An Investigation of Multiple-Injection Strategy in a Diesel PCCI Combustion Engine

Multiple-injection strategy for Premixed Charge Compression Ignition (PCCI) combustion was investigated in a four-valve, direct-injection diesel engine by CFD simulation using KIVA-3V code [ 1 ] coupled with detailed chemistry. The effects of fuel splitting proportion, injection timing, included spray angles, injecting velocity, and the combined effects of injection parameters and EGR rate and boost pressure were examined. The mixing process and formations of soot emission and NO _x were investigated as the main concern of the research. The results show that the fuel splitting proportion and the injection timing significantly impacted the combustion and emissions due to the considerable changes of the mixing process and fuel distribution in cylinder. The soot emission and unburned HC (UHC) were affected by included spray angles since the massive influences of the fuel distribution resulted from the change in spray targeting point on piston bowl. As a result of improved evaporation, faster combustion and a rise of NO _x emission were obtained when injecting velocity increased. Soot emission increased significantly when the velocity at injector increase, which caused worse impinging on piston bowl. High EGR rate was shown as an approach to yield a low NO _x and soot solution in the research, while this approach faced the cruel problems of poor efficiency and high CO and UHC. According to the study about the effects of boost pressure, properly raise boost pressure was considered as a method with prospect which can resolve the problems result from high EGR rate.