Critical radius for hot-jet ignition of hydrogen–air mixtures

Abstract

a b s t r a c tThis study addresses deflagration initiation of lean and stoichiometric hydrogeneair mixtures by the sudden discharge of a hot jet of their adiabatic combustion products. The objective is to compute the minimum jet radius required for ignition, a relevant quantity of interest for safety and technological applications. For sufficiently small discharge velocities, the numerical solution of the problem requires integration of the axisymmetric NaviereStokes equations for chemically reacting ideal-gas mixtures, supplemented by standard descriptions of the molecular transport terms and a suitably reduced chemicalkinetic mechanism for the chemistry description. The computations provide the variation of the critical radius for hot-jet ignition with both the jet velocity and the equivalence ratio of the mixture, giving values that vary between a few tens microns to a few hundred microns in the range of conditions explored. For a given equivalence ratio, the critical radius is found to increase with increasing injection velocities, although the increase is only moderately large. On the other hand, for a given injection velocity, the smallest critical radius is found at stoichiometric conditions. .

Adaptive mesh refinement based simulations of three-dimensional detonation combustion in supersonic combustible mixtures with a detailed reaction model

“…It is indicated that at this point the detonation is at the attenuation stage. On the other hand, the Mach stem gradually becomes longer from the wall boundary to 16 the center of the flowfield, suggesting that the reflection of slapping waves on the side walls gradually reaches the center of the flowfield. Finally in Fig.13(d) a new collision in the center of the flowfield is formed and results in the generation of a small bump shown by the blue circle.…”

“…Except for direct initiation [6][7][8][9] which can realize initiation immediately but need large energy, an alternative is to use a hot jet that can also realize quick initiation [10] . Researches on detonation initiation with a hot jet have been numerously investigated [11][12][13][14][15][16] , but most of them are carried out only in quiescent combustible mixtures. Detonation initiation and propagation using a hot jet were conducted experimentally by Ishii et al [17] , where the Mach numbers of combustible mixtures were 0.9 and 1.2.…”

Adaptive simulations of cavity-based detonation in supersonic hydrogen–oxygen mixture

“…An alternative approach is the utilization of a hot jet which can also ignite detonation initiation very fast [8] , because the flame acceleration process of deflagration to detonation transition (DDT) is bypassed essentially. The hot jet initiation has been investigated comprehensively in quiescent combustible mixtures [9][10][11][12] , but in supersonic combustible mixtures only a few experimental researches have been carried out [13][14][15] . Ishii et al [13] conducted experiments in combustible mixtures whose Mach numbers were 0.9 and 1.2 to investigate detonations using a hot jet initiation.…”

Ignition by transient hot turbulent jets: An investigation of ignition mechanisms by means of a PDF/REDIM method

“…gas impinges through a narrow nozzle into a quiescent hydrogen/air mixture due to an explosion in another chamber. More recently, numerical investigations were carried out by Iglesias et al [7] and Carpio et al [8] for hot jets. [8] investigated the minimum jet radius of the nozzle required to ignite the surrounding hydrogen/air mixture.…”

“…More recently, numerical investigations were carried out by Iglesias et al [7] and Carpio et al [8] for hot jets. [8] investigated the minimum jet radius of the nozzle required to ignite the surrounding hydrogen/air mixture. The impact of turbulence and mixing on the autoignition of non-premixed fuel, released from a nozzle into a turbulent hot co-flow of air in a pipe, was investigated experimentally by Markides and Mastorakos [9].…”