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

Abstract

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 ϕ-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° to –40° 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° after top dead center by adjusting the exhaust gas recirculation rate.