Abstract: A high compression ratio internal combustion engine operable on a fuel capable of being pressurized and vaporized to pressures above atmospheric pressure and having dual fuel introduction means respectively communicating with dual fuel sources. The first fuel introduction means is a low pressure fuel supply means by which fuel is introduced into the engine at low pressure in a fuel/air ratio mixture lower than which supports self-ignition under the temperatures generated by the compression thereof within the combustion chamber of the engine. A secondary--or auxiliary--fuel supply is provided and is capable of introducing predetermined amounts of only fuel in an atomized state and at elevated pressures greater than the pressure developed on the compression stroke within the combustion chamber.