Intake air strategy for low HC and CO emissions in dual-fuel (CNG-diesel) premixed charge compression ignition engine

Single fueled advanced combustion technologies, such as homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI), and low temperature diesel combustion (LTC), could make it possible to escape nitrogen oxides (NOx) and particulate matter (PM) generation. However, single fueled advanced combustion technologies have several challenges to overcome in order to be commercialized, such as combustion phase control, low combustion stability, narrow operating ranges, high level of maximum pressure rise rate (MPRR), and high amounts of unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. Dual-fuel premixed charge compression ignition (DF-PCCI) combustion concepts have suggested many solutions to overcome the drawbacks of single-fueled advanced combustion technologies, such as combustion phase control, combustion stability, and limited operating range. However, high amounts of unburned HC and CO emissions are still regarded as the main hurdles of DF-PCCI combustion. In this study, the effects of global equivalence ratio (ϕglobal) and initial charge temperature, which were controlled by means of intake throttling, charge heating, and exhaust gas recirculation (EGR) strategies, were investigated to overcome the bulk quenching phenomenon under low load conditions of DF-PCCI operation in a heavy-duty (HD) single cylinder engine. The optimized intake charge strategy which used the throttle and hot-EGR, showed the possibility of simultaneous HC and CO reduction, combustion efficiency (ηc) improvement, and combustion stability enhancement while satisfying NOx and PM emissions under EU-VI regulations. The results suggest that controlling the charge air quantity and charge temperature is an effective way to mitigate the bulk quenching phenomenon under low load conditions on DF-PCCI.