An internal combustion engine in which each cylinder or combustion volume includes a separate ignition chamber which communicates with the main combustion chamber through a relatively narrow channel or channels. The combustible mixture is delivered to the separate chamber exclusively through these channels by the compressive action of the piston and is ignited there by a suitable electrical spark, for example. There is no additional admission of fuel or fuel mixture to the separate ignition chamber. The channel or channels terminate in the ignition chamber in such a manner, for example, tangentially, that one or more vortices are generated in the chamber prior to ignition. The channels are so oriented that the emerging igniter flames are directed to potential hot cells in the main combustion chamber where auto-ignition could occur.