Abstract: An internal combustion rotary engine is disclosed having leading and trailing spark plugs with their respective spark electrodes arranged in peripherally spaced ignition openings in the inner peripheral wall of the engine's rotor housing. The leading ignition opening is located in a zone where the leading apex seal of the passing chambers experiences a relatively low pressure differential which decreases in the direction of rotor rotation whereas the trailing ignition opening is located in a zone where the trailing apex seal of the passing chambers also experiences a relatively low pressure differential but which increases in the direction of rotor rotation.