Quote:
Commonly BSFC is expressed in units of grams per kilowatt-hour (g/(kW·h)). The conversion factor is as follows:
BSFC [g/(kW·h)] = BSFC [g/J]×(3.6×106)
To calculate the actual efficiency of an engine requires the energy density of the fuel being used.
Different fuels have different energy densities defined by the fuels heating value. The lower heating value LHV is used for internal combustion engines efficiency calculations because the heat at temperatures below 150 °C (300 °F) cannot be put to use.
Some examples of lower heating values for vehicle fuels are:
Certification gasoline = 18640 BTU/lb = 0.01204 kW·h/g
Regular gasoline = 18917 BTU/lb = 0.0122225 kW·h/g
Diesel fuel = 18500 BTU/lb = 0.0119531 kW·h/g
Thus a diesel engine's efficiency = 1/(BSFC*0.0119531)
and a gasoline engine's efficiency = 1/(BSFC*0.0122225)
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Brake specific fuel consumption - Wikipedia, the free encyclopedia
Using 200 for diesel and 250 for a typical gasser, that gives a diesel efficiency of 42% and a gasser efficiency of 33% independent of the fuel energy density.
From the charts dcb linked, it looks like the hybrid engines are coming close to rivaling the TDI if operated in a specific manner. The Insight uses lean burn techniques, and the Prius uses a high static compression of 13.5:1 ratio to get the expansion volume coupled with a late intake closing to get a more manageable 9.5:1 dynamically.
The TDI has a 19:1 static compression ratio.