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

Abstract

Different simplified and detailed chemical models and their impact on simulations of combustion regimes initiating by the initial temperature gradient in methane/air mixtures are studied. The limits of the regimes of reaction wave propagation depend upon the spontaneous wave speed and the characteristic velocities of the problem. The present study mainly focus to identify conditions required for the development a detonation and to compare the difference between simplified chemical models and detailed chemistry. It is shown that a widely used simplified chemical schemes, such as one-step, two-step and other simplified models, do not reproduce correctly the ignition process in methane/air mixtures. The ignition delay times calculated using simplified models are in orders of magnitude shorter than the ignition delay times calculated using detailed chemical models and measured experimentally. This results in considerably different times when the exothermic reaction affects significantly the ignition, evolution, and coupling of the spontaneous reaction wave and pressure waves. We show that the temperature gradient capable to trigger detonation calculated using detailed chemical models is much shallower (the size of the hot spot is much larger) than that, predicted by simulations with simplified chemical models. These findings suggest that the scenario leading to the deflagration to detonation transition (DDT) may depend greatly on the chemical model used in simulations and that the Zel'dovich gradient mechanism is not necessary a universal mechanism triggering DDT. The obtained results indicate that the conclusions derived from the simulations of DDT with simplified chemical models should be viewed with great caution.

Autoignition and detonation development from a hot spot inside a closed chamber: Effects of end wall reflection

“…The autoignition front propagation initiated by a hot spot in large or open space has been extensively studied [8,9,14,[17][18][19][20][21][22]. According to the Zel'dovich theory [7] the critical condition for detonation development by the temperature gradient is defined as the condition of coupling of the reaction wave and the pressure wave.…”

“…This detonation peninsular was widely utilized in the studies on knock and super-knock [3,[10][11][12][13]. Besides, Liberman and co-workers [14,15] studied the combustion regimes induced by the initial temperature gradient. They found that the temperature gradient initiated a detonation predicted by detailed chemical models greatly differs from that predicted using a one-step chemistry.…”

Spontaneous initiation and development of hydrogen–oxygen detonation with ozone sensitization

“…After the intersection of the spontaneous wave front and the pressure wave, the spontaneous wave evolves into a combustion wave and the pressure wave steepens into the shock wave. The pressure peak becomes large enough and steepens into a detonation wave [7]. This process is defined as a spontaneous initiation.…”

“…Liberman & Wang et al [7,8] found that the sustenance of detonation initiated by spontaneous reaction wave is closely related to the ambient temperature and pressure at the end and outside of the temperature gradient. Dai, Qi & Chen et al [9] studied the development of a spontaneous reaction wave in a hot spot with high initial pressure and temperature for large hydrocarbon fuels with low-temperature chemistry which is prone to exhibit the negative temperature coefficient (NTC) phenomena.…”

Convergence properties of detonation simulations

“…In particular, it was shown that the minimal slope of the temperature gradient required for triggering detonation and other combustion modes obtained in simulations with simplified chemical models, for example a one-step model, is orders of magnitude smaller than those obtained in simulations with a detailed chemical model. Wang et al (2018) and Liberman et al (2019) studied the influence of the chemical reaction model on detonation ignited by a temperature gradient for hydrogen-air and methane-air mixtures. They concluded that the one-step model and other simplified models usually cannot describe correctly the ignition processes.…”