Abstract: When an engine operates in a low and medium load area and in a low and medium speed area, the combustion mode is established to a compression ignition combustion and when the engine operates in other load and speed areas, the combustion mode is established to a spark ignition combustion. Further, when the compression ignition combustion is performed, the mixture is stratified in the combustion chamber and an ultra lean combustion is realized. As a result, both NOx reduction in an ultra lean condition and HC/CO reduction in an oxidation atmosphere can be obtained. On the other hand, when the spark ignition combustion is performed, a normal feedback control of air-fuel ratio activates a three-way catalyst to reduce HC, CO and NOx simultaneously.

Abstract: When an engine operates in a low and medium load area and in a low and medium speed area, the combustion mode is established to a compression ignition combustion and when the engine operates in other load and speed areas, the combustion mode is established to a spark ignition combustion. Further, when the compression ignition combustion is performed, the mixture is stratified in the combustion chamber and an ultra lean combustion is realized. As a result, both NOx reduction in an ultra lean condition and HC/CO reduction in an oxidation atmosphere can be obtained. On the other hand, when the spark ignition combustion is performed, a normal feedback control of air-fuel ratio activates a three-way catalyst to reduce HC, CO and NOx simultaneously.

Abstract: In a self-igniting possible range, both intake and exhaust valves are placed in a closure condition for a period from the end of an exhaust stroke and the beginning of an intake stroke for establishing a negative overlap period in which a residual gas is pressurized to increase its temperature, thus raising the air fuel mixture temperature in a combustion chamber up to a self-igniting possible temperature. In addition, when a crank angle reaches a predetermined crank angle in the first half of an intake stroke, a fuel is injected from an in-cylinder injector into the combustion chamber. This fuel injected becomes a premixed air fuel because of being evaporated by the gas temperature in the combustion chamber, and on shifting to a compression stroke afterwards, the temperature in the combustion chamber reaches the self-igniting possible temperature.

Abstract: In a self-igniting possible range, both intake and exhaust valves are placed in a closure condition for a period from the end of an exhaust stroke and the beginning of an intake stroke for establishing a negative overlap period in which a residual gas is pressurized to increase its temperature, thus raising the air fuel mixture temperature in a combustion chamber up to a self-igniting possible temperature. In addition, when a crank angle reaches a predetermined crank angle in the first half of an intake stroke, a fuel is injected from an in-cylinder injector into the combustion chamber. This fuel injected becomes a premixed air fuel because of being evaporated by the gas temperature in the combustion chamber, and on shifting to a compression stroke afterwards, the temperature in the combustion chamber reaches the self-igniting possible temperature.