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

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).cite web
url=http://www.eere.energy.gov/afdc/pdfs/fueltable.pdf
title=Properties of fuels
publisher=DOE: Energy Efficiency and Renewable Energy
author=
date=
accessdate=2008-10-08]

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." [cite web
url=http://ts.nist.gov/WeightsAndMeasures/Publications/upload/13_IV_EngFuelReg04.doc#_Toc48655096
title=Uniform Engine Fuels, Petroleum Products and Automotive Lubricants Regulation
publisher=NIST
pages=pp.149-164
author=
date=
accessdate=2008-10-08]

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. Fact|date=October 2008 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).Fact|date=October 2008

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).

See also

* Miles per gallon of gasoline equivalent (MPGe)

References