-Laboratory Correlation Exercise, Final Report. European Commission, Joint Research Centre, Institute for Environment and Sustainability, Ispra (2007) [3] Bernhardt, M.: Filtry spalin silników o zapłonie samoczynnym. Politechnika Warszawska, Warszawa (1996)

References

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[4] Czerwinski, J., Zimmerli, Y., Heeb, N., Mayer, A., D’Urbano, G.: Investigations of Diesel Emissions with DPF+SCR for Retrofitting. In: FAD Conference, Dresden, November 3-4 (2010) [5] De Filippo, A., Trombley, D.: GM-AE Activities on Particle Number and Size Emissions from Diesel Engines & Vehicles. In: 2nd International Exhaust Emissions Symposium, Bielsko-Biala, May 26-27 (2011) [6] Filtration Mechanisms. Donaldson Company, http://www.shoptalk.donaldson.com (accessed August 11, 2014) [7] Fuć, P.: Studium pasywnej regeneracji filtrów cząstek stałych w silnikach o zapłonie samoczynnym. Rozprawa habilitacyjna, Wyd. Politechniki Poznańskiej, Poznań (2012) [8] Görsmann, C.F., Walker, A.P., Phillips, P.R., Wylie, J.A.: Diesel Exhaust Aftertreatment Technologies for Future Emission Requirements. In: FAD Conference, Dresden, November 3-4 (2010) [9] Harle, V., Rocher, L., Seguelong, T., Pudlarz, M., Macduff, M.: New Generation Fuel Borne Catalyst for Reliable DPF Operation in Globally Diverse Fuels. In: FAD Conference, Dresden, November 3-4 (2011) [10] Kassel, R., Couch, P., Conolly, M., Hammer-Barulich, A.: Ultrafine Particulate Matter and the Benefits of Reducing Particle Numbers in the United States. A report to the Manufacturers of Emission Controls Association (MECA). Gladstein, Neandross & Associates (July 2013) [11] Kruczyński, S.: Filtracja cząstek stałych w spalinach pojazdów samochodowych. Instytut Naukowo-Wydawniczy “Spatium”, Radom (2011) [12] Lüders, H., Krüger, M., Stommel, P., Lüers, B.: The Role of Sampling Conditions in Particle Size Distribution Measurements. SAE Technical Paper Series 981374 (1998) [13] Majewski, A., Kahir, M.: Diesel Emissions and their Control. SAE Intrernational, Warrendale (2006) [14] May, J.: Emissions Control Technologies to Meet Current and Future European Vehicle Emissions Legislation. In: 2nd International Exhaust Emissions Symposium, Bielsko-Biała, May 26-27 (2011) [15] Mayer, A.: Experience with 10’000 DPF – Retrofits of Construction Machines, Locomotives and Transit Buses in Switzerland. In: International Conference on Ultrafines, Los Angeles (2006) [16] Merkisz, J., Pielecha J.: Particulate Emissions from Automotive Sources. Wydawnictwo Politechniki Poznańskiej, Poznań (2014) [17] Mizutani, T., Iwasaki, S., Miyairi, Y., Yuuki, K., Makino, M., Kurachi, H.: Performance Verification of Next Generation Diesel Particulate Filter. SAE Paper 2010-010531 (2010) [18] Peitz, D., Kröcher, O., Gerhart, C., Jacob, E.: Catalytic Decomposition of Guanidinium Formate for Onboard Ammonia Gas Production, Independent of Engine Operation. In: FAD Conference, Dresden, November 3-4 (2011) [19] Schäffner, G., Rusch, K., Chatterjee, D., Zitzler, G.: Diesel Particulate Filter: Exhaust Aftertreatment for the Reduction of Soot Emissions, http://www.mtu-online.com (accessed July 7, 2014)

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[20] Ström, H.: Particulate Flows in Aftertreatment Systems. Model development and numerical simulations. Chalmers University of Technology, Göteborg (2011) [21] Tölkes, E.: NOx – CO2 Diesel Emission Reduction Trade-off. ITDC Regulations & Environment, General Motors Europe (2010) [22] Vogt, C.D., Schäfer-Sindlinger, A., Aoki, T., Kattouah, P., Fischer, S.: Advanced Emission Control for Future EU6 HDV Emission Standards. In: FAD Conference, Dresden, November 3-4 (2010)

Chapter 10

Conclusions 10 Conclus ions

Limited resources of liquid fuels and prevention of the harmful emissions associated with the combustion of these fuels, as well as international competition are the main factors in the current rapid development of motor vehicles. The main trends in the design of vehicles and their engines are currently determined by the requirements of provisions relating to the reduction of harmful emissions in the exhaust gas and carbon dioxide emissions [24, 27, 28]. The introduction of the Euro 5 and Euro 6 emission standards and a general emphasis on reducing greenhouse gas emissions in the EU, mainly CO2 – which means a reduction in fuel consumption – directs research and development work towards designing new, low-emission vehicles, the use of alternative fuels, the development of new types of engines and to increase the efficiency of currently produced vehicle propulsion units [1, 5–8, 18, 31]. The maximum permissible specific emissions of harmful compounds in exhaust gas introduced by the Euro 5 standard are significantly reduced in relation to the requirements of Euro 4 standard (limits tightened by 20–80%). Some of the limit values for the road emission of particle mass will continue to be reduced after the introduction of the subsequent Euro 6 standard [11, 21, 38]. Euro 6 regulations can be met only by passenger cars whose total emissions of HC, CO, NOx and PM will be less than 1 g/km, which is a challenge for both engine designs with catalytic systems for exhaust gas purification, and for analytical and measuring apparatus (Fig. 10.1 and 10.2). The lower emissions limits set out in present and future standards require equipment with an increased measuring accuracy, minimizing the impact of measurement uncertainty on the outcome. Proposals for penalty payments for excess vehicle fleet average CO2 emissions (up to 95 Euros in 2015) enforce the need for accurate and repeatable emissions measurements. Requirements for the accuracy of the measurements and their statistical significance will be reflected in the proposed EPA standards for light-duty vehicles (standard 1064). Apart from tightening emission limits for harmful compounds, work is ongoing to adapt the research procedures (used in this type of tests) to the real traffic conditions occurring in different parts of the world. One of the effects of these actions has been the introduction, in the requirements of the EU, EPA and CARB, of the obligation to carry out © Springer International Publishing Switzerland 2015 J. Merkisz and J. Pielecha, Nanoparticle Emissions from Combustion Engines, Springer Tracts on Transportation and Traffic 8, DOI: 10.1007/978-3-319-15928-7_10

131

132

10 Conclusions

type-approval tests at sub-zero ambient temperature. According to these studies, the emission tests are carried out in the laboratory at an ambient temperature of – 7oC [11] and –6.7oC [10], and so the testing laboratory must be adapted to carry out those tests in such conditions throughout the whole year.

Fig. 10.1 Change in emissions regulations for passenger cars [12, 13]

The Euro 5 + and Euro 6 standards have introduced a new limit – a limit on the particle number for light commercial vehicles with diesel and gasoline engines [17]. This is much more challenging compared to the particle mass limit [2, 9, 17], and because of this, measurements of particle number are currently the main subject of study on particulate matter emissions. Counting particles in the exhaust gas is a more formal and rigorous measurement, with a higher repeatability, than measurement of exhaust gas opacity [29]. Particulate matter emissions are a phenomenon occurring mainly in diesel engines, but it also occurs in modern gasoline engines with direct fuel injection, as well as in engines fueled with natural gas (Fig. 10.3) [15, 23]. The limit value of 6·1011 1/km (for vehicles equipped with DI gasoline engines) has been changed – there is a three-year transitional period during which the limit is increased 10 times to a value of 6·1012 1/km. On the basis of the analysis of diesel engines so far produced and prospects for their development, it can be concluded that there are no problems with the fulfilment of the limiting standards on emissions of carbon monoxide and hydrocarbons, while it seems to be harder to comply with the requirements limiting the emission of nitrogen oxides. An increase in the sales of

10 Conclusions

133

Fig. 10.2 Change in emissions provisions for heavy goods vehicles [12, 13]

Fig. 10.3 Road emissions of particle mass and particle number for light-duty vehicles with different fuels [17, 20]

134

10 Conclusionns

exhaust gas purification systems s as additional equipment for vehicles already iin service has been noted (in ( 2010: 24,640 pcs.; in 2011: 20,177 pcs.; of whichh: DPFs – 57%, DOCs – 23% %). Worldwide production of various types of particulaate filters (Table 10.1) amoun nted to 25.5 million pcs. in 2010, and it is anticipated thhat in 2014 this figure will reach 40 million [16, 19, 25]. The increased use exh haust gas purification systems capable of regeneratioon leads to the developmentt of test procedures for such equipment, which must bbe tested immediately after, just before and during the regeneration phase. The puurpose of these procedures is to assess the impact of regeneration on particle mass and number emissions. At A the same time, however, the aim should be to reducce the sulfur content in the fu uel (Fig. 10.4). New requirements con ncerning tests on emissions of harmful compounds from heavy-duty vehicles have introduced an obligation to specify not only the mass oof emitted particles, which is determined by means of the gravimetric method (bby measuring the mass of particles deposited on the filters of a sampling apparatuus which takes samples from m the dilution tunnel), but also the particle number in thhe WHSC and WHTC test, for f the range of particle diameters from 23 to 300 nm foor vehicles equipped with diesel d engines (Fig. 10.5) [4]. Measurement of particle number in the exhaust gas of cars with diesel combustion engines with particulaate Table 10.1 Types of regenerration of particulate filters and materials used [37] Application

Systtem of the particulate filter

DPF regeneration

Material

PC, LDV

use of fuel additives

active

silicon carbide

PC, LDV, HDV

DPF coated with catalyst

partly active/ passive

silicon carbide/ cordieritee

HDV, off road

DPF coated with catalyst/ without catalyst coating

passive

cordieritee

10 Conclusions

1335

filters is much more accu urate than measuring the mass of emitted particles, due tto the difficulty in determin ning the exact mass of particles emitted by low-emissioon vehicles. Additionally, th his method is characterized by greater repeatability oof measurements at low valu ues of particulate matter emissions [3].

Fig. 10.4 The relationship beetween provisions on the toxicity of exhaust gas and fuel sulffur content [14]

Fig. 10.5 Changes in particlee number (concentration or specific emission) in relation to thhe sampling point [22]

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Exhaust gas purification systems comprise an integral part of the engine and have to be designed and subjected to tests simultaneously. Further development of the design of combustion engines and exhaust gas purification systems (Table 10.2) require intensive investigation of the issues such as emissions at cold start [3, 26, 30], a reduction of the value of emissions of other exhaust gas components, which are currently not legally limited, an increase in interest in alternative and gaseous fuels and their impact on the emission of harmful compounds in the exhaust gas. Intensive research is ongoing to adapt particulate filters for use on vehicles with DI gasoline engines. At first, such products have an efficiency of 80% (in FTP75 tests), but at the same time they increase fuel consumption by about 5–10%, depending on traffic conditions. Table 10.2 An analysis of the possibilities of reducing exhaust gas emissions with the use of different technologies Internal

NOx

PM

HC

CO

CO2

NOx

PM

HC

CO

CO2

increase the degree of EGR cooling reducing the compression degree to 16.5 combustion with the preliminary mixing improved injection system 4 valves per cylinder variable valve control External particulate filter NOx slip cat selective catalytic reduction initial oxidizing catalytic converter

As combustion engines will be the basic propulsion units for different vehicles and types of machinery for many years to come, the reduction of emissions of harmful compounds, including emissions of particulate matter and, in particular, nanoparticles remains one of the most important problems to be solved by designers of engines and vehicles equipped not only with diesel engines, but also with DI gasoline engines [33]. Particulate matter emissions are limited by legal provisions relating to the maximum particle mass emitted and collected on measuring filters during the test and, for some types of engines, to the number of emitted nanoparticles, which will be limited for all types of combustion engines in their various applications [32–36]. The correlation of particle mass and number is very difficult; in the provisions of the European Union both of these values are currently limited for automotive engines. For modern vehicles equipped with diesel engines and

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fitted with particulate filters, which to a large extent restrict emissions of particle mass and number, it is the measurement of particle number which is the key to determine the engine particulate matter emissions with regard to the limits in force. Currently, a discussion is underway on the introduction of a particle number limit in the regulations of the USA and Japan. New technologies in the design of catalytic converters and new alloys of precious metals, which are currently under development, will ensure that catalytic exhaust gas purification systems play a significant role in reducing total emissions of exhaust gas from the engine. Similarly, the increase in the use of biofuels and technologically advanced lubricating oils will also significantly affect the reduction of exhaust gas emissions and emissions of greenhouse gases and will enhance energy security and enforce a more cost-effective use of fuel resources by the transport sector.

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