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Partially-premixed low-temperature combustion avoids the soot and NOx generation area on the Ф-T diagram to reduce both engine NOx and soot emissions. Compared with the HCCI combustion mode, partially-premixed combustion (PPC) has better combustion controllability. The purpose of controlling the combustion phase can be achieved by adjusting injection timing and strategy. Based on a 4 cylinder turbocharged diesel engine, this paper aims at investigating the influence of injection strategy to the engine combustion and emission formation under the condition of single injection and split injection PPC strategy respectively, in which the primary purpose focus on the emission characteristics of particles. Results show that the early-injection PPC formed by single injection can reduce the quantity, quality and geometric mean diameter (GMD) of particles obviously.

The partially premixed combustion (PPC) was realized in a 6-cylinder heavy turbocharged diesel engine with single injection and EGR strategies. Combined with chemical reaction mechanism, the combustion and emission processes of this mode was analyzed using level-set turbulent flame propagation model. Based on the experiments and simulations, the impacts of PPC on the heat release, NOx and PM emissions were further investigated. The results show that both the early-injection and late-injection strategies have a two-stage heat release and significantly higher premixed combustion proportion than the conventional combustion mode, however, mixing controlled combustion was also observed in the late-injection mode. The NOx and PM emission was reduced simultaneously in PPC. However, in the late-injection strategy, this was achieved at the expense of increased HC emission. The dynamic process of the core components in PPC was much different from those in conventional diesel spray combustion.