A Comparison of Mixing-Controlled and Flamelet Models for Diesel Combustion

In this paper, results from multidimensional computations in which a flamelet model is employed to model heat release rates and NO in transient jets under Diesel conditions are presented. These results are compared with those obtained by employing a Local Equilibrium Characteristic Time (LECT) model which is a combination of mixing-limited and kinetic-limited submodels. The LECT model has been widely employed in Diesel engine computations in prior work. Several variables, arising in the implementation of the flamelet model, are considered in detail to determine the sensitivity of the computed results to the variables themselves. These include probability density functions (PDFs), strain rates and kinetics. It is shown that the heat release rate results are not significantly sensitive to the PDFs selected and the strain rates. It is also shown that the heat release rates are relatively insensitive to the choice of detailed or reduced kinetics. In the case of heat release rates, the LECT model and the flamelet model give results that are within 5% of each other. In the case of NO, the results are qualitatively the same though there are quantitative differences.