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In the Premixed-Charge Compression Ignition (PCCI) combustion mode, fuel is injected fairly early before top-dead-center (TDC) of compression compared to the conventional near-TDC injection combustion mode. Early fuel injection into a low temperature in-cylinder environment results in long ignition delay and high peak heat release rate. Since the onset of ignition occurs after the end of injection, importance of spray and bowl induced flow field and mixing is not so obvious. In the present work, computational analysis is used to investigate the effects of spray-bowl interactions on PCCI combustion and emissions at a light-load (4Bar BMEP) operation of a medium-duty, direct injection diesel engine. Multidimensional CFD code KIVA-3V coupled with detailed chemical kinetics is used to perform combustion simulations.

The combustion and emissions of a diesel/natural gas dual-fuel engine are studied. Available engine experimental data demonstrates that the dual-fuel configuration provides a potential alternative to diesel engine operation for reducing emissions. The experiments are compared to multi-dimensional model results. The computer code used is based on the KIVA-3V code and consists of updated sub-models to simulate more accurately the fuel spray atomization, auto-ignition, combustion and emissions processes. The model results show that dual-fuel engine combustion and emissions are well predicted by the present multi-dimensional model. Significant reduction in NOx emissions is observed in both the experiments and simulations when natural gas is substituted for diesel fuel. The HC emissions are under predicted by numerical model as the natural gas substitution is increased.

Present paper discusses the advantages and disadvantages of fuel injection rate shaping for a medium-duty diesel engine using computational analysis. The analysis was performed using three-dimensional (3D) Computational Fluid Dynamics (CFD) code KIVA-3V. Fuel injection rate-shape is parameterized and a Design of Experiments (DoE) is constructed. CFD simulations are performed at discrete DoE points to construct a statistical model, which is then used to predict the engine response for variation in injection shape parameters. Trends of NOx, soot, noise and Indicated Mean Effective Pressure (IMEP) are investigated to understand the impact and potential of injection rate-shaping on engine performance. It is found that slow increase in injection rate leads to reduction in NOx and IMEP, but has almost no effect on soot emissions. Effect of rate shaping during fall of injection rate does not show strong influence on emissions and performance.

Although in-cylinder optical diagnostics have provided significant understanding of conventional diesel combustion, most alternative combustion strategies have not yet been explored to the same extent. In an effort to build the knowledge base for alternative low-temperature combustion strategies, this paper presents a comparison of three alternative low-temperature combustion strategies to two high-temperature conventional diesel combustion conditions. The baseline conditions, representative of conventional high-temperature diesel combustion, have either a short or a long ignition delay. The other three conditions are representative of some alternative combustion strategies, employing significant charge-gas dilution along with either early or late fuel injection, or a combination of both (double-injection).