MPGe

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Miles per Gallon of Gasoline Equivalent (MPGe) is a unit of measurement that relates efficiencies of different systems to the traditional unit of measurement for fuel efficiency (miles per gallon of gasoline).

Contents

[edit] Description

MPGe is based on the quantity of heat energy that can be obtained by burning a US gallon of gasoline (115,000 BTUs).[1] The equivalent in terms of another fuel is the amount of such other fuel that would produce that same amount of heat. That other fuel equivalent is then the unit that enables mileage per that unit. On this basis MPGe is a meaningful measurement.

[edit] Energy conversions

See the following table for energy conversions. (Note that electricity is a means of transferring mechanical energy from one rotating machine to another, thus an equivalent unit of electrical energy must represent the equivalent heat energy used by the machine that produced it.):

Fuel Amount of fuel = 1 US gallon of gasoline

(measured in units for fuel type)

 Emissions of CO2
lb/US gal kg/L
Gasoline (regular unleaded)[2] 1 US gallon 19.4 2.32
Diesel[3] 0.88 US gallons 19.54 2.34
Liquid Natural Gas 13.3 1.59
Compressed Natural Gas 13.3 1.59
Liquefied Petroleum Gas 1.35 US gallons 15.9 1.91
Methanol 2.01 US gallons data needed data needed
Ethanol 100% 1.500 US gallons data needed data needed
Ethanol 85% 1.425 US gallons data needed data needed
Ethanol 10% 1.050 US gallons data needed data needed
Jet fuel (naphtha) 0.97 US gallons [4] data needed data needed
Jet fuel (kerosene) 0.90 US gallons [5] data needed data needed
Electricity (coal) 11 Kilowatt hours (2.91 kWh/L) 23.4 2.80
Electricity (natural gas) 14 Kilowatt hours (3.70 kWh/L) 15.9 1.91
Electricity (solar,wind,hydro) 33.7 Kilowatt hours 0 0
  • Data for electricity is based on data for 2005 for total US electricity production by fuel types.
  • Lower heating value (net) is used for this table because the latent heat of vaporization of water in the fuel and the reaction products is not recovered in power applications such as transportation.

[edit] Electricity equivalence

(The appropriate choice to use for the type of electricity is not in general agreement. However, the economic advantage is for solar, wind, or hydro, if these sources are not already fully utilized. The fuel used to generate electricity in response to an added load, such as that of an electric car, will have to come from existing unused capacity. While most unused capacity is in natural gas fired facilities, the far more economical unused capacity is in coal fired facilities. It also must be noted that EIA indicates significant expansion of coal facilities over the next 20 years.)

Attempts are often made to equate the heat that electric energy can produce with the heat needed to produce that electricity. It is not a two way conversion and the fact that the units suggest that it is, is an unfortunate point of confusion. Many try to avoid this confusion by referring to heat in units of BTU and electric energy in units of kilowatt hours. It might be reasonable to ignore this problem if it was just a matter of ignoring small inefficiencies of energy transfer and conversion, but in this case we are talking about heat engine effects. Because these are subject to the second law of thermodynamics very large losses are very difficult to avoid. The reality of electric power production in the US from burning fossil fuels is that for every unit of electric energy that is produced, about twice as much heat energy is lost.[6] The same reality applies to all combustion (heat) engines used in vehicles of course.

Cogeneration plants can recover some "waste" heat from generating electricity which may not be possible in a vehicle based generator or motor. This speaks to the possible economic and useful energy to GHG advantage of electric vehicles over conventional ones.

The maximum theoretical efficiency of fuel cells is 83% but current efficiencies are closer to 40%.[7]

The book "Handbook of Transportation Engineering" By Myer Kutz states that the thermal efficiency of the diesel [locomotive] engine is about 33%.[8] These are very large diesel engine which output the equivalent of about 11 kWh per gasoline gallon equivalent (GGE).[9]


[edit] Cost

If for a given electric vehicle, we assume that coal is the energy source of choice for comparison, from the table above, we get about 11 kWh to a GGE of fuel so we can assign costs to a GGE from an electric source.

Since one US gallon of gasoline equals one GGE from the table above, using U.S data, given the 2007 average price of $2.84,[10] we get $2.84 per GGE/11 kWh per GGE = $0.25/kWh. As long as the cost of power is below $0.25 per kWh, we have better cost economy for an electric vehicle compared to an equivalent (in MPGe) gasoline vehicle.[citation needed]

[edit] Carbon dioxide emission

The carbon dioxide emissions generated from burning one U.S. gallon of gasoline and equivalent emissions from burning other fuels (for electricity) can be easily compared through the MPGe conversion.

When done as described here, MPGe allows a fair comparison of the energy efficiency of vehicles using different fuels.[citation needed] The results seem sensible since the real efficiency of vehicles is mostly determined by the mechanical energy needed to push the car down the road.[original research?] Most cars are subject to drag forces that are roughly similar. For example, the Tesla Roadster electric car achieves 4.7 mi/kWh (132 Wh/km) or 52/66 MPGe (coal/natural gas). (Not 158 MPGe as some would calculate it on the basis of incorrect representation of electrical energy).[citation needed] The 2005 Diesel Volkswagen Beetle 5-speed achieved 41 mpg–U.S. (5.74 L/100 km / 49.2 mpg–imp) highway[citation needed] or 36 MPGe. The 2007 Honda Civic GX averages 39 mpg–U.S. (6.03 L/100 km / 46.8 mpg–imp) highway[citation needed] (X MPG of CNG?) or 52 MPGe. A Flexible-fuel vehicle at 30 mpg–U.S. (7.84 L/100 km / 36 mpg–imp) on E85 is getting 43 MPGe, or it would get 43 mpg–U.S. (5.47 L/100 km / 51.6 mpg–imp) on gasoline.[citation needed] The Honda Civic VX which travels 82.08 kilometers (51 mi) for every U.S. gallon of gasoline used.

(Data is still not entered for all the carbon dioxide emissions of the listed fuels.) (The amount of energy needed to produce the fuels is also relevant, but it is at least very roughly balanced out when the calculation is done as prescribed above.)

[edit] Example

Mode Efficiency per passenger. Avg occupancy.

Transportation 11 kWh (Coal) 14 kWh (Gas) 30 kWh (Theoretical max.)
aaa (please ignore) 0 0 0
Bicycling 0.4 L/100 p·km (653 p·MPGeUS) sm=n 0.4 L/100 p·km (653 p·MPGeUS) sm=n 0.4 L/100 p·km (653 p·MPGeUS) sm=n
Electric bicycle (single test)[11] 0.5 L/100 p·km (496 p·MPGeUS) sm=n 0.4 L/100 p·km (631 p·MPGeUS) sm=n 0.2 L/100 p·km (1,353 p·MPGeUS) sm=n
Walking 1 L/100 p·km (235 p·MPGeUS) sm=n 1 L/100 p·km (235 p·MPGeUS) 1 L/100 p·km (235 p·MPGeUS)
TGV train[12] 1.4 L/100 p·km (167 p·MPGeUS) sm=n 1.1 L/100 p·km (212 p·MPGeUS) 0.5 L/100 p·km (454 p·MPGeUS)
Neighborhood electric vehicle[13] 2.8 L/100 p·km (85 p·MPGeUS) sm=n 2.2 L/100 p·km (108 p·MPGeUS) 1 L/100 p·km (231 p·MPGeUS)
Rail (Passenger - avg UK)
 3.1 L/100 p·km (75 p·MPGeUS) sm=n 3.1 L/100 p·km (75 p·MPGeUS) 3.1 L/100 p·km (75 p·MPGeUS)
Toyota Prius (hybrid vehicle) (US data)[14] 3.9 L/100 p·km (60 p·MPGeUS) sm=n 3.9 L/100 p·km (60 p·MPGeUS) 3.9 L/100 p·km (60 p·MPGeUS)
Toyota Prius (hybrid vehicle (UK data)[15]
(4.3 L/100 km/66 mpg (imp)/55 mpg (US))
(occupancy 1.58)[16]		 2.7 L/100 p·km (87 p·MPGeUS) sm=n 2.7 L/100 p·km (87 p·MPGeUS) 2.7 L/100 p·km (87 p·MPGeUS)
Motorcycles (avg US)[17] 4.7 L/100 p·km (50 p·MPGeUS) sm=n 4.7 L/100 p·km (50 p·MPGeUS) 4.7 L/100 p·km (50 p·MPGeUS)
Rail (Commuter - avg US)[17] 5.3 L/100 p·km (44 p·MPGeUS) sm=n 5.3 L/100 p·km (44 p·MPGeUS) 5.3 L/100 p·km (44 p·MPGeUS)
Rail (Intercity Amtrak - avg US)[17] 5.7 L/100 p·km (41 p·MPGeUS) sm=n 5.7 L/100 p·km (41 p·MPGeUS) 5.7 L/100 p·km (41 p·MPGeUS)
Rail (Transit Light & Heavy - avg US)[17] 5.7 L/100 p·km (42 p·MPGeUS) sm=n 5.7 L/100 p·km (42 p·MPGeUS) 5.7 L/100 p·km (42 p·MPGeUS)
Automobile (avg US)[18] 7.2 L/100 p·km (33 p·MPGeUS) sm=n 7.2 L/100 p·km (33 p·MPGeUS) 7.2 L/100 p·km (33 p·MPGeUS)
Air (avg US)[17] 8.2 L/100 p·km (29 p·MPGeUS) sm=n 8.2 L/100 p·km (29 p·MPGeUS) 8.2 L/100 p·km (29 p·MPGeUS)
Buses (avg US)[17] 8.9 L/100 p·km (26 p·MPGeUS) sm=n 8.9 L/100 p·km (26 p·MPGeUS) 8.9 L/100 p·km (26 p·MPGeUS)
Hydrogen automobile[19] 9.4 L/100 p·km (25 p·MPGeUS) sm=n 9.4 L/100 p·km (25 p·MPGeUS) 9.4 L/100 p·km (25 p·MPGeUS)
Steamship (estimate) 19.6 L/100 p·km (12 p·MPGeUS) sm=n 19.6 L/100 p·km (12 p·MPGeUS) sm=n 19.6 L/100 p·km (12 p·MPGeUS) sm=n
Helicopter (estimate) 58.8 L/100 p·km (4 p·MPGeUS) sm=n 58.8 L/100 p·km (4 p·MPGeUS) 58.8 L/100 p·km (4 p·MPGeUS)
zzz (please ignore) 1000000 1000000 1000000

[edit] See also


[edit] Notes

[edit] References

  1. ^ Bioenergy Conversion Factors
  2. ^ 2005 - http://www.epa.gov/OMS/climate/420f05004.htm
  3. ^ 2005 - http://www.epa.gov/OMS/climate/420f05001.htm
  4. ^ 118,700 Btu/gal (net) - http://www.eia.doe.gov/emeu/rtecs/nhts_survey/2001/tablefiles/c0464(2005).pdf
  5. ^ 128,100 Btu/gal (net) - http://www.eia.doe.gov/emeu/rtecs/nhts_survey/2001/tablefiles/c0464(2005).pdf
  6. ^ Miastrada Motors - Analyses
  7. ^ EVWORLD FEATURE: Fuel Cell Efficiency: A Reality Check:FUEL | CELL | FUEL-CELL | HYDROGEN | DIESEL | HYBRID | REALITY | EFFICIENCY | H2 |
  8. ^ http://books.google.ca/books?id=fMZlnmS5YDMC&pg=PT589&lpg=PT589&dq=diesel+%22thermal+efficiency%22+locomotive&source=web&ots=nfEhSACtJk&sig=dyOtW8jpDJtZAjqSc_Dh983EIYg&hl=en#PPT589,M1
  9. ^ 33.4 kWh (gasoline BTU equivalent in kWh) × 33% thermal efficiency ~= 11 kWh
  10. ^ U.S. All Grades All Formulations Retail Gasoline Prices (Cents per Gallon)
  11. ^ Test: 250 W electric bicycle efficiency = 1512 MPG equivalent (5.41 miles) on 0.12 kWh
  12. ^ 64.80 MJ/km × 436 passengers
  13. ^ 169 Wh/mi × 1.3 passengers
  14. ^ Compare Old and New EPA MPG Estimates 46 × 1.3=60
  15. ^ Vehicle details for Prius 1.5 VVT-i Hybrid E-CVT. UK Vehicle Certification Agency. Retrieved on 2008-03-22.
  16. ^ Transport trends: current edition. UK Department for Transport (2008-01-08). Retrieved on 2008-03-23.
  17. ^ a b c d e f [http://cta.ornl.gov/data/tedb26/Edition26_Chapter02.pdf Transportation Energy Data Book, 2007]
  18. ^ US fleet mileage averages 23 mpg, occupancy avg is 1.57
  19. ^ 27 MPGe × 60% × 1.57 passengers