Soret effects on the diffusion-chemistry interaction of hydrogen-air edge flames propagating in transverse gradient evolving mixing layers.

The effects of Soret diffusion (SD) on the hydrogen-air edge flame propagation and the diffusion-chemistry interaction are investigated through simulation facilitated by the numerical code MultiDiffFOAM. The edge flames in this study gradually develop from a flame kernel into a tri-brachial structure in a hydrogen-air mixing layer that temporally evolves due to transverse reactant concentration gradient. We demonstrate that the responses of flame displacement speed S d to flame curvature K , stretch rate κ and scalar dissipation rate χ are distinctly influenced by SD. For the linear S d - K and S d - κ correlations, SD would result in a smaller Markstein length. Moreover, SD is shown to lead to shifting of the S d - χ curve towards the regime with larger χ. Compared with the weak influences of SD on the tangential diffusion component S d , t and normal diffusion component S d , n , the chemical reaction component S d , r is significantly weakened by SD. The important chemical reactions for edge flame propagation are identified based on sensitivity analysis and their rates are found to be smaller when SD is considered. For the local composition at the flame marker, the mass fraction of H 2 is slightly larger and that of H is obviously smaller when SD is considered. The SD flux of H 2 j H 2 S D and that of H j H S D are both coupled with the driving force ∇ (l n T) along the mixture fraction coordinate. However, the j H 2 S D is mainly concentrated on the unburnt side while the j H S D is on the burnt side. The analyses on decomposed fluxes of H 2 and H along the flame normal direction further suggest that SD would enhance the H 2 mass diffusion but weaken the H mass diffusion. Such opposite effects stem from the distribution features that H 2 is mainly on the unburnt side while H on the burnt side. • Soret diffusion decreases flame displacement speed S d through chemical reaction component S d , r. • Soret diffusion leads to smaller Markstein length through lateral "compensating" flux of H 2 for curved flame front. • Rates of important reaction are decreased by Soret diffusion due to obviously smaller local mass fraction of H. • Soret diffusion has opposite effects on H 2 and H transport due to different species distribution features relative to flame front. [ABSTRACT FROM AUTHOR]