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 allows consumers to compare the energy content of competing fuels against a commonly known fuel—gasoline. GGE also compares gasoline to fuels sold as a gas (Natural Gas, Propane, Hydrogen) and electricity.
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." 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) (volume at atmospheric conditions), 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.
Using GGE to compare fuels for use in an internal combustion engine is only the first part of the equation whose bottom line is useful work. A common definition for useful work is articulated as Miles Per Gallon (MPG). Substituting one fuel for another may permit successful startup of a given engine and the combination may do useful work. However getting optimum efficiency from each fuel/engine combination requires adjusting the mix of air and fuel. This can be a manual adjustment using tools and test instruments or automatic as in a multi-fuel vehicle. Fine tuning of the optimum fuel/air mix may be facilitated by using a supercharger or turbocharger.
In battery/electric vehicles, calculating efficiency of useful work begins with the charge/discharge rate of the battery pack, generally 80% to 90%. Next is the conversion of potential energy (BTU) of the charge to distance traveled under power. For example, batteries in a 2012 Nissan Leaf have a listed capacity of 24 kWh. This translates to 0.72 gallons under to a GGE / BTU translations. A standard small gasoline-powered car with 25 MPG efficiency can go 18 miles on this much fuel. However the Nissan Leaf can go 80–100 miles on this much battery charge, or a 111 to 139 MPG equivalent (or 100 to 125 MPG if calculating fuel costs with a battery pack efficiency of 90%). See table below translating retail electricity costs for a GGE in BTU.
GGE - Gasoline Gallon Equivalent (US Gallons) tables
|Fuel - Liquid, US Gallons||GGE||GGE %||BTU/Gal||kWh/Gal||HP-hr/Gal||Cal/litre|
|Gasoline (conventional, summer)||0.9960||100.40%||114,500||33.56||44.99||7624.5|
|Gasoline (conventional, winter)||1.0130||98.72%||112,500||32.97||44.20||7496.5|
|Gasoline (reformulated gasoline, ethanol)||1.0190||98.14%||111,836||32.78||43.94||7452.4|
|Gasoline (reformulated gasoline, ETBE)||1.0190||98.14%||111,811||32.77||43.93||7452.4|
|Gasoline (reformulated gasoline, MTBE)||1.0200||98.04%||111,745||32.75||43.90||7445.1|
|Gasoline (10% MTBE)||1.0200||98.04%||112,000||32.83||44.00||7445.1|
|Gasoline (regular unleaded)||1.0000||100.00%||114,100||33.44||44.83||7594.0|
|Bio Diesel (B20)||0.9000||111.11%||127,250||37.12||49.76||8437.7|
|Liquid natural gas (LNG)||1.5362||65.10%||75,000||21.75||29.16||4943.3|
|Liquefied petroleum gas (propane) (LPG)||1.3500||74.04%||84,300||24.75||33.18||5625.2|
|Methanol fuel (M100)||2.0100||49.75%||56,800||16.62||22.28||3778.1|
|Ethanol fuel (E100)||1.5000||66.67%||76,100||22.27||29.85||5062.7|
|Jet fuel (naphtha)||0.9700||103.09%||118,700||34.44||46.17||7828.9|
|Jet fuel (kerosene)||0.9000||111.11%||128,100||37.12||49.76||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)||20,268 BTU/lb|
|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
Compressed natural gas
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.
Ethanol and Fuels Like E85
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.
Generally speaking, an electrical motor is more efficient than an internal combustion engine at converting potential energy into work - turning the wheels that may move a car down the road.
The efficiency of converting a unit of fuel to rotation of the driving wheels includes many points of friction loss and heat loss through the exhaust or cooling system. 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. Friction outside the engine includes 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 MPG of a given vehicle starts with the thermal efficiency of the fuel and engine, less all of the above elements of friction.
Miles per gallon of gasoline equivalent (MPGe)
For a complete description of MPGe, see the main article: 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, 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.
- Miles per gallon of gasoline equivalent (MPGe)
- Engine Efficiency
- Thermal Efficiency
- Potential Energy
- Work - Thermodynamics
- Work - Physics
- Diesel Cycle Engines
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- Nick Bunkley (2010-11-22). "Nissan Says Its Electric Leaf Gets Equivalent of 99 M.P.G.". The New York Times. Retrieved 2011-02-17.
- Fred Meier (2010-11-24). "Volt is rated 93 mpg on electricity alone, 37 mpg on gas generator". USA Today. Retrieved 2011-02-17.
- "Fuel Economy Label". U.S. Environmental Protection Agency. 2011-02-14. Retrieved 2011-02-17.