PURPOSE: To raise the mechanical efficiency of an engine, by turning an impeller by taking out energy produced by explosion in a cylinder to the outside of the cylinder, and transmitting the driving force to a crank shaft.

CONSTITUTION: Gas drawn into a suction cylinder 1 is supplied under compression into a combustion chamber 10 in a combustion cylinder 3 when a piston valve 4 is opened, and the gas is ignited and exploded in the combustion chamber 10 by means of an ignition plug 9. When a piston 5 is moved downward and an exhaust port 11 is opened, high-pressure gas is blown onto an impeller 6 for turning the same. Rotation of the impeller 6 is transmitted to a crank shaft 7 via gears and used again for moving the piston 5.