For many years ion feedback has been utilized on spark ignited gasoline engines running at stoichiometric air-fuel ratios.1,2,3,4 When used in conjunction with proper ion signal detecting circuitry, the spark plug serves as an effective combustion ion sensor and can detect certain characteristics about combustion. Ion sensing has also been employed on stoichiometric natural gas engines with very positive results. However, attempts to extract useful ion signals from high BMEP lean-burn gas engines have previously proven to be unsuccessful. Recently developments in signal recognition, along with correlations between combustion chamber and spark plug design have made ion sensing for lean-burn gas engines a realistic diagnostic technique. Algorithms have been demonstrated for misfire, knock and combustion quality. Test results show that ion sensing can produce combustion monitoring for lean-burn gas engines that previously required cylinder pressure transducers. With proper integration into the ignition controller and engine management system, the ion feedback signal can allow gas engines to operate at the limit of misfire and knock. This allows minimizing of NOx emissions and fuel consumption.

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