To provide a lean combustion control method for an internal combustion engine which can detect misfire with satisfactory responsiveness, eliminate misfire while enabling lean combustion, purify exhaust gas and improve fuel consumption performance even with variation of engine characteristics.
A gas engine (internal combustion engine) 1 has at least an engine speed sensor (engine rotational speed sensing means) 9 and a fuel control valve 23. In a lean combustion control method of the engine through throttling the fuel control valve 23 with a specified load and specified speed, a decreasing rate of the engine per every specified time or an absolute decreasing rate of the engine speed in the specified time is calculated. In the case that the calculated value is a specfied value or more, misfire is determined. An opening of the fuel control valve 23 is shifted to a rich side for misfire prevention controlling up to the opening of determining the misfire or immediately before misfire determination. It is thus possible to determine misfire through the decreasing rate of the engine speed per specified time or an absolute decreasing rate of the engine speed in the specified time.
OBA TATSUJI
KISHIDA HAJIME
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