Miles per gallon gasoline equivalent
Encyclopedia
Miles per gallon gasoline equivalent (MPGe or MPGge) is a measure of the average distance traveled per unit of energy consumed. MPGe is used by the U.S. Environmental Protection Agency (EPA) to compare energy consumption of alternative fuel vehicle
s, plug-in electric vehicle
s and other advanced technology vehicles with the fuel economy
of conventional internal combustion vehicles expressed as miles per US
gallon
.
The MPGe metric was introduced in November 2010 by EPA in the Monroney label of the Nissan Leaf
electric car
and the Chevrolet Volt
plug-in hybrid. The ratings are based on EPA's formula, in which 33.7 kilowatt hours of electricity is equivalent to one gallon of gasoline, and the energy consumption of each vehicle during EPA's five standard drive cycle tests simulating varying driving conditions. All new cars and light-duty trucks sold in the U.S. are required to have this label showing the EPA's estimate of fuel economy of the vehicle.
In a joint ruling issued in May 2011 the National Highway Traffic Safety Administration
(NHTSA) and EPA established the new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with model year
2013. This ruling uses miles per gallon gasoline equivalent for all fuel and advanced technology vehicles available in the U.S. market including plug-in hybrids, electric vehicle
s, flexible-fuel vehicle
s, hydrogen fuel cell vehicle
, natural gas vehicle
s, diesel-powered
vehicles, and gasoline-powered vehicles. In addition to being displayed on new vehicles, fuel economy ratings are used by the U.S. Department of Energy (DOE) to publish the annual Fuel Economy Guide; the U.S. Department of Transportation (DOT) to administer the Corporate Average Fuel Economy
(CAFE) program; and the Internal Revenue Service
(IRS) to collect gas guzzler tax
es.
Fuel economy estimates for window stickers and CAFE standard compliance are different. The EPA MPGe rating shown in the Monroney label is based on the consumption of the on-board energy content stored in the fuel tank or in the vehicle's battery, or any other energy source, and only represents the tank-to-wheel energy consumption. CAFE estimates are based on a well-to-wheel basis and in the case of liquid fuels and electric drive vehicles also account for the energy consumed upstream to produce the fuel or electricity and deliver it to the vehicle. Fuel economy for CAFE purposes include an incentive adjustment for alternative fuel vehicles and plug-in electric vehicles which results in higher MPGe than those estimated for window stickers.
(CAFE) incentives for the manufacture of vehicles that use ethanol
, methanol
, or natural gas fuels
, either powered exclusively on these alternative fuels or in conjunction with gasoline or diesel fuel, such flexible-fuel vehicle
s. In order to provide incentives for the widespread use of these fuels and to promote the production of alternative fuel vehicles, AMFA allows manufacturers producing alternative fuel vehicle
s to gain CAFE credits by manufacturing these vehicles, which allows them to raise their overall fleet fuel economy levels to comply with the CAFE standards until the established cap level.
Beginning in 1993, manufacturers of qualified alternative fuel vehicles can benefit for their CAFE estimation, by computing the weighted average of the fuel economy of the produced alternative fuel vehicles by dividing the alcohol fuel economy by a factor of 0.15. As an example, a dedicated alternative fuel vehicle that would achieve 15 mpg fuel economy while operating on alcohol would have a CAFE calculated as follows:
FE = (1/0.15)(15) = 100 miles per gallon
For alternative dual-fuel vehicles, an assumption is made that the vehicles would operate 50% of the time on the alternative fuel and 50% of the time on conventional fuel, resulting in a fuel economy that is based on a harmonic average of alternative fuel and conventional fuel. For example, for an alternative dual-fuel model that achieves 15 miles per gallon operating on an alcohol fuel and 25 mpg on the conventional fuel, the resulting CAFE would be:
FE = 1 / [(0.5/25) + (0.5/100)] = 40 miles per gallon
Calculation of fuel economy for natural gas vehicles is similar. For the purposes of this calculation, the fuel economy is equal to the weighted average of the fuel economy while operating on natural gas and while operating on either gasoline or diesel fuel. AMFA specifies the energy equivalency of 100 cubic feet of natural gas to be equal to 0.823 gallons of gasoline, with the gallon equivalency of natural gas to be considered to have a fuel content, similar to that for alcohol fuels, equal to 0.15 gallons of fuel. For example, under this conversion and gallon equivalency, a dedicated natural gas vehicle that achieves 25 miles per 100 cubic feet of natural gas would have a CAFE value as follows:
FE = (25/100) x (100/0.823)(1/0.15) = 203 miles per gallon
The Energy Policy Act of 1992
expanded the definition of alternative fuel to include liquefied petroleum gas, hydrogen
, liquid fuels derived from coal and biological materials, electricity
and any other fuel that the Secretary of Transportation determines to be substantially non-petroleum based and has environmental and energy security benefits. Beginning in 1993, manufacturers of these other alternative fuel automobiles that meet the qualifying requirements can also benefit for special treatment in the calculation of their CAFE.
(NIST) introduced gasoline gallon equivalent (GGE) as a metric for fuel economy for natural gas vehicle
s. NIST defined a gasoline gallon equivalent (GGE) as 5.660 pounds of natural gas, and gasoline liter equivalent (GLE) as 0.678 kilograms of natural gas.
During the late 1990s and early 2000s several electric car
s were produced in limited quantities as a result of the California Air Resources Board
(CARB) mandate for more fuel-efficient zero-emissions vehicle
s. Popular models available in California
included the General Motors EV1
and the Toyota RAV4 EV
. The US DoE and EPA rating for on board energy efficiency for these electric vehicles was expressed as kilowatt-hour/mile (KWh/mi), the most commonly known metric in science and engineering for measuring energy consumption, and used as the billing unit for energy delivered to consumers by electric utilities.
In order to address the Corporate Average Fuel Economy
(CAFE) regulations mandated by the US Congress in 1975, the U.S. Department of Energy established in July 2000 a methodology for calculating the petroleum-equivalent fuel economy of electric vehicle
s on a well-to-wheel basis. The methodology considers the upstream efficiency of the processes involved in the two fuel cycles, including efficiency factors for petroleum refining and distribution, as well as the national average efficiency for electricity generation and transmission.
The formula also includes a fuel efficiency incentive factor of 1/0.15 to benefit electric vehicles. This reward factor is intended provide an incentive for vehicle manufactures to produce and sell electric vehicles, as a higher equivalent fuel economy for EVs improves the carmaker overall fleet fuel economy levels in complying with the CAFE standards, and Congress anticipated that such an incentive would help accelerate the commercialization of electric vehicles. The incentive factor chosen by DoE for EVs is the same 1/0.15 factor already applied in the regulatory treatment of other types of alternative fuel vehicle
s. When all factors are considered in DoE's formula, the energy efficiency or equivalent fuel economy of electric vehicles increases from 33,705 Wh/gallon (plug-to-wheel) to 82,049 Wh/gallon (well-to-wheel).
for super-efficient vehicles that can achieve at least 100 MPGe. In February 2009, Consumer Reports
announced that, as part of a partnership with the X Prize Foundation, they planned to report MPGe as one of several measures that will help consumers understand and compare vehicle efficiency for alternative fuel vehicle
s.
, greenhouse gas emissions, and other air pollutants. The U.S. Environmental Protection Agency and the National Highway Traffic Safety Administration
(NHTSA) have conducted a series of studies to determine the best way to redesign this label to provide consumers with simple energy and environmental comparisons across all vehicles types, including battery electric vehicle
s (BEV), plug-in hybrid electric vehicle
s (PHEV), and conventional internal combustion engine
vehicles powered by gasoline and diesel, in order to help consumers choose more efficient and environmentally friendly vehicles. These changes are proposed to be introduced in new vehicles beginning with model year 2012.
As part of the research and redesign process, EPA conducted focus group
s where participants were presented with several options to express the consumption of electricity for plug-in electric vehicle
s. The research showed that participants did not understand the concept of a kilowatt hour as a measure of electric energy use in spite of the fact that this is the metric used in their monthly electric bills. Instead, participants favored a miles per gallon equivalent, MPGe, as the metric to compare with the familiar miles per gallon used for gasoline vehicles. The research also concluded that the kW-hrs per 100 miles metric was more confusing to focus group participants compared to a miles per kW-hr. Based on these results, EPA decided to use the following fuel economy and fuel consumption metrics on the redesigned labels: MPG (city and highway, and combined); MPGe (city and highway, and combined); Gallons per 100 miles; kW-hrs per 100 miles.
The proposed design and final content for two options of the new sticker label that will be introduced in 2013 model year
cars and trucks were consulted for 60 days with the public in 2010, and both include miles per gallon equivalent and kW-hrs per 100 miles as the fuel economy metrics for plug-in cars, but in one option MPGe and annual electricity cost are the two most prominent metrics. In November 2010, EPA introduced MPGe as comparison metric on its new sticker for fuel economy for the Nissan Leaf
and the Chevrolet Volt
.
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. The ruling includes new labels for alternative fuel
and alternative propulsion vehicles available in the US market, such as plug-in hybrids, electric vehicle
s, flexible-fuel vehicle
s, hydrogen fuel cell vehicle
, and natural gas vehicle
s. 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.
The new labels also show for the first time an estimate of how much fuel or electricity it takes to drive 100 miles (160.9 km), introducing to 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.".
For alternative fuels, energy required to manufacture the fuel may also be considered. For electrical power, the energy of any fuels used to generate the electricity and the transmission efficiency must be considered.
To convert the mile per gallon rating into other units of distance per unit energy used, the mile per gallon value can be multiplied by one of the following factors to obtain other units:
vehicles, cubic feet
for compressed natural gas
, pounds
for propane
or Liquefied petroleum gas vehicles, and gallons for liquefied natural gas
vehicles. Special cases for specific alternative fuels are discussed below, but a general formula for MPGe is:
Depending on the purpose, total energy consumption for the vehicle may also need to include the energy used in the production of whatever energy carrier (fuel) is used for the vehicle and the energy used in filling the "tank". For example, with electrically powered vehicles, a full accounting of total energy consumption would include the efficiency factor for conversion of primary fuels into electricity (the energy of the fuel used to generate and transmit electricity) and the efficiency factor of charging the battery from the electrical plug.
Basic values for the energy content of various fuels are given by the defaults used in the Department of Energy GREET (Greenhouse gases, Regulated Emissions, and Energy used in Transportation) model, as follows:
Note: 1 KWH is equivalent to 3,412 BTU
The energy content of a particular fuel can vary somewhat given its specific chemistry and production method. For example, in the new efficiency ratings that have been developed by the United States Environmental Protection Agency
(EPA) for battery electric vehicle
s (BEVs) and plug-in hybrid electric vehicle
s (PHEVs) – see below – the energy content of a gallon of gasoline is assumed to be 114,984 BTUs.
s (BEVs), which are powered exclusively on electricity, and plug-in hybrid electric vehicle
s (PHEVs), which use electricity together with a liquid fuel stored in an on-board fuel tank, usually gasoline, but it might be also powered by diesel
, ethanol
, or flex-fuel engines.
For battery electric vehicles, the U.S. Environmental Protection Agencys formula to calculate the battery-to wheel MPGe is based on energy standards established by the U.S. Department of Energy in 2000:
where
energy content per gallon of gasoline = 115,000 BTUs/gallon, as set by U.S. DoE and reported by the Alternative Fuel Data Center.
battery-to-wheel electrical energy consumed per mile (Wh
/mi) as measured through EPA's five standard drive cycle tests for electric cars.
energy per KWatt-hour of electricity (BTU/Wh) = 3.412
The formula employed by the EPA for calculating their rated MPGe does not account for any fuel or energy consumed upstream such as the generation and transmission of electrical power, or well-to-wheel life cycle, as EPA's comparison with internal combustion vehicles is made on a tank-to-wheel versus battery-to wheel basis.
The California Air Resources Board
uses a different dynamometer
testing than EPA, and considers reformulated gasoline sold in that state. For CARB estimates the formula becomes:
The new SAE
J1711 standard for measuring the exhaust emissions and fuel economy of hybrid electric vehicle
s and plug-in hybrids was approved in July 2010. The recommended procedures for PHEVs were revised at Argonne National Laboratory
, and EPA's new regulation to define PHEV fuel economy reporting protocol is expected to be based on SAE J1711. In November 2010 EPA decided to rate electric mode and gasoline only mode separately, and these are the two figures prominently displayed in the window sticker of the 2011 Chevrolet Volt
. In electric mode the Volt's rating is estimated with the same formula as an electric car. The overall or composite fuel economy rating combining electricity and gasoline powered are displayed in the Monroney label in a much smaller type, and as part of the comparison of the Volt's fuel economy among all vehicles and within compact car
s. EPA has considered several methodologies for rating the overall fuel economy of PHEVs, but as of February 2011 EPA has not announced the final methodology that will be applied for the purposes of estimating the new manufacture's 2012-2016 Corporate Average Fuel Economy
(CAFE) credits for plug-in hybrids.
electric car
with a combined fuel economy
of 99 MPGe, and rated the Chevrolet Volt plug-in hybrid with a combined fuel economy of 93 MPGe in all-electric mode, 37 MPG when operating with gasoline only, and an overall fuel economy rating of 60 mpg-US (3.9 L/100 km) combining power from electricity and gasoline. For both vehicles EPA calculated the MPGe rating under its five-cycle tests using the formula displayed earlier with a conversion factor of 33.7 kW-hr of electricity being the energy equivalent of a gallon of gasoline.
The following table illustrates EPA's fuel economy comparison and out-of-pocket fuel costs among two plug-in electric vehicle
s rated in MPGe and the most fuel efficient gasoline-electric hybrid car available in the U.S. market. Also shown in the fuel efficiency for plug-in expressed as KW-hrs/100 mile, the metric used by EPA to rate electric cars before November 2010.
/kg (113,738 BTU/kg), by converting this energy density to a GGE, it is found that 1.012 kg of hydrogen
is needed to meet the equivalent energy of one gallon of gasoline. This conversion factor can now be used to calculate the MPGe for this vehicle.
,
or well-to-wheel life cycle. Rather, the EPA presents MPGe in the same manner as MPG for conventional internal combustion engine
vehicles as displayed in the Monroney sticker
, and in both cases the rating only considers the tank-to-wheel or battery-to-wheel energy consumption. The EPA ratings displayed in window stickers do not account for the energy consumption upstream, which includes the energy or fuel required to generate the electricity or to extract and produce the liquid fuel; the energy losses due to power transmission; or the energy consumed for the transportation of the fuel from the well.
(DOE) established the methodology for calculating the petroleum-equivalent fuel economy of electric vehicles based on the well-to-wheel (WTW) gasoline-equivalent energy content of electricity (Eg). The methodology considers the upstream efficiency of the processes involved in the two fuel cycles, and considers the national average electricity generation and transmission efficiencies because a battery electric vehicle
burns its fuel (mainly fossil fuels) off-board at the power generation plant. This methodology is used by carmakers to estimate credits into their overall Corporate Average Fuel Economy
(CAFE) for manufacturing electric drive vehicles.
The equations for determining the petroleum equivalent fuel economy of electric vehicles are the following:
The gasoline-equivalent energy content of electricity factor, abbreviated as E.g., is defined as:
The petroleum-fueled accessory factor, AF, is equal to 1 if the electric drive vehicle does not have petroleum-powered accessories installed, and 0.90 if it does.
The driving pattern factor, DPF, is equal to 1, as DoE considered that electric vehicles eligible for inclusion in CAFE will offer capabilities, perhaps excepting driving range, similar to those of conventional vehicles.
In the example provided by the US DoE in its final rule, an electric car
with an energy consumption of 265 Watt-hour
per mile in urban driving, and 220 Watt-hour per mile in highway driving, resulted in a petroleum-equivalent fuel economy of 335.24 miles per gallon, based on a driving schedule factor of 55 percent urban, and 45 percent highway, and using a petroleum equivalency factor of 82,049 Watt-hours per gallon.
Alternative fuel vehicle
An alternative fuel vehicle is a vehicle that runs on a fuel other than "traditional" petroleum fuels ; and also refers to any technology of powering an engine that does not involve solely petroleum...
s, plug-in electric vehicle
Plug-in electric vehicle
A 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 and other advanced technology vehicles with the fuel economy
Fuel economy in automobiles
Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....
of conventional internal combustion vehicles expressed as miles per US
United States customary units
United States customary units are a system of measurements commonly used in the United States. Many U.S. units are virtually identical to their imperial counterparts, but the U.S. customary system developed from English units used in the British Empire before the system of imperial units was...
gallon
Gallon
The gallon is a measure of volume. Historically it has had many different definitions, but there are three definitions in current use: the imperial gallon which is used in the United Kingdom and semi-officially within Canada, the United States liquid gallon and the lesser used United States dry...
.
The MPGe metric was introduced in November 2010 by EPA in the Monroney label of the Nissan Leaf
Nissan Leaf
Nissan 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...
electric car
Electric car
An 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...
and the Chevrolet Volt
Chevrolet Volt
The 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...
plug-in hybrid. The ratings are based on EPA's formula, in which 33.7 kilowatt hours of electricity is equivalent to one gallon of gasoline, and the energy consumption of each vehicle during EPA's five standard drive cycle tests simulating varying driving conditions. All new cars and light-duty trucks sold in the U.S. are required to have this label showing the EPA's estimate of fuel economy of the vehicle.
In a joint ruling issued in May 2011 the National Highway Traffic Safety Administration
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...
(NHTSA) and EPA established the new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with model year
Model year
The 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. This ruling uses miles per gallon gasoline equivalent for all fuel and advanced technology vehicles available in the U.S. market including plug-in hybrids, electric vehicle
Electric vehicle
An electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
s, flexible-fuel vehicle
Flexible-fuel vehicle
A 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 vehicle
Fuel cell vehicle
A 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...
, natural gas vehicle
Natural gas vehicle
thumb|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, diesel-powered
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...
vehicles, and gasoline-powered vehicles. In addition to being displayed on new vehicles, fuel economy ratings are used by the U.S. Department of Energy (DOE) to publish the annual Fuel Economy Guide; the U.S. Department of Transportation (DOT) to administer the Corporate Average Fuel Economy
Corporate Average Fuel Economy
The Corporate Average Fuel Economy are regulations in the United States, first enacted by the U.S. Congress in 1975, and intended to improve the average fuel economy of cars and light trucks sold in the US in the wake of the 1973 Arab Oil Embargo...
(CAFE) program; and the Internal Revenue Service
Internal Revenue Service
The 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...
(IRS) to collect gas guzzler tax
Gas Guzzler Tax
The National Energy Act: Energy Tax Act of 1978 , or the Gas Guzzler Tax, imposed set tax penalties on car manufacturers who fail to meet the minimum fuel economy level of in the United States. This does not include minivans, sport utility vehicles or pick-up trucks. It is intended to discourage...
es.
Fuel economy estimates for window stickers and CAFE standard compliance are different. The EPA MPGe rating shown in the Monroney label is based on the consumption of the on-board energy content stored in the fuel tank or in the vehicle's battery, or any other energy source, and only represents the tank-to-wheel energy consumption. CAFE estimates are based on a well-to-wheel basis and in the case of liquid fuels and electric drive vehicles also account for the energy consumed upstream to produce the fuel or electricity and deliver it to the vehicle. Fuel economy for CAFE purposes include an incentive adjustment for alternative fuel vehicles and plug-in electric vehicles which results in higher MPGe than those estimated for window stickers.
1988: Alternative Motor Fuels Act
The Alternative Motor Fuels Act (AMFA) enacted in 1988 provides Corporate Average Fuel EconomyCorporate Average Fuel Economy
The Corporate Average Fuel Economy are regulations in the United States, first enacted by the U.S. Congress in 1975, and intended to improve the average fuel economy of cars and light trucks sold in the US in the wake of the 1973 Arab Oil Embargo...
(CAFE) incentives for the manufacture of vehicles that use ethanol
Ethanol fuel
Ethanol fuel is ethanol , the same type of alcohol found in alcoholic beverages. It is most often used as a motor fuel, mainly as a biofuel additive for gasoline. World ethanol production for transport fuel tripled between 2000 and 2007 from 17 billion to more than 52 billion litres...
, methanol
Methanol fuel
Methanol is an alternative fuel for internal combustion and other engines, either in combination with gasoline or directly . It is used in racing cars and in China...
, or natural gas fuels
Compressed natural gas
Compressed 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...
, either powered exclusively on these alternative fuels or in conjunction with gasoline or diesel fuel, such flexible-fuel vehicle
Flexible-fuel vehicle
A 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. In order to provide incentives for the widespread use of these fuels and to promote the production of alternative fuel vehicles, AMFA allows manufacturers producing alternative fuel vehicle
Alternative fuel vehicle
An alternative fuel vehicle is a vehicle that runs on a fuel other than "traditional" petroleum fuels ; and also refers to any technology of powering an engine that does not involve solely petroleum...
s to gain CAFE credits by manufacturing these vehicles, which allows them to raise their overall fleet fuel economy levels to comply with the CAFE standards until the established cap level.
Beginning in 1993, manufacturers of qualified alternative fuel vehicles can benefit for their CAFE estimation, by computing the weighted average of the fuel economy of the produced alternative fuel vehicles by dividing the alcohol fuel economy by a factor of 0.15. As an example, a dedicated alternative fuel vehicle that would achieve 15 mpg fuel economy while operating on alcohol would have a CAFE calculated as follows:
FE = (1/0.15)(15) = 100 miles per gallon
For alternative dual-fuel vehicles, an assumption is made that the vehicles would operate 50% of the time on the alternative fuel and 50% of the time on conventional fuel, resulting in a fuel economy that is based on a harmonic average of alternative fuel and conventional fuel. For example, for an alternative dual-fuel model that achieves 15 miles per gallon operating on an alcohol fuel and 25 mpg on the conventional fuel, the resulting CAFE would be:
FE = 1 / [(0.5/25) + (0.5/100)] = 40 miles per gallon
Calculation of fuel economy for natural gas vehicles is similar. For the purposes of this calculation, the fuel economy is equal to the weighted average of the fuel economy while operating on natural gas and while operating on either gasoline or diesel fuel. AMFA specifies the energy equivalency of 100 cubic feet of natural gas to be equal to 0.823 gallons of gasoline, with the gallon equivalency of natural gas to be considered to have a fuel content, similar to that for alcohol fuels, equal to 0.15 gallons of fuel. For example, under this conversion and gallon equivalency, a dedicated natural gas vehicle that achieves 25 miles per 100 cubic feet of natural gas would have a CAFE value as follows:
FE = (25/100) x (100/0.823)(1/0.15) = 203 miles per gallon
The Energy Policy Act of 1992
Energy Policy Act of 1992
The Energy Policy Act is a United States government act.It was passed by Congress and addressed energy efficiency, energy conservation and energy management , natural gas imports and exports , alternative fuels and requiring certain fleets to acquire alternative fuel vehicles, which are capable of...
expanded the definition of alternative fuel to include liquefied petroleum gas, hydrogen
Hydrogen vehicle
A hydrogen vehicle is a vehicle that uses hydrogen as its onboard fuel for motive power. Hydrogen vehicles include hydrogen fueled space rockets, as well as automobiles and other transportation vehicles...
, liquid fuels derived from coal and biological materials, electricity
Electric vehicle
An electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
and any other fuel that the Secretary of Transportation determines to be substantially non-petroleum based and has environmental and energy security benefits. Beginning in 1993, manufacturers of these other alternative fuel automobiles that meet the qualifying requirements can also benefit for special treatment in the calculation of their CAFE.
1994: Gasoline gallon equivalent
In 1994 the U.S. National Institute of Standards and TechnologyNational Institute of Standards and Technology
The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
(NIST) introduced gasoline gallon equivalent (GGE) as a metric for fuel economy for natural gas vehicle
Natural gas vehicle
thumb|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. NIST defined a gasoline gallon equivalent (GGE) as 5.660 pounds of natural gas, and gasoline liter equivalent (GLE) as 0.678 kilograms of natural gas.
2000: Petroleum-equivalent fuel economy
| Energy efficiency for selected electric car Electric car An 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... s leased in California California California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area... between 1996–2003 |
|||
| Vehicle | Model year |
Type of battery |
Energy use (Wh Watt-hour The kilowatt hour, or kilowatt-hour, is a unit of energy equal to 1000 watt hours or 3.6 megajoules.For constant power, energy in watt hours is the product of power in watts and time in hours... /mi) |
| GM EV1 | 1997 | Lead acid | 164 |
| GM EV1 | 1999 | NiMH NIMH NIMH or NiMH may refer to:*Nickel-metal hydride battery, a type of rechargeable battery*National Institute of Mental Health, a part of the United States National Institutes of Health... |
179 |
| Toyota RAV4 EV Toyota RAV4 EV The RAV4 EV was an all-electric version of the popular RAV4 SUV produced by Toyota. It was leased from 1997 to 2003, and at the lessees request, many units were sold after the vehicle was discontinued. A total of 1,485 were leased and/or sold in California to meet the state’s mandate for... |
1996 | Lead acid | 235 |
| Toyota RAV4 EV Toyota RAV4 EV The RAV4 EV was an all-electric version of the popular RAV4 SUV produced by Toyota. It was leased from 1997 to 2003, and at the lessees request, many units were sold after the vehicle was discontinued. A total of 1,485 were leased and/or sold in California to meet the state’s mandate for... |
2000 | NiMH NIMH NIMH or NiMH may refer to:*Nickel-metal hydride battery, a type of rechargeable battery*National Institute of Mental Health, a part of the United States National Institutes of Health... |
400 |
| Ford Ranger EV Ford Ranger EV The Ford Ranger EV is a battery electric vehicle produced by Ford Motor Company. It was produced starting in the 1998 model year through 2002 and is no longer in production. It is built upon a light truck chassis used in the Ford Ranger. A few vehicles with lead-acid batteries were sold, but most... |
1998 | Lead acid | 337 |
| Chevrolet S-10 EV | 1997 | Lead acid | 292 |
During the late 1990s and early 2000s several electric car
Electric car
An 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...
s were produced in limited quantities as a result of the California Air Resources Board
California Air Resources Board
The 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...
(CARB) mandate for more fuel-efficient zero-emissions vehicle
Zero-emissions vehicle
A zero-emissions vehicle, or ZEV, is a vehicle that emits no tailpipe pollutants from the onboard source of power. Harmful pollutants to the health and the environment include particulates , hydrocarbons, carbon monoxide, ozone, lead, and various oxides of nitrogen. Although not considered emission...
s. Popular models available in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
included the General Motors EV1
General Motors EV1
The General Motors EV1 was an electric car produced and leased by the General Motors Corporation from 1996 to 1999. It was the first mass-produced and purpose-designed electric vehicle of the modern era from a major automaker, and the first GM car designed to be an electric vehicle from the...
and the Toyota RAV4 EV
Toyota RAV4 EV
The RAV4 EV was an all-electric version of the popular RAV4 SUV produced by Toyota. It was leased from 1997 to 2003, and at the lessees request, many units were sold after the vehicle was discontinued. A total of 1,485 were leased and/or sold in California to meet the state’s mandate for...
. The US DoE and EPA rating for on board energy efficiency for these electric vehicles was expressed as kilowatt-hour/mile (KWh/mi), the most commonly known metric in science and engineering for measuring energy consumption, and used as the billing unit for energy delivered to consumers by electric utilities.
In order to address the Corporate Average Fuel Economy
Corporate Average Fuel Economy
The Corporate Average Fuel Economy are regulations in the United States, first enacted by the U.S. Congress in 1975, and intended to improve the average fuel economy of cars and light trucks sold in the US in the wake of the 1973 Arab Oil Embargo...
(CAFE) regulations mandated by the US Congress in 1975, the U.S. Department of Energy established in July 2000 a methodology for calculating the petroleum-equivalent fuel economy of electric vehicle
Electric vehicle
An electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
s on a well-to-wheel basis. The methodology considers the upstream efficiency of the processes involved in the two fuel cycles, including efficiency factors for petroleum refining and distribution, as well as the national average efficiency for electricity generation and transmission.
The formula also includes a fuel efficiency incentive factor of 1/0.15 to benefit electric vehicles. This reward factor is intended provide an incentive for vehicle manufactures to produce and sell electric vehicles, as a higher equivalent fuel economy for EVs improves the carmaker overall fleet fuel economy levels in complying with the CAFE standards, and Congress anticipated that such an incentive would help accelerate the commercialization of electric vehicles. The incentive factor chosen by DoE for EVs is the same 1/0.15 factor already applied in the regulatory treatment of other types of alternative fuel vehicle
Alternative fuel vehicle
An alternative fuel vehicle is a vehicle that runs on a fuel other than "traditional" petroleum fuels ; and also refers to any technology of powering an engine that does not involve solely petroleum...
s. When all factors are considered in DoE's formula, the energy efficiency or equivalent fuel economy of electric vehicles increases from 33,705 Wh/gallon (plug-to-wheel) to 82,049 Wh/gallon (well-to-wheel).
2007: X Prize
In April 2007, as part of Draft Competition Guidelines released at the New York Auto Show, MPGe was announced as the main merit metric for the Progressive Insurance Automotive X Prize, a competition developed by the X Prize FoundationX Prize Foundation
The X PRIZE Foundation is a non-profit organization that designs and manages public competitions intended to encourage technological development that could benefit mankind....
for super-efficient vehicles that can achieve at least 100 MPGe. In February 2009, Consumer Reports
Consumer Reports
Consumer 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...
announced that, as part of a partnership with the X Prize Foundation, they planned to report MPGe as one of several measures that will help consumers understand and compare vehicle efficiency for alternative fuel vehicle
Alternative fuel vehicle
An alternative fuel vehicle is a vehicle that runs on a fuel other than "traditional" petroleum fuels ; and also refers to any technology of powering an engine that does not involve solely petroleum...
s.
2010–2011: Miles per gallon equivalent
As required by the 2007 Energy Independence and Security Act (EISA), with the introduction of advanced-technology vehicles in the U.S. new information should be incorporated in the Monroney label of new cars and light-duty trucks sold in the country, such as ratings on fuel economyFuel economy in automobiles
Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....
, greenhouse gas emissions, and other air pollutants. The U.S. Environmental Protection Agency and the National Highway Traffic Safety Administration
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...
(NHTSA) have conducted a series of studies to determine the best way to redesign this label to provide consumers with simple energy and environmental comparisons across all vehicles types, including battery electric vehicle
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...
s (BEV), plug-in hybrid electric vehicle
Plug-in hybrid electric vehicle
A plug-in hybrid electric vehicle , plug-in hybrid vehicle , or plug-in hybrid is a hybrid vehicle which utilizes rechargeable batteries, or another energy storage device, that can be restored to full charge by connecting a plug to an external electric power source...
s (PHEV), and conventional internal combustion engine
Internal combustion engine
The 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 powered by gasoline and diesel, in order to help consumers choose more efficient and environmentally friendly vehicles. These changes are proposed to be introduced in new vehicles beginning with model year 2012.
As part of the research and redesign process, EPA conducted focus group
Focus group
A focus group is a form of qualitative research in which a group of people are asked about their perceptions, opinions, beliefs and attitudes towards a product, service, concept, advertisement, idea, or packaging...
s where participants were presented with several options to express the consumption of electricity for plug-in electric vehicle
Plug-in electric vehicle
A 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. The research showed that participants did not understand the concept of a kilowatt hour as a measure of electric energy use in spite of the fact that this is the metric used in their monthly electric bills. Instead, participants favored a miles per gallon equivalent, MPGe, as the metric to compare with the familiar miles per gallon used for gasoline vehicles. The research also concluded that the kW-hrs per 100 miles metric was more confusing to focus group participants compared to a miles per kW-hr. Based on these results, EPA decided to use the following fuel economy and fuel consumption metrics on the redesigned labels: MPG (city and highway, and combined); MPGe (city and highway, and combined); Gallons per 100 miles; kW-hrs per 100 miles.
The proposed design and final content for two options of the new sticker label that will be introduced in 2013 model year
Model year
The 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....
cars and trucks were consulted for 60 days with the public in 2010, and both include miles per gallon equivalent and kW-hrs per 100 miles as the fuel economy metrics for plug-in cars, but in one option MPGe and annual electricity cost are the two most prominent metrics. In November 2010, EPA introduced MPGe as comparison metric on its new sticker for fuel economy for the Nissan Leaf
Nissan Leaf
Nissan 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...
and the Chevrolet Volt
Chevrolet Volt
The 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...
.
In May 2011, the National Highway Traffic Safety Administration
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...
(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
Model year
The 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. The ruling includes new labels for alternative fuel
Alternative fuel
Alternative 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 vehicle
Electric vehicle
An electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
s, flexible-fuel vehicle
Flexible-fuel vehicle
A 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 vehicle
Fuel cell vehicle
A 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 vehicle
Natural gas vehicle
thumb|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 engine
Internal combustion engine
The 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 gas
Compressed natural gas
Compressed 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 hydrogen
Hydrogen
Hydrogen 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 show for the first time an estimate of how much fuel or electricity it takes to drive 100 miles (160.9 km), introducing to 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.".
Description
The miles per gallon gasoline equivalent is based on the energy content of gasoline. The energy obtainable from burning one US gallon is 115,000 BTU. Thus one mile per gallon gasoline equivalent is equal to 115,000 BTU per mile.For alternative fuels, energy required to manufacture the fuel may also be considered. For electrical power, the energy of any fuels used to generate the electricity and the transmission efficiency must be considered.
To convert the mile per gallon rating into other units of distance per unit energy used, the mile per gallon value can be multiplied by one of the following factors to obtain other units:
| 1 MPGe | = 8.55 miles/ million BTU |
| ≈ 0.0292 miles/kW·h | |
| ≈ 0.0182 km/kW·h | |
| ≈ 0.005 km/MJ |
Conversion to MPGe
MPGe is determined by converting the vehicle consumption per unit distance, as determined through computer modeling or completion of an actual driving cycle, from its native units into a gasoline energy equivalent. Examples of native units include W·h for electric vehicles, kg-H2 for hydrogen vehicles, gallons for biodieselBiodiesel
Biodiesel refers to a vegetable oil- or animal fat-based diesel fuel consisting of long-chain alkyl esters. Biodiesel is typically made by chemically reacting lipids with an alcohol....
vehicles, cubic feet
Cubic foot
The cubic foot is an Imperial and US customary unit of volume, used in the United States and the United Kingdom. It is defined as the volume of a cube with sides of one foot in length.-Conversions:- Symbols :...
for compressed natural gas
Compressed natural gas
Compressed 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...
, pounds
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
for propane
Propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...
or Liquefied petroleum gas vehicles, and gallons for liquefied natural gas
Liquefied natural gas
Liquefied natural gas or LNG is natural gas that has been converted temporarily to liquid form for ease of storage or transport....
vehicles. Special cases for specific alternative fuels are discussed below, but a general formula for MPGe is:
Depending on the purpose, total energy consumption for the vehicle may also need to include the energy used in the production of whatever energy carrier (fuel) is used for the vehicle and the energy used in filling the "tank". For example, with electrically powered vehicles, a full accounting of total energy consumption would include the efficiency factor for conversion of primary fuels into electricity (the energy of the fuel used to generate and transmit electricity) and the efficiency factor of charging the battery from the electrical plug.
Basic values for the energy content of various fuels are given by the defaults used in the Department of Energy GREET (Greenhouse gases, Regulated Emissions, and Energy used in Transportation) model, as follows:
Note: 1 KWH is equivalent to 3,412 BTU
| Fuel | Unit | Btu/Unit | KWH/Unit |
|---|---|---|---|
| gasoline | gallon | 116,090 | 34.02 |
| diesel | gallon | 129,488 | 37.95 |
| biodiesel | gallon | 119,550 | 35.04 |
| ethanol | gallon | 76,330 | 22.37 |
| E85 | gallon | 82,000 | 24.03 |
| CNG | 100 SCF | 98,300 | 28.81 |
| H2-Gas | 100 SCF | 28,900 | 8.47 |
| H2-Liq | gallon | 30,500 | 8.94 |
| LPG | gallon | 84,950 | 24.9 |
| methanol | gallon | 57,250 | 16.78 |
The energy content of a particular fuel can vary somewhat given its specific chemistry and production method. For example, in the new efficiency ratings that have been developed by the United States Environmental Protection Agency
United States Environmental Protection Agency
The 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...
(EPA) for battery electric vehicle
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...
s (BEVs) and plug-in hybrid electric vehicle
Plug-in hybrid electric vehicle
A plug-in hybrid electric vehicle , plug-in hybrid vehicle , or plug-in hybrid is a hybrid vehicle which utilizes rechargeable batteries, or another energy storage device, that can be restored to full charge by connecting a plug to an external electric power source...
s (PHEVs) – see below – the energy content of a gallon of gasoline is assumed to be 114,984 BTUs.
Electric and plug-in hybrid electric vehicles
Between 2008 and 2010 several major automakers began commercializing battery electric vehicleBattery 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...
s (BEVs), which are powered exclusively on electricity, and plug-in hybrid electric vehicle
Plug-in hybrid electric vehicle
A plug-in hybrid electric vehicle , plug-in hybrid vehicle , or plug-in hybrid is a hybrid vehicle which utilizes rechargeable batteries, or another energy storage device, that can be restored to full charge by connecting a plug to an external electric power source...
s (PHEVs), which use electricity together with a liquid fuel stored in an on-board fuel tank, usually gasoline, but it might be also powered by diesel
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...
, ethanol
Ethanol fuel
Ethanol fuel is ethanol , the same type of alcohol found in alcoholic beverages. It is most often used as a motor fuel, mainly as a biofuel additive for gasoline. World ethanol production for transport fuel tripled between 2000 and 2007 from 17 billion to more than 52 billion litres...
, or flex-fuel engines.
For battery electric vehicles, the U.S. Environmental Protection Agencys formula to calculate the battery-to wheel MPGe is based on energy standards established by the U.S. Department of Energy in 2000:
where
-
is expressed as miles per gallon gasoline equivalent (as shown in the Monroney label)
energy content per gallon of gasoline = 115,000 BTUs/gallon, as set by U.S. DoE and reported by the Alternative Fuel Data Center. battery-to-wheel electrical energy consumed per mile (WhWatt-hour
The kilowatt hour, or kilowatt-hour, is a unit of energy equal to 1000 watt hours or 3.6 megajoules.For constant power, energy in watt hours is the product of power in watts and time in hours...
/mi) as measured through EPA's five standard drive cycle tests for electric cars.
energy per KWatt-hour of electricity (BTU/Wh) = 3.412The formula employed by the EPA for calculating their rated MPGe does not account for any fuel or energy consumed upstream such as the generation and transmission of electrical power, or well-to-wheel life cycle, as EPA's comparison with internal combustion vehicles is made on a tank-to-wheel versus battery-to wheel basis.
The California Air Resources Board
California Air Resources Board
The 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...
uses a different dynamometer
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...
testing than EPA, and considers reformulated gasoline sold in that state. For CARB estimates the formula becomes:
The new SAE
SAE International
SAE International is an organization for engineering professionals in the aerospace, automotive, and commercial vehicle industries. The Society is a standards development organization for the engineering of powered vehicles of all kinds, including cars, trucks, boats, aircraft, and others.SAE...
J1711 standard for measuring the exhaust emissions and fuel economy of hybrid electric vehicle
Hybrid electric vehicle
A 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...
s and plug-in hybrids was approved in July 2010. The recommended procedures for PHEVs were revised at Argonne National Laboratory
Argonne National Laboratory
Argonne National Laboratory is the first science and engineering research national laboratory in the United States, receiving this designation on July 1, 1946. It is the largest national laboratory by size and scope in the Midwest...
, and EPA's new regulation to define PHEV fuel economy reporting protocol is expected to be based on SAE J1711. In November 2010 EPA decided to rate electric mode and gasoline only mode separately, and these are the two figures prominently displayed in the window sticker of the 2011 Chevrolet Volt
Chevrolet Volt
The 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...
. In electric mode the Volt's rating is estimated with the same formula as an electric car. The overall or composite fuel economy rating combining electricity and gasoline powered are displayed in the Monroney label in a much smaller type, and as part of the comparison of the Volt's fuel economy among all vehicles and within compact car
Compact car
A compact car , or small family car , is a classification of cars which are larger than a supermini but smaller than or equal to a mid-size car...
s. EPA has considered several methodologies for rating the overall fuel economy of PHEVs, but as of February 2011 EPA has not announced the final methodology that will be applied for the purposes of estimating the new manufacture's 2012-2016 Corporate Average Fuel Economy
Corporate Average Fuel Economy
The Corporate Average Fuel Economy are regulations in the United States, first enacted by the U.S. Congress in 1975, and intended to improve the average fuel economy of cars and light trucks sold in the US in the wake of the 1973 Arab Oil Embargo...
(CAFE) credits for plug-in hybrids.
Examples
In November 2010 the EPA began including "MPGe" in its new sticker for fuel economy and environmental comparisons. The EPA rated the Nissan LeafNissan Leaf
Nissan 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...
electric car
Electric car
An 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...
with a combined fuel economy
Fuel economy in automobiles
Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....
of 99 MPGe, and rated the Chevrolet Volt plug-in hybrid with a combined fuel economy of 93 MPGe in all-electric mode, 37 MPG when operating with gasoline only, and an overall fuel economy rating of 60 mpg-US (3.9 L/100 km) combining power from electricity and gasoline. For both vehicles EPA calculated the MPGe rating under its five-cycle tests using the formula displayed earlier with a conversion factor of 33.7 kW-hr of electricity being the energy equivalent of a gallon of gasoline.
The following table illustrates EPA's fuel economy comparison and out-of-pocket fuel costs among two plug-in electric vehicle
Plug-in electric vehicle
A 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 rated in MPGe and the most fuel efficient gasoline-electric hybrid car available in the U.S. market. Also shown in the fuel efficiency for plug-in expressed as KW-hrs/100 mile, the metric used by EPA to rate electric cars before November 2010.
| Comparison of fuel economy and fuel economics for automobiles rated by EPA with MPGe and conventional MPG (as displayed in the Monroney label and the US DoE fueleconomy.gov website) |
||||||||
|---|---|---|---|---|---|---|---|---|
| Vehicle | Year model |
Operating mode |
EPA United States Environmental Protection Agency The 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... rated Combined fuel economy Fuel economy in automobiles Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed.... |
EPA United States Environmental Protection Agency The 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... rated City fuel economy Fuel economy in automobiles Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed.... |
EPA rated Highway fuel economy Fuel economy in automobiles Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed.... |
Fuel cost to drive 25 miles |
Annual fuel cost (15,000 mi) |
Notes |
| Nissan Leaf Nissan Leaf Nissan 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... |
2011 | All-electric | 99 mpg-e (34 kW-hrs/100 miles) |
106 mpg-e (32 kW-hrs/100 miles) |
92 mpg-e (37 kW-hrs/100 miles) |
$0.94 | $561 | See (1) |
| Chevrolet Volt Chevrolet Volt The 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... |
2011 | Electricity only | 93 mpg-e (36 kW-hrs/100 miles) |
95 mpg-e (35.7 kW-hrs/100 miles) |
90 mpg-e (37.4 kW-hrs/100 miles) |
$0.99 | $594 | See (1) |
| Gasoline only | 37 mpg | 35 mpg | 40 mpg | $2.72 | $1,632 | |||
| Toyota Prius Toyota Prius (XW30) The Toyota Prius is a mid-size hatchback that has been produced by Toyota. Toyota debuted the third generation Prius at the January 2009 North American International Auto Show, and sales began in Japan on May 18, 2009. Replacing the XW20 series, the XW30 represents the third generation of the... |
2011 | Gasoline-electric hybrid Hybrid electric vehicle A 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... |
50 mpg | 51 mpg | 48 mpg | $1.90 | $1,137 | See (2) |
| Notes: (1) Electricity cost of $0.11/kw-hr and premium gasoline price of $4.01 per gallon (as of mid April 2011). Conversion 1 gallon of gasoline=33.7 kW-hr. (2) Based on 45% highway and 55% city driving. Regular gasoline price of $3.79 per gallon (as of mid April 2011). |
||||||||
Conversion using GGE
The same method can be applied to any other alternative fuel vehicle when that vehicle's energy consumption is known. Generally the energy consumption of the vehicle is expressed in units other than W·h/mile, or Btu/mile so additional arithmetic is required to convert to a gasoline gallon equivalent (GGE) of 115,000 BTU/mile.Hydrogen example with GGE
The 2008 Honda FCX Clarity is advertised to have a vehicle consumption of 72 mi/kg-. Hydrogen has an energy density of 120 MJJoule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
/kg (113,738 BTU/kg), by converting this energy density to a GGE, it is found that 1.012 kg of hydrogen
Hydrogen
Hydrogen 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...
is needed to meet the equivalent energy of one gallon of gasoline. This conversion factor can now be used to calculate the MPGe for this vehicle.
,Tank-to-wheel
EPA's miles per gallon equivalent metric shown in the window sticker does not measure a vehicle's full cycle energy efficiencyEnergy conversion efficiency
Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat.-Overview:...
or well-to-wheel life cycle. Rather, the EPA presents MPGe in the same manner as MPG for conventional internal combustion engine
Internal combustion engine
The 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 as displayed in the Monroney sticker
Monroney sticker
The 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...
, and in both cases the rating only considers the tank-to-wheel or battery-to-wheel energy consumption. The EPA ratings displayed in window stickers do not account for the energy consumption upstream, which includes the energy or fuel required to generate the electricity or to extract and produce the liquid fuel; the energy losses due to power transmission; or the energy consumed for the transportation of the fuel from the well.
Petroleum-equivalency factor (PEF) — a CAFE metric
In 2000 the United States Department of EnergyUnited States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
(DOE) established the methodology for calculating the petroleum-equivalent fuel economy of electric vehicles based on the well-to-wheel (WTW) gasoline-equivalent energy content of electricity (Eg). The methodology considers the upstream efficiency of the processes involved in the two fuel cycles, and considers the national average electricity generation and transmission efficiencies because a battery electric vehicle
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...
burns its fuel (mainly fossil fuels) off-board at the power generation plant. This methodology is used by carmakers to estimate credits into their overall Corporate Average Fuel Economy
Corporate Average Fuel Economy
The Corporate Average Fuel Economy are regulations in the United States, first enacted by the U.S. Congress in 1975, and intended to improve the average fuel economy of cars and light trucks sold in the US in the wake of the 1973 Arab Oil Embargo...
(CAFE) for manufacturing electric drive vehicles.
The equations for determining the petroleum equivalent fuel economy of electric vehicles are the following:
- PEF = Eg * 1/0.15 * AF * DPF
- where:
- PEF = Petroleum-equivalent fuel economy
- Eg = Gasoline-equivalent energy content of electricity factor
- 1/0.15 = "Fuel content" factor or incentive factor. DoE selected this value to keep consistency with existing regulatory and statutory procedures, and to provide a similar treatment to manufacturers of all types of alternative fuel vehicleAlternative fuel vehicleAn alternative fuel vehicle is a vehicle that runs on a fuel other than "traditional" petroleum fuels ; and also refers to any technology of powering an engine that does not involve solely petroleum...
s - AF = Petroleum-fueled accessory factor
- DPF = Driving pattern factor
- where:
The gasoline-equivalent energy content of electricity factor, abbreviated as E.g., is defined as:
- Eg = gasoline-equivalent energy content of electricity = (Tg * Tt * C) / Tp
- where:
- Tg = U.S. average fossil-fuel electricity generation efficiency = 0.328
- Tt = U.S. average electricity transmission efficiency = 0.924
- Tp = Petroleum refining and distribution efficiency = 0.830
- C = Watt-hours of energy per gallon of gasoline conversion factor = 33,705 Wh/gal
- Eg = (0.328 * 0.924 * 33705)/0.830 = 12,307 Wh/gal
- where:
- PEF = Eg * 1/0.15 * AF * DPF = 12,307 Wh/gal/0.15 * AF * DPF
- PEF = 82,049 Wh/gal * AF * DPF
The petroleum-fueled accessory factor, AF, is equal to 1 if the electric drive vehicle does not have petroleum-powered accessories installed, and 0.90 if it does.
The driving pattern factor, DPF, is equal to 1, as DoE considered that electric vehicles eligible for inclusion in CAFE will offer capabilities, perhaps excepting driving range, similar to those of conventional vehicles.
In the example provided by the US DoE in its final rule, an electric car
Electric car
An 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...
with an energy consumption of 265 Watt-hour
Watt-hour
The kilowatt hour, or kilowatt-hour, is a unit of energy equal to 1000 watt hours or 3.6 megajoules.For constant power, energy in watt hours is the product of power in watts and time in hours...
per mile in urban driving, and 220 Watt-hour per mile in highway driving, resulted in a petroleum-equivalent fuel economy of 335.24 miles per gallon, based on a driving schedule factor of 55 percent urban, and 45 percent highway, and using a petroleum equivalency factor of 82,049 Watt-hours per gallon.
See also
- Alternative propulsion
- Corporate Average Fuel EconomyCorporate Average Fuel EconomyThe Corporate Average Fuel Economy are regulations in the United States, first enacted by the U.S. Congress in 1975, and intended to improve the average fuel economy of cars and light trucks sold in the US in the wake of the 1973 Arab Oil Embargo...
(CAFE) - Energy conversion efficiencyEnergy conversion efficiencyEnergy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat.-Overview:...
- Energy densityEnergy densityEnergy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
- Fuel efficiency in transportationFuel efficiency in transportationThe 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...