Premixed charge compression ignition combustion modelling with a multi-zone approach including inter-zonal mixing

Abstract

Premixed charge compression ignition combustion is a clean and efficient alternative to classical diesel combustion. The concept of premixed charge compression ignition combustion is associated with early injection of the fuel while applying high exhaust gas recirculation levels and operation with a highly lean mixture such that ignition takes place (well) after the injection event. Thus, it is possible to reduce the soot emissions and the nitrogen oxide emissions simultaneously. Premixed charge compression ignition combustion is analysed using a multi-zone model. In the multi-zone model, chemical mechanisms which are much more detailed than those used in the computational fluid dynamics approaches can be introduced directly. The computational fluid dynamics model is still used to predict the initial fuel stratification in the cylinder, which is important to improve the quality of the model. For the analysis, dedicated experiments with n-heptane are used to evaluate the results of the model. In such a multi-zone model, 10 zones prove to be sufficient to describe the stratification with adequate resolution. It is observed that different fuel distributions have a large influence on the emissions when there is no mixing between the zones. To overcome this dependence, basic inter-zonal diffusive mixing is applied. The level of mixing is estimated with a sensitivity study. When the inter-zonal mixing is included, the emission results become much less sensitive to the crank angle at which the charge stratification is sampled and the simulation is initialized.