Combustion Modeling of Diesel Combustion with Partially Premixed Conditions

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. LES-CHEMKIN-FTS), CHEMKIN was responsible for the low-temperature phase to provide sufficient chemical kinetic information whereas the FTS model played its role in the high-temperature phase to account for subgrid mixing-chemistry effects and save CPU time. We showed that LES-CHEMKIN-FTS performed better than LES-CHEMKIN under conventional diesel-type combustion.