Abstract: An internal combustion engine in which each cylinder is connected to sources both of air and of fuel held as a gas under pressure and in which the compression stroke, during which a full charge of air is drawn and compressed, is substantially completed before the fuel charge is then admitted and the mixture ignited to start the subsequent power stroke. The fuel may be admitted through a unit doubling as admission valve and igniter, and conventional diesel or gasoline-fuelled engines may be converted by designing that unit to fit into the conventional injector or spark plug holes. The compressed gaseous fuel may be methane, or other natural gas. The invention includes both stationary and mobile engines, especially automobile engines, and methods of operating them.