Multi-zone Modeling of PCCI Combustion with CFD Coupling for Stratification

PCCI combustion is a viable alternative for diesel combustion. The concept of PCCI combustion is associated with early injection of the fuel whilst applying high EGR levels and operation with a highly lean mixture such that ignition is (well) after the injection event. In this way, a premixed mixture is formed and the operation is performed at relatively lower temperatures. Thus, it is possible to reduce soot and NOx emissions to very low values. PCCI combustion is analyzed using a multi-zone model. In the multi-zone model, complicated transport equations are ignored so that much more detailed chemical mechanisms compared to CFD models can be introduced. The model is still coupled to a CFD model to estimate the fuel distribution which is important to improve the quality of the model. The effects of different chemical mechanisms and CFD coupling timings (i.e. different fuel distributions) are studied. For the analysis, dedicated model fuel experimental results are used to evaluate the quality of the modeling results. In the multi zone model, 10 zones are sufficient to describe the stratification with sufficient resolution. The analysis shows that emission trends are mainly predicted qualitatively similar to those of experiments with respect to the injection timing. This is generally correct for different fuel distributions which have a big influence on the emissions but not on the combustion phasing.