Shock-initiated exothermic reactions. III. The oxidation of hydrogen

Abstract

Reactions were initiated with reflected shocks in mixtures of hydrogen with oxygen or nitrous oxide or nitric oxide which were diluted with argon. Comparison of measured and computed reflected shock speeds indicates that the H₂-O₂ system does not convert to equilibrium products immediately behind the shock. The intermediate stage of reactivity is not the partial equilibrium state as defined by Schott. Absorption spectroscopy at 3070 Ǻ gave the induction periods (_T) for OH formation. The activation energy of the rate-determining reaction for OH formation is available from plots of log(_T[O₂]) against inverse temperature for oxygen-rich and stoicheiometric mixtures. However, log(_T[O₂]^1/2[H₂]^1/2) should be used for fuel-rich mixtures.     Activation energies determined, for the H₂-N₂O and H₂-NO reactions suggest that rate-controlling mechanisms are not simple. The former reaction leads to equilibrium products immediately behind the shock but, at temperatures below 3000°K, the latter reaction is incomplete due to regeneration of nitric oxide in the reaction OH + HNO → H₂O + NO.