Each cylinder of an internal combustion engine is provided with a main combustion chamber and an auxiliary combustion chamber connected by a torch nozzle. A rich mixture is heated before entering into the auxiliary chamber where it is ignited by a spark plug to project a flame through the torch nozzle to ignite a lean mixture in the main combustion chamber. The heating of the rich intake mixture may be accomplished by utilizing heat from the engine exhaust system, and a liner pipe insulated from the water cooled cylinder head carries the rich mixture to the auxiliary chamber to minimize condensation of fuel.