Regimes of High-Speed Hydrogen Flame Propagation in Channels: Classification and Criteria of Realization

Abstract

ABSTRACTThe paper discusses high-speed combustion regimes inside confined volumes on the example of hydrogen-containing gaseous mixtures. A unified description of high-speed combustion regimes is proposed on the basis of systematic analysis of flame evolution. The stage of the so-called chocked flame is shown to be the necessary step on the way to the formation of high-speed flames and detonation. Further flame evolution could proceed in different ways including quasi-steady transonic flame, deflagration-to-detonation transition or sequential auto-ignitions ahead of the primary flame front. The paper proposes a method for estimation of probability of different devastating high-speed combustion regimes, including detonation, relying only on the mixture composition and its initial thermodynamic state. Herewith, since in the process of flame acceleration inside confined volume the compression is yielded by the series of compression waves, the initial state and the state corresponded to the high-speed stage of flame propagation could be related via Hugoniot adiabat. The conducted parametric study of hydrogen flames allowed obtaining criteria according to which the possibility of one or another regime of high-speed combustion can be estimated. The obtained results correlate well with the experimental data on the different high-speed regimes taking place in hydrogen–air mixtures, stoichiometric hydrogen–oxygen, and equimolar hydrogen–oxygen mixtures. It is shown that to assess the probability of detonation onset in obstructed channels, the proposed technique is not enough and one should apply it together with the geometrical criteria. Results obtained with combined technique agree well with the available data on the criteria of deflagration-to-detonation transition in hydrogen–air mixtures of different compounds.