IC Engine Retard Ignition Timing Limit Detection and Control using In-Cylinder Ionization Signal

Internal combustion engines are designed to maximize power subject to meeting exhaust emission requirements and minimizing fuel consumption. However, the usable range of ignition timing is often limited by knock in the advance direction and by combustion instability (partial burn and misfire) in the retard direction. This paper details a retard limit management system utilizing ionization signals in order to maintain the desired combustion quality and prevent the occurrence of misfire without using fixed limits. In-cylinder ionization signals are processed to derive a metric for combustion quality and closeness of combustion to partial burn/misfire limit, which is used to provide a limiting value for the baseline ignition timing in the retard direction. For normal operations, this assures that the combustion variability is kept within an acceptable range. During start-up operations, the retard limit management can be used as a rapid catalyst light-off strategy by maximally delaying the combustion as long as misfire and partial-burn are avoided. This improved start-up strategy reduces cold-start HC emissions by reducing the time required to increase the catalysts temperature to its light-off level. The closed loop nature of the system provides maximum usage of the possible ignition timing range in the retard direction at any given operating condition.