An internal combustion engine having a combustion chamber incorporates a fuel conditioner and injector employs a vessel having a wall exposed within the combustion chamber to be heated by combusting fuel. The vessel encompasses an expansion chamber and has at least one open fuel injection passage through the wall into combustion chamber. An inlet conduit receives liquid fuel at a predetermined pressure from a fuel delivery system. A nozzle interconnects the inlet conduit and the expansion chamber. A pin operably seals the nozzle for timed injection of liquid fuel into the expansion chamber. An operator actuates the pin from a closed position sealing the nozzle to an open position placing the fuel injection volume in fluid communication with the expansion chamber. Liquid fuel injected into the expansion chamber at a predetermined time is simultaneously adiabatically heated, and pressurized to a state above a critical point using heat in the vessel wall and self-injects through the at least one open fuel injection passage into the combustion chamber of the engine.