Experimental investigation of the developing process of an unsteady diffusion flame

Park, Jeong; Shin, Hyun Dong

doi:10.1016/s0010-2180(97)00060-6

Cited by 23 publications

(10 citation statements)

References 17 publications

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“…1, in subcritical configurations with ∆ < ∆ c the weaklyreactive jet that develops for t 1 is steady and slender. The resulting solution can be described by integrating the original conservation equations (5)- (9) with the time derivative neglected in (11). A critical Damköhler number (∆ c ) S was determined as part of the steady computations, so that convergence of the integration was found to be possible only for ∆ ≤ (∆ c ) S , whereas for ∆ > (∆ c ) S a converged solution satisfying the prescribed boundary conditions could not be attained.…”

Section: Steady Computationsmentioning

confidence: 99%

“…Also, the problem has been studied recently for hydrogen-air mixtures by a combination of experimental and numerical methods [9], providing increased understanding of the influence of the jet temperature and mixing process on the ignition occurrence. A related problem also addressed in the past [10,11] is that of jet diffusion flames formed by the sudden discharge of a fuel jet into an oxidizer atmosphere.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Steady Computationsmentioning

confidence: 99%

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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“…Experiments using non-premixed flames are more difficult and initially were carried out in water using an acid-base reaction to simulate the flame [13] or employed quite different configurations such as jet flames submitted to natural or forced vortical instabilities [14][15][16][17]; more recently, burning rings [18,19] were studied under microgravity conditions. Considering that experiments on diffusion flames are in high demand, a counterflow burner was built in our laboratory to investigate the effect of vortices in nonpremixed cases [1,20].…”

Section: Introductionmentioning

confidence: 99%

Regimes of non-premixed flame-vortex interactions

Thévenin

Renard

Fiechtner

et al. 2000

Proceedings of the Combustion Institute

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“…As ambient pressure increases in all cases, the overlap of fuel and oxidizer that is an indicator of the degree of nonequilibrium is shown to become smaller. As reported in the previous researches (Tsuji et al, 1966;Tsuji, 1984;Dixon-Lewis et al, 1984;Drake, 1988;Lutz et al, 1997;Park and Shin, 1997), the increase of axial velocity gradient makes the overlap of fuel and oxidizer to be much larger. Because of a relatively small molecular weight, the high di!usion velocity of H compared with that of CO gives rise to a larger penetration into the oxidizer side for the whole cases.…”

Section: Resultsmentioning

confidence: 56%

“…As a result, numerous research e!orts have been focused on understanding of the interaction of #ames with #ow "eld through counter#ow con"gurations (Tsuji and Yamoka, 1966;Tsuji, 1984;Dixon-Lewis et al, 1984;Drake, 1988;Lutz et al, 1997). As extensive researches, the unsteady interaction of #ames with #ow "eld showed a possibility that the extinction limit might be extended under unsteady situations (Darabiha, 1992;Park and Shin, 1997). The application of the modi"ed laminar #amelet model to turbulent #ames gave excellent agreement with experimental results (Mauss et al, 1990).…”

Section: Introductionmentioning

confidence: 99%

Effects of ambient pressure on flame structure of CO/H2/N2 counterflow diffusion flame

Park

Lee²,

Lee

2001

Int. J. Energy Res.

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SUMMARYA numerical study has been conducted for the understanding of #ame structure with the fuel composition of 40 per cent CO, 30 per cent H , 30 per cent N and an oxidizer composition of 79 per cent N and 21 per cent O in a counter#ow di!usion #ame. Numerical results are obtained for #ames over wide-ranged conditions of axial velocity gradients and ambient pressures. Main concern is specially given to e!ects of axial velocity gradient and ambient pressure on #ame structure.It is seen that the role of axial velocity gradient on combustion processes is globally opposite to that of ambient pressure, on the basis of the DamkoK hler number considering the balance of convection, di!usion, and chemical reaction. That is, chemical non-equilibrium e!ects become dominant with increasing axial velocity gradient, but are suppressed with increasing ambient pressure. Flame strength is globally weakened by the increase of axial velocity gradient but is augmented by the increase of ambient pressure. However, #ame extinction is described better on the basis of only chemical reaction and in this case axial velocity gradient and ambient pressure play a similar role conceptually such that the increase of axial velocity gradient and ambient pressure cause the #ame not to be extinguished and extend the extinction limit, respectively. It is suggested that a combustion process like #ame extinction is mainly in#uenced by the competition between the radical formation reaction and the third-body recombination reaction.

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Experimental investigation of the developing process of an unsteady diffusion flame

Cited by 23 publications

References 17 publications

Numerical analyses of deflagration initiation by a hot jet

Numerical analyses of deflagration initiation by a hot jet

Regimes of non-premixed flame-vortex interactions

Effects of ambient pressure on flame structure of CO/H2/N2 counterflow diffusion flame

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