Numerical Simulation Of The Turbulent Non-Premixed Flame Structure With Multi-dimensional Conditional Moment Closure

Based on the multi-dimensional conditional moment closure(CMC), a program used to simulate turbulent non-premixed flame is established. This program can provide a detailed description of multi-dimensional flame structure with detailed chemical kinetics mechanism. In the framework of this numerical platform, the turbulent non-premixed jet flame is numerically investigated, and the combustion phenomenon such as local extinction, differential diffusion effect, stabilization mechanism of lifted flame and inhibition effect of organophosphorus compounds are discussed. The numerical results confirm that, as a grounded model, CMC can well reflect the complex interaction between the turbulence and the chemistry.Conditional moment closure and laminar flamelet model both belong to the turbulent combustion model which effectively use the conserved scalar, and construction of CMC is often accompanied with the need to take an understanding of laminar flamelet model. On the basis of theoretically comparative analysis of these two models and the similarity between parabolic CMC and Lagrangian flamelet model, numerical analysis is conducted for the simulation of turbulent non-premixed jet flames (H₂/N₂, CH₄/H₂/N₂) with different Reynolds number and turbulence-chemistry interaction characteristics. Owing to the fact that, in these two flames, radiation in the downstream flame zone can significantly influence the flame structure, the different modeling approach of these two models for the conditional velocity leads to different computed results.Turbulent lifted-jet flame has more complex thermodynamic characteristics, autoignition is considered as the main stabilization mechanism. The elliptic CMC model is employed to numerically study the lifted-jet flame in a hot coflow. The computed axial distribution of temperature and minor species, especially the HO₂, along the surface of stoichiometric mixture fraction and r/D=1.04 indicates the importance of autoignition in the stabilization of this lifted flame base. Meanwhile, an analysis of transport budgets of convection, turbulent diffusion and chemical reaction terms for conditional temperature in the region of flame stabilization also implies the existence of autoignition at the flame base. In addition, this flame appears to be sensitive to chemical reaction mechanism, and, compared with GRI2.11-mechanism, Mueller mechanism leads to more reasonable computed results in this work. As one of the promising replacements for halons(CF₃Br), organophosphorus compounds can effectively decrease the flame burning velocity and final temperature. Numerical study of the inhibition effect of trimethyl-phosphate(TMP) in turbulent non-premixed H₂/N₂ flame with conditional moment closure not only demonstrates that the inhibition cycle HOPO PO₂ is crucial for flame suppression, but also reveals that different modes of addition can noticeably influence the inhibition effect of TMP.