surface of the head 24 connected to passageway 120 is shaped to form a tapered groove 121 the nozzle passageway 102 points toward the tapered groove 121 the fuel cell 50 is an auto ignition fuel cell i e a fuel cell which only has an auto ignition chamber 100 and excludes the use of a spark means i e spark plug or similar external ignition means in direct communication with the chamber 100 referring now to fig5 7 and 9 the cylinder head assembly 128 includes a cover 129 which when removed exposes the orientation of gas inlet or admission valves 26 and the exhaust valves 28 with the torch cell assembly 50 being disposed intermediate thereof hardened rings 130 and 132 are installed in the valve seats 26 and 28 respectively as best seen in fig8 the pistons 22 utilized with this invention preferably have a truncated spherical configuration in their upper end surface 23 the piston may be of the one piece cast variety or may be of the two piece configuration illustrated with a steel head 142 fastened to the piston trunk 140 suitable sealing rings 144 are provided as well as a bushing variety of bearing 144 for the piston pin not shown this truncated spherical.