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Owing to the potentials for low NOx and soot emissions, diesel PCCI combustion has been widely studied over last 10 years. However, its control is still the main barrier to constrain it to be applied on production engines. As there are a number of variables which affect the mixing and combustion process, it is difficult to develop control strategies with adequate functions but simple control order for implementing them. In the current research, a reformed Homogeneity Factor (HF) of in-cylinder charge has been explored as a control medium for simplifying the control model structure. Based on multi-pulse injection, the effects of operating parameters on the Homogeneity Factor and the relationship between Homogeneity Factor and mixing, combustion processes, emissions were investigated in a four-valve, direct-injection diesel engine by CFD simulation using KIVA-3V code coupled with detailed chemistry.

Diesel homogeneous charge compression ignition (HCCI) engines with early injection can result in significant spray/wall impingement which seriously affects the fuel efficiency and emissions. In this paper, the spray/wall interaction models which are available in the literatures are reviewed, and the characteristics of modeling including spray impingement regime, splash threshold, mass fraction, size and velocity of the second droplets are summarized. Then three well developed spray/wall interaction models, O'Rourke and Amsden (OA) model, Bai and Gosman (BG) model and Han, Xu and Trigui (HXT) model, are implemented into KIVA-3V code, and validated by the experimental data from recent literatures under the conditions related to diesel HCCI engines. By comparing the spray pattern, droplet mass, size and velocity after the impingement, the thickness of the wall film and vapor distribution with the experimental data, the performance of these three models are evaluated.