An Evaluation of a Flamelet Approach to Modeling Heat Release in Diesel Engines

In multidimensional models for Diesel combustion, the local equilibrium characteristic time (LECT) is widely employed to model the heat release rate. Recent work has also explored the possibility of employing flamelet models (Pitsch et al., SAE paper 962051 ,1996). In principle, this approach rvould appear to be consistent with recent experimental findin-es of the struòture of the flame in Diesel combustion during fuel injection (Dec, 1997). In this paper, we compare the two approaches. The CHEMKIN (OppDIF) package and a one-dimensional Diffusion Laminar Flamelet Code (DLFC) are employed to generate the flamelet libraries. These two approaches to generating the libraries are also critically evaluated and diicussed. It is shown that the flamelet approach to modeling the heat release rate gives realistic results during fuel injection. Differential diffusion and non-unity Lewis number effects are proposed to be the key issues that determine the applicability of the flamelet libraries in a conserved scalar approach. The effect of probability density functions is studied by employing delta, beta and clipped-gaussian functions.