MULTIDIMENSIONAL MODELING OF DIESEL IGNITION AND COMBUSTION USING A MULTISTEP KINETICS MODEL

Ignition and combustion mechanisms in diesel engines were studied usin g the KIVA code, with modifications to the combustion, heat transfer, crevice flow, and spray models. A laminar-and-turbulent characteristic -time combustion model that has been used successfully for spark-ignit ed engine studies was extended to allow predictions of ignition and co mbustion in diesel engines. A more accurate prediction of ignition del ay was achieved by using a multistep chemical kinetics model. The Shel l knock model was implemented for this purpose and was found to be cap able of predicting successfully the autoignition of homogeneous mixtur es in a rapid compression machine and diesel spray ignition under engi ne conditions. The physical significance of the model parameters is di scussed and the sensitivity of results to the model constants is asses sed. The ignition kinetics model was also applied to simulate the igni tion process in a Cummins diesel engine. The post-ignition combustion was simulated using both a single-step Arrhenius kinetics model and al so the characteristic-time model to account for the energy release dur ing the mixing-controlled combustion phase. The present model differs from that used in earlier multidimensional computations of diesel igni tion in that it also includes state-of-the-art turbulence and spray at omization models. In addition, in this study the model predictions are compared to engine data. It is found that good levels of agreement wi th the experimental data are obtained using the multistep chemical kin etics model for diesel ignition modeling. However, further study is ne eded of the effects of turbulent mixing on post-ignition combustion.