Fuel Distribution and Combustion Characteristics in a Direct-Injection, Spark-Ignited (DISI) Engine Under Stratified Operation

The characteristics of the combustion process in direct-injected, spark-ignited (DISI), stratified-operation engines, are intimately related to the fuel distribution in the combustion chamber. Engine performance, and particularly emissions of hydrocarbons, nitric oxides and particulate matter are strongly dependent on the manner in which the fuel charge is distributed. The present paper investigates the fuel distribution and combustion characteristics of a side-injected DISI engine under stratified operation and late injection, using optical diagnostics without compromising on the use of a realistic bowl geometry. Laser-induced fluorescence, laser-induced elastic scatter and color and luminosity visualization are employed to identify the relationship between fuel distribution and combustion characteristics. The results show that the mixture is strongly stratified, with combustion starting primarily in the fuel-lean to stoichiometric region surrounding the spark, followed by propagation into fuel-rich zones. Intense soot luminosity and particulate matter is observed in the fuel rich regions close to the piston throughout the expansion stroke.