To reduce noise of a diesel engine by injecting fuel in air foggily and compressing it, or injecting fuel in compressed air, if necessary, agitating it so as to manufacture fine foggy or bubbly fuel, and injecting it from a fuel injector into the combustion chamber of a high temperature and high pressure.

Air is fed from an air sucking port A in an agitator H passing an air compressor B, and fuel is supplied from a fuel sucking port C into the agitator H passing a fuel pump D. An agitating chamber E, an agitating rod G, a rotating impeller F are arranged in the agitator H, air and fuel are mixed with each other so as to manufacture fog or bubbles of fuel. Fog or bubbles of fuel are supplied from the agitating chamber E into a fuel injector J passing a fuel feed pipe I, Fuel containing air is injected into a combustion chamber R on the compressing stroke of a piston P by the fuel injector J matching with a period of the top dead point of the combustion chamber R. Injecting fuel is ignited and exploded in air of the high temperature and high pressure.