Comparison and Coupling of Homogeneous Reactor and Flamelet Library Soot Modeling Approaches for Diesel Combustion

Soot models applied to Diesel combustion can be grouped into two classes, one based on the flamelet concept and the other based on the homogeneous reactor concept. The first assumes that the laminar diffusion flame structure of the reaction zone, in the mixture fraction space, is preserved while convected and strained by the turbulent flow. The second assumes that the properties of the reaction zone are locally homogeneous. Thus the aerodynamic and chemical reaction interactions are modeled with opposing assumptions: the first assumes fast chemistry, the second fast mixing.

In this work, we first compare results obtained with a flamelet library approach to those with a homogeneous reactor approach. Recognizing that both types of models apply in different regions of Diesel combustion, we then propose a new approach for soot modeling in which they are coupled. The source terms for soot from each model are weighted and added with a criterion based on a comparison between characteristic times for turbulence and fuel oxidation. In all calculations a new spray model based on an extended Lagrangian-Eulerian approach and a new combustion model which allows a description of the fuel/oxidizer subgrid mixing are used. The results of the above three models are compared to experimental data in a high pressure combustion cell.