Parametric Investigation of Various Factors Affecting Engine Performance and Emissions in a Homogeneous Charge with Direct Injection Strategy at High Load: A CFD Approach 2022-01-1048

Over the years, much progress has been made in automotive vehicle technology to achieve high efficiency and clean combustion. Reactivity controlled compression ignition (RCCI) is one of the most widely studied high-efficiency, clean combustion strategies. However, complex dual-fuel injection systems and associated controls, high unburned hydrocarbon (UHC), and carbon monoxide (CO) emissions limit RCCI use in practical applications. Recently, single fuel RCCI strategies are gaining more attention as the above shortcomings are effectively addressed. Homogeneous charge with direct injection (HCDI) is a single fuel RCCI strategy that results in high thermal efficiency and lower UHC and CO emissions. In HCDI, the port-injected diesel fuel vapour and air are inducted during the intake stroke and ignited with direct-injected diesel fuel near the end of the compression stroke. However, high oxides of nitrogen (NO_x) make HCDI less viable for practical applications. Water vapour dilution proved an effective method to suppress NO_x emissions without reducing thermal efficiency in HCDI. However, thermal and dilution effects at higher loads resulted in a NO_x-soot trade-off and high soot emissions. A parametric study of different parameters and their combined impact on the performance and emissions of a light-duty diesel engine operated in HCDI mode is evaluated in the present study. A commercial CFD code, CONVERGE, validated with experimental data, is used for parametric investigations. Different parameters such as direct-injected fuel timing, fuel injection pressure, boost pressure and dilution are varied. The results show that increasing boost pressure improves air-fuel mixing and reduces soot formation among the investigated parameters. The combined effects of increased dilution, higher injection and boost pressure increased thermal efficiency by ~13%, with a penalty in NO_x and 37.8% soot reduction.