EFFECT OF SPARK-IGNITION ON COMBUSTION PERIODS DURING SPARK-ASSISTED COMPRESSION IGNITION

Previous works employed pressure-based heat release analysis, spark-discharge current/voltage measurements, and cycle-resolved combustion imaging to identify four periods of stratified-charge spark-assisted compression ignition: spark discharge, early kernel growth (EKG), flame propagation, and compression ignition. While it was found that variability in the EKG, and not the spark discharge, influenced combustion phasing, the influence of the spark discharge on the EKG could not be assessed because the imaging system was incapable of recording both the spark discharge and the flame development from the same cycle. This limitation has been overcome here by recording images of both the spark discharge and combustion chemiluminescence during each engine cycle. Additionally, the spark discharge plasmas were recorded from two nearly-orthogonal views to assure that out-of-plane excursions were measured; such are not available from a single view. The results in this study demonstrate that the spark discharge event was not deterministic of the EKG. Circumstantial evidence is given to suggest that the fuel/air distribution and velocity at the spark plug dominate the EKG period variability, though this could not be confirmed definitively.