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Two turbulent combustion modeling approaches, which were large eddy simulations in conjunction with detailed kinetics (LES-CHEMKIN) and Reynolds Averaged Navier Stokes with detailed kinetics (RANS-CHEMKIN), were used to model two partially premixed engine conditions. The results were compared with average pressure and heat release data, as well as images of in-cylinder ignition chemiluminescence and OH radical distributions. Both LES-CHEMKIN and RANS-CHEMKIN match well with experimental average data. However, LES-CHEMKIN has advantages over RANS-CHEMKIN in predicting the details of location of ignition sites, temperature as well as OH radical distributions. Therefore, LES offers more realistic representations of the combustion process. As a further improvement aiming at saving computational cost and accounting for turbulence-chemistry interactions, a flamelet time scale (FTS) combustion model is coupled with CHEMKIN to predict the entire combustion process. In this new approach (i.e.

A general combustion model, in the context of large eddy simulations, was developed to simulate the full range of combustion in conventional diesel-type and HCCI-type diesels. The combustion model consisted of a Chemkin sub-model and an Extended Flamelet Time Scale (EFTS) sub-model. Specifically, Chemkin was used to simulate auto-ignition process. In the post-ignition phase, the combustion model was switched to EFTS. In the EFTS sub-model, combustion was assumed to be a combination of two elementary combustion modes: homogeneous combustion and flamelet combustion. The combustion index acted as a weighting factor blending the contributions from these two modes. The Chemkin sub-model neglected the subgrid scale turbulence-chemistry interactions whereas the EFTS model took them into account through a presumed PDF approach. The model was used to simulate an early injection mode of a Cummins DI diesel engine and a mode of a Caterpillar DI diesel engine.