Experimental study of independent two-stage in-cylinder heat release using jet controlled compression ignition

Abstract

To extend the load range of premixed combustion, the jet controlled compression ignition (JCCI) mode with dual-direct injectors was adopted in a high-speed light-duty diesel engine. The pre-mixture was flexibly prepared by the direct pre-injection of blended fuels, and the ignition timing could be controlled robustly by the diesel jet-injection. Engine experiments were conducted at 75% engine load with an engine speed of 3000 rpm. The results indicate that an obvious two-stage high-temperature heat release process is achieved by modulating the injection parameters of dual-direct injectors independently. The late combustion phasing resulted from the retarded diesel jet-injection effectively depress the reaction rate. When the pre-injection is delayed within the sensitivity interval, the local richer premixed charge accelerates the pre-mixture combustion stage. The indicated thermal efficiency is increased by 7.4%, and nitrogen oxide emission is reduced by 16.9% compared to the conventional diesel combustion mode. The increased pre-injection pressure can suppress the reaction rate but causes wall-wetting issues. The stratification of the equivalence ratio prepared by the double direct pre-injection strategy diminishes the maximum pressure rise rate by over 64% compared to that with single direct pre-injection. It is also revealed that the start of the second pre-injection plays a dominant role in modulating the combustion process, which illustrates the potential to extend the engine load of premixed combustion mode.