Fuel usage in automobiles refers to the
fuel efficiencyFuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...
relationship between
distanceDistance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...
traveled by an automobile and the amount of
fuelFuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
consumed.
There are no quantities or units for fuel usage defined in the
International StandardThe International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
ISO 80000 Quantities and Units, so the nationally-defined reciprocal quantities
fuel economy and
fuel consumption are used in this article.
Units of measure
The two most common ways to measure automobile fuel usage are:
Fuel consumption: The amount of fuel used per distance; Often an arbitrary distance, most commonly litres per 100 kilometres (L/100 km). This measure is used in Europe, China, South Africa, Australia and New Zealand. Canadian law allows for use of either litres per 100 kilometres or miles per gallon.
Fuel economy: Efficiency is defined as output per input. In automobiles it is the distance traveled per unit of fuel used; in miles per gallon (mpg) or kilometres per litre (km/L), commonly used in the UK, US (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 US gallon.
Fuel economy and fuel consumption are reciprocal quantities. To convert either way between L/100 km and miles per US 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 to L/100 km, divide 235 by 30, giving 7.83 L/100 km; or from 10 L/100 km to mpg (US), 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 dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
produced as a result of the combustion process, typically measured in grams of CO
2 per kilometre (CO
2 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 CO
2 emissions are relatively constant per kilogram, 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 15000 miles (24,140.1 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, both can be misinterpreted. Gallons per mile is more useful than miles per gallon when comparing the fuel consumption of different cars, while miles per gallon is more useful when comparing the fuel efficiency of different cars.
One should note that mpg works differently from 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 improvement percentages will not equate, because the values are
reciprocalIn mathematics, a multiplicative inverse or reciprocal for a number x, denoted by 1/x or x−1, is a number which when multiplied by x yields the multiplicative identity, 1. The multiplicative inverse of a fraction a/b is b/a. For the multiplicative inverse of a real number, divide 1 by the...
.
For example, 20% lower l/100 km does not mean 20%, but 25% more distance. This comes from the following calculation: 20% is 0.8 times less fuel, therefore 100% / 0.8 = 125% of the original distance, or 25% further on every litre.
Because consumption is an inverse function of MPG, MPG can be misinterpreted in terms of fuel consumption improvement. Some 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 a one-for-one comparison of the 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. Inversely this becomes a moot point to the driver who wishes to get the most traveling out of a tank of fuel. Here the MPG values give a clear measure of "bang for your buck" and are directly comparable; an improvement of 20% MPG means 20% more traveling for any car. In this case comparing the difference in GPM values would be misleading. (e.g. an improvement from 0.2 to 0.1 GPM gets the driver twice as far on a tank, but an improvement of 0.3 to 0.2 GPM only gets the driver 50% further.) Since many people do not know how far they will drive, but know how large their fuel tank is, the MPG value remains more useful to them.
However, for vehicles with zero or very low fuel consumption, the distance traveled per unit of fuel would
not be definedIn mathematics, division by zero is division where the divisor is zero. Such a division can be formally expressed as a / 0 where a is the dividend . Whether this expression can be assigned a well-defined value depends upon the mathematical setting...
, and so the litres per kilometre scale would be most suitable.
Gallons per mile
Gallons per mile (GPM) is a way of measuring the fuel consumption 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 the improvement from 34 miles per US gallon saves more fuel than the improvement from 15 miles per US gallon because they look at the difference (or percentage change) between MPG levels. The improvement of 15 to 19 mpg 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 | L/100 km |
| 10 |
10 |
1,000 |
24 |
| 11 |
9 |
909 |
21 |
| 12.5 |
8 |
800 |
18.8 |
| 14 |
7 |
714 |
17 |
| 16.5 |
6 |
606 |
14.3 |
| 20 |
5 |
500 |
12 |
| 25 |
4 |
400 |
9.4 |
| 33 |
3 |
303 |
7.1 |
| 50 |
2 |
200 |
4.7 |
| 100 |
1 |
100 |
2.4 |
A focus on fuel consumption makes clear the benefits of removing the most inefficient vehicles, as in the
Car Allowance Rebate SystemThe Car Allowance Rebate System , colloquially known as "Cash for Clunkers", was a $3 billion U.S. federal scrappage program intended to provide economic incentives to U.S. residents to purchase a new, more fuel-efficient vehicle when trading in a less fuel-efficient vehicle...
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 16 mpg
-US (19 mpg
-imp or 15 L/100 km) with a car that gets 30 mpg
-US (36 mpg
-imp or 8 L/100 km) saves 3 US gallons (2.5 imp gal) of fuel every 100 miles (7 L/100 km). Because the combustion of 1 US gallon of fuel emits 20 pounds of carbon dioxide (burning 1 imp gal emits 24 lb and burning 1 L emits 2.4 kg), this saves 3 short tons (2.7 long tons) of carbon dioxide every 10,000 miles (1.7 t every 10,000 km) of driving.
Fuel economy statistics
While the ability of petroleum
enginesThe internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
to maximize the transformed chemical energy of the fuel (their
fuel efficiencyFuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...
) has increased since the beginning of the
automotive eraThe history of the automobile begins as early as 1769, with the creation of steam engined automobiles capable of human transport. In 1806, the first cars powered by an internal combustion engine running on fuel gas appeared, which led to the introduction in 1885 of the ubiquitous modern gasoline-...
, 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 fuelTop Fuel racing is a class of drag racing in which the cars are run on a mix of approximately 90% nitromethane and 10% methanol rather than gasoline or simply methanol. The cars are purpose-built for drag racing, with an exaggerated layout that in some ways resembles open-wheel circuit racing...
dragsterDrag racing is a competition in which specially prepared automobiles or motorcycles compete two at a time to be the first to cross a set finish line, from a standing start, in a straight line, over a measured distance, most commonly a ¼-mile straight track....
can consume 6 US gallons (23 L) of
nitromethaneNitromethane is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a slightly viscous, highly polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent...
for a quarter-mile (400 m) run in about 4.5 seconds, which comes out to 24 US gallons per mile (5,600 L per 100 km). The other extreme was set by PAC-Car II in the 2005
Eco-MarathonThe Eco-Marathon is an annual competition sponsored by Shell, in which participants build special vehicles to achieve the highest possible fuel efficiency. The Eco-Marathon is held around the world with events in Finland, France, Germany, The Netherlands, Japan, and the USA...
, which managed 5384 kilometres per litre (12,664 mpgU.S.).
Both such vehicles are extremes, and most people drive ordinary cars that typically average 15 to 40 miles per US gallon (19 to 50 miles per imperial gallon or 5.6 to 15 L per 100 km). However, due to environmental concerns caused by CO
2 emissions, new EU regulations are being introduced to reduce the average emissions of cars sold beginning in 2012, to 130 g/km of CO
2, equivalent to 4.5 L/100 km (52 mpg
-US, 63 mpg
-imp) for a diesel-fueled car, and 5.0 L/100 km (47 mpg
-US, 56 mpg
-imp) for a gasoline (petrol)-fueled car.
It should be borne in mind that the average consumption across the fleet is not immediately affected by the
new vehicle fuel economy, for example Australia's car fleet average in 2004 was 11.5 L/100 km (20.5 mpg
-US), compared with the average new car consumption in the same year of 25.3 mpg
US
New Zealand:
United Kingdom:
United States EPA:
Physics
The power to overcome
air resistanceIn fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
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) requires 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 per unit distance 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
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 (105 rather than 72 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). The proportion of driving on high speed roadways varies from 4% in
IrelandIreland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
to 41% in
NetherlandsThe Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
.
When the U.S. National 55 mi/h speed limit was mandated, there were complaints that fuel economy could decrease instead of increase. 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 mi/h. Other vehicles tested had from 1.4 to 20.2% better fuel-efficiency at 55 mi/h vs. 65 mi/h. Their best economy was reached at speeds of 25 to 55 mph (see graph).
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
Fuel economy standards and testing procedures
Gasoline new passenger car fuel efficiency
| Country |
2004 average |
Requirement |
| 2004 |
2005 |
2008 |
Later |
People's Republic of ChinaChina , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
|
|
|
6.9 L/100 km |
6.9 L/100 km |
6.1 L/100 km |
| United States |
24.6 mpg (9.5 L/100 km) (cars and trucks)* |
27 mpg (8.7 L/100 km) (cars only)* |
|
|
35.5 mpg (6.6 L/100 km) (2016) |
| European Union |
|
|
|
|
5 L/100 km (2012) |
| Japan |
|
|
|
|
6.7 L/100 km CAFE eq (2010) |
| Australia |
8.08 L/100 km CAFE eq (2002) |
none |
|
|
6.7 L/100 km CAFE eq (2010) (voluntary) |
* highway ** combined
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 CO
2 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 KorrandoThe SsangYong Korando is a small SUV produced from 1983–2006 and from 2010-onwards. The name Korando is a contraction of "Korea Can Do".-First generation:...
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 CO
2 per km, while a rating of zero is more than 440 g/km CO
2. The highest greenhouse rating of any 2009 car listed is the Toyota Prius, with 106 g/km CO
2 and 4.4 l/100 km. Several other cars also received the same rating of 8.5 for greenhouse. The lowest rated was the Ferrari 575 at 499 g/km CO
2 and 21.8 l/100 km. The Bentley also received a zero rating, at 465 g/km CO
2. The best fuel economy of any year is the 2004–2005
Honda InsightThe Honda Insight is a hybrid electric vehicle manufactured by Honda and the first production vehicle to feature Honda's Integrated Motor Assist system. The first-generation Insight was produced from 1999 to 2006 as a three-door hatchback...
, at 3.4 l/100 km.
Europe
In the European Union, 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 consumption numbers tend to be considerably lower than corresponding US EPA test results for the same vehicle. For example, the 2011
Honda CR-ZThe Honda CR-Z is a compact hybrid electric automobile manufactured by Honda and marketed as a "sport hybrid coupe." The CR-Z combines a hybrid gasoline-electric powertrain with traditional sports car elements...
with a six-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 dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO
2)-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 CO
2 emissions: A: <= 100 g/km, B: 100–120, C: 121–150, D: 151–165, E: 166–185, F: 186–225, and G: 226+. Depending on the type of fuel used, for gasoline A corresponds to about 4.1 l/100 km and G about 9.5 l/100 km. Ireland has a very similar label, but the ranges are slightly different, with A: <= 120 g/km, B: 121–140, C: 141–155, D: 156–170, E: 171–190, F: 191–225, and G: 226+.
New Zealand
Starting on 7 April 2008 all cars of up to 3.5 tonnes GVW sold other than private sale need to have a fuel economy sticker applied (if available) that shows the rating from one half star to six stars with the most economic cars having the most stars and the more fuel hungry cars the least, along with the fuel economy in L/100 km and the estimated annual fuel cost for driving 14,000 km. The stickers must also appear on vehicles to be leased for more than 4 months. All new cars currently rated range from 6.9 l/100 km to 3.8 l/100 km and received respectively from 4.5 to 5.5 stars.
United States
U.S. Energy Tax Act
The
Energy Tax ActThe Energy Tax Act is a law passed by the U.S. Congress as part of the National Energy Act. The objective of this law was shift from oil and gas supply toward energy conservation; thus, to promote fuel efficiency and renewable energy through taxes and tax credits.- Tax credits for conservation...
of 1978 in the U.S. established a gas guzzler tax on the sale of new model year vehicles whose fuel economy fails to meet certain statutory levels. The tax applies only to cars (not trucks) and is collected by the
IRSThe Internal Revenue Service is the revenue service of the United States federal government. The agency is a bureau of the Department of the Treasury, and is under the immediate direction of the Commissioner of Internal Revenue...
. Its purpose is to discourage the production and purchase of fuel-inefficient vehicles. The tax was phased in over ten years with rates increasing over time. It applies only to manufacturers and importers of vehicles, although presumably some or all of the tax is passed along to automobile consumers in the form of higher prices. Only new vehicles are subject to the tax, so no tax is imposed on used car sales. The tax is graduated to apply a higher tax rate for less-fuel-efficient vehicles. To determine the tax rate, manufacturers test all the vehicles at their laboratories for fuel economy. The U.S.
Environmental Protection AgencyThe U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
confirms a portion of those tests at an EPA lab.
EPA testing procedure through 2007
Two separate fuel economy tests simulate city driving and highway driving: the "city" driving program or Urban Dynamometer Driving Schedule or (UDDS) is defined in and consists of starting with a cold engine and making 23 stops over a period of 31 minutes for an average speed of 20 mph (32 km/h) and with a top speed of 56 mph (90 km/h).
The "highway" program or Highway Fuel Economy Driving Schedule (HWFET) is defined in and uses a warmed-up engine and makes no stops, averaging 48 mph (77 km/h) with a top speed of 60 mph (97 km/h) over a 10 miles (16.1 km) distance. The measurements are then adjusted downward by 10% (city) and 22% (highway) to more accurately reflect real-world results. A weight average of city (55%) and highway (45%) fuel economies is used to determine the guzzler tax.
In some cases, this tax may only apply to certain variants of a given model; for example, the 2004–2006 Pontiac GTO (captive import version of the
Holden MonaroThe Holden Monaro is an automobile that was produced by GM Holden Ltd, an Australian subsidiary of General Motors, between 1968 and 1977 and between 2001 and 2005...
) did incur the tax when ordered with the four-speed automatic transmission, but did not incur the tax when ordered with the six-speed manual transmission.
Because EPA figures had almost always indicated better efficiency than real-world fuel-efficiency, the EPA has modified the method starting with 2008. Updated estimates are available for vehicles back to the 1985 model year.
EPA testing procedure: 2008 and beyond
As a means of reflecting real world fuel economy more accurately, the EPA adds three new tests that will combine with the current city and highway cycles to determine fuel economy of new vehicles, beginning with the 2008 model year. A high speed/quick acceleration loops lasts 10 minutes, covers 8 miles (12.9 km), averages 48 mi/h and reaches a top speed of 80 mi/h. Four stops are included, and brisk acceleration maximizes at a rate of 8.46 mi/h per second. The engine begins warm and air conditioning is not used. Ambient temperature varies between 68 °F (20 °C) to 86 °F (30 °C).
The air conditioning test raises ambient temperatures to 95 °F (35 °C), and the vehicle's climate control system is put to use. Lasting 9.9 minutes, the 3.6 miles (5.8 km) loop averages 22 mi/h and maximizes at a rate of 54.8 mi/h. Five stops are included, idling occurs 19 percent of the time and acceleration of 5.1 mph/sec is achieved. Engine temperatures begin warm. Lastly, a cold temperature cycle uses the same parameters as the current city loop, except that ambient temperature is set to 20 °F (-6.7 °C).
EPA tests for fuel economy do not include electrical load tests beyond climate control, which may account for some of the discrepancy between EPA and real world fuel-efficiency. A 200 W electrical load can produce a 0.4 km/L (0.94 mpg) reduction in efficiency on the FTP 75 cycle test.
Advanced technology vehicles
Following the efficiency claims made for vehicles such as
Chevrolet VoltThe Chevrolet Volt is a plug-in hybrid electric vehicle manufactured by General Motors. The Volt has been on sale in the U.S. market since mid-December 2010, and is the most fuel-efficient compact car sold in the United States, as rated by the United States Environmental Protection Agency...
and
Nissan LeafNissan introduced its first battery electric vehicle, the Nissan Altra at the Los Angeles International Auto Show on 29 December 1997. The Altra EV was produced between 1998 and 2002, only about 200 vehicles were ever produced, and it was mainly used as a fleet vehicle for companies such as...
, the
National Renewable Energy LaboratoryThe National Renewable Energy Laboratory , located in Golden, Colorado, is the United States' primary laboratory for renewable energy and energy efficiency research and development. The National Renewable Energy Laboratory is a government-owned, contractor-operated facility; it is funded through...
recommended to use EPA's new vehicle fuel efficiency formula that gives different values depending on fuel used. In November 2010 the EPA introduced the first fuel economy ratings in the
Monroney stickerThe Monroney sticker or window sticker is a label required in the United States to be displayed in all new automobiles and includes the listing of certain official information about the car. Since the mid-seventies the U.S. Environmental Protection Agency provides fuel economy metrics in the label...
s for
plug-in electric vehicleA plug-in electric vehicle is any motor vehicle that can be recharged from any external source of electricity, such as wall sockets, and the electricity stored in the rechargeable battery packs drives or contributes to drive the wheels...
s.
For the fuel economy label of the Chevy Volt plug-in hybrid EPA rated the car separately for all-electric mode expressed in
miles per gallon gasoline equivalentMiles per gallon gasoline equivalent is a measure of the average distance traveled per unit of energy consumed. MPGe is used by the U.S...
(MPG-e) and for gasoline-only mode expressed in conventional miles per gallon. EPA also estimated an overall combined city/highway gas-electricity fuel economy rating expressed in miles per gallon gasoline equivalent (MPG-e). The label also includes a table showing fuel economy and electricity consumed for five different scenarios: 30, 45, 60 and 75 miles (120.7 km) driven between a full charge, and a never charge scenario. This information was included in order to make the consumers aware of the variability of the fuel economy outcome depending on miles driven between charges. Also the fuel economy for a gasoline-only scenario (never charge) was included. For electric-only mode the energy consumption estimated in kWh per 100 miles is also shown.
For the fuel economy label of the Nissan Leaf
electric carAn electric car is an automobile which is propelled by electric motor, using electrical energy stored in batteries or another energy storage device. Electric cars were popular in the late-19th century and early 20th century, until advances in internal combustion engine technology and mass...
EPA rated the combined fuel economy in terms of
miles per gallon gasoline equivalentMiles per gallon gasoline equivalent is a measure of the average distance traveled per unit of energy consumed. MPGe is used by the U.S...
, with a separate rating for city and highway driving. This fuel economy equivalence is based on the energy consumption estimated in kWh per 100 miles, and also shown in the Monroney label.
In May 2011, the
National Highway Traffic Safety AdministrationThe National Highway Traffic Safety Administration is an agency of the Executive Branch of the U.S. government, part of the Department of Transportation...
(NHTSA) and EPA issued a joint final rule establishing new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with
model yearThe model year of a product is a number used worldwide, but with a high level of prominence in North America, to describe approximately when a product was produced, and indicates the coinciding base specification of that product....
2013, and voluntary for 2012 models. The ruling include include new labels for
alternative fuelAlternative fuels, known as non-conventional or advanced fuels, are any materials or substances that can be used as fuels, other than conventional fuels...
and alternative propulsion vehicles available in the US market, such as plug-in hybrids,
electric vehicleAn electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
s,
flexible-fuel vehicleA flexible-fuel vehicle or dual-fuel vehicle is an alternative fuel vehicle with an internal combustion engine designed to run on more than one fuel, usually gasoline blended with either ethanol or methanol fuel, and both fuels are stored in the same common tank...
s,
hydrogen fuel cell vehicleA Fuel cell vehicle or Fuel Cell Electric Vehicle is a type of hydrogen vehicle which uses a fuel cell to produce electricity, powering its on-board electric motor...
, and
natural gas vehiclethumb|right|200px|2009 [[Honda Civic GX]] hooked up to Phill refueling system.A natural gas vehicle or NGV is an alternative fuel vehicle that uses compressed natural gas or liquefied natural gas as a clean alternative to other fossil fuels...
s. The common fuel economy metric adopted to allow the comparison of alternative fuel and advanced technology vehicles with conventional
internal combustion engineThe internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
vehicles is miles per gallon of gasoline equivalent (MPGe). A gallon of gasoline equivalent means the number of kilowatt-hours of electricity, cubic feet of
compressed natural gasCompressed natural gas is a fossil fuel substitute for gasoline , diesel, or propane/LPG. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other fuels in the event of a spill...
(CNG) , or kilograms of
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
that is equal to the energy in a gallon of gasoline.
The new labels also include for the first time an estimate of how much fuel or electricity it takes to drive 100 miles (160.9 km), providing U.S. consumers with fuel consumption per distance traveled, the metric commonly used in many other countries. EPA explained that the objective is to avoid the traditional miles per gallon metric that can be potentially misleading when consumers compare fuel economy improvements, and known as the "MPG illusion." EPA explained that the new gallons-per mile metric provides a more accurate measure of fuel efficiency.
CAFE standards
The Corporate Average Fuel Economy (CAFE) regulations in the United States, first enacted by Congress in 1975, are federal regulations intended to improve the average fuel economy of cars and light trucks (trucks, vans and
sport utility vehicleA sport utility vehicle is a generic marketing term for a vehicle similar to a station wagon, but built on a light-truck chassis. It is usually equipped with four-wheel drive for on- or off-road ability, and with some pretension or ability to be used as an off-road vehicle. Not all four-wheel...
s) sold in the U.S. in the wake of the 1973 Arab Oil Embargo. Historically, it is the sales-weighted average fuel economy of a manufacturer's fleet of current
model yearThe model year of a product is a number used worldwide, but with a high level of prominence in North America, to describe approximately when a product was produced, and indicates the coinciding base specification of that product....
passenger cars or light trucks, manufactured for sale in the United States. Under Truck CAFE standards 2008–2011 this changes to a "footprint" model where larger trucks are allowed to consume more fuel. The standards are limited to vehicles under a certain weight, but those weight classes will be expanding in 2011 if current law (as of April 2006) holds.
State regulations
The states are pre-empted by federal law, and are not allowed to make fuel efficiency standards. However, California has a special dispensation from the Clean Air Act to make emissions standards (which other states may adopt instead of the federal standards). The
California Air Resources BoardThe California Air Resources Board, also known as CARB or ARB, is the "clean air agency" in the government of California. Established in 1967 in the Mulford-Carrell Act, combining the Bureau of Air Sanitation and the Motor Vehicle Pollution Control Board, CARB is a department within the...
is implementing some legislation that limits
greenhouse gasA greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
emissions. A legal dispute has emerged over whether this is effectually a fuel efficiency standard.
Energy considerations
Since the total force opposing the vehicle's motion (at constant speed) multiplied by the distance through which the vehicle travels represents the work that the vehicle's engine must perform, the study of mileage (the amount of energy consumed per unit of distance travelled) requires a detailed analysis of the forces that oppose a vehicle's motion. In terms of physics, Force = rate at which the amount of work generated (energy delivered) varies with the distance travelled, or:
Note: The amount of work generated by the vehicle's power source (energy delivered by the engine) would be exactly proportional to the amount of fuel energy consumed by the engine if the engine's efficiency is the same regardless of power output, but this is not necessarily the case due to the operating characteristics of the internal combustion engine.
For a vehicle whose source of power is a heat engine (an engine that uses heat to perform useful work), the amount of fuel energy that a vehicle consumes per unit of distance (level road) depends upon:
- The thermodynamic efficiency of the heat engine;
- The forces of friction within the mechanical system that delivers engine output to the wheels;
- The forces of friction in the wheels and between the road and the wheels (rolling friction);
- Other internal forces that the engine works against (electrical generator, air conditioner etc., water pump, engine fan etc.);
- External forces that resist motion (e.g., wind, rain);
- Non-regenerative braking force (brakes that turn motion energy into heat rather than storing it in a useful form; e.g., electrical energy in hybrid vehicles).
Ideally, a car traveling at a constant velocity on level ground in a vacuum with frictionless wheels could travel at any speed without consuming any energy beyond what is needed to get the car up to speed. Less ideally, any vehicle must expend energy on overcoming road load forces, which consist of aerodynamic drag, tire rolling resistance, and inertial energy that is lost when the vehicle is decelerated by friction brakes. With ideal regenerative braking, the inertial energy could be completely recovered, but there are few options for reducing aerodynamic drag or rolling resistance other than optimizing the vehicle's shape and the tire design. Road load energy, or the energy demanded at the wheels, can be calculated by evaluating the vehicle equation of motion over a specific driving cycle. The vehicle powertrain must then provide this minimum energy in order to move the vehicle, and will lose a large amount of additional energy in the process of converting fuel energy into work and transmitting it to the wheels. Overall, the sources of energy loss in moving a vehicle may be summarized as follows:
- Engine efficiency
Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work...
, which varies with engine type, the mass of the automobile and its load, and engine speed (usually measured in RPMRevolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
).
- Aerodynamic drag force, which increases roughly by the square of the car's speed
In fluid dynamics, the drag equation is a practical formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid....
, but note that drag power goes by the cube of the car's speed.
- Rolling friction.
- Braking, although regenerative braking captures some of the energy that would otherwise be lost.
- Losses in the transmission
A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...
. (Manual transmissionA manual transmission, also known as a manual gearbox or standard transmission is a type of transmission used in motor vehicle applications...
s can be up to 94% efficient whereas older automatic transmissionAn automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...
s may be as low as 70% efficient Automatically controlled shifting of gearboxes that have the same internals as manual boxes will give the same efficiency as a pure manual gearbox plus the bonus of added intelligence selecting optimal shifting points
- Air conditioning. The power required for the engine to turn the compressor decreases the fuel-efficiency, though only when in use. This may be offset by the reduced drag of the vehicle compared with driving with the windows down. The efficiency of AC systems gradually detoriates due to dirty filters etc.; regular maintenance prevents this. The extra mass of the air conditioning system will cause a slight increase in fuel consumption.
- Power steering. Older hydraulic power steering systems are powered by a hydraulic pump constantly engaged to the engine. Power assistance required for steering is inversely proportional to the vehicle speed so the constant load on the engine from a hydraulic pump reduces fuel efficiency. More modern designs improve fuel efficiency by only activating the power assistance when needed; this is done by using either direct electrical power steering assistance or an electrically powered hydraulic pump.
- Cooling. Older cooling systems used a constantly engaged mechanical fan to draw air through the radiator at a rate directly related to the engine speed. This constant load reduces efficiency. More modern systems use electrical fans to draw additional air through the radiator when extra cooling is required.
- Electrical systems. Headlights, battery charging, active suspension, circulating fans, defrosters, media systems, speakers, and other electronics can also significantly increase fuel consumption, as the energy to power these devices causes increased load on the alternator. Since alternators are commonly only 40–60% efficient, the added load from electronics on the engine can be as high as 3 hp at any speed including idle. In the FTP 75 cycle test, a 200 watt load on the alternator reduces fuel efficiency by 1.7 mpg. Headlights, for example, consume 110 watts on low and up to 240 watts on high. These electrical loads can cause much of the discrepancy between real world and EPA tests, which only include the electrical loads required to run the engine and basic climate control.
Fuel-efficiency decreases from electrical loads are most pronounced at lower speeds because most electrical loads are constant while engine load increases with speed. So at a lower speed a higher proportion of engine horsepower is used by electrical loads. Hybrid cars see the greatest effect on fuel-efficiency from electrical loads because of this proportional effect.
Fuel economy-boosting technologies
- Using lighter materials for moving parts such as piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
s, crankshaftThe crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
, gearA gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
s and alloy wheelAlloy wheels are automobile wheels which are made from an alloy of aluminium or magnesium. They are typically lighter for the same strength...
s
- Using thinner engine oils that require less energy to circulate
- Reducing the volume of water-based cooling systems so that engines reach their efficient operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
sooner
- Using coolant additives that increase the thermal efficiency of the cooling system
- Designing the exterior of the vehicle to reduce aerodynamic drag
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
- Replacing tires with low rolling resistance (LRR) models
- Using lower-friction lubricant
A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...
s (engine oilMotor oil or engine oil is an oil used for lubrication of various internal combustion engines. The main function is to lubricate moving parts; it also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts.Motor oils are derived from...
, transmission fluid, axle fluid)
- Incorporating Locking torque converters in automatic transmissions to reduce slip and power losses in the converter
- Using a manual gearbox or continuously variable transmission
A continuously variable transmission is a transmission that can change steplessly through an infinite number of effective gear ratios between maximum and minimum values. This contrasts with other mechanical transmissions that offer a fixed number of gear ratios...
automatic gearbox instead of epicyclic gearboxes with torque converter couplings
- Increasing the number of gearbox ratios in manual gearboxes
- Augmenting a downsized engine with an electric drive system and battery (hybrid vehicle
A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles , which combine an internal combustion engine and one or more electric motors.-Power:...
s) hybrid electric vehicleA hybrid electric vehicle is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional...
- Replacing petrol engines with more efficient diesel engines
- Installing an alternator disconnect and supplying electrical system from deep cycle battery pack that is charged at home (although the added weight of the larger battery would have to be considered in calculating the possible fuel savings from this concept)
- Automatically shutting off engine when vehicle is stopped (mild hybrid
Mild hybrids are essentially conventional fossil-fuel vehicles equipped with a large electric machine allowing the engine to be turned off whenever the car is coasting, braking, or stopped, yet restart quickly...
)
- Recapturing wasted energy while braking (regenerative braking)
- Recapturing wasted energy in the vehicle suspension
- The use of two-wheel drive only, on road vehicles not used for towing
- Optimising other engine combustion strategies:
- Optimising engine running temperature by electronic control of the cooling system
- Stratified Charge
In a stratified charge engine, the fuel is injected into the cylinder just before ignition. This allows for higher compression ratios without "knock," and leaner air/fuel mixtures than in conventional internal combustion engines....
combustion
- Lean burn
Lean burn refers to the use of lean mixtures in an internal combustion engine. The air-fuel ratios can be as high as 65:1, so the mixture has considerably less fuel in comparison to the stoichiometric combustion ratio ....
combustion
- HCCI
Homogeneous charge compression ignition is a form of internal combustion in which well-mixed fuel and oxidizer are compressed to the point of auto-ignition...
(Homogeneous Charge Compression Ignition) combustion
- Variable valve timing
In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...
- Supercharging
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
or twinchargingTwincharger refers to a compound forced induction system used on some piston-type internal combustion engines. It is a combination of an exhaust-driven turbocharger and an engine-driven supercharger, each mitigating the weaknesses of the other...
(when coupled with a downsized engine)
- Turbocharged Direct Injection
TDI or Turbocharged Direct Injection is a design of turbodiesel engines, which feature turbocharging and cylinder-direct fuel injection, developed and produced by Volkswagen Group. These TDI engines are widely used in all mainstream Volkswagen Group marques of passenger cars and light commercial...
diesel engines
- Gasoline direct injection
In internal combustion engines, gasoline direct injection , also known as petrol direct injection or direct petrol injection, is a variant of fuel injection employed in modern two-stroke and four-stroke gasoline engines...
petrol engines
- Common Rail
Common rail direct fuel injection is a modern variant of direct fuel injection system for petrol and diesel engines.On diesel engines, it features a high-pressure fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding unit injectors...
diesel engines
- Variable geometry turbocharging
Variable-geometry turbochargers are a family of turbochargers, usually designed to allow the effective aspect ratio of the turbo to be altered as conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds...
- Reducing vehicle weight by using materials such as aluminum, fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
, plastic, high-strength steelHigh-strength low-alloy steel is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. HSLA steels vary from other steels in that they are not made to meet a specific chemical composition but rather to specific mechanical properties...
and carbon fiberCarbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
instead of mild steel and iron
- Reducing vehicle weight by improving vehicle packaging and space utilisation to enable downsizing without loss of functionality
- Active highway management (matching speed limits and vehicles allowed to join motorways/freeways to traffic density), to maintain traffic throughput and fuel efficiency.
Future technologies
Technologies that may improve fuel efficiency, but are not yet on the market, include:
- Compound engines
- Two-stroke diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
s
- High-efficiency gas turbine engines
- BMW's Turbosteamer
A turbosteamer is a term used by BMW to describe a combined cycle engine. It uses a steam engine to convert waste heat energy from an internal combustion engine into supplemental power for the vehicle. The turbosteamer device is affixed to the exhaust and cooling system...
– using the heat from the engine to spin a mini turbine to generate power
- Vehicle electronic control systems that automatically maintain distances between vehicles on motorways/freeways that reduce ripple back braking, and consequent re-acceleration.
- Time-optimized piston path, to capture energy from hot gases in the cylinders when they are at their highest temperatures
Many aftermarket consumer products exist that are purported to increase fuel economy; many of these claims have been discredited. In the United States, the Environmental Protection Agency maintains a list of devices that have been tested by independent laboratories and makes the test results available to the public.
Fuel economy data reliability
The mandatory publication of the fuel consumption by the manufacturer led some to use dubious practices to reach better values in the past. If the test is on a test stand, the vehicle may detect open doors and adapt the engine control. Also when driven according to the test regime, the parameters may adapt automatically. Test laboratories use a "golden car" that is tested in each one to check that each lab produces the same set of measurements for a given drive cycle.
Correctly aligning the vehicle wheels is something that should be normal practice for the vehicle users. Tire pressures and lubricants have to be as recommended by the manufacturer (Higher tire pressures are required on a particular dyno type, but this is to compensate for the different rolling resistance of the dyno, not to produce an unrealistic load on the vehicle). Normally the quoted figures a manufacturer publishes have to be proved by the relevant authority witnessing vehicle/engine tests. A lot of Governments independently test emissions from customer vehicles, and as a final measure can force a recall of all of a particular type of vehicle if the customer vehicles do not fulfil manufacturers' claims within reasonable limits. The expense and bad publicity from such a recall means manufacturers should be very cautious not to publish unrealistic figures. The U.S. Federal government retests 10–15% of models), to make sure that the manufacturer's tests are accurate.
Concerns over EPA estimates
For many years critics have claimed that EPA estimated fuel economy figures have been misleading. The primary arguments of the EPA detractors were focused on the lack of real world testing, and the very limited scale (i.e., city or highway).
EPA changes in 2008
Partly as a response to these criticisms, the EPA changed their fuel economy rating system in 2008 in an attempt to more adequately address these concerns. Instead of testing simply in two presumed modes, the testing now covers:
- Faster speeds and acceleration
- Air conditioner user
- Colder outside temperatures
Other attempts to improve MPG accuracy
While the new EPA standards may represent an improvement, real world user data may still be the best way to gather and collect accurate fuel economy information. As such the EPA has also set up a
http://www.fueleconomy.gov/mpg/MPG.do?action=browseList website where drivers can enter and track their own real-world fuel economy numbers.
There are also a number of websites that attempt to track and report individual user fuel economy data. Sites or publications such as
Consumer ReportsConsumer Reports is an American magazine published monthly by Consumers Union since 1936. It publishes reviews and comparisons of consumer products and services based on reporting and results from its in-house testing laboratory. It also publishes cleaning and general buying guides...
,
Edmunds.comEdmunds.com is a provider of automotive information via Web sites, books, and other media. The company is headquartered in Santa Monica, California and maintains an office outside of Detroit, Michigan...
, and
TrueDelta.comTrueDelta.com is a car information site that claims over 30,000 registered members as of December 2008 and 40,000 registered cars. The site focuses on the reporting of automobile reliability and gas mileage, and also contains vehicle pricing and comparison information...
offer this service and claim more accurate numbers than those listed by the EPA.
Fuel economy maximizing behaviors
Governments, various
environmentalistAn environmentalist broadly supports the goals of the environmental movement, "a political and ethical movement that seeks to improve and protect the quality of the natural environment through changes to environmentally harmful human activities"...
organizations, and companies like Toyota and
Shell Oil CompanyShell Oil Company is the United States-based subsidiary of Royal Dutch Shell, a multinational oil company of Anglo Dutch origins, which is amongst the largest oil companies in the world. Approximately 22,000 Shell employees are based in the U.S. The head office in the U.S. is in Houston, Texas...
have historically urged drivers to maintain adequate air pressure in
tireA tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
s and careful acceleration/deceleration habits.
Fuel economy as part of quality management regimes
Environmental management systems
EMASEMAS may be:* EMAS , a global offshore contractor and provider of integrated offshore solutions to the oil and gas industry and operating brand for Ezra Holdings....
as well as good fleet management do include record keeping of the fuel consumption of the fleet. Quality management on top of this uses those figures to steer the measures acting on the fleets. You may check whether procurement, driving, and maintenance in total have contributed to changes in the fleets overall consumption.
Units
Miles per gallon (
MPG) is a
unit of measurementA unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of...
that measures fuel economy in automobiles, that is, how many miles a vehicle can travel on one gallon of fuel. It is used similarly in United States and the
United KingdomThe United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, although the U.S. gallon is about 83% of the Imperial gallon previously used in the UK.
Most countries other than the U.S. use the
metricThe International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...
units litre (approximately 0.220 Imperial gallons or 0.264 U.S. liquid gallons) and km (approximately 0.621 statute miles). These can be combined to either km/l (efficiency) or l/100 km (consumption). The UK is a special case in this respect, as distances are measured in miles but fuel is sold by the litre. As a result, both MPG and l/100 km are usually quoted for any given vehicle. Note that because the imperial gallon is significantly larger than the U.S. gallon, MPG figures are 20.095% higher in the UK than in the U.S. for the same real fuel economy.
U.S. Gallons
- 1 MPG ≈ 0.425 km/l
- 235.2/MPG ≈ l/100 km
- 1 MPG ≈ 1.201 MPG (Imp)
Imperial gallons
- 1 MPG ≈ 0.354 km/l
- 282/MPG ≈ l/100 km
- 1 MPG ≈ 0.833 MPG (U.S.)
Conversion tables
The conversion tables give a quick overview of the relationship between the different measurement units, MPG (U.S.), MPG (Imperial), km/l, and l/100 km.
Conversion from MPG
| MPG (Imp.) |
MPG (U.S.) |
km/l |
l/100 km |
| 5 |
4.2 |
1.8 |
56.5 |
| 10 |
8.3 |
3.5 |
28.2 |
| 15 |
12.5 |
5.3 |
18.8 |
| 20 |
16.7 |
7.1 |
14.1 |
| 25 |
20.8 |
8.9 |
11.3 |
| 30 |
25.0 |
10.6 |
9.4 |
| 35 |
29.1 |
12.4 |
8.1 |
| 40 |
33.3 |
14.2 |
7.1 |
| 45 |
37.5 |
15.9 |
6.3 |
| 50 |
41.6 |
17.7 |
5.6 |
| 55 |
45.8 |
19.5 |
5.1 |
| 60 |
50.0 |
21.2 |
4.7 |
| 65 |
54.1 |
23.0 |
4.3 |
| 70 |
58.3 |
24.8 |
4.0 |
| 75 |
62.5 |
26.6 |
3.8 |
| 80 |
66.6 |
28.3 |
3.5 |
| 85 |
70.8 |
30.1 |
3.3 |
| 90 |
74.9 |
31.9 |
3.1 |
| 95 |
79.1 |
33.6 |
3.0 |
| 100 |
83.3 |
35.4 |
2.8 |
| MPG (U.S.) |
MPG (Imp.) |
km/l |
l/100 km |
| 5 |
6.0 |
2.1 |
47.0 |
| 10 |
12.0 |
4.3 |
23.5 |
| 15 |
18.0 |
6.4 |
15.7 |
| 20 |
24.0 |
8.5 |
11.8 |
| 25 |
30.0 |
10.6 |
9.4 |
| 30 |
36.0 |
12.8 |
7.8 |
| 35 |
42.0 |
14.9 |
6.7 |
| 40 |
48.0 |
17.0 |
5.9 |
| 45 |
54.0 |
19.1 |
5.2 |
| 50 |
60.0 |
21.3 |
4.7 |
| 55 |
66.1 |
23.4 |
4.3 |
| 60 |
72.1 |
25.5 |
3.9 |
| 65 |
78.1 |
27.6 |
3.6 |
| 70 |
84.1 |
29.8 |
3.4 |
| 75 |
90.1 |
31.9 |
3.1 |
| 80 |
96.1 |
34.0 |
2.9 |
| 85 |
102.1 |
36.1 |
2.8 |
| 90 |
108.1 |
38.3 |
2.6 |
| 95 |
114.1 |
40.4 |
2.5 |
| 100 |
120.1 |
42.5 |
2.4 |
Conversion from km/l and l/100 km
| l/100 km |
km/l |
MPG (U.S.) |
MPG (Imp.) |
| 1 |
100.0 |
235.2 |
282.5 |
| 2 |
50.0 |
117.6 |
141.2 |
| 3 |
33.3 |
78.4 |
94.2 |
| 4 |
25.0 |
58.8 |
70.6 |
| 5 |
20.0 |
47.0 |
56.5 |
| 6 |
16.7 |
39.2 |
47.1 |
| 7 |
14.3 |
33.6 |
40.4 |
| 8 |
12.5 |
29.4 |
35.3 |
| 9 |
11.1 |
26.1 |
31.4 |
| 10 |
10.0 |
23.5 |
28.2 |
| 15 |
6.7 |
15.7 |
18.8 |
| 20 |
5.0 |
11.8 |
14.1 |
| 25 |
4.0 |
9.4 |
11.3 |
| 30 |
3.3 |
7.8 |
9.4 |
| 35 |
2.9 |
6.7 |
8.1 |
| 40 |
2.5 |
5.9 |
7.1 |
| 45 |
2.2 |
5.2 |
6.3 |
| 50 |
2.0 |
4.7 |
5.6 |
| 55 |
1.8 |
4.3 |
5.1 |
| 60 |
1.7 |
3.9 |
4.7 |
| km/l |
l/100 km |
MPG (U.S.) |
MPG (Imp.) |
| 5 |
20.0 |
11.8 |
14.1 |
| 10 |
10.0 |
23.5 |
28.2 |
| 15 |
6.7 |
35.3 |
42.4 |
| 20 |
5.0 |
47.0 |
56.5 |
| 25 |
4.0 |
58.8 |
70.6 |
| 30 |
3.3 |
70.6 |
84.7 |
| 35 |
2.9 |
82.3 |
98.9 |
| 40 |
2.5 |
94.1 |
113.0 |
| 45 |
2.2 |
105.8 |
127.1 |
| 50 |
2.0 |
117.6 |
141.2 |
| 55 |
1.8 |
129.4 |
155.4 |
| 60 |
1.7 |
141.1 |
169.5 |
| 65 |
1.5 |
152.9 |
183.6 |
| 70 |
1.4 |
164.7 |
197.7 |
| 75 |
1.3 |
176.4 |
211.9 |
| 80 |
1.3 |
188.2 |
226.0 |
| 85 |
1.2 |
199.9 |
240.1 |
| 90 |
1.1 |
211.7 |
254.2 |
| 95 |
1.1 |
223.5 |
268.4 |
| 100 |
1.0 |
235.2 |
282.5 |
See also
- ACEA agreement
The ACEA agreement refers to a voluntary agreement between the European Automobile Manufacturers Association and the European Commission to limit the amount of carbon dioxide emitted by passenger cars sold in Europe...
- Car tuning
Car tuning is both an industry and a hobby, in which an automobile is modified in order to improve its performance, handling and appearance. As most vehicles leave the factory set up for average driver expectations and average conditions, tuning has become a way to personalize the characteristics...
- Battery electric vehicle
A battery electric vehicle, or BEV, is a type of electric vehicle that uses chemical energy stored in rechargeable battery packs. BEVs use electric motors and motor controllers instead of, or in addition to, internal combustion engines for propulsion.A battery-only electric vehicle or...
- Dynamometer
A dynamometer or "dyno" for short, is a device for measuring force, moment of force , or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed .A dynamometer can also be used to determine...
- Emission standard
Emission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles and other powered vehicles but they can also regulate emissions from industry, power...
- Energy conservation
Energy conservation refers to efforts made to reduce energy consumption. Energy conservation can be achieved through increased efficient energy use, in conjunction with decreased energy consumption and/or reduced consumption from conventional energy sources...
- Fuel economy-maximizing behaviors
Fuel economy-maximizing behaviors describe techniques that drivers can use to optimize their automobile fuel economy. The energy in fuel consumed in driving is lost in many ways, including engine inefficiency, aerodynamic drag, rolling friction, and kinetic energy lost to braking...
- 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...
- Fuel saving devices
Fuel saving devices are sold on the aftermarket with claims to improve the fuel economy and/or the exhaust emissions of a vehicle. There are numerous different types of device; many purport to optimize ignition, air flow, or fuel flow in some way...
- Gasoline gallon equivalent
- Liters per 100 km
Fuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...
- Low-energy vehicle
A Low-energy vehicle is any type of vehicle that uses less energy than a regular fossil fuel vehicle.Higher efficiency can be achieved by changing the vehicle's design, and/or by modifying its powertrain. Energy consumption as low as 5-12.5 kWh/100 km is achieved directly by battery electric...
- Miles per gallon gasoline equivalent
Miles per gallon gasoline equivalent is a measure of the average distance traveled per unit of energy consumed. MPGe is used by the U.S...
- U.S. National Highway Traffic Safety Administration
The National Highway Traffic Safety Administration is an agency of the Executive Branch of the U.S. government, part of the Department of Transportation...
- Passenger miles per gallon
Passenger miles per gallon is a metric to evaluate the energy efficiency of a vehicle or transportation mode. The PMPG can be obtained by multiplying the miles per gallon of fuel by the passenger capacity or average occupancy...
- The Very Light Car
thumb|right|The Very Light Car prototypeThe Very Light Car is a prototype design for 2- and 4-passenger automobiles powered by small one-cylinder E85-gasohol-fueled internal combustion engines. It was developed by the Edison2 team in the Automotive X Prize competition...
- Vehicle Efficiency Initiative
The Vehicle Efficiency Incentive was introduced in the 2007 Canadian federal government budget, aimed at promoting fuel efficient vehicles...
- Vehicle metrics
There are a broad range of metrics that denote the relative capabilities of various vehicles. Most of them apply to all vehicles while others are type-specific....
- Fuel efficiency at higher speeds
External links