Analysis of NO Formation in Counterflow Premixed Hydrogen-Air Flame

Abstract

Though hydrogen fuel reduces the carbon dioxide emission, it still produces NOx. However, gaps exist in the fundamental understanding of hydrogen-air combustion and the NO emission; most previous research has focused on the flames burning with mixture such as H2 mixed with CH4, rather than pure H2 flame. Here, a computational study is presented to investigate the effects of stretch rate on NO formation in counter-flow premixed hydrogen-air flame. The simulations of premixed hydrogen flames were performed with OPPDIF code with UCSD chemical mechanism. Results indicate that the NO formation is affected by three factors: radical concentration, flame temperature, and residence time of reactants. The flame temperature, the reaction rate of NO, and the NO emission index all decrease when the stretch rate increases. Moreover, the formation of NO through thermal mechanism, NNH mechanism, and N2O mechanism are discussed, as well as the percentages of their contribution.