1995-10-01

A Multidimensional Numerical Model for Turbulent Premixed Flames with Fractal Geometries 952386

We present a multidimensional numerical model that calculates turbulent premixed flame propagation, assuming the flames have fractal geometries. Two scaling transformations, previously developed for laminar flames, are used to incorporate the fractal burning model in KIVA-II1, a numerical hydrodynamics code for chemically reactive flows. In this work the model is implemented for propane/air mixtures. For applications to internal combustion engines, we have also developed a fractal model for early flame kernel growth.
Our multidimensional model can be used in experimental comparisons to test postulated fractal parameters, and we begin this task by comparing calculated results with measurements of propane/air combustion in a spark ignition engine. Good agreement is obtained between computed and measured flame positions and pressures in all cases except a low engine speed case. The calculations do predict an early increase in the ratio of the turbulent to laminar flame speeds that is also observed in the experiments. The calculated increase occurs during early flame kernel growth, when the outer length scale cutoff is limited by the flame kernel size. Because of its ability to predict such phenomena, the fractal flame model shows considerable promise in predicting spark ignition engine combustion.

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