Abstract: Internal combustion engines to increase the engine output without altering the cylinder capacity, and comprising liquid injection valves (26, 46) by which fixed quantities of prescribed liquids are injected into combustion chambers (14a, 14b), timed to the detonation process in the internal combustion engine, and heating means by which the liquids injected from the liquid injection valves (26, 46) are heated beforehand to a predetermined high temperature by utilizing the intense heat generating around and nearby said combustion chambers (14a, 14b), so that the device enables effective utilization of heat energy generating around and nearby cylinders as well as increasing the engine output by the sudden expansion of the liquid injected into the combustion chamber pressing the piston therein with a powerful downward stroke.