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Gasoline gallon equivalent (GGE) or gasoline-equivalent gallon (GEG) is the amount of alternative fuel it takes to equal the energy content of one liquid gallon of gasoline. In 1994, the U.S. National Institute of Standards and Technology or NIST defined "gasoline gallon equivalent (GGE) means 5.660 pounds of natural gas."
GGE allows consumers to compare the energy content of competing fuels against a commonly known fuel—gasoline. Compressed natural gas (CNG), for example, is a gas rather than a liquid. It can be measured by its volume in cubic feet (ft³), by its weight in pounds (lb) or by its energy content in joules (J) or British thermal units (BTU) or kilowatt-hours (kW·h). It is difficult to compare the cost of gasoline with other fuels if they are sold in different units. GGE solves this. A GGE of CNG and a GGE of electricity all have the same energy content as one gallon of gasoline. CNG sold at filling stations is priced in dollars per GGE.
One important point that somewhat clouds the practical utility of a GGE for comparing different fuels to each other is that machines which run on them produce usable energy from different fuels at different efficiencies. For example a 2012 Nissan Leaf has a battery capacity of 24 kWh, or a GGE size of 0.72 gallons. A standard small gasoline-powered car with 25 MPG efficiency can go 18 miles on this much fuel. But the higher efficiency Nissan Leaf can go 80-100 miles on this much battery charge.
|Fuel - Liquid, US Gallons||GGE||GGE %||BTU/Gal||kWh/Gal||Cal/litre|
|Gasoline (conventional, summer)||0.9960||100.40%||114,500||33.56||7624.5|
|Gasoline (conventional, winter)||1.0130||98.72%||112,500||32.97||7496.5|
|Gasoline (reformulated gasoline, ethanol)||1.0190||98.14%||111,836||32.78||7452.4|
|Gasoline (reformulated gasoline, ETBE)||1.0190||98.14%||111,811||32.77||7452.4|
|Gasoline (reformulated gasoline, MTBE)||1.0200||98.04%||111,745||32.75||7445.1|
|Gasoline (10% MBTE)||1.0200||98.04%||112,000||32.83||7445.1|
|Gasoline (regular unleaded)||1.0000||100.00%||114,100||33.44||7594|
|Bio Diesel (B20)||0.9000||111.11%||127,250||37.12||8437.7|
|Liquid natural gas (LNG)||1.5362||65.10%||75,000||21.75||4943.3|
|Liquefied petroleum gas (propane) (LPG)||1.3500||74.04%||84,300||24.75||5625.2|
|Methanol fuel (M100)||2.0100||49.75%||56,800||16.62||3778.1|
|Ethanol fuel (E100)||1.5000||66.67%||76,100||22.27||5062.7|
|Jet fuel (naphtha)||0.9700||103.09%||118,700||34.44||7828.9|
|Jet fuel (kerosene)||0.9000||111.11%||128,100||37.12||8437.7|
|Fuel - Non Liquid||GGE||GGE %||BTU/unit||kWh/Unit|
|Gasoline (base)||1.0000||100.00%||114,000 BTU/gal||33.41|
|Compressed natural gas (CNG)||126.67 cu ft (3.587 m3)||900 BTU/cu ft|
|Hydrogen at 101.325 kPa||357.37 cu ft||319 BTU/cu ft|
|Hydrogen by weight||0.997 kg (2.198 lb)||119.9 MJ/kg (51,500 BTU/lb)|
|Electricity||33.40 kilowatt-hours||3,413 BTU/(kW·h) ||33.40|
|1 GGE = 33.40 kWh|
|For Local Rate|
One GGE of natural gas is 126.67 cubic feet (3.587 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: 900 BTU/cu ft of natural gas and 115,000 BTU/gal of gasoline).
One GGE of CNG pressurized at 2,400 psi (17 MPa) is 0.77 cubic foot (21.8 liters). This volume of CNG at 2,400 psi has the same energy content as one US gallon of gasoline (based on lower heating values: 148,144 BTU/cu ft of CNG and 115,000 BTU/gal of gasoline. Using Boyle's Law, the equivalent GGE at 3,600 psi (25 MPa) is 0.51 cubic foot (14.4 L or 3.82 actual US gal).
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."
When consumers refuel their CNG vehicles in the USA, the CNG is usually measured and sold in GGE units. This is fairly helpful as a comparison to gallons of gasoline.
1.5 gallons of ethanol has the same energy content as 1.0 gallon of gasoline.
The energy content of 1.0 US gallon of ethanol is 76,100 BTU, compared to 114,100 BTU for gasoline. (see chart above)
A flex-fuel vehicle may experience as much as 25% lower MPG when using E85 (85% ethanol) products. This is in part because the engine's compression ratio is fixed mechanically and electronic sensors can only modify the timing of the spark and/or instruct the fuel injection system to provide more of the reduced energy-content fuel.
A 2006 University of California Berkley study, after analyzing six separate studies, concluded that producing ethanol from corn uses much less petroleum than producing gasoline.
The efficiency of converting a unit of fuel to rotation of the driving wheels, includes many points of friction (loss): Heat that goes out the exhaust pipe or through the engine block to the radiator. Friction inside the engine, happens along the cylinder walls, crank, cam and main bearings; plus drive chains or gears. Friction outside the engine, includes loads from the generator, power steering pump, power brake pump, A/C pump, transmission, differential and universal joints; plus rolling resistance of the pneumatic tires.
The MPG of a given vehicle starts with the thermal efficiency of the fuel and engine, less all of the above elements of friction.