CHEMICAL-MODELS FOR PDF MODELING OF HYDROGEN AIR NONPREMIXED TURBULENT FLAMES

Development of simplified chemical models is necessary for probability density function (pdf) modeling of turbulent flames with multiple species. Two promising approaches, the reduced mechanism method and the constrained equilibrium method, have been extensively studied to develop six plausible chemical models for nonpremixed combustion of hydrogen with air. Examination of the thermodynamic properties predicted by these chemical models in the allowable domains reveals that in regions where temperatures are above 1400 K, all six models yield similar results. In regions near the pure mixing limits, the partial equilibrium assumption for bimolecular reactions breaks down and yields unrealistic results. Reasonable agreement between the measured temperatures and those from Monte Carlo simulations with all six chemical models has been obtained for a nonpremixed turbulent jet flame at low mixing rates. As mixing rate increases, flame blowout has been predicted only by a chemical model that treats the hydrogen atom H by its kinetics rate equation, which is based on the reduced mechanism method. The predicted jet velocity at flame blowout is much higher than that observed in experiments. One of the implications from the present results is the need for improved submodels for mixing processes. © 1990.