The invention relates to a cylinder piston unit, especially for steam engines with expansion by heat influx, which is constructed as follows: a piston guided in the cylinder element has a displacer, a heating device is mounted on the cylinder element for the stroke area of a non-compacting displacer, the working medium is supplied in a vapour or liquid state in the area of the upper dead point, the expanded working medium is discharged at least in the area of the lower dead point. A pore burner is assigned to the cylinder piston unit in an advantageous mamler. To this end, the invention provides for the heat transfer sections (B, C) of a pore burner (50) which surrounds the cylinder head (43) along part of its height to be arranged at the level of the warm section (41) of the cylinder in the stroke area of the displacer (3) and at the level of the cylinder head (43).