PURPOSE: To reduce the blow-bye loss of air-fuel mixture and to reduce consumption of lubricating oil, by supplying compressed air into a combustion chamber before the exhaust stroke of a cylinder is terminated by an air compressing means disposed on the outside of the cylinder.

CONSTITUTION: Air compressed by a compression pump 8 is once stored in a compression tank 9 and supplied under pressure into a combustion chamber 4 when an intake valve 5 is opened. On the other hand, fuel is injected into the combustion chamber 4 from a fuel injection nozzle 11. By employing such an arrangement, it is made unnecessary to compress air-fuel mixture in the combustion chamber 4, so that the compression stroke can be made unnecessary. By thus reducing the blow-bye loss of mixture, it is enabled to raise the suction volumetric efficiency of an engine. Further, since the crank chamber is not used for feeding intake air, it is enabled to prevent useless consumption of lubricating oil.