Pdf Modeling of Turbulent Nonpremixed Methane Jet Flames

Abstract

Anexpanded model of turbulent nonpremixed combustion is herein presented. In the model, the scalar mixing and reactions are described by a probability density function (pdf) submodel capable or handling five scalars, while the turbulent velocity field is described by a second-order moment closure. Two plausible chemical reaction models are considered: a five-scalar, four-step, reduced reaction mechanism and a four-scalar constrainted equilibrium model. Detailed comparisons of model predictions with laser Raman experimental data provide a valuable evaluation of the model's ability in predicting nonequilibrium chemistry in turbulent nonpremixed flames. Overall, the model fails to predict greater departure from chemical equilibrium as mixing rates are increased. Interestingly, this failure is not due to the chemical model, both of which perform satisfactorily. Instead, the failure to predict greater departure from chemical equilibrium is a subtle artifact of the current Monte Carlo simulation of turbulent mixing and chemical reaction.