Initiation of Combustion in Lean Mixtures by Flame Jets

Murase, Eiichi; Ono, Shinsuke; Hanada, K.; Oppenheim, A. K.

doi:10.1080/00102209608935492

Cited by 30 publications

(12 citation statements)

References 3 publications

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“…A low-Mach-number approximation was employed when writing the energy equation and the equation of state. A three-step reduced chemical-kinetic mechanism involving H 2 , O 2 , H 2 O, HO 2 , and H as reactive species, which has been tested to provide accurate results under a wide range of conditions including autoignition and deflagration propagation [9], was used for the chemistry description. This reduced mechanism has been recently shown to describe accurately autoignition of hydrogen in high-speed turbulent jets [10] and is therefore particularly suitable for the problem at hand.…”

Section: Numerical Modelmentioning

confidence: 99%

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

Carpio

Iglesias

Vera

et al. 2013

International Journal of Hydrogen Energy

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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. .

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Section: Numerical Modelmentioning

confidence: 99%

“…[2], with applications to hydrogen-fired engines [3]. The problem of hot-jet ignition has been studied for hydrogeneair mixtures by a combination of experimental and numerical methods [4], providing increased understanding of the influence of the jet temperature and mixing process on ignition occurrence.…”

Section: Introductionmentioning

confidence: 99%

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

Carpio

Iglesias

Vera

et al. 2013

International Journal of Hydrogen Energy

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“…The initiation of a detonation requires much larger values of a, on the order of δ d ∼ 10 −1 m [6]. The present paper deals with hot jets of transverse size much smaller than δ d , of interest for pulsed combustion jet systems [2]. This problem is also relevant in connection with the design of flameproof enclosures of electrical equipment [7], whose orifices and gaps must be sufficiently small to ensure that, if a reactive mixture enters the enclosure and becomes ignited, the jet of combustion products escaping outside is unable to ignite the surrounding gas mixture.…”

Section: Introductionmentioning

confidence: 99%

“…The problem has important implications in connection with the transport, handling, and storage of fuels, particularly hydrogen, and may also find application in engine ignition systems [2].…”

Section: Introductionmentioning

confidence: 99%

Numerical analyses of deflagration initiation by a hot jet

Iglesias

Vera

Sánchez

et al. 2012

Combustion Theory and Modelling

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Unsteady numerical simulations of axisymmetric reactive jets with one-step Arrhenius kinetics are used to investigate the problem of deflagration initiation in a premixed fuel-air mixture by the sudden discharge of a hot jet of its adiabatic reaction products. For the moderately large values of the jet Reynolds number considered in the computations, chemical reaction is seen to occur initially in the thin mixing layer that separates the hot products from the cold reactants. This mixing layer is wrapped around by the starting vortex, thereby enhancing mixing at the jet leading head, which is followed by an annular mixing layer that trails behind, connecting the leading vortex with the orifice rim. A successful deflagration is seen to develop for values of the orifice radius larger than a critical value, ac, of the order of the flame thickness of the planar deflagration, δL. Introduction of appropriate scales for the different flow variables provides the dimensionless formulation of the problem, with flame initiation characterized in terms of a critical Damköhler number ∆c = (ac/δL) 2 , whose parametric dependence is investigated. The numerical computations reveal that, while the jet Reynolds number exerts a limited influence on the criticality conditions, the effect of the reactant diffusivity on ignition is much more pronounced, with the value of ∆c increasing significantly with increasing Lewis numbers Le. The reactant diffusivity affects also the way ignition takes place, so that for reactants with Le > ∼ 1 the flame develops as a result of ignition in the annular mixing layer surrounding the developing jet stem, whereas for highly diffusive reactants with Lewis numbers sufficiently smaller than unity combustion is initiated in the mixed core formed around the starting vortex. Steady computations of weakly reactive subcritical jets are also employed to determine ∆c, giving results in close agreement with those of unsteady computations for Le > ∼ 1, when the role of the leading vortex is secondary. The boundary-layer problem that emerges in the limit of high jet Reynolds numbers is used to ascertain the effect of density variations and variable transport properties on the predicted critical Damköhler numbers, and to confirm the small influence of other dimensionless parameters such as the Zeldovich number, provided that its value is sufficiently large. The analysis provides increased understanding of deflagration initiation processes, including effects of differential diffusion, and points the need for further investigations incorporating detailed chemistry models for specific fuel-air mixtures.

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“…Ignition of fuel/air mixtures by impinging hot gas jets is a very important process in various fields ranging from industrial explosions and nuclear safety to supersonic combustors and to the development of combustion engines [1]. In explosive environments, hot jet ignition may take place due to a hot jet escaping from flameproof enclosures through inevitable gaps [2], e.g., like the ones present at the shaft bearing of an electrical motor.…”

Section: Introduction and Theoretical Backgroundmentioning

confidence: 99%

Detailed investigation of ignition by hot gas jets

Sadanandan

Markus

Schießl

et al. 2007

Proceedings of the Combustion Institute

107

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Experimental and numerical investigations of the ignition of hydrogen/air mixtures by jets of hot exhaust gases are reported. An experimental realisation of such an ignition process, where a jet of hot exhaust gas impinges through a narrow nozzle into a quiescent hydrogen/air mixture, possibly initiating ignition and combustion, is studied. High-speed laser-induced fluorescence (LIF) image sequences of the hydroxyl radical (OH) and laser Schlieren methods are used to gain information about the spatial and temporal evolution of the ignition process. Recording temporally resolved pressure traces yields information about ambient conditions for the process. Numerical experiments are performed that allow linking these observables to certain characteristic states of the gas mixture. The outcome of numerical modelling and experiments indicates the important influence of the hot jet temperature and speed of mixing between the hot and cold gases on the ignition process. The results show the quenching of the flame inside the nozzle and the subsequent ignition of the mixture by the hot exhaust jet. These detailed examinations of the ignition process improve the knowledge concerning flame transmission out of electrical equipment of the type of protection flameproof enclosure.

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Initiation of Combustion in Lean Mixtures by Flame Jets

Cited by 30 publications

References 3 publications

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

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

Numerical analyses of deflagration initiation by a hot jet

Detailed investigation of ignition by hot gas jets

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