An internal combustion engine 10 comprising an engine management unit 11, a combustion chamber 12 having an inlet port 16 and an outlet port 17, a valve train mechanism 19, to permit introduction of air to the inlet port 16 of the combustion chamber 12 and release exhaust gases from the outlet port 17 of the combustion chamber, and an external exhaust gas recirculating (EGR) system 23. Whereby exhaust gases from the outlet port 17 may be passed to the inlet port 16, wherein the engine management unit 11 is operable to control the valve train mechanism 23 to retain and/or rebreath exhaust gases within the combustion chamber 12 (internal exhaust gas recirculation), to cause the engine to operate in a controlled auto ignition combustion mode. Said system controls the external recycling system to supply exhaust gases to the inlet port 16 in the controlled auto ignition combustion mode. Sensors may be provided to detect one or more engine parameters (air mass flow, exhaust composition 34, crank shaft position 35, cam shaft position, exhaust gas temperature 33, intake pressure 31, and intake temperature). The quantity of exhaust gasses re-breathed and/or recirculated may be based on one of these parameters. Further control may be provided by controlling the fuel supply and the throttle 15. The engine may also comprise a spark plug 26 to facilitate a mode of spark ignition combustion.
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