Analysis in cyclic combustion Variation in a Lean Operating S.I. Engine

The causes of the cyclic combustion variation in a lean operating SI engine have been identified using multivariate analysis on the pressure-time data. Principal component analysis on the combustion characteristics obtained from the pressure-time data was conducted in order to select an index of an optimal released heat pattern for analyzing the causes of the cyclic combustion variation. Using this index and the released heat quantity, the IMEP variation was subjected to multiple regression analysis to identify the causes of the cyclic combustion variation.

Optimizing the fuel injection timing and swirl ratio made it possible to enrich the mixture near the spark plug. With the lean limit thus extended, a SI engine was operated in a lean range, and the resultant pressure-time data were analyzed. It was found that the main cause of the IMEP variation in the lean operating SI engine was the released heat quantity variation. In a relatively stable mixture range, the released heat quantity variation occured due to the combustion rate variation in the terminal stage of combustion, while around the lean limit, it occured due to the combustion rate variation in the early stage.