gasoline gallon equivalent

In 1994, the US National Institute of Standards and Technology (NIST) defined "gasoline gallon equivalent (GGE) [as] 5.660 pounds of natural gas."{{cite book |editor1-first= Tina |editor1-last= Butcher |editor2-first= Linda |editor2-last= Crown |editor3-first= Lynn |editor3-last= Sebring |editor4-first= Richard |editor4-last= Suiter |editor5-first= Juana |editor5-last= Williams |name-list-style=amp |chapter-url= https://www.nist.gov/pml/wmd/pubs/upload/AppendD-08-HB44-FINAL.pdf |id= Handbook 44 |chapter= Appendix D: Definitions |title= Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, as Adopted by the 91st National Conference on Weights and Measures 2006 |url= https://www.nist.gov/pml/wmd/pubs/h44-07.cfm |location= Gaithersburg, MD |publisher= National Institute of Standards and Technology |year= 2006 |edition= 2007 |page= D-8 |access-date= January 2, 2009 }} Compressed natural gas (CNG), for example, is a gas rather than a liquid. It can be measured by its volume in standard cubic feet (ft³) at atmospheric conditions, by its weight in pounds (lb), or by its energy content in joules (J), British thermal units (BTU), or kilowatt-hours (kW·h). CNG sold at filling stations in the US is priced in dollars per GGE.

Using GGE as a measure to compare the stored energy of various fuels for use in an internal combustion engine is only one input for consumers, who typically are interested in the annual cost of driving a vehicle, which requires considering the amount of useful work that can be extracted from a given fuel. This is measured by the car's overall efficiency. In the context of GGE, a real world measure of overall efficiency is the fuel economy or fuel consumption advertised by motor vehicle manufacturers.

{{main|Fuel economy in automobiles}}

To start, only a fraction of the stored energy of a given fuel (measured in BTU or kW-hr) can be converted to useful work by the vehicle's engine. The measure of this is engine efficiency, often called thermal efficiency in the case of internal combustion engines. A diesel cycle engine can be as much as 40% to 50% efficient at converting fuel into work,{{cite book |doi=10.1533/9780857097422.2.225 |author1=Xin, Q. |author2=Pinzon, C.F. |title=Alternative Fuels and Advanced Vehicle Technologies for Improved Environmental Performance Towards Zero Carbon Transportation |chapter=9 - Improving the environmental performance of heavy-duty vehicles and engines: key issues and system design approaches |isbn=978-0-85709-742-2 |publisher=Woodhead Publishing Limited |pages=225–278 |date=2014}} where a typical automotive gasoline engine's efficiency is about 25% to 30%.{{cite news |url=https://www.cnet.com/roadshow/news/nissan-e-power-gasoline-engine-50-percent-thermally-efficient/ |title=Nissan claims it's made a more thermally efficient gas engine, but there's a catch |author=Hyatt, Kyle |date=February 26, 2021 |work=Road/Show |publisher=CNet |access-date=19 April 2022}}{{cite journal |doi=10.4271/2015-01-1263 |author1=Ikeya, K. |author2=Takazawa, M. |author3=Yamada, T. |author4=Park, S. |author5=Tagishi, R. |issn=1946-3936 |title=Thermal Efficiency Enhancement of a Gasoline Engine |journal=SAE International Journal of Engines |volume=8 |number=4 |pages=1579–1586 |date=2015}}

In general, an engine is designed to run on a single fuel source and substituting one fuel for another may affect the thermal efficiency. Each fuel–engine combination requires adjusting the mix of air and fuel. This can be a manual adjustment using tools and test instruments or done automatically in computer-controlled fuel injected and multi-fuel vehicles. Forced induction for an internal combustion engine using supercharger or turbocharger may also affect the optimum fuel–air mix and thermal efficiency.

The overall efficiency of converting a unit of fuel to useful work (rotation of the driving wheels) includes consideration of thermal efficiency along with dynamic losses that are inherent and specific to the design of a given vehicle. Thermal efficiency is affected by both friction and heat losses; for internal combustion engines, some of the stored energy is lost as heat through the exhaust or cooling system. In addition, friction inside the engine happens along the cylinder walls, crankshaft rod bearings and main bearings, camshaft bearings, drive chains or gears, plus other miscellaneous and minor bearing surfaces. Other dynamic losses can be caused by friction outside the motor/engine, including loads from the generator / alternator, power steering pump, A/C compressor, transmission, transfer case (if four-wheel-drive), differential(s) and universal joints, plus rolling resistance of the pneumatic tires. The vehicle's external styling affects its aerodynamic drag, which is another dynamic loss that must be considered for overall efficiency.

In battery or electric vehicles, calculating the vehicle's overall efficiency of useful work begins with the charge–discharge rate of the battery pack, generally 80% to 90%. Next is the conversion of stored energy to distance traveled under power. Generally speaking, an electrical motor is far more efficient than an internal combustion engine at converting the stored potential energy into useful work; in an electric vehicle, traction motor efficiency can approach 90%, as there is minimal waste heat coming off the motor parts, and zero heat cast off by the coolant radiator and out of the exhaust. An electric motor typically has internal friction only at the main axle bearings.{{Citation needed|date=December 2012}} Additional losses will affect the overall efficiency, similar to a conventional internal combustion car, including rolling resistance, aerodynamic drag, accessory power, climate control, and drivetrain losses. See table below translating retail electricity costs for a GGE in BTU.

Overall efficiency is measured and reported, typically by government testing, through operating the vehicle in a standardized driving cycle designed to replicate typical use, while providing a consistent basis for comparison between vehicles. Cars sold in the United States are advertised by their measured overall efficiency (fuel economy) in miles per gallon (mpg). The MPG of a given vehicle starts with the thermal efficiency of the fuel and engine, less all of the above elements of friction. The fuel consumption is an equivalent measure for cars sold outside the United States, typically measured in litres per 100 km traveled; in general, the fuel consumption and miles per gallon would be reciprocals with appropriate conversion factors, but because different countries use different driving cycles to measure fuel consumption, fuel economy and fuel consumption are not always directly comparable.

{{main|Miles per gallon gasoline equivalent}}

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 (giving a heating value of {{cvt|33.705|kWh/gal|BTU/usgal|-1|disp=out}}), and the energy consumption of each vehicle during EPA's five standard drive cycle tests simulating varying driving conditions.{{cite news |url= https://www.nytimes.com/2010/11/23/business/23leaf.html?_r=1&hpw |title= Nissan Says Its Electric Leaf Gets Equivalent of 99 MPG |work=The New York Times |first= Nick |last= Bunkley |date= November 22, 2010 |access-date= February 17, 2011}}{{cite news |url= http://content.usatoday.com/communities/driveon/post/2010/11/volt-is-rated-93-mpg-on-electricity-alone-37-mpg-on-gas-generator/1 |title= Volt Is Rated 93 MPG on Electricity Alone, 37 MPG on Gas Generator |first= Fred |last= Meier |work= USA Today |date= November 24, 2010 |access-date= February 17, 2011}} 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.{{cite web |url= http://www.epa.gov/fueleconomy/ |title= Fuel Economy Label |publisher= United States Environmental Protection Agency |date= February 14, 2011 |access-date= February 17, 2011}}

Rates per kWh for residential electricity in the USA range from $0.0728 (Idaho) to $0.166 (Alaska),

$0.22 (San Diego Tier 1, while Tier 2 is $.40) and $0.2783 (Hawaii).{{cite web |url=http://www.electricchoice.com/electricity-prices-by-state.php |title=Electricity Prices by State: National Electric Rate Information |publisher= Eisenbach Consulting, LLC }}{{cite web |url=http://www.electricrates.us/articles/20627/Average-Retail-Price-of-Electricity |title=Average Retail Price of Electricity |publisher=ElectricRates.us |access-date=January 4, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150104105343/http://www.electricrates.us/articles/20627/Average-Retail-Price-of-Electricity |archive-date=January 4, 2015 |df=mdy-all }}

One GGE of natural gas is {{convert|{{#expr:114000/900 round 2}}|ft3|m3}} at standard conditions. This volume of natural gas has the same energy content as one US gallon of gasoline (based on lower heating values: {{convert|900|btu/ft3|kWh/m3|abbr=on}} of natural gas and {{convert|114000|btu/usgal|kWh/L|abbr=on}} for gasoline).{{cite web |agency= Alternative Fuels Data Center |date= October 29, 2014|url=http://www.eere.energy.gov/afdc/pdfs/fueltable.pdf |title=Properties of Fuels |publisher= United States Department of Energy |work= Energy Efficiency and Renewable Energy |access-date= January 1, 2015}}

One GGE of CNG pressurized at {{convert|2400|psi|MPa|abbr=on}} is {{convert|{{#expr:114000/148144 round 2}}|ft3|l usgal|abbr=off}}. This volume of CNG at 2,400 psi has the same energy content as one US gallon of gasoline (based on lower heating values: {{convert|148144|btu/ft3|kWh/m3|abbr=on}} of CNG and {{convert|114000|btu/usgal|kWh/L|abbr=on}} of gasoline. Using Boyle's law, the equivalent GGE at {{convert|3600|psi|MPa|abbr=on}} is {{convert|{{#expr:114000/148144/1.5 round 2}}|ft3|l usgal|abbr=off}}.

The National Conference of Weights & Measurements (NCWM) has developed a standard unit of measurement for compressed natural gas, defined in the NIST Handbook 44 Appendix D as follows:

"1 Gasoline [US] gallon equivalent (GGE) means 2.567 kg (5.660 lb) of natural gas."{{cite web |url=https://www.nist.gov/system/files/documents/2019/02/06/appd-19-hb44-final.pdf |title=Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices - Appendix D |publisher=National Institute of Standards and Technology |pages=D-13 |access-date=August 23, 2020}}

When consumers refuel their CNG vehicles in the US, the CNG is usually measured and sold in GGE units. This is fairly helpful as a comparison to gallons of gasoline.

{{convert|1.5|usgal|L|abbr=off}} of ethanol has the same energy content as {{convert|1.0|usgal|L|abbr=on}} of gasoline.

The energy content of ethanol is {{convert|76100|btu/usgal|kWh/L|abbr=in}}, compared to {{convert|114100|btu/usgal|kWh/L|abbr=on}} for gasoline. (see chart above)

A flex-fuel vehicle will experience about 76% of the fuel mileage MPG when using E85 (85% ethanol) products as compared to 100% gasoline. Simple calculations of the BTU values of the ethanol and the gasoline indicate the reduced heat values available to the internal combustion engine. Pure ethanol provides 2/3 of the heat value available in pure gasoline.

In the most common calculation, that is, the BTU value of pure gasoline vs gasoline with 10% ethanol, the latter has just over 96% BTU value of pure gasoline. Gasoline BTU varies relating to the Reid vapor pressure (causing easier vaporization in winter blends containing ethanol (ethanol is difficult to start a vehicle on when it is cold out) and anti-knock additives. Such additives offer a reduction in BTU value.

• Engine efficiency
• Thermal efficiency
• Potential energy
• Work (thermodynamics)
• Work (physics)
• Diesel cycle engines
• Efficiency
• Friction
• Kilowatt hour

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Category:Units of energy

Category:Equivalent units