Patent ID: 7801668

Claim:
A method of controlling combustion in a gas engine connected to an electric generator to compose a power generator unit, the unit being installed near a coal mine site, the gas engine being of a pilot ignition type gas engine which can utilize recovered methane gas and ventilation air methane gas taken out from the coal mine as its fuel by adjusting methane concentration to produce lean air-methane gas mixture, wherein output torque of the gas engine is controlled so that a relation |ΔTd|−|ΔTs|>0 is maintained between |ΔTd| which is absolute value of change rate of load torque Td required to drive the generator in relation to engine rotation speed n and |ΔTs| which is absolute value of change rate of output torque Ts in relation to engine rotation speed n at an intersection point of a Ts-n curve and a Td-n curve, and excess air ratio is controlled to be 2 or larger so that lean mixture burning is performed while avoiding misfiring and knocking by controlling mixing ratio of recovered methane gas with ventilation air methane.