Modeling Diesel Engine Combustion with Detailed Chemistry Using a Progress Variable Approach

In this work, we present an unsteady flamelet progress variable approach for diesel engine CFD combustion modelling. The progress variable is based on sensible enthalpy integrated over the flamelet and describes the transient flamelet ignition process. By using an unsteady flamelet library for the progress variable, the impact of local effects, for example variations in the turbulence field, effects of wall heat transfer, etc., on the autoignition chemistry can be considered on a cell level. The coupling between the unsteady flamelet library and the transport equation for total enthalpy follows the ideas of the representative interactive flamelet approach. Since the progress variable gives a direct description of the state in the flamelet, the method can be compared to having a flamelet in each computational cell in the CFD grid. The progress variable approach is applied to high-EGR, late injection operating conditions, and we demonstrate that the model can be applied for 3D engine simulations