the glow area 44 has a short axial distance from the front side 42 of the combustion chamber wall lining part 36 and a short distance from a bulge 46 of the combustion chamber bottom 22 the glow plug 4 is screwed into the socket 24 the glow plug 4 is connected via two current conductors not shown to a control device not shown from which the glow plug 4 is supplied with electricity when ignition in the heater is necessary the aforementioned bulge 46 of the combustion chamber bottom 22 is designed such that the glow plug 4 can be accommodated in its intended positioning concerning right and left in fig2 and concerning the axial direction of the combustion chamber 2 the combustion chamber bottom lining part 38 differs from the complete disk shape in that the material is omitted to the left of and above the limiting line 48 shown in fig2 which extends like a leg of a right angle a recessed space 50 is thus formed which is approximately cylindrical with a vertical axis and has a sufficient size for accommodating the glow area 44 of the glow plug 4 the recessed space 50 is limited axially in the rear left hand part in fig1 and on.