An ignition system for rotary piston engines includes a glow plug in addition to the normal leading spark plug and trailing spark plug. The glow plug is mounted in the housing of the engine on the leading side with respect to the trochoidal minor axis in the direction of the rotor rotation and performs continuous ignition of the mixture during low speed and load operation of the engine. Thus, during the low speed and load operation the glow plug performs ignition in place of the leading spark plug whereas during other engine operating conditions the leading spark plug and the trailing spark plug perform the ignition of the mixture.