Keys to Understanding Spray-guided Combustion of a Narrow-spacing Gasoline Direct Injection SI Engine with a Centrally Mounted Multi-hole Injector

Spray-guided gasoline direct injection SI engines attract as one of new generation lean-burn engines to promise CO2 reduction. These typically adopt “narrow-spacing” concept in which an injector is centrally mounted close to a spark plug. Therefore, geometric targets of the fuel spray and a position of the spark plug have to be exactly limited to maintain a proper mixture in the spark gap. In addition, the stable combustion window is narrow because the spark ignition is limited in a short time during and immediately after the injection. These spatial and temporal restrictions involve some intractable problems concerning the combustion robustness due to the complicate phenomena around the spark plug. The local mixture preparation near the spark plug significantly depends on the spray-induced charge motion. The intense flow induced by the motion blows out and stretches the spark, thereby affecting the spark discharge performance. Moreover, the fuel interaction with the spark plug affects not only the spark discharge performance but also the mixture preparation. These phenomena significantly make impacts on the combustion and cause misfires in the worst case because there is a possibility of changing the stable combustion window. This paper describes a study of the spray-guided combustion using a narrow-spacing gasoline direct injection SI engine with a multi-hole injector. A goal of this study is to understand the factors affecting the local mixture preparation at the spark gap and the spark discharge performance. Additionally, the effects of the phenomena on the combustion robustness were investigated.