Abstract: This invention relates to a pre-ignition, combustion system of the type used in combination with an internal combustion engine whereby a vaporized fuel charge is created due to the exposure of heat to saturated fuel vapor. The fuel vapor is further heated to a point of near combustion immediately prior to introduction into the intake manifold of an I. C. engine. A thermerator element is provided which defines a heating chamber in which fuel is vaporized due to direct exposure with the exhaust gases of the internal combustion engine through appropriate directing of the introduced fuel or fuel vapor in direct heat transfer relation to the exhaust gases passing through at least a portion of the heating chamber defined in the thermerator. The fuel source including a substantially conventional fuel tank has air supply means leading thereto so as to supply positive air pressure serving to aid fuel passing from the fuel tank into the thermerator through a first fuel supply conduit.