On the Nature of the Nonmonotonic Dependence of the Pressure Flame Limits on Temperature CH₄ + 2O₂ Mixtures

In the present work, for the first time for stoichiometric methane–oxygen mixtures, two numerical kinetic methods reproduce the nonmonotonic boundary of the “three pressure limits” region obtained by N.N. Semenov’ coworkers experimentally in a wide pressure range ~20–600 Torr. In where take place the llow pressure ignition peninsula, range of parameters, the simulation of self-ignition delays was carried out. In this case, a nonlinear scheme of methane oxidation (150 reactions) was used to calculate ignition delays. According to the linear part of the same scheme (~20 reactions of the methyl peroxide cycle), formulas for the corresponding Jacobi matrix determinant were obtained for the first time, and for each given temperature, from the equation that determines its zero, three pressure roots were found, from which the boundary line of the region, nonmonotonic in pressure, was constructed self-ignition. Satisfactory convergence of the experimental and calculated data is shown both in terms of delay times and in terms of the position of the limits in the P–T space.