Abstract: An engine comprising one pair of scavenge ports alternately covered and uncovered by a piston, a richer air-fuel mixture and a leaner air-fuel mixture being separately fed into the cylinder from the scavenge ports, the richer air-fuel mixture flowing into the cylinder towards the inner wall thereof, located opposite the exhaust port, and the leaner air-fuel mixture flowing into the cylinder so that it overlays the richer air-fuel mixture.

Abstract: A 2-stroke engine having a combustion chamber and a scavenge port which is open to the combustion chamber. When the engine is operating under a light load in which a large amount of unburned components, incompletely burned components and oxygen remains in the combustion chamber, fresh air is fed into the combustion chamber from the scavenge port at a low speed so that the fresh air does not disturb the residual gas in the combustion chamber. As a result of this, oxidation of the unburned components and the incompletely burned components continues without interruption during the expansion stroke and the compression stroke and causes self-ignition of the residual gas at the end of the compression stroke. The self-ignited residual gas causes ignition of the fuel injected into the combustion chamber from a fuel injector.