PURPOSE: To increase power generating volume and improve thermal efficiency by means of providing an evaporating chamber in which mixed air with steam is produced in such a way that combustion gas to be flowed from a combustion chamber is bumped against supplied water and mixed together in a mixed air generator.

CONSTITUTION: In a stationary combustion engine, after air is sucked and compressed in a cylinder 2, the compressed air is fed through the cylinder 2 into a combustion chamber 70 which is formed in a mixed air generator 7, and mixed with fuel from a fuel injection nozzle 703, which are ignited and burned by means of an ignition plug 705. At the same time as the combustion gas preheats supplied water in a water supply pipe 710, it is fed into an evaporating chamber 71, bumped and mixed with the supplied water 711 resulting in producing mixed air composed of steam and combustion gas. The mixed air is sucked in the cylinder 2 and expanded therein, so that power can be effectively generated. Thus generating volume of power can be increased, and combustion heat can be prevented from being radiated to the outside.