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# Fuel consumption / efficiency for gas engine

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## Fuel consumption / efficiency for gas engine

(OP)
What is electric efficiency and thermal efficiency for a gas engine ? If power output is given , how to calculate the fuel consumption ? Which efficiency will come in the calculation, electric or thermal ?

### RE: Fuel consumption / efficiency for gas engine

Would you accept Brake Specific Fuel Consumption in place of Thermal Efficiency?

For non diesel, non direct injection gas(oline) engines it is HIGHLY load and rpm dependent.

I'm guessing yours will likely look something like this -
http://www.pattakon.com/tempman/Saturn_BSFC.gif

The best/lowest BSFC is around .4 lbs/HP hr or .25g/kW hr but that is generally not attainable at max output.

### RE: Fuel consumption / efficiency for gas engine

What do you mean by a "gas engine"?

If you know what the brake power of an IC engine is, and what the fuel mass flow rate is at that operating point, you can calculate BTE or BSFC from the fuel's LHV. What is of concern is the engine's efficiency at converting chemical energy of the fuel to mechanical work. This can be expressed in whatever terms you like, including grams/kW-hr or lbs/hp-hr.

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