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Gasoline gallon equivalent

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. GGE is a way of comparing equivalent amounts of fuel based on their energy content. Compressed Natural Gas (CNG) for example, is a gas rather than a liquid. Its volume is measured in cubic feet (CF), rather than in gallons. And, electricity is neither a solid, a liquid nor a gas and it is measured in Kilowatt-hours. One gallon of gasoline has the same amount of energy as 126.67 cu. ft of gas and 33.56 Kilowatt-hours.

Table of GGE

Fuel Gallon Gasoline Equivalent BTUs/Unit
Gasoline (regular unleaded) 1 US gallon 114,100 BTU/gallon
Gasoline (10% MBTE) 1.02 US gallon 112,000 BTU/gallon
Diesel #2 0.88 US gallons 129,500 BTU/gallon
Biodiesel (B100) 0.96 US gallons 118,300 BTU/gallon
Bio Diesel (B20) 0.90 US gallons 127,250 BTU/gallon
Liquid natural gas (LNG) 1.52 US gallons 75,000 BTU/gallon
Compressed natural gas (CNG) 126.67 cu. ft 900 BTU/cu. ft
Compressed hydrogen 357.37 cu. ft 319 BTU/cu. ft
Liquid hydrogen data needed data needed
Liquefied petroleum gas (LPG) 1.35 US gallons 84,300 BTU/gallon
Methanol fuel (M100) 2.01 US gallons 56,800 BTU/gallon
Ethanol fuel (E100) 1.500 US gallons 76,100 BTU/gallon
Ethanol (E85) 1.39 US gallons 81,800 BTU/gallon
Ethanol 10% data needed data needed
Jet fuel (naphtha) 0.97 US gallons 118,700 BTU/gal
Jet fuel (kerosene) 0.90 US gallons 128,100 BTU/gal
Electricity 33.56 Kilowatt hours 3,400 BTU/Kwh

Compressed Natural Gas

One GGE of natural gas is 127.77 cubic feet. This volume of natural gas has the same energy content as one US gallon of gasoline (based on lower heating values: 900 BTU/CF of natural gas and 115,000 BTU/gallon of gasoline).

One GGE of CNG pressurized at 2,400 psi is 0.77 cubic feet. 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/CF of CNG and 115,000 BTU/gallon of gasoline. Using Boyle's Law, the equivalent GGE at 3,600 psi is 0.51 cubic feet which corresponds to 14.5 liters or 3.82 actual US gallons.

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.

Ethanol

One GGE of ethanol is 1.5 gallons. This volume of ethanol has the same energy content as one US gallon of gasoline. This is because a gallon of ethanol has a lower heat value or energy content (76,100 BTU) when compared to a gallon of gasoline (114,100 BTU).

Ethanol burns more slowly and at a lower temperature than gasoline. This makes it easier to extract the chemical energy stored inside it. While a gallon of gasoline has about 50% more energy than ethanol, cars that run on ethanol can get very similar mileage to gasoline powered vehicles when they are optimized to take advantage of ethanol's higher octane rating. This optimization involves increasing the engine's compression ratio from a normal of 9 or 10 to one, to as high as 16 to one. This involves significant and expensive refitting with different pistons (to reduce the combustion chamber size) and mechanical alterations to assure valve to piston clearance. When this optimization is completed, the engine is no longer suitable to operate on 100% gasoline, as the high compression ratio will cause severe knocking (which is very harmful to the engine).

E85

Ordinary consumers driving a "flex-fuel" vehicle can expect a substantial drop in fuel mileage when using 85% ethanol products (the compression ratio is fixed mechanically, and electronic sensors can only modify the timing of the spark and allow the electronic fuel injectors to provide more of the reduced BTU value fuel).

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References

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