The Relationship Between BSFC Numbers and Efficiency
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 fuel's heating value. The lower heating value (LHV) is used for internal combustion engine 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 = 18,640 BTU/lb (0.01204 kW·h/g)
- Regular gasoline = 18,917 BTU/lb (0.0122225 kW·h/g)
- Diesel fuel = 18,500 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)
Read more about this topic: Brake Specific Fuel Consumption
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