A method of compressing a medium in the combustion chamber of a combustion engine, by which method a liquid, in the state of a spray, is introduced into the compression chamber during a compression stroke, the liquid is pressurized and heated before it is introduced into the compression chamber to such a degree that at least a part of the droplets of the spray explode spontaneously upon entrance in the compression chamber, the liquid being pressurized to such an extent that, at the moment of introduction, it has a steam pressure that is above the pressure that, at the moment of introduction, exists in the compression chamber, and the liquid being heated to such an extent that, at the moment of introduction, it has a temperature that ex­ceeds the boiling point of the liquid for the temperature and the pres­sure that, at the moment of introduction, exists in the compression chamber, and the heat being water. The liquid is heated to such an extent that, at the moment of introduction, it has a temperature that is below the temperature of the medium at the moment of introduc­tion of the liquid.