Fuel Distribution Effects on the Combustion of a Direct-injection Stratified-Charge Engine 950460
Simultaneous fuel distribution images (by shadowgraph and laser-induced fluorescence) and cylinder pressure measurements are reported for a combusting stratified-charge engine with a square cup in the head at 800 RPM and light load for two spark locations with and without swirl. Air-assisted direct-injection occurred from 130°-150° after bottom dead center (ABDC) and ignition was at 148° ABDC. The engine is ported and injection and combustion take place every 6th cycle. The complicated interaction of the squish, fuel/air jet, square cup, spark plug geometry and weak tumble gives rise to a weak crossflow toward the intake side of the engine with no swirl, but toward the exhaust side in the presence of strong swirl, skewing the spray slightly to that side. Ignitability was good, and the combustion repeatable for a spark location on the side that the spray was skewed toward, but misfires were present for a spark location on the side away from which the spray is skewed when an occasionally stronger crossflow excessively leans the mixture at the spark plug. Occasional spray angle broadening was observed in the no-swirl condition, but not in the swirl condition. A high degree of spray broadening resulted in misfires or retarded cycles, but a lesser degree of spray broadening was found to correlate strongly with fast burning cycles as measured by the crankangle location of the peak pressure. The presence of swirl suppressed the broadening of the spray angle and resulted in more repeatable combustion. The cycles with the highest mean effective pressures at each of the configurations did not indicate a unique fuel distribution for optimum performance at this condition. The direct correlation of the shadowgraph and fluorescence images and the pressure measurements has been useful for identifying and understanding the correlation between fuel distribution and atypical combustion events.