The impact of detailed multicomponent transport and thermal diffusion effects on soot formation in ethylene/air flames

Abstract

As the drive toward greater accuracy in flame simulation continues, there is a need for more detail in the modeling of soot formation and its related phenomena. In this study we investigate computationally the effect of multicomponent transport and thermal diffusion on soot formation in ethylene/air flames. In the counterflow configuration, laminar diffusion flames and partially premixed flames are investigated using complex chemistry and detailed transport. The gas phase equations are coupled to a sectional soot model and the resulting set of partial differential equations admits a well-known similarity solution. Arc length continuation is used to compute flames for varying strain rates. In the coflow configuration, a modified vorticity–velocity formulation is used and the governing equations are solved on an adaptively refined grid using pseudo-transient continuation and Newton’s method nested with a Bi-CGSTAB iterative linear system solver. All transport coefficients, including thermal diffusion coefficients, are evaluated using cost-effective, accurate algorithms derived from the kinetic theory of gases. The numerical results for the counterflow model provide a quantitative assessment of the effects of detailed multicomponent transport and thermal diffusion on soot concentrations as a function of strain rate for both a diffusion flame and partially premixed flame. The fidelity of the commonly used Fickian diffusion model is tested and it is shown that in certain cases, the impacts of detailed multicomponent transport and thermal diffusion modeling on soot concentrations are significant. The numerical results for the coflow model demonstrate that although minimal changes in flame shape and temperature profiles arise when transport models are varied, changes in the soot profiles can be seen.