313 59 3MB
English Pages 108 Year 2011
266 30 1MB Read more
The hydrogen car has been proposed as the solution to our oil problems, but how would it work, and what potential proble
250 27 1MB Read more
Economists have long studied the efficiency of firms, industries, and entire economies. This volume brings together lead
260 39 8MB Read more
Due to the huge quantity and diverse nature of their metabolic pathways, fungi have great potential to be used for the p
238 24 11MB Read more
This is the primary reference, how-to guide, and sourcebook for energy conservation. It lets you improve efficiency and
448 21 52MB Read more
First Edition, 2011
© All rights reserved.
Published by: The English Press 4735/ 22 Prakashdeep Bldg, Ansari Road, Darya Ganj , Delhi - 110002 Email: [email protected]
Table of Contents Chapter 1- Fuel Efficiency in Transportation Chapter 2 - Fuel Economy in Automobiles Chapter 3 - Fuel Economy-Maximizing Behaviors Chapter 4 - Fuel Efficiency Boosting Technologies Chapter 5 - Specimens for Transport Fuel Efficiency Chapter 6 - Corporate Average Fuel Economy
Fuel Efficiency in Transportation
The fuel efficiency in transportation ranges from some hundred kilojoule per kilometre for a bicycle to several megajoule for a helicopter. Efficiency can be expressed in terms of consumption per unit distance per vehicle, consumption per unit distance per passenger or consumption per unit distance per unit mass of cargo transported.
Transportation modes For freight transport, rail and ship transport are generally much more efficient than trucking, and air freight is much less efficient.)
Walking • •
A 140 lb person walking at 3 mi/h requires approximately 80 kcal (330 kJ) of food energy per mile. Given that 1 gallon of gasoline contains about 114,000 BTU (120 MJ) of energy, this converts to roughly 360 MPG.
Bicycling As a relatively light and slow vehicle, with low-friction tires, and an efficient chaindriven drivetrain, the bicycle can be an efficient form of transport. A 140lb (64kg) cyclist riding at 16km/h requires about half the energy per unit distance of walking: 43kcal/mi. This figure depends on the speed and mass of the rider: greater speeds give higher air drag and heavier riders also consume more energy per unit distance. This converts to about 670 MPG. A motorized bicycle such as the Velosolex affords the rider to cycle under human power or with the assistance of a 49 cm3 (3.0 cu in) engine which equates to a range of 160–200
mpg-US (1.5–1.2 L/100 km; 190–240 mpg-imp). Electric pedal assisted bikes run on as little as 1.0 kilowatt-hour per 100 kilometres (0.036 MJ/km; 0.016 kW·h/mi), while maintaining speeds in excess of 30 km/h (19 mph). These best-case figures rely on a human doing 70% of the work, with around 3.6 MJ/100 km (55 BTU/mi) coming from the engine. Including the human energy dramatically changes the quoted efficiency of cycles. This would include the caloric efficiency of human muscle, cardio vascular efficiency, and the energy costs of producing, transporting, packaging and waste disposal of the food itself. Of course, to make a meaningful comparison with motor vehicles the energy costs of producing, transporting, packaging and waste disposal incurred in providing the fuel for motorized vehicles would have to be included in calculating their efficiency.
Automobiles Automobile fuel efficiency is often expressed in volume fuel consumed per one hundred kilometres (i.e., L/100 km) but in distance per volume fuel consumed (i.e., miles per gallon) in the US. This is complicated by the different energy content of fuels (compare petrol and diesel). The Oak Ridge National Laboratory (ORNL) state that the energy content of unleaded gasoline is 115,000 BTU per US gallon (32 MJ/L) compared to 130,500 BTU per US gallon (36.4 MJ/L) for diesel. A second important consideration is the energy costs of producing these fuels. Bio-fuels, electricity and hydrogen, for instance, have significant energy inputs in their production. Because of this, the 50-70% efficiency of hydrogen production has to be combined with the vehicle efficiency to yield net efficiency. A third consideration to take into account is the occupancy rate of the vehicle. As the number of passengers per vehicle increases the consumption per unit distance per vehicle increases. However this increase is slight compared to the reduction in consumption per unit distance per passenger. We can compare, for instance, the estimated average occupancy rate of about 1.3 passengers per car in the San Francisco Bay Area to the 2006 UK estimated average of 1.58. Example consumption figures •
• • •
The Volkswagen Polo 1.4 TDI Bluemotion and the Seat Ibiza 1.4 TDI Ecomotion, both rated at 3.8 L/100 km (74 mpg-imp; 62 mpg-US) (combined) are the most fuel efficient cars on sale in the UK as of 22 March 2008. Honda Insight - achieves 48 mpg-US (4.9 L/100 km; 58 mpg-imp) under real-world conditions. Honda Civic Hybrid- regularly averages around 45 mpg-US (5.2 L/100 km; 54 mpg-imp). Toyota Prius - According to the US EPA's revised estimates, the combined fuel consumption for the 2008 Prius is 46 mpg-US (5.1 L/100 km; 55 mpg-imp), making it the most fuel efficient US car of 2008 according to the EPA. In the UK, the
official fuel consumption figure (combined) for the Prius is 4.3 L/100 km (66 mpg-imp; 55 mpg-US). The General Motors EV1 was rated in a test with a charging efficiency of 373 Wh-AC/mile or 23 kWh/100km (translates approximately to 2.6L/100km). The four passenger GEM NER also uses 169 Wh/mile or 10.4 kWh/100 km, which equates to 2.6 kWh/100 km per person when fully occupied, albeit at only 24 mph (39 km/h).
Aircraft A principal determinant of fuel consumption in aircraft is drag, which must be opposed by thrust for the aircraft to progress. Drag is proportional to the lift required for flight, which is equal to the weight of the aircraft. However, beginning at transonic speeds of around Mach 0.85, shockwaves form increasing drag. For supersonic flight, it is difficult to achieve a lift to drag ratio greater than five and fuel consumption is increased in proportion. As induced drag increases with weight, mass reduction, with improvements in engine efficiency and reductions in aerodynamic drag, has been a principal source of efficiency gains in aircraft, with a rule-of-thumb being that a 1% weight reduction corresponds to around a .75% reduction in fuel consumption. Flight altitude affects both parasitic drag and engine efficiency. Jet-engine efficiency increases at altitude up to the tropopause, the temperature minimum of the atmosphere; at lower temperatures, the Carnot efficiency is higher. Jet engine efficiency is also increased at high speeds, but above about Mach 0.85 the airframe aerodynamic losses increase faster. Concorde fuel efficiency comparison
Gulfstream G550 business jet
passenger miles/imperial gallon
passenger miles/US gallon
litres/passenger 100 km
Passenger airplanes averaged 4.8 L/100 km per passenger (1.4 MJ/passenger-km) (49 passenger-miles per gallon) in 1998. Note that on average 20% of seats are left unoccupied. Jet aircraft efficiencies are improving: Between 1960 and 2000 there was a 55% overall fuel efficiency gain (if one were to exclude the inefficient and limited fleet of the DH Comet 4 and to consider the Boeing 707 as the base case).. Most of the improvements in efficiency were gained in the first decade when jet craft first came into widespread commercial use. Compared to the most advanced turboprop aircraft of the 1950s, the modern aircraft is only marginally more efficient per passenger-mile. Between 1971 and 1998 the fleet-average annual improvement per available seat-kilometre was
estimated at 2.4%. As over 80% of the fully laden take-off weight of a modern aircraft such as the Airbus A380 is craft and fuel, there remains considerable room for future improvements in efficiency. •
Airbus state that their A380 consumes fuel at the rate of less than 3 L/100 km per passenger. CNN reports that the fuel consumption figures provided by Airbus for the A380, given as 2.9 L/100 km per passenger, are "slightly misleading", because they assume a passenger count of 555, but do not allow for any luggage or cargo. Typical occupancy figures are unknown at this time. NASA and Boeing are conducting tests on a 500 lb (230 kg) "blended wing" aircraft. This design allows for greater fuel efficiency since the whole craft produces lift, not just the wings. The Sikorsky S-76C++ twin turbine helicopter gets about 1.65 mpg-US (143 L/100 km; 1.98 mpg-imp) at 140 knots (260 km/h; 160 mph) and carries 12 for about 19.8 passenger-miles per gallon (11.9 litres per 100 passenger-kilometres). The Bell 407 single-engine turbine helicopter burns 51 gallons per hour at 120 knots carrying one pilot and six passengers. 2.35 NM per gal for 14.1 passengermiles per gallon. If the pilot is counted as a passenger, it's 16.4 people-miles per gallon. Increased altitudes can yield better fuel rates. It has operated at 47 gal/hr. Concorde the supersonic transport managed about 17 miles to the gallon per passenger; similar to a business jet, but much worse than a subsonic turbofan aircraft.
Cunard state that their liner, the RMS Queen Elizabeth 2, travels 49.5 feet per imperial gallon of diesel oil (3.32 m/L or 41.2 ft/US gal), and that it has a passenger capacity of 1777. Thus carrying 1777 passengers we can calculate an efficiency of 16.7 passenger-miles per imperial gallon (16.9 L/100 p·km or 13.9 p·mpg–US).
Trains UK Freight train average about 1.5-2.0 MPG Loaded. Compared with road transport it is very efficient; if lorries did the same trip they would use 70% more fuel than a freight train. Uk Passenger trains average from 8MPG - 12MPG. • •
Freight: the AAR claims an energy efficiency of 457 ton-miles per gallon of diesel fuel in 2008 The East Japan Railway Company claims for 2004 an energy intensity of 20.6 MJ/car-km, or about 0.35 MJ/passenger-km
a 1997 EC study on page 74 claims 18.00 kWh/train-km for the TGV Duplex assuming 3 intermediate stops between Paris and Lyon. This equates to 64.80 MJ/train-km. With 80% of the 545 seats filled on average this is 0.15 MJ/passenger-km. Actual train consumption depends on gradients, maximum speeds and stopping patterns. Data was produced for the European MEET project (Methodologies for Estimating Air Pollutant Emissions) and illustrates the different consumption patterns over several track sections. The results show the consumption for a German ICE High speed train varied from around 19–33 kW·h/km (68–120 MJ/km; 31–53 kW·h/mi). The data also reflects the weight of the train per passenger. For example, the TGV double-deck ‘Duplex’ trains use lightweight materials in order to keep axle loads down and reduce damage to track, this saves considerable energy. A Siemens study of Combino light rail vehicles in service in Basel, Switzerland over 56 days showed net consumption of 1.53 kWh/vehicle-km, or 5.51 MJ/vehicle-km. Average passenger load was estimated to be 65 people, resulting in average energy efficiency of 0.085 MJ/passenger-km. The Combino in this configuration can carry as many as 180 with standees. 41.6% of the total energy consumed was recovered through regenerative braking. A trial of a Colorado Railcar double-deck DMU hauling two Bombardier Bi-level coaches found fuel consumption to be 128 US gallons (480 l; 107 imp gal) for 144 miles (232 km), or 1.125 mpg-US (209.1 L/100 km; 1.351 mpg-imp). The DMU has 92 seats, the coaches typically have 162 seats, for a total of 416 seats. With all seats filled the efficiency would be 468 passenger-miles per US gallon (0.503 L/100 passenger-km; 562 passenger-mpg-imp). Note that intercity rail in the US reports 3.17 MJ/passenger-km which is several times higher than reported from Japan. Independent transportation researcher David Lawyer attributes this difference to the fact that the losses in electricity generation may not have been taken into account for Japan and that Japanese trains have a larger number of passengers per car. Modern electric trains like the shinkansen use regenerative braking to return current into the catenary while they brake. This method results in significant energy savings, where-as diesel locomotives (in use on unelectrified railway networks) typically dispose of the energy generated by dynamic braking as heat into the ambient air. This Swiss Railroad company SBB-CFF-FFS cites 0.082 kWh per passenger-km for traction. AEA carried out a detailed study of road and rail for the United Kingdom Department for Transport. Final report
Amtrak reports 2005 energy use of 2,935 BTU per passenger-mile (1.9 MJ/passenger-km). The Passenger Rail (Urban and Intercity) and Scheduled Intercity and All Charter Bus Industries Technological and Operational Improvements - FINAL REPORT states that "Commuter operations can dissipate more than half of their total traction energy in braking for stops." and that "We estimate hotel power to be 35 percent (but it could possibly be as high as 45 percent) of total energy consumed by commuter railways." Having to accelerate and decelerate a heavy train load of people at every stop is inefficient despite regenerative braking which can recover typically around 20% of the energy wasted in braking.
Buses • •
In July 2005, the average occupancy for buses in the UK was stated to be 9. The fleet of 244 40-foot (12 m) 1982 New Flyer trolley buses in local service with BC Transit in Vancouver, Canada, in 1994/95 consumed 35454170 kW·h for 12966285 vehicle-km, or 9.84 MJ/vehicle-km. Exact ridership on trolleybuses is not known, but with all 34 seats filled this would equate to 0.32 MJ/passengerkm. It is quite common to see people standing on Vancouver trolleybuses. Note that this is a local transit service with many stops per kilometre; part of the reason for the efficiency is the use of regenerative braking. A diesel bus commuter service in Santa Barbara, CA, USA found average diesel bus efficiency of 6.0 mpg-US (39 L/100 km; 7.2 mpg-imp) (using MCI 102DL3 buses). With all 55 seats filled this equates to 330 passenger-mpg, with 70% filled the efficiency would be 231 passenger-mpg. At the typical average passenger load of 9 people, the efficiency is only 54 passenger-mpg and could be half of this figure when many stops are made in urban routes.
Rockets Unlike other forms of transportation, rockets are commonly designed for putting objects into orbit. Once in sufficiently high orbit, objects have almost negligible air drag, and the orbits decay so slowly that a satellite can be still orbiting decades after launch. For these reasons rocket and space propulsion efficiency is rarely measured in terms of distance per unit of fuel, but in terms of specific impulse which gives how much change in momentum (i.e. impulse) can be obtained from a unit of propellant. However, to give a concrete example, NASA's space shuttle fires its engines for around 8.5 minutes, consuming 1,000 tons of solid propellant (containing 16% aluminium) and an additional 2,000,000 litres of liquid propellant (106,261 kg of liquid hydrogen fuel) to lift the 100,000 kg vehicle (including the 25,000 kg payload) to an altitude of 111 km and an orbital velocity of 30,000 km/h. With a specific energy of 31MJ per kg for aluminum
and 143 MJ/kg for liquid hydrogen, this means that the vehicle consumes around 5 TJ of solid propellant and 15 TJ of hydrogen fuel. Once in orbit at 200 km and around 7.8 km/s velocity, the orbiter requires no further fuel. At this altitude and velocity, the vehicle has a kinetic energy of about 3 TJ and a potential energy of roughly 200 GJ. Given the energy input of 20 TJ, the Space Shuttle is about 16% energy efficient at launching the orbiter and payload just 4% efficiency if the payload alone is considered. If the Space Shuttle were used to transport people or freight from a point to another on the Earth, using the theoretical largest ground distance (antipodal) flight of 20,000 km, energy usage would be about 0.04 MJ/km/kg of payload.
NASA's Crawler-Transporter is used to move the Shuttle from storage to the launch pad. It uses diesel and has one of the highest fuel consumption rates on record, 150 US gallons per mile (350 l/km; 120 imp gal/mi).
International transport comparisons UK Public transport Rail and bus are generally required to serve 'off peak' and rural services, which by their nature have lower loads than city bus routes and inter city train lines. Moreover, due to their 'walk on' ticketing it is much harder to match daily demand and passenger numbers. As a consequence, the overall load factor on UK railways is 35% or 90 people per train : Conversely, Air services work on point-to-point networks between large population centres and are 'pre-book' in nature. Using Yield management overall loads can be raised to around 70-90%. However, recently intercity train operators have been using similar techniques, with loads reaching typically 71% overall for TGV services in France and a similar figure for the UK's Virgin trains services.
US Passenger transportation The US Transportation Energy Data Book states the following figures for Passenger transportation in 2006:
Transport mode Vanpool Efficient Hybrid
Average passengers per vehicle 6.1 1.57
BTU per passenger-mile
MJ per passengerkilometre
Motorcycles Rail (Intercity Amtrak) Rail (Transit Light & Heavy) Rail (Commuter) Air Cars Personal Trucks Buses (Transit)
31.3 96.2 1.57 1.72 8.8
2,996 3,261 3,512 3,944 4,235
1.964 2.138 2.302 2.586 2.776
US Freight transportation The US Transportation Energy book states the following figures for Freight transportation in 2004: Fuel consumption BTU per short ton mile kJ per tonne kilometre Class 1 Railroads 341 246 Domestic Waterborne 510 370 Heavy Trucks 3,357 2,426 Air freight (approx) 9,600 6,900 Transportation mode
Caveats Comparing fuel efficiency in transportation is like comparing apples and oranges. Here are a few things to consider. Traction energy Metrics produced by the UK Rail and Safety •
There is a distinction between vehicle MPGe and passenger MPGe. Most of these entries cite passenger MPGe even if not explicitly stated. It is important not to compare energy figures that relate to unsimilar journeys. An airline jet cannot be used for an urban commute so when comparing aircraft with cars the car figures must take this into account. There is currently no agreed upon method of comparing electric vehicle efficiency to heat engine (fossil fuel) vehicle efficiency. However, current typical emissions and thermal energy consumption can be compared. If the issue is rapid investment in new electric mass transit it is important to use emissions associated with the most polluting fuel because increased demand for electricity increases the use of polluting fuel used in generation for the immediate future, as well as low emissions fuels in the case of some countries.
Systems that re-use vehicles like trains and buses can't be directly compared to vehicles that get parked at their destination. They use energy to return (less full) for more passengers and must sometimes run on schedules and routes with little patronage. These factors greatly affect overall system efficiencies. The energy costs of accumulating load need to be included. In the case of most mass transit distributing and accumulating load over many stops means that passenger kilometres are inherently a small proportion of vehicle kilometres see Transport Energy Metrics, Lessons from the west Coast Main line Modernisation and figures for London Underground in transport statistics for Great Britain 2003. Lessons from the west coast mainline modernisation suggest that long passenger rail should operate at less than 40% capacity utilisation and for London underground the figure is probably less than 15%. Most cars run at less than full capacity, with the usual average load being between 1 and 2. Cars are also subject to inefficiencies because of congestion and the need to negotiate road junctions. Vehicles are not isolated systems. They usually form a part of larger systems whose design inherently determines energy consumption. Judging the value of transport systems by comparing the performance of their vehicles alone can be misleading. For instance, metro systems may have a poor energy efficiency per passenger kilometre, but their high throughput and low physical footprint makes the existence of high urban population densities viable. Total energy consumption per capita declines sharply as population density increases, since journeys become shorter.
Fuel Economy in Automobiles
Fuel consumption monitor from a 2006 Honda Airwave.
A 1916 experiment in creating a fuel-economic automobile in the United States. The vehicle weighed only 135 pounds (61.2 kg) and was an adaptation of a small gasoline engine originally designed to power a bicycle. Fuel usage in automobiles refers to the relationship between distance traveled by an automobile and the amount of fuel consumed. There are no quantities or units for fuel usage defined in the International Standard ISO 80000 Quantities and Units, so the nationally-defined reciprocal quantities fuel economy and fuel consumption are used here.
Units of measure
MPG to L/100km conversion chart: blue: U.S. gal, red: imp gal (UK) The two most common ways to measure automobile fuel usage are: Fuel consumption The amount of fuel used per unit distance; most commonly, litres per 100 kilometres (L/100 km). This measure is used in Europe, China, Canada, Australia and New Zealand. Fuel economy The distance traveled per unit of fuel used; in miles per gallon (mpg) or kilometres per litre (km/L), commonly used in in the UK, U.S. (mpg) and Japan, Korea, India, Pakistan, parts of Africa, The Netherlands, Denmark and Latin America (km/L). If mpg is used, it is important to know which gallon is being referred to; the imperial gallon is about 20% larger than the U.S. gallon. Fuel economy and fuel consumption are reciprocal quantities. To convert either way between L/100 km and miles per U.S. gallon, divide 235 by the number in question; for miles per imperial gallon, divide 282 by either number. For example, to convert from 30 mpg (U.S.) to L/100 km, divide 235 by 30, giving 7.83 L/100 km; or from 10 L/100 km to mpg (U.S.), divide 235 by 10, giving 23.5 mpg. To convert between L/100 km and km/L, divide 100 by the number in question. A related measure is the amount of carbon dioxide produced as a result of the combustion process, typically measured in grams of CO2 per kilometre (CO2 g/km). A petrol
(gasoline) engine will produce around 2.32 kg of carbon dioxide for each litre of petrol consumed (19.4 lb/gal). A typical diesel engine produces 2.66 kg/L (22.23 lb/gal) though typically burns fewer litres per kilometre for an otherwise identical car. Since the CO2 emissions are relatively constant per litre, they are proportional to fuel consumption.
Inverse or reciprocal scale A modest improvement in fuel economy for a relatively inefficient vehicle can provide greater savings in terms of financial cost to the driver and environmental impact than a proportionately larger increase for a more economical vehicle. This is most intuitively demonstrated using the inverse scale — gallons per mile or liters per kilometer. If a driver who travels 15,000 miles (24,000 km) a year switches from a vehicle with 10 mpg to 12 mpg average fuel economy (0.10 gallons per mile to 0.083 gallons per mile), 250 gallons are saved. A similar 20% improvement in exchanging a 30 mpg for a 36 mpg (0.033 gallons per mile for 0.027) vehicle saves only 83 gallons. Because mpg and fuel consumption are inversely related, mpg can cause illusions. Gallons Per Mile is more useful than mpg when comparing the fuel consumption of different cars. One should note that MPG works differently than litres per hundred kilometres. l/100 km denotes a rate of fuel consumption, while MPG is a measure of fuel economy (or 'gas mileage'). If a car uses less fuel, the MPG increases, and l/100 km decreases, but the percentages will not match, because the values are reciprocal. For example, 20% better MPG does not mean 20%, but 16.7% less fuel. This comes from the following calculation: 20% is 1.2 times bigger distance, therefore 100% / 1.2 = 83.3% of the original fuel consumption, or 16.7% less fuel. Because consumption is an inverse function of MPG, MPG can be a misleading indicator of fuel efficiency gains. People intuitively take the difference in MPG when comparing two cars. This leads them to underestimate the savings from small improvements on low MPG cars (e.g., 14 to 20 MPG, which saves twice as much fuel over a given distance as the improvement from 33 to 50 MPG). A measure of gallons per mile (GPM), such as gallons per 100 miles, provides an accurate view of consumption for a given distance of driving. Unlike MPG, the GPM of one car can be subtracted from the GPM of another car to get a direct measure of fuel savings.
Gallons per mile Gallons per mile (GPM) is a way of measuring the fuel efficiency of a vehicle. It conveys the amount of fuel that will be used more intuitively than Miles per gallon, which can be misleading. For example, many people incorrectly believe that the improvement from 34 to 44 MPG saves more fuel than the improvement from 15 to 19 MPG because they look at the difference (or percentage change) between MPG levels. The improvement of 15 to 19 MPG change saves about twice as much fuel as the improvement of 34 to 44 MPG over a given distance of driving. "Gallons per 100 miles"
(GPHM) corrects these illusions. When comparing the fuel savings of different vehicles, GPHM can be subtracted. MPG cannot. Because using "gallons per mile" yields small numbers, it is useful to use a longer distance as the base, such as "gallons per hundred miles" (GPHM) or "gallons per 10,000 miles." Many countries use a measure of volume over distance to measure fuel consumption. The following table shows how MPG translates to "gallons per 100 miles" (GPHM) and gallons per 10,000 miles (GP10K), with small rounding: MPG GPHM GP10K 10 10 1,000 11 9 909 12.5 8 800 14 7 714 16.5 6 606 20 5 500 25 4 400 33 3 303 50 2 200 100 1 100 A focus on fuel consumption makes clear the benefits of removing the most inefficient vehicles, as in the Car Allowance Rebate System program. Seemingly small MPG improvements on inefficient cars saves a large amount of fuel over a given distance of driving. For example, replacing a car that gets 14 MPG with a car that gets 25 MPG saves 3 gallons of fuel every 100 miles. That improvement saves more fuel than can be saved by any improvement to a 33 MPG vehicle. Because a gallon of fuel emits 20 pounds of carbon dioxide, saving 3 gallons of fuel every 100 miles saves 3 tons of carbon dioxide every 10,000 miles of driving.
Fuel economy statistics While the ability of petroleum engines to maximize the transformed chemical energy of the fuel (their fuel efficiency) has increased since the beginning of the automotive era, this has not necessarily translated into increased fuel economy or decreased fuel consumption, which is additionally affected by the mass, shape, and size of the car, and the goals of an automobile's designers, which may be to produce greater power and speed rather than greater economy and range. The choice of car and how it is driven drastically affects the fuel economy. A top fuel dragster can consume 6 U.S. gallons (23 L) of nitromethane for a quarter-mile (400 m)
run in about 4.5 seconds, which comes out to 24 U.S. gallons per mile (5,600 L per 100 km). The other extreme was set by PAC-Car II in the 2005 Eco-Marathon, which managed 5384 kilometres per litre (15,210 mpg-imp; 12,660 mpg-US). Both such vehicles are extremes, and most people drive ordinary cars that typically average 15 to 40 miles per U.S. gallon (19 to 50 miles per imperial gallon) or (5.6 to 15 L per 100 km). However, due to environmental concerns caused by CO2 emissions, new EU regulations are being introduced to reduce the average emissions of cars sold beginning in 2012, to 130 g/km of CO2, equivalent to 4.5 L per 100 km (52 mpg U.S., 63 MPG imperial) for a diesel-fueled car, and 5.0 L per 100 km (47 mpg U.S., 56 MPG imperial) for a gasoline (petrol)-fueled car. It should be borne in mind that the average consumption across the fleet is not immediately directly affected by the new vehicle fuel economy, for example Australia's car fleet average in 2004 was 11.5 L/100 km (20.5 mpgU.S.), compared with the average new car consumption in the same year of 25.3 mpgU.S. New Zealand •
United Kingdom • •
May 2008 August 2008
United States EPA • •
Physics The power to overcome air resistance increases roughly with the cube of the speed, and thus the energy required per unit distance is roughly proportional to the square of speed. Because air resistance increases so rapidly with speed, above about 30 mph (48 km/h), it becomes a dominant limiting factor. Driving at 45 rather than 65 mph (72 rather than 105 km/h) results in about one-third the power to overcome wind resistance, or about one-half the energy per unit distance, and much greater fuel economy can be achieved. Increasing speed to 90 mph (145 km/h) from 65 mph (105 km/h) increases the power requirement by 2.6 times, the energy by 1.9 times, and decreases fuel economy. In real world vehicles the change in fuel economy is less than the values quoted above due to complicating factors. The power needed to overcome the rolling resistance is roughly proportional to the speed, and thus the energy required per unit distance is roughly constant. At very low speeds the
dominant losses are internal friction. A hybrid can achieve greater fuel economy in city driving than on the highway because the engine shuts off when it is not needed to charge the battery and has little to no consumption at stops. In addition, regenerative braking puts energy back into the battery.
Speed and fuel economy studies
1997 fuel economy statistics for various U.S. models Fuel economy at steady speeds with selected vehicles was studied in 2010. The most recent study indicates greater fuel efficiency at higher speeds than earlier studies; for example, some vehicles achieve better mileage at 65 than at 45 mph (72 rather than 105 km/h), although not their best economy, such as the 1994 Oldsmobile Cutlass, which has its best economy at 55 mph (29.1 mpg), and gets 2 mpg better economy at 65 than at 45 (25 vs 23 mpg). All cars demonstrated decreasing fuel economy beyond 65 mph (105 km/h), with wind resistance the dominant factor, and may save up to 25% by slowing from 70 mph (110 km/h) to 55 mph (89 km/h). However, the proportion of driving on high speed roadways varies from 4% in Ireland to 41% in Netherlands. There were complaints when the U.S. National 55 mph (89 km/h) speed limit was mandated that it could lower, instead of increase fuel economy. The 1997 Toyota Celica got 1 mpg better fuel-efficiency at 65 than it did at 55 (43.5 vs 42.5), although almost 5 mpg better at 60 than at 65 (48.4 vs 43.5), and its best economy (52.6 mpg) at only
25 mph (40 km/h). Other vehicles tested had from 1.4 to 20.2% better fuel-efficiency at 55 mph (89 km/h) vs. 65 mph (105 km/h). Their best economy was reached at speeds of 25 to 55 mph.
Differing measuring regimes Identical vehicles can have varying fuel consumption figures listed depending upon the testing methods of the jurisdiction. Lexus IS 250 - petrol 2.5 L 4GR-FSE V6, 204 hp (153 kW), 6 speed automatic, rear wheel drive • • •
Australia (L/100 km) - 'combined' 9.1, 'urban' 12.7, 'extra-urban' 7.0 European Union (L/100 km) - 'combined' 8.9, 'urban' 12.5, 'extra-urban' 6.9 United States (L/100 km) - 'combined' 9.8, 'city' 11.2, 'highway' 8.1
2006–2008 Lexus IS 250 (GSE20; U.S.)
2006–2008 Lexus IS 250 (GSE20; Europe)
Fuel economy standards and testing procedures Gasoline new passenger car fuel efficiency Country 2004 average
People's Republic of China United States
Requirement 2005 2008
6.1 L/100 km 5.7 L/100 km 24.6 mpg 27 mpg (9.5 L/100 km) (8.7 L/100 km) (cars and (cars only)* trucks)*
European Union Japan 8.08 L/100 km Australia CAFE eq none (2002) * highway ** combined
35.5 mpg (6.6 L/100 km) (2016) 5 L/100 km (2012) 6.7 L/100 km CAFE eq (2010) 6.7 L/100 km CAFE eq (2010) (voluntary)
Australia Beginning in October 2008, all new cars will need to be sold with a sticker on the windscreen showing the fuel consumption and the CO2 emissions. Fuel consumption figures are expressed as urban, extra urban and combined. Previously, only the combined number was given. Australia also uses a star rating system, from one to five stars, that combines greenhouse gases with pollution, rating each from 0 to 10 with ten being best. To get 5 stars a combined score of 16 or better is needed, so a car with a 10 for economy (greenhouse) and a 6 for emission or 6 for economy and 10 for emission, or anything in between would get the highest 5 star rating. The lowest rated car is the Ssangyong Korrando with automatic transmission, with one star, while the highest rated was the Toyota Prius hybrid. The Fiat 500, Fiat Punto and Fiat Ritmo as well as the Citroen C3 also received 5 stars. The greenhouse rating depends on the fuel economy and the type of fuel used. A greenhouse rating of 10 requires 60 or less grams of CO2 per km, while a rating of zero is more than 440 g/km CO2. The highest greenhouse rating of any 2009 car listed is the Toyota Prius, with 106 g/km CO2 and 4.4 litres per 100 kilometres (64 mpg-imp; 53 mpgUS). Several other cars also received the same rating of 8.5 for greenhouse. The lowest rated was the Ferrari 575 at 499 g/km CO2 and 21.8 litres per 100 kilometres (13.0 mpgimp; 10.8 mpg-US). The Bentley also received a zero rating, at 465 g/km CO2. The best fuel economy of any year is the 2004–2005 Honda Insight, at 3.4 litres per 100 kilometres (83 mpg-imp; 69 mpg-US).
Irish fuel economy label. In the European Union and the UK, passenger vehicles are commonly tested using two drive cycles, and corresponding fuel economies are reported as 'urban' and 'extra-urban', in liters per 100 km and (in the UK) in miles per imperial gallon. The urban economy is measured using the test cycle known as ECE-15, introduced by the EEC Directive 90/C81/01 in 1999. It simulates a 4,052 m (2.518 mile) urban trip at an average speed of 18.7 km/h (11.6 mph) and at a maximum speed of 50 km/h (31 mph). The extra-urban cycle or EUDC lasts 400 seconds (6 minutes 40 seconds) at an average speed 62.6 km/h (39 mph) and a top speed of 120 km/h (74.6 mph). EU fuel economy numbers tend to be considerably lower than corresponding US EPA test results for the
same vehicle. For example, the 2011 Honda CR-Z with a five-speed manual transmission is rated 6.1/4.4 l/100 km in Europe and 7.6/6.4 l/100 km in the United States. In the European Union advertising has to show Carbon dioxide (CO2)-emission and fuel consumption data in a clear way as described in the UK Statutory Instrument 2004 No 1661. Since September 2005 a color-coded "Green Rating" sticker has been available in the UK, which rates fuel economy by CO2 emissions: A: