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PPCI in diesel engine is a combustion mode between conventional diesel combustion and homogeneous charge compression ignition (HCCI) combustion, which has the potential to simultaneously reduce NOX and soot emissions and improve thermal efficiency. N-butanol as a kind of clean and renewable biofuel can effectively prolong ignition delay and enhance fuel/air mixing because of their low cetane number, high volatility fuel characteristics, which make it a better alternative fuel to achieve PPCI. In this paper, PPCI combustion in a boosted four-cylinder diesel engine fueled with n-butanol-diesel blends is realized by adjusting injection timing and EGR rate based on single injection. The results show that both early and late injection have long premixed duration, which is helpful to form more homogeneous mixture, and no diffusion combustion is found in heat release rate curve. Premixed combustion and low temperature combustion are the key factors to reduce PM and NOX.

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.