Brake-specific fuel consumption

It is typically used for comparing the efficiency of internal combustion engines with a shaft output.

For example, the cycle average value of BSFC for a gasoline engine is 322 g/(kW⋅h), translating to an efficiency of 25% (1/(322 × 0.0122225) = 0.2540).

Actual efficiency can be lower or higher than the engine’s average due to varying operating conditions.

An iso-BSFC map (fuel island plot) of a diesel engine is shown.

Engines of different classes like diesels and gasoline engines will have very different BSFC numbers, ranging from less than 200 g/(kW⋅h) (diesel at low speed and high torque) to more than 1,000 g/(kW⋅h) (turboprop at low power level).

The following table takes values as an example for the specific fuel consumption of several types of engines.