Abstract: An internal combustion engine having at least one cylinder within which is a reciprocable piston movable in a compression stroke followed by movement in a power stroke and wherein a combustible fuel mixture is injected into the combustion chamber, compressed, ignited, and burned to produce the power stroke of the piston. After the fuel has been ignited and during the compression of such mixture a quantity of water from a reservoir is injected into the combustion chamber and converted by the heat of combustion into superheated steam, thereby generating within the combustion chamber a force which assists in driving the piston through its power stroke. The products of combustion and steam are discharged from the cylinder following the power stroke and cooled in a heat exchanger in which the steam is condensed, following which the gases are exhausted and the condensate returned to the water reservoir.