On the Nature of the Nonmonotonic Dependence of Pressure Ignition Limits on the Temperature of СН 4 + 2О 2 Mixtures

The nonmonotonic boundary of the “three pressure limits” region experimentally obtained by N.N. Semenov and coworkers in a wide pressure range of ~20–600 Torr was reproduced for the first time by two numerical kinetic methods for stoichiometric methane–oxygen mixtures. The self-ignition delays were modeled in the same range of parameters in which three pressure limits were also found experimentally from delays. A nonlinear scheme of methane oxidation (150 reactions) was used to calculate the ignition delays. From the linear part of the same scheme (~20 reactions of the methyl peroxide cycle), formulas for the corresponding Jacobian matrix determinant were obtained, and three roots with respect to pressure were found for each given temperature from the equation for zero determinant, which were used to construct the nonmonotonic (according to pressure) boundary line of the self-ignition region. Satisfactory convergence of the experimental and calculated data was obtained both in terms of delay times and position of the limits in the P–T space.