PURPOSE: To give air supply and flow to combustion flame by controlling periods of beginning and terminating the air supply or timing of the periods with a valve provided between a high pressure air chamber and an air injection nozzle to be controllably opened and closed.

CONSTITUTION: A solenoid valve 30 is released right before a piston 20 is lifted into the compression stroke and reaches the upper dead point, and high pressure air in a high pressure air chamber 26 is injected from an air injection nozzle 24 into a combustion chamber 22 to give air flow. Next, when fuel is injected from a fuel injection valve 23, fuel positively collides and is mixed with air by air flow and injection to provide a satisfactory combustion condition. Further, the supply of high pressure air may be carried out in the early period of fuel injection. The periods of beginning and terminating the supply or timing of supply periods can be freely selected by controlling the solenoid valve 30.