PDF modeling of turbulent nonpremixed CO/H₂/N₂ jet flames with reduced mechanisms

A three-step reduced reaction mechanism for nonpremixed CO/H₂/N₂-air combustion is developed and applied to predicting turbulent jet flames. For Tsuji type laminar, non-premixed, opposed-flow flames, the reduced mechanism predicts reasonably good results compared to those from a parent mechanism. Application of the proposed reduced mechanism for predicting turbulent nonpremixed jet flames is carried out with a hybrid pdf-moment closure method. The performance of the pdf-moment closure method is evaluated by comparision of predictions with the experimental data by Masri and Dibble (1988). At high jet velocities, the model predicts bimodal joint statistics among the scalars demonstrating the capability of predicting local flame extinction. However, the experimental data indicates no occurrence of local flame extinction. Besides possible experimental uncertainty, the effects of pilot flame and differential diffusion are plausible reasons for the discrepancy.