PURPOSE: In a diesel engine whose portion facing a combustion chamber is made of a ceramic to insulate the heat of the combustion chamber, to enhance the output power of the engine per unit fuel quantity and improve the fresh air intake efficiency of the engine, by injecting an appropriate quantity of water into the combustion chamber at appropriate time to produce high-pressure steam.

CONSTITUTION: In a heat-insulated ceramic engine 100, fresh air sucked into a combustion chamber 140 is compressd in a heat-insulated state. Immediately before a piston 130 reaches the top dead center, fuel is atomized into the combustion chamber 140 through a fuel injection valve 113 so that the fuel is spontaneously ignited. The piston 130 is pushed down by high-pressure combustion gas to take out motive power. High-pressure water is injected into the combustion chamber 140 through a water injection valve 114 in a crankshaft angle position past the maximum combustion pressure at the expansion stroke after warm-up, so that the water is instantaneously evaporated into high-pressure steam by the high-temperature combustion gas, thus increasing the mean effective pressure on the piston 130.