Abstract: A four or two cycle internal combustion engine is provided with a device for introducing evaporable liquid into a cylinder of the engine in a manner such that the evaporable liquid is contacted by the gases being compressed during compression phase, is separated, segregated or concealed during most of the combustion phase, and exposed and contacted by the combusting fuel gases primarily after most of the combustion of the fuel gases has occurred for absorbing some of the heat of combustion in the liquid and vaporizing the liquid. The invention is useful both for construction of new Otto or Diesel cycle internal combustion engines, and modification of existing engines.