The effect of reaction mechanism on OH* chemiluminescence in methane inverse diffusion flame

Abstract

The OH* chemiluminescence is closely related to flame properties in the study of combustion diagnosis. In this work, numerical investigation of the OH* reaction mechanism in methane inverse diffusion flames for evaluating the OH* chemiluminescence is presented. The two-dimensional distribution of OH* emission intensity in laminar inverse diffusion flames was obtained by CCD imaging system and agreed well with the numerical simulation results. By changing oxygen/fuel equivalence ratios, the effect of elementary reactions on OH* chemiluminescence was analyzed. The results show that the OH* distribution depends upon the formation reactions, quenching reactions and diffusion characteristics. The OH* is generated by R1 (H + O + M <=> OH* + M) and R2 (CH + O2 <=> OH* + CO). The trend of R1 distribution is consistent with the OH* molar concentration distribution at different oxygen/fuel equivalence ratios. Although the R1 reaction rate is strongest at the root of flame, the OH* molar concentration is relatively low due to the strong quenching reactions, where the OH* is mainly quenched with H2O and O2. In the pure diffusion zone, the generation and destruction reaction rate of OH* is unbalanced. At the root of the flame, OH* diffuses from the net generation zone to both sides.