An explicit reduced mechanism for H2–air combustion

Abstract

For hydrogen–oxygen–inert systems, just as for other fuel–oxidizer mixtures, systematically reduced chemistry has in the past been developed separately for premixed and diffusion flames and for autoignition. In computational work that addresses turbulent combustion or the transition from deflagration to detonation, however, autoignition and flames both may occur, and reduced chemistry may be required because of computer limitations. To fill that need, systematically reduced chemistry is presented here that encompasses autoignition and flames. The description involves three global steps among five reacting species, H2;O2;H2O;H and HO2, being based on approximations to chemical-kinetic steady states for O, OH and H2O2. These steady states apply well under all conditions except during autoignition in lean and stoichiometric mixtures, where they underpredict induction times substantially. To remedy this deficiency, which occurs only when HO2 is not in steady state, an autoignition analysis is employed to derive a correction factor that reduces the value of the reaction rates to produce agreement of calculated ignition delays. Introduction of a criterion for inclusion of this correction factor, based on a test for the HO2 steady state, results in a generally applicable three-step chemical-kinetic description for hydrogen–air combustion that possesses reasonable accuracy for most computational purposes.