A series of
combustion forms including initial low-temperature
combustion, premixed
combustion, and diffusive combustion are performed when an engine operates under a
low load and a medium load. The initial low-temperature combustion is carried out by performing a small-amount injection while performing an operation for lowering the encounter rate between
oxygen and a
fuel spray in a cylinder, and thereby the
heat generation rate is kept low and the amount of
NOx generated is suppressed. The premixed combustion is carried out as fuel receives heat in the initial low-temperature combustion, and the amount of
smoke generated is suppressed. The diffusive combustion is accomplished as fuel travels through the combustion field of the premixed combustion, and by controlling the
fuel injection timing thereof, it is possible to suitably control the timing at which the
heat generation rate reaches its maximum in the aforementioned series of combustion. Thereby, it is possible to concurrently suppress the amount of
NOx generated, suppress the amount of
smoke generated, and secure the required torque.