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 US National Institute of Standards and Technology (NIST) defined "gasoline gallon equivalent (GGE) means 5.660 pounds of natural gas."[1] 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. One GGE of CNG and one GGE of electricity have exactly 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. In the context of GGE, a real world kind of "useful work" is miles per gallon (MPG) as advertised by motor vehicle manufacturers.

Substituting one fuel for another in a given engine may start and 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 done automatically in computer controlled fuel injected and multi-fuel vehicles. Fine tuning of the optimum fuel–air mix may be facilitated by using a supercharger or turbocharger.

In battery or 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. See table below translating retail electricity costs for a GGE in BTU.

Note that throughout this article, 'gallon' refers to the US gallon of approximately 3.8 litres, as opposed to the imperial gallon of approximately 4.5 litres

Gasoline gallon equivalent tables

GGE calculated for gasoline in US gallons at 114000 BTU per gallon,
or 7594 kilocalories per litre[2]
Fuel: liquid, US gallons GGE GGE % BTU/gal kWh/gal HP-hr/gal Cal/litre
Gasoline (base)[3] 1.0000 100.00% 114,000 33.41 44.79 7594.0
Gasoline (conventional, summer)[3] 0.9960 100.40% 114,500 33.56 44.99 7624.5
Gasoline (conventional, winter)[3] 1.0130 98.72% 112,500 32.97 44.20 7496.5
Gasoline (reformulated gasoline, E10 - ethanol)[3] 1.0190 98.14% 111,836 32.78 43.94 7452.4
Gasoline (reformulated gasoline, ETBE)[3] 1.0190 98.14% 111,811 32.77 43.93 7452.4
Gasoline (reformulated gasoline, MTBE)[3] 1.0200 98.04% 111,745 32.75 43.90 7445.1
Gasoline (10% MTBE)[4] 1.0200 98.04% 112,000 32.83 44.00 7445.1
Gasoline (regular unleaded)[5] 1.0000 100.00% 114,100 33.44 44.83 7594.0
Diesel #2[5] 0.8800 113.64% 129,500 37.95 50.87 8629.8
Biodiesel (B100)[5] 0.9600 104.17% 118,300 34.80 46.65 8629.5
Bio Diesel (B20)[5] 0.9000 111.11% 127,250 37.12 49.76 8437.7
Liquid natural gas (LNG)[5] 1.5362 65.10% 75,000 21.75 29.16 4943.3
Liquefied petroleum gas (propane) (LPG)[5] 1.3500 74.04% 84,300 24.75 33.18 5625.2
Methanol fuel (M100)[5] 2.0100 49.75% 56,800 16.62 22.28 3778.1
Ethanol fuel (E100)[5] 1.5000 66.67% 76,100 22.27 29.85 5062.7
Ethanol (E85)[5] 1.3900 71.94% 81,800 24.04 32.23 5463.3
Jet fuel (naphtha)[6] 0.9700 103.09% 118,700 34.44 46.17 7828.9
Jet fuel (kerosene)[6] 0.9000 111.11% 128,100 37.12 49.76 8437.7
Nitromethane fuel ~2.3 41.23% 47,000
GGE calculated on non-liquid fuels
Fuel: non-liquid GGE GGE % BTU/unit kWh/unit
Gasoline (base)[3][7] 1.0000 100.00% 114,000 BTU/gal 33.41
Compressed natural gas (CNG)[8] 126.67 cu ft (3.587 m3) 20,268 BTU/lb
Hydrogen at 101.325 kPa 357.37 cu ft 319 BTU/cu ft[9]
Hydrogen by weight 0.997 kg (2.198 lb)[10] 119.9 MJ/kg (51,500 BTU/lb)[11]
Electricity 33.40 kilowatt-hours 3,413 BTU/(kW·h) [12][13] 33.40
Electricity costs
for 1 GGE
1 GGE = 33.40 kWh
For Local Rate
Per kWh		 $/Gallon
Equivalent
$0.07 $2.338
$0.08 $2.670
$0.09 $3.006
$0.10 $3.340
$0.11 $3.674
$0.12 $4.000
$0.13 $4.342
$0.14 $4.670
$0.15 $5.010
$0.16 $5.344
$0.17 $5.678
$0.18 $6.012
$0.19 $6.346
$0.20 $6.680
$0.25 $8.350
$0.27 $9.018
$0.28 $9.352
$0.29 $9.686
$0.30 $10.020

Rates per kWh for residential electricity in the USA range from $0.0728 (Idaho) to $0.166 (Alaska) and $0.2783 (Hawaii).[14][15]

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).[16]

One GGE of CNG pressurized at 2,400 psi (17 MPa) is 0.77 cubic foot (21.8 liters or 5.75 Gallons). 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.[16] 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."[17]

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 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, for easier starting) and anti-knock additives. Such additives offer a slight reduction in BTU value.

Efficiency

A concept closely related to the BTU or kWh potential of a given fuel is engine efficiency, often called thermal efficiency in the case of internal combustion engines.

Generally speaking, an electrical motor is far more efficient than an internal combustion engine at converting potential energy into work - turning the wheels that may move a car down the road, 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.

A diesel cycle engine can be as much as 40% to 50% efficient at converting fuel into work, where a typical automotive gasoline engine's efficiency is about 25% to 30%.

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. An electric motor has internal friction only at the main axle bearings. Friction outside the motor/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.[18][19] 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.[20]

See also

References

  1. ↑ Butcher, Tina; Crown, Linda; Sebring, Lynn; Suiter, Richard & Williams, Juana, eds. (2006). "Appendix D: Definitions" (PDF). Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, as Adopted by the 91st National Conference on Weights and Measures 2006 (2007 ed.). Gaithersburg, MD: National Institute of Standards and Technology. p. D-8. Handbook 44. Retrieved January 2, 2009.
  2. ↑ "114000 BTU per Gallon to Calories per Litre". Wolfram-Alpha. Retrieved January 4, 2015.
  3. 1 2 3 4 5 6 7 "Fuel Economy Impact Analysis of RFG". United States Environmental Protection Agency. August 14, 2007. Retrieved July 1, 2014.
  4. ↑ "Energy Equivalents of Various Fuels". NAFA Fleet Management Association. Archived from the original on June 15, 2010.
  5. 1 2 3 4 5 6 7 8 9 Gable, Christine & Gable, Scott. "Fuel Energy Comparisons: Gasoline Gallon Equivalents". About.com. Retrieved January 4, 2015.
  6. 1 2 Energy Information Administration (November 2005). "Appendix C: Quality of the Data" (PDF). Household Vehicles Energy Use: Latest Data & Trends. Washington, DC: United States Department of Energy. pp. 151–161. DOE/EIA-0464(2005). Archived from the original (PDF) on May 23, 2011.
  7. ↑ Fuel Economy Impact Analysis of RFG. US Environmental Protection Agency. August 1, 1995.
  8. ↑ "Alternative Fuels Data Center Fuel Properties Comparison" (PDF). United States Department of Energy. February 27, 2013. Retrieved August 9, 2013.
  9. ↑ Johnson, C (January 2, 2015). "Hydrogen as a Fuel for Vehicles". Public Services Home Page. MB-Soft. Retrieved January 4, 2015.
  10. ↑ Fuel Specifications Subcommittee (June 19, 2008). "Appendix E—The Starting Point: A Discussion Paper Describing a Proposed Method of Sale and Quality Specification for Hydrogen Vehicle Fuel" (PDF). U.S. National Work Group Meeting for the Development of Commercial Hydrogen Measurement Standards. National Institute of Standards and Technology. Archived from the original (PDF) on June 8, 2011.
  11. ↑ Chandler, Kevin & Eudy, Leslie (June 2008). SunLine Transit Agency Hydrogen-Powered Transit Buses: Third Evaluation Report—Appendices (PDF). Golden, CO: National Renewable Energy Laboratory. NREL/TP-560-43741-2. Retrieved January 4, 2015.
  12. ↑ Bioenergy Feedstock Development Programs. "Energy Conversions". Oak Ridge National Laboratory. Retrieved January 1, 2009.
  13. ↑ "Conserving Energy and Water: Energy Terms/Conversions". Pacific Northwest National Laboratory. June 2008. Archived from the original on November 2, 2008. Retrieved January 1, 2009.
  14. ↑ "Electricity Prices by State: National Electric Rate Information". Eisenbach Consulting, LLC.
  15. ↑ "Average Retail Price of Electricity". ElectricRates.us. Retrieved January 4, 2015.
  16. 1 2 "Properties of Fuels" (PDF). Energy Efficiency and Renewable Energy. United States Department of Energy. Alternative Fuels Data Center. October 29, 2014. Retrieved January 1, 2015.
  17. ↑ "Uniform Engine Fuels, Petroleum Products and Automotive Lubricants Regulation" (DOC). National Institute of Standards and Technology. pp. 149–164. Retrieved October 8, 2008.
  18. ↑ Bunkley, Nick (November 22, 2010). "Nissan Says Its Electric Leaf Gets Equivalent of 99 MPG". The New York Times. Retrieved February 17, 2011.
  19. ↑ Meier, Fred (November 24, 2010). "Volt Is Rated 93 MPG on Electricity Alone, 37 MPG on Gas Generator". USA Today. Retrieved February 17, 2011.
  20. ↑ "Fuel Economy Label". United States Environmental Protection Agency. February 14, 2011. Retrieved February 17, 2011.
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