Specific features of the oxidation of hydrogen and methane near the third ignition limit in quartz and metal reactors

Heat release during the sublimit reaction, induction period, and explosion in stoichiometric hydrogen-oxygen and methane-oxygen mixtures near the third ignition limit is measured. It is shown that, for the hydrogen-oxygen reaction, the third limit pressure, sublimit reaction rate, and reaction rate during the induction period depend not only on the state and nature of the reactor wall surface, but also on the sequence of introduction of the reactants. It was found that heat released during the induction period is close to that released during the explosion. Changing the order of introduction of the explosive mixture components into the reactor leads to a drastic change in the dark reaction rate. It was found that the main reaction (90%) in detonating gas below the ignition limit and during the induction period occurs with the participation of the reactor wall surface. The main product of the heterogeneous reaction is hydrogen peroxide, which accumulates and, together with the initial mixture, creates conditions for ignition. An analysis of the results and literature data suggests that the ignition of detonating gas is a degenerate process (in N.N. Semenov’s terminology). For the methane-oxygen reaction, the third limit pressure, as well as the rates of the sublimit and induction-period reactions, depend on the state and nature of the reactor wall surface, while being independent of the order of introduction of the reactants.