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 ?
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.