Fuel economy in automobiles: Difference between revisions
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*[http://www.fueleconomytuneup.com/2012/05/improved-fuel-efficiency-improved-fuel-economy-reduced-internal-engine-friction-and-better-gas-mileage/ Reduced Internal Engine Friction] |
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*[http://www.epa.gov:80/fueleconomy/label.htm US Fuel Economy Label] ([[United States Environmental Protection Agency]]). |
*[http://www.epa.gov:80/fueleconomy/label.htm US Fuel Economy Label] ([[United States Environmental Protection Agency]]). |
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*[http://www.environment.gov.au/settlements/transport/fuelguide/label.html Australian Fuel Consumption Label] |
*[http://www.environment.gov.au/settlements/transport/fuelguide/label.html Australian Fuel Consumption Label] |
Revision as of 12:42, 12 May 2012
This article's lead section may be too short to adequately summarize the key points. (February 2012) |
![](http://upload.wikimedia.org/wikipedia/commons/thumb/3/35/2006_Honda_Airwave_fuel_efficiency_meter.jpg/220px-2006_Honda_Airwave_fuel_efficiency_meter.jpg)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/0/02/Fuel_Economy%2C_1916.jpg/220px-Fuel_Economy%2C_1916.jpg)
Fuel usage in automobiles refers to the fuel efficiency 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 in this article.
Units of measure
![](http://upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Chart_MPG_to_L-100km_v2009-10-08.svg/400px-Chart_MPG_to_L-100km_v2009-10-08.svg.png)
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.[2]
- 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 the gallon should be identified, since an 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 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)[3][4] though typically burns fewer litres per kilometre for an otherwise identical car. Since the CO2 emissions are relatively constant per kilogram, they are proportional to fuel consumption.[5]
Inverse or reciprocal scale
Expressing the fuel economy of an automobile in terms of distance traveled per volume of fuel used has the disadvantage that the value (in terms of fuel saved) of a numerical change in the rating varies, depending on the rating. A modest decline in (distance per volume) fuel economy for a relatively inefficient vehicle can provide greater fuel saving than a proportionately larger increase for a more economical vehicle.
An inverse scale eliminates this effect by calculation fuel used to cover a set distance – gallons per mile or liters per kilometer. A unit change in this rating has the same value to a vehicle operator, no matter what the rating, for the same annual operating distance.
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, both can be misinterpreted.[6]
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% farther on every litre. Changing from 14 to 20 MPG saves twice as much fuel over a given distance as the improvement from 33 to 50 MPG[7]).
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.
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 to 44 MPG (US) saves more fuel than the improvement from 15 to 19 MPG (US) 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.[8] 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".[8][9] 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 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 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),[10] 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 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 US gallons (23 L) of nitromethane 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-Marathon, which managed 5,384 kilometres per litre (15,210 mpg‑imp; 12,660 mpg‑US).[11]
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 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/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.[12]
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),[13] compared with the average new car consumption in the same year of 25.3 mpgUS[14]
- New Zealand
- United Kingdom
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) 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,[15] 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
![](http://upload.wikimedia.org/wikipedia/commons/thumb/a/a9/Fuel_economy_vs_speed_1997.png/220px-Fuel_economy_vs_speed_1997.png)
Fuel economy at steady speeds with selected vehicles was studied in 2010. The most recent study[16] indicates greater fuel efficiency at higher speeds than earlier studies; for example, some vehicles achieve better mileage at 65 mph (105 km/h) rather than at 45 mph (72 km/h),[16] although not their best economy, such as the 1994 Oldsmobile Cutlass, which has its best economy at 55 miles per hour (89 km/h) (29.1 mpg‑US (8.1 l/100 km)), and gets 2 mpg better economy at 65 mph (105 km/h) than at 45 mph (72 km/h) (25 mpg‑US (9.4 l/100 km) vs 23 mpg‑US (10 l/100 km)). The proportion of driving on high speed roadways varies from 4% in Ireland to 41% in Netherlands.
When the National Maximum Speed Law's 55 mph (89 km/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 mph (105 km/h) than it did at 45 mph (72 km/h) (43.5 mpg‑US (5.41 l/100 km) vs 42.5 mpg‑US (5.53 l/100 km)), although almost 5 mpg better at 60 mph (97 km/h) than at 65 mph (105 km/h) (48.4 mpg‑US (4.86 l/100 km) vs 43.5 mpg‑US (5.41 l/100 km)), and its best economy (52.6 mpg‑US (4.47 l/100 km)) 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 (40 to 89 km/h) (see graph).[16]
Officials hoped that the 55 mph limit, combined with a ban on ornamental lighting, no gasoline sales on Sunday, and a 15% cut in gasoline production, would reduce total gas consumption by 200,000 barrels a day, representing a 2.2% drop from annualized 1973 gasoline consumption levels.[17][a] This was partly based this on a belief that cars achieve maximum efficiency between 40 and 50 mph (64 and 80 km/h) and that trucks and buses were most efficient at 55 mph (89 km/h).[19]
However, the United States Department of Transportation's Office of Driver Research found total fuel savings of the 55 mph limit to be 1%, and independent studies found a 0.5% savings.[20]
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[21]
- European Union (L/100 km) – 'combined' 8.9, 'urban' 12.5, 'extra-urban' 6.9[22]
- United States (L/100 km) – 'combined' 9.8, 'city' 11.2, 'highway' 8.1[23]
Fuel economy standards and testing procedures
Country | 2004 average | Requirement | |||
---|---|---|---|---|---|
2004 | 2005 | 2008 | Later | ||
People's Republic of China[24] | 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[14] | 6.7 L/100 km CAFE eq (2010) | ||||
Australia[14] | 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 CO2 emissions.[25] 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.[26] 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.[27] 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 l/100 km (64 mpg‑imp; 53 mpg‑US). 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 l/100 km (13.0 mpg‑imp; 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 l/100 km (83 mpg‑imp; 69 mpg‑US).
Europe
![](http://upload.wikimedia.org/wikipedia/commons/thumb/6/67/Irish_Car_CO2_Label.svg/220px-Irish_Car_CO2_Label.svg.png)
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 litres 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).[28] 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-Z 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[citation needed].
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.[29] Since September 2005 a colour-coded "Green Rating" sticker has been available in the UK, which rates fuel economy by CO2 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 (69 mpg‑imp; 57 mpg‑US)* and G about 9.5 l/100 km (30 mpg‑imp; 25 mpg‑US)*.[30] 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+.[31]
Japan
10–15 mode
The 10–15 mode driving cycle test is the official fuel economy and emission certification test for new light duty vehicles in Japan. Fuel economy is expressed in km/l (kilometers per litre) and emissions are expressed in g/km. The test is carried out on a dynamometer and consist of 25 tests which cover idling, acceleration, steady running and deceleration, and simulate typical urban and/or expressway driving patterns. The running pattern begins with a warm start, lasts for 660 seconds and runs at speeds up to 70 km/h.[32][33] The distance of the cycle is 6.34 km, average speed 25.6 km/h, and duration 892 seconds, including the initial 15 mode segment).[33]
JC08
A new more demanding test, called the JC08, was established in December 2006 for Japan’s new standard that goes into effect in 2015, but it is already being by several car manufacturers for new cars. The JC08 test is significantly longer and more rigorous than the 10–15 mode test. The running pattern with JC08 stretches out to 1200 seconds, and there are both cold and warm start measurements and top speed is 82 km/h. The economy ratings of the JC08 are lower than the 10–15 mode cycle, but they are expected to be more real world.[32] The Toyota Prius became the first car to meet Japan’s new 2015 Fuel Economy Standards measured under the JC08 test.[34]
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 (41 mpg‑imp; 34 mpg‑US)* to 3.8 l/100 km (74 mpg‑imp; 62 mpg‑US)* and received respectively from 4.5 to 5.5 stars.[35]
United States
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Motor_vehicle_efficiency.png/220px-Motor_vehicle_efficiency.png)
US Energy Tax Act
The Energy Tax Act of 1978[36] in the US 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 IRS. 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 US Environmental Protection Agency confirms a portion of those tests at an EPA lab.
EPA testing procedure through 2007
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/bd/Uddsdds.gif/200px-Uddsdds.gif)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Hwfetdds.gif/200px-Hwfetdds.gif)
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 40 CFR 86.I 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 40 CFR 600.I 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-mile (16 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.[37][38]
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 Monaro) 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.[39]
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.[37][40]
EPA testing procedure: 2008 and beyond
![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Fuel_economy_label_EPA_2008.jpg/220px-Fuel_economy_label_EPA_2008.jpg)
As a means of reflecting real world fuel economy more accurately, the EPA adds three new tests[41] that will combine with the current city and highway cycles to determine fuel economy of new vehicles, beginning with the 2008 model year.[42] A high speed/quick acceleration loops lasts 10 minutes, covers 8 miles (13 km), averages 48 mph (77 km/h) and reaches a top speed of 80 mph (130 km/h). Four stops are included, and brisk acceleration maximizes at a rate of 8.46 mph (13.62 km/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-mile (5.8 km) loop averages 22 mph (35 km/h) and maximizes at a rate of 54.8 mph (88.2 km/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 (−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.[43]
Advanced technology vehicles
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/23/Chevy_Volt_EPA_Fuel_Economy_Official_Label.png/220px-Chevy_Volt_EPA_Fuel_Economy_Official_Label.png)
Following the efficiency claims made for vehicles such as Chevrolet Volt and Nissan Leaf, the National Renewable Energy Laboratory recommended to use EPA's new vehicle fuel efficiency formula that gives different values depending on fuel used.[44] In November 2010 the EPA introduced the first fuel economy ratings in the Monroney stickers for plug-in electric vehicles.
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 equivalent (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 (121 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.[45][46]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d0/Nissan_Leaf_EPA_fuel_economy_label.jpg/220px-Nissan_Leaf_EPA_fuel_economy_label.jpg)
For the fuel economy label of the Nissan Leaf electric car EPA rated the combined fuel economy in terms of miles per gallon gasoline equivalent, 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.[47]
In May 2011, the National Highway Traffic Safety Administration (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 year 2013, and voluntary for 2012 models. The ruling include include new labels for alternative fuel and alternative propulsion vehicles available in the US market, such as plug-in hybrids, electric vehicles, flexible-fuel vehicles, hydrogen fuel cell vehicle, and natural gas vehicles.[48][49] The common fuel economy metric adopted to allow the comparison of alternative fuel and advanced technology vehicles with conventional internal combustion 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 gas (CNG) , or kilograms of hydrogen that is equal to the energy in a gallon of gasoline.[48]
The new labels also include for the first time an estimate of how much fuel or electricity it takes to drive 100 miles (160 km), providing US 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.[48][50]
CAFE standards
The Corporate Average Fuel Economy (CAFE) regulations in the United States, first enacted by Congress in 1975,[51] are federal regulations intended to improve the average fuel economy of cars and light trucks (trucks, vans and sport utility vehicles) sold in the US 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 year 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 were limited to vehicles under a certain weight, but those weight classes were expanded in 2011.
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 Board is implementing some legislation that limits greenhouse gas emissions. A legal dispute has emerged over whether this is effectually a fuel efficiency standard.
Energy considerations
![]() | This section needs expansion. You can help by adding to it. (June 2007) |
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).
![](http://upload.wikimedia.org/wikipedia/commons/thumb/0/05/Energy_flows_in_car.svg/400px-Energy_flows_in_car.svg.png)
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.[52] 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, which varies with engine type, the mass of the automobile and its load, and engine speed (usually measured in RPM).
- Aerodynamic drag force, which increases roughly by the square of the car's speed, 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. (Manual transmissions can be up to 94% efficient whereas older automatic transmissions may be as low as 70% efficient[53] 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 horsepower (2.2 kW) 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.[43] 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 pistons, crankshaft, gears and alloy wheels
- 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 sooner
- Using coolant additives that increase the thermal efficiency of the cooling system
- Designing the exterior of the vehicle to reduce aerodynamic drag
- Replacing tires with low rolling resistance (LRR) models[54]
- Using lower-friction lubricants (engine oil, 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 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 vehicles) hybrid electric vehicle
- 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)
- Recapturing wasted energy while braking (regenerative braking)
- Recapturing wasted energy in the vehicle suspension[55]
- 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 combustion
- Lean burn combustion
- HCCI (Homogeneous Charge Compression Ignition) combustion
- Variable valve timing
- Supercharging or twincharging (when coupled with a downsized engine)
- Turbocharged Direct Injection diesel engines
- Gasoline direct injection petrol engines
- Common Rail diesel engines
- Variable geometry turbocharging
- Reducing vehicle weight by using materials such as aluminum, fiberglass, plastic, high-strength steel and carbon 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.
- Maintaining a steady RPM[56]
Future technologies
Technologies that may improve fuel efficiency, but are not yet on the market, include:
- Scuderi Engine
- Compound engines
- Two-stroke diesel engines
- High-efficiency gas turbine engines
- BMW's Turbosteamer – 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[citation needed]
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.[57]
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.[58]
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 US Federal government retests 10–15% of models[59]), 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).[60]
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:[61]
- 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 Reports, Edmunds.com, and TrueDelta.com offer this service and claim more accurate numbers than those listed by the EPA.
Fuel economy maximizing behaviors
Governments, various environmentalist organizations, and companies like Toyota and Shell Oil Company have historically urged drivers to maintain adequate air pressure in tires and careful acceleration/deceleration habits.
Fuel economy as part of quality management regimes
Environmental management systems EMAS 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.[62]
Units
Miles per gallon (MPG) is a unit of measurement 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 Kingdom, although the US gallon is about 83% of the Imperial gallon previously used in the UK.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Chart_MPG_to_L-100km_v2009-10-08.svg/400px-Chart_MPG_to_L-100km_v2009-10-08.svg.png)
Most countries other than the US use the metric units litre (approximately 0.220 Imperial gallons or 0.264 US 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 US gallon, MPG figures are 20.095% higher in the UK than in the US for the same real fuel economy.
- US 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 (US)
Conversion tables
The conversion tables give a quick overview of the relationship between the different measurement units, MPG (US), MPG (Imperial), km/l, and l/100 km.
Conversion from MPG
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Conversion from km/l and l/100 km
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See also
- ACEA agreement
- Car tuning
- Battery electric vehicle
- Dynamometer
- Emission standard
- Energy conservation
- Fuel economy-maximizing behaviors
- Fuel efficiency in transportation
- Fuel saving devices
- Gasoline gallon equivalent
- Liters per 100 km
- Low-energy vehicle
- Miles per gallon gasoline equivalent
- US National Highway Traffic Safety Administration
- Passenger miles per gallon
- The Very Light Car
- Vehicle Efficiency Initiative
- Vehicle metrics
- Fuel efficiency at higher speeds
Annotations
- ^ The 2.2% drop figure was calculated by finding daily consumption to be 9,299,684 barrels of petroleum. Obtain 1973's petroleum consumption from transportation sector at 2.1e from the Energy Consumption by Sector section, then convert to barrels using A1 in the Thermal Conversion Factors section (assume "conventional motor gasoline" since ethanol-based or purportedly smog-reducing gas was not common in 1973).[18]
References
- ^ Page, Walter Hines; Page, Arthur Wilson (1916). "Man and His Machines". The World's Work. XXXIII. Garden City, New York: Doubleday, Page & Co.
- ^ "Fuel Consumption Ratings". Government of Canada. 2011. Retrieved 8 June 2011.
{{cite web}}
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ignored (help) - ^ Average Carbon Dioxide Emissions Resulting from Gasoline and Diesel Fuel. Epa.gov. Retrieved on 21 September 2011.
- ^ What is a carbon footprint – definition. Timeforchange.org. Retrieved on 21 September 2011.
- ^ sugre.info conversion tool
- ^ www.mpgillusion.com. www.mpgillusion.com (2011-06-17). Retrieved on 21 September 2011.
- ^ http://www.mpgillusion.com www.mpgillusion.com
- ^ a b http://www.sciencemag.org/cgi/content/full/320/5883/1593?ijkey=3pScQm7pQBzqs&keytype=ref&siteid=sci
- ^ Why We Should Measure by Gallons per Mile, Not Miles per Gallon. Popular Mechanics (2009-10-01). Retrieved on 21 September 2011.
- ^ Emission Facts: Average Carbon Dioxide Emissions Resulting from Gasoline and Diesel Fuel | US EPA. Epa.gov. Retrieved on 21 September 2011.
- ^ National Geographic News "Hydrogen-Fueled Race Car Showcases Future Technologies" by John Roach. News.nationalgeographic.com (2010-10-28). Retrieved on 21 September 2011.
- ^ Reducing CO2 emissions from passenger cars – Policies – Climate Action – European Commission. Ec.europa.eu (2010-12-09). Retrieved on 21 September 2011.
- ^ Myth: Cars are becoming more fuel efficient. Ptua.org.au. Retrieved on 21 September 2011.
- ^ a b c Comparison of Passenger Vehicle Fuel Economy and GHG Emission Standards Around the World at Pew Center on Global Climate Change. (PDF) . Retrieved on 21 September 2011.
- ^ Tires and Passenger Vehicle Fuel Economy. Committee for the National Tire Efficiency Study. Transportation Research Board Board on Energy and Environmental Systems. 2006. ISBN 0-309-09421-6
- ^ a b c Steady Speed Fuel Economy "The two earlier studies by the Federal Highway Administration (FHWA) indicate maximum fuel efficiency was achieved at speeds of 35 to 40 mph. The recent FHWA study indicates greater fuel efficiency at higher speeds."
- ^ Cowan, Edward (27 November. 1973). "Politics and Energy: Nixon's Silence on Rationing Reflects Hope That Austerity Can Be Avoided". The New York Times. p. 30. Retrieved 22 July 2008.
{{cite news}}
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(help) (subscription required) - ^ Staff (28 June 2008). Annual Energy Review (PDF) (2007 ed.). Washington, DC: Energy Information Administration.
- ^ "55 Mile-per-hour Speed Limit Approved by House". United Press International. 4 December 1973. p. 30. Retrieved 22 July 2008. (subscription required)
- ^ Copulos, Milton R. (9 September 1986). "The High Cost of the 55 MPH Speed Limit" (PDF). The Backgrounder (532). Washington, DC: The Heritage Foundation: 1–8. Retrieved 1 August 2011.
- ^ Lexus IS250 2.5L 6cyl, Auto 6 speed Sedan, 5 seats, 2WD
- ^ IS 250 Kraftstoffverbrauch kombiniert 8,9 l/100 km (innerorts 12,5 l/ außerorts 6,9 l) bei CO2-Emissionen von 209 g/km nach dem vorgeschriebenen EU-Messverfahren http://www.lexus.de/range/is/index.aspx
- ^ 2009 Lexus IS 250 6 cyl, 2.5 L, Automatic (S6), Premium http://www.fueleconomy.gov/feg/findacar.htm
- ^ Chinese Fuel Economy Laws. Treehugger.com. Retrieved on 21 September 2011.
- ^ Vehicles & the Environment. Infrastructure.gov.au. Retrieved on 21 September 2011.
- ^ Information on Green Vehicle Guide Ratings and Measurement. Australian Department of Infrastructure and Transport
- ^ Green Vehicle Guide. Green Vehicle Guide. Retrieved on 21 September 2011.
- ^ Vehicle test cycles. Herkules.oulu.fi. Retrieved on 21 September 2011.
- ^ Guidance notes and examples. (PDF) . Retrieved on 21 September 2011.
- ^ Fuel Economy Label. Dft.gov.uk. Retrieved on 21 September 2011.
- ^ Vehicle Labelling. Environ.ie (2008-07-01). Retrieved on 21 September 2011.
- ^ a b Japan Automobile Manufacturers Association (JAMA) (2009). "From 10•15 to JC08: Japan's new economy formula". News from JAMA. Retrieved 9 April 2012. Issue No. 2, 2009.
- ^ a b "Japanese 10–15 Mode". Diesel.net. Retrieved 9 April 2012.
- ^ "Prius Certified to Japanese 2015 Fuel Economy Standards with JC08 Test Cycle". Green Car Congress. 11 August 2007. Retrieved 9 April 2012.
- ^ Vehicle Fuel Economy Labelling – FAQs[dead link]
- ^ Frequently Asked Questions. Fueleconomy.gov. Retrieved on 21 September 2011.
- ^ a b "Dynamometer Driver's Aid". US EPA. Retrieved 11 January 2011.
- ^ How the EPA Tests and Rates Fuel Economy. Auto.howstuffworks.com (2005-09-07). Retrieved on 21 September 2011.
- ^ Steven Cole Smith (28 April 2005). "2005 Pontiac GTO". Orlando Sentinel via Cars.com.
- ^ Find a Car 1985 to 2009. Fueleconomy.gov. Retrieved on 21 September 2011.
- ^ Earthcars: EPA fuel economy ratings – what's coming in 2008. Web.archive.org (2007-10-08). Retrieved on 21 September 2011.
- ^ 7 Passenger Vehicles: Most Fuel Efficient Cars of 2011. 7passengervehicleshq.com. Retrieved on 21 September 2011.
- ^ a b Automotive Electrical Systems Circa 2005. Spectrum.ieee.org. Retrieved on 21 September 2011.
- ^ Roth, Dan. (2009-10-01) REPORT: EPA planning to address outlandish fuel economy claims of electric cars. Autoblog.com. Retrieved on 21 September 2011.
- ^ "Volt receives EPA ratings and label: 93 mpg-e all-electric, 37 mpg gas-only, 60 mpg-e combined". Green Car Congress. 24 November 2010. Retrieved 24 November 2010.
- ^ US Environmental Protection Agency and US Department of Energy (4 May 2011 (last updated)). "2011 Chevrolet Volt". Fueleconomy.gov. Retrieved 21 May 2011.
{{cite web}}
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(help) - ^ Nick Bunkley (22 November 2010). "Nissan Says Its Electric Leaf Gets Equivalent of 99 M.P.G." The New York Times. Retrieved 23 November 2010.
- ^ a b c EPA (May 2011). "Fact Sheet: New Fuel Economy and Environment Labels for a New Generation of Vehicles". US Environmental Protection Agency. Retrieved 25 May 2011. EPA-420-F-11-017
- ^ "EPA, DOT unveil the next generation of fuel economy labels". Green Car Congress. 25 May 2011. Retrieved 25 May 2011.
- ^ John M. Broder (25 May 2011). "New Mileage Stickers Include Greenhouse Gas Data". The New York Times. Retrieved 26 May 2011.
- ^ "CAFE Overview: "What is the origin of CAFE?"". NHTSA. Retrieved 9 July 2008.
- ^ Wheels, online road load and MPG calculator. Virtual-car.org (2009-08-03). Retrieved on 21 September 2011.
- ^ An Overview of Current Automatic, Manual and Continuously Variable Transmission Efficiencies and Their Projected Future Improvements. Sae.org (1999-03-01). Retrieved on 21 September 2011.
- ^ Low-rolling resistance tires
- ^ Chandler, David (9 February 2009). "More power from bumps in the road". Retrieved 8 October 2009.
- ^ "How efficient is your car?". The Hindu. India. 26 January 2012. Retrieved 12 April 2012.
- ^ Gas Saving and Emission Reduction Devices Evaluation | Cars and Light Trucks | US EPA. Epa.gov. Retrieved on 21 September 2011.
- ^ Environmental Nanoparticles – Exploring the links between Vehicle Emissions and Ambient Air. (PDF). A meeting of the Automation and Analytical Management Group of the Royal Society of Chemistry. 8 June 2005. Retrieved on 21 September 2011.
- ^ EPA. Fueleconomy.gov. Retrieved on 21 September 2011.
- ^ [1][dead link]
- ^ Vehicle Selection – Make. Fueleconomy.gov. Retrieved on 21 September 2011.
- ^ The EU sponsored RECODRIVE project is further developing this approach
External links
![]() | This article's use of external links may not follow Wikipedia's policies or guidelines. (April 2012) |
- Reduced Internal Engine Friction
- US Fuel Economy Label (United States Environmental Protection Agency).
- Australian Fuel Consumption Label