In-cylinder mixture distribution research of stratified lean-burn strategy and stratified stoichiometric strategy in a GDI engine using laser-induced fluorescence

Planar laser-induced fluorescence(PLIF)was applied to investigate in-cylinder mixture distribution of stratified lean-burn strategy and stratified stoichiometric strategy for their importance in gasoline direct injection (GDI) combustion characteristics. Based on the image results, equivalent ratio of fuel to air near the spark plug under different strategies, cycle-to-cycle variation and the method for evaluating the distribution were discussed. Appropriate second injection timing led to rich area suitable for ignition near the spark plug under lean-burn strategy with an average equivalent ratio of fuel to air of 0.4. Most strategies under stoichiometric condition can achieve suitable equivalent ratio of fuel to air near the spark plug but the richest area varied in position. The results of 3 stoichiometric strategies with the second injection at 100° CA BTDC showed that the best stratified stoichiometric mixture appeared when the fuel amount proportion of the twice injctions was 6:1. The analysis of cycle-to-cycle variation in consecutive 20 cycles showed that for most strategies the variation was within ±15% in the richest area and that for some strategies had a variation of less than ±10%.