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Different simplified and detailed chemical models and their impact onsimulations of combustion regimes initiating by the initial temperaturegradient in methane/air mixtures are studied. The limits of the regimes ofreaction wave propagation depend upon the spontaneous wave speed and thecharacteristic velocities of the problem. The present study mainly focus toidentify conditions required for the development a detonation and to comparethe difference between simplified chemical models and detailed chemistry. It isshown that a widely used simplified chemical schemes, such as one-step,two-step and other simplified models, do not reproduce correctly the ignitionprocess in methane/air mixtures. The ignition delay times calculated usingsimplified models are in orders of magnitude shorter than the ignition delaytimes calculated using detailed chemical models and measured experimentally.This results in considerably different times when the exothermic reactionaffects significantly the ignition, evolution, and coupling of the spontaneousreaction wave and pressure waves. We show that the temperature gradient capableto trigger detonation calculated using detailed chemical models is muchshallower (the size of the hot spot is much larger) than that, predicted bysimulations with simplified chemical models. These findings suggest that thescenario leading to the deflagration to detonation transition (DDT) may dependgreatly on the chemical model used in simulations and that the Zeldovichgradient mechanism is not necessary a universal mechanism triggering DDT. Theobtained results indicate that the conclusions derived from the simulations ofDDT with simplified chemical models should be viewed with great caution.

Influence of chemical kinetics on detonation initiating by temperature gradients in methane/air