PURPOSE: To rotate an engine smoothly and extract, as a form of force, a pact of heat generated by combustion, which has been dumped, utilizing volume expansion by vaporization of water by extracting output efficiently during complete combustion and performing compression stroke in parallel with the stroke of explosion and expansion.

CONSTITUTION: A set of two cylinders share one crankshaft. Also a cylinder 1 functions only to suck and compress air, and a cylinder 2 functions only to explode and expand mixture and exhaust burned gas. The relation between the strokes of these cylinders is set so that the piston of the cylinder 1 compresses air when the cylinder 2 is in the stroke of explosion and expansion. In such a stroke separation engine, a device to inject spray water is installed on the cylinder 2.