A Study of Coupled Turbulent Mixing, Soot Chemistry, and Radiation Effects Using the Linear Eddy Model (original) (raw)

Soot formation in turbulent non premixed flames

A coupled radiation/flamelet combustion model is applied to the simulation of a turbulent diffusion flame fed with natural gas. The major species and temperature fields are calculated using the Steady Laminar Flamelet and the Eddy Dissipation Concept models. The formation of soot particles is predicted using the method of moments (MOM), coupled with simple semi-empirical models of soot nucleation, growth, oxidation and aggregation. The interaction of turbulence and soot chemistry is described by a probability density approach based on the laminar flamelet formulation. The scope of this work is mainly to investigate the accuracy and reliability of available soot semi-empirical models by comparison with experimental data in turbulent flames. Particular attention is devoted to the effects of turbulent fluctuations on the closure of soot source terms in the moment equations. The predicted soot amount in the turbulent flame investigated is found relatively insensitive to the nucleation models. On the contrary, growth and oxidation models significantly influence soot formation.

Large eddy simulation of soot formation in a turbulent non-premixed jet flame

Combustion and Flame, 2009

A recently developed subgrid model for soot dynamics [H. El-Asrag, T. Lu, C.K. Law, S. Menon, Combust. Flame 150 (2007) 108–126] is used to study the soot formation in a non-premixed turbulent flame. The model allows coupling between reaction, diffusion and soot (including soot diffusion and thermophoretic forces) processes in the subgrid domain without requiring ad hoc filtering or model parameter adjustments. The combined model includes the entire process, from the initial phase, when the soot nucleus diameter is much smaller than the mean free path, to the final phase, after coagulation and aggregation, where it can be considered in the continuum regime. A relatively detailed but reduced kinetics for ethylene–air is used to simulate an experimentally studied non-premixed ethylene/air jet diffusion flame. Acetylene is used as a soot precursor species. The soot volume fraction order of magnitude, the location of its maxima, and the soot particle size distribution are all captured reasonably. Along the centerline, an initial region dominated by nucleation and surface growth is established followed by an oxidation region. The diffusion effect is found to be most important in the nucleation regime, while the thermophoretic forces become more influential downstream of the potential core in the oxidation zone. The particle size distribution shows a log–normal distribution in the nucleation region, and a more Gaussian like distribution further downstream. Limitations of the current approach and possible solution strategies are also discussed.