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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.

The performance of Partially Premixed Combustion (PPC) relies heavily on the proper mixing between the injected fuel and the in-cylinder gas mixture. This pre-mixing aims to eliminate over-rich regions where the mixture forms soot, and at the same time to avoid the NOX formation region by lowering the combustion temperature by introduction of a large amount of EGR The main effort of this paper focuses on investigating the characteristic of PPC combustion and a suitable injection strategy for achieving the PPC combustion mode. Two injection strategies (i.e. double and single injection) were investigated on a four-cylinder heavy-duty diesel engine operating at low, medium and high load conditions.