Improving the controllability of partial fuel stratification at low boost levels by applying a double late injection strategy

摘要

This experimental study has two objectives. The first objective is to investigate the combustion performance of partial fuel stratification on a high compression ratio, light-duty diesel engine at a practical boost level of 1.6 bar. The second objective is to study the effects of a double late injection strategy on the phi-stratification gradient and combustion performance of partial fuel stratification, and verify the improvement in controllability with insufficient gasoline phi-sensitivity (i.e. gasoline does not exhibit strong phi-sensitivity at lower pressure conditions). The total targeted fuel flow rate was 16 mg/cycle throughout all of the experiments. Consequently, the global charge-mass equivalence ratio was fixed at 0.35. In order to investigate the combustion performance, start of injection timing sweeps were performed from -140 degrees to -40 degrees after top dead center, with the split fraction (i.e. the premixed fuel portion) varying from 70% to 90%. The combustion phasing was fixed at 8.6 degrees after top dead center by adjusting the exhaust gas recirculation rate.