To provide a combustion control device for an internal combustion engine for attaining control of fuel-injection timing in response to a cetane number of a fuel in use without additionally providing an expensive sensor, etc.
Intake air flow Q-air is obtained (S310), and fuel injection quantity Q-main is obtained from an engine speed Ne and a load L (S320). A real air-fuel ratio AF-real is obtained on the basis of signals of an air-fuel ratio sensor of an exhaust system (S330). In prescribed operating conditions, a real fuel-supply weight G-main is obtained by dividing the intake-air flow Q-air by the real air-fuel ratio AF-real. A true specific gravity G-fuel is obtained by dividing the real fuel-supply weight G-main by a main fuel-injection quantity Q-main (S350). A standard specific gravity G-std at 20°C is obtained by correcting the obtained true specific gravity G-fuel in reference to fuel temperature TF (S360). The higher the fuel gravity is, the further the fuel-injection timing is corrected to the advance side. When the specific gravity is high, the cetane number is low, but combustion degradation resulting from the cetane-number decrease can be compensated by advancing the injection timing.
Hiromichi Kobayashi
Tomioka Kiyoshi
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