PURPOSE: To eliminate knocking without impairing the suction efficiency by boring a suction port in a cylinder surface, and furnishing an exhaust port in the upper part of cylinder, wherein the exhaust port is opened and closed by an exhaust valve under appropriate control.

CONSTITUTION: A suction port 13 is bored in that surface of cylinder 1 which mates with the oversurface position of a piston near its lower dead point. A turbo-charger 4 presses forward the suction gas from this suction port 13 into the cylinder 1. An exhaust port opened and closed by an exhaust valve 24 under appropriate control is provided in the upper part of this cylinder 1. The suction port 13 is insulated from the exhaust port in thermal terms to shut off heat conduction from the exhaust port. This accomplishes stable operation, which is free from generation of knockings as well as drop of the suction effi ciency.