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The cycle-to-cycle and cylinder-to-cylinder variations that occur in a spark ignited engine create the opportunity for monitoring combustion in real time to provide useful benefits for engine control. Reduction of variation and operation of the engine at closer-to-optimum conditions is possible if real time feedback of the combustion process is available. An in-cylinder pressure sensor with pressure-based control algorithms is one method of monitoring the combustion process. However, such a solution presents new challenges of an additional cylinder penetration location, sensor packaging and added cost. A substitute for the in-cylinder pressure sensor is a device which measures the flame conductivity, commonly known as an ionization current sensor. It can be integrated with the spark plug in the case of SI engines, or with the glow plug in the case of compression ignition engines.