METHOD FOR OPERATING GASOLINE ENGINE

PROBLEM TO BE SOLVED: To solve a problem that heavy knocking occurs since self ignition easily occurs if spark ignition is executed under a state that temperature in a cylinder is high due to internal EGR when ignition is changed over from pre-mixed compression ignition to spark ignition in a gasoline engine executing pre-mixed compression ignition. SOLUTION: In the gasoline engine executing pre-mixed compression ignition with forming a negative overlap period during which both of an exhaust valve and an intake valve are closed in a neighborhood of exhaust top dead center, and executing spark ignition with forming the negative overlap period shorter than at most that in a case of pre-mixed compression ignition, the negative overlap period is shortened when the engine shifts from a zone of operation by pre-mixed compression ignition to a zone of operation by spark ignition, fuel is injected in such a manner that completion timing of injection period is at start timing of expansion stroke or later while the negative overlap period is shortened, and the fuel is ignited after completion of injection. COPYRIGHT: (C)2009,JPO&INPIT