Impact of Delayed Spark Restrike on the Dynamics of Cyclic Variability in Dilute SI Combustion 2016-01-0691
Spark-ignition (SI) engines can derive substantial efficiency gains from operation at high dilution levels, but sufficiently high-dilution operation increases the occurrence of misfires and partial burns, which induce higher levels of cyclic-variability in engine operation. This variability has been shown to have both stochastic and deterministic components, with residual fraction impacts on charge composition being the major source of the deterministic component through its non-linear effect on ignition and flame propagation characteristics. This deterministic coupling between cycles offers potential for next-cycle control approaches to allow operation near the edge of stability. This paper aims to understand the effect of spark strategies, specifically the use of a second spark (restrike) after the main spark, on the deterministic coupling between engine cycles by operating at high dilution levels using both excess air (i.e. lean combustion) and EGR. Addition of a restrike spark was found to be effective in improving combustion quality, but sufficiently late restrikes were shown to lead to a de-coupling between engine cycles and destruction of the deterministic features that could be used for active control.