THE EFFECTS OF SORET DIFFUSION ON EXTINCTION LIMIT IN PREMIXED AND DIFFUSION COUNTERFLOW n-BUTANE/AIR FLAMES

摘要

The effect of Soret diffusion on flame burning intensity and extinction limit in rich/lean premixed counterflow and diffusion counterflow n-butanelair flames was computationally studied using a detailed reaction mechanism and transport properties. Through temperature sensitivity analysis of the point at the strain rate of near-extinction, it is found that the most important species affecting the flame burning intensity is the ft radical in both premixed and diffusion counterflow flames. However, the Soret diffusion of the H radical has almost no influence on the flame burning intensity and extinction limit in rich/lean premixed counterflow n-butanelair flames for the narrow overlap region consisting of weakened rear part of gradTIT profile and reduced front part of H mole fraction profile. The essential reason for such an overlap region is due to the inherent feature of heat release rate and broader consumption layer of H in premixed n-butanelair flames. Unlike the premixed counterflow flames, the diffusion counterflow flame is more prone to extinction for considering Soret effect, while such effects are less than 3%. It is found that the Soret diffusion drives the heavy species C_4H_(10) away from the flame and therefore reduces the total enthalpy supplied to the reaction zone. This is the reason why the total Soret effect weakens the burning intensity and extinction strain rate in the counterflow diffusion flame. It is demonstrated that the effects of Soret diffusion of heavy species play more important role than light species Hand H_2 in such flames.