Preliminary results of a numerical-experimental study of the dynamic structure of a buoyant jet diffusion flame

Davis, Ronald W.; Moore, E. F.; Roquemore, W. M.; Chen, L.-D.; Vilimpoc, V.; Goss, L. P.

doi:10.1016/0010-2180(91)90074-l

Cited by 100 publications

(28 citation statements)

References 8 publications

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“…The variation of flickering amplitude with V R implies that the buoyancy-induced instability can be controlled by varying the ratio of coflow velocity to inner jet velocity. This result is consistent with those of previous experimental and numerical investigations dealing with nonpremixed flames [12,22,28] and partially-premixed triple flames [27] at normal gravity. As indicated in these investigations, increasing the coflow velocity decreases the vortex size and the oscillation amplitude.…”

Section: Effect Of Coflow Velocity On Flame Structuresupporting

confidence: 93%

“…The role of buoyancy-induced instability in nonpremixed flames has been investigated in previous experimental [11] and computational studies [12][13]. The instability leads to the flame flickering phenomena, whereby the nonpremixed flame is periodically pinched by convecting vortices, causing large-scale, low-frequency oscillation in the flame surface.…”

Section: Unsteady Partially Premixed Flamesmentioning

confidence: 99%

“…Another prominent effect of buoyant acceleration is to induce a well-organized, periodic oscillation or flickering of the outer nonpremixed reaction zone of the 1-g flame. The flame flicker, whereby the flame is periodically pinched by a convecting vortex generated by an buoyancy-induced instability, has been examined in previous experimental and computational studies; see for example, Yuan et al [11], Davis et al [12] and Ellzey and Oran [13]. However, these studies have discussed this phenomenon in the context of either nonpremixed or premixed flames, but not with respect to a PPF.…”

Section: Comparison Of 1-g and 0-g Flame Structuresmentioning

confidence: 99%

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Structure of Unsteady Partially Premixed Flames and the Existence of State Relationships

Aggarwal

2009

International Journal of Spray and Combustion Dynamics

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In this study, we examine the structure and existence of state relationships in unsteady partially premixed flames (PPFs) subjected to buoyancy-induced and external perturbations. A detailed numerical model is employed to simulate the steady and unsteady two-dimensional PPFs established using a slot burner under normal and zero-gravity conditions. The coflow velocity is parametrically varied. The methane-air chemistry is modeled using a fairly detailed mechanism that contains 81 elementary reactions and 24 species. Validation of the computational model is provided through comparisons of predictions with nonintrusive measurements. The combustion proceeds in two reaction zones, one a rich premixed zone and the other a nonpremixed zone. These reaction zones are spatially separated, but involve strong interactions between them due to thermochemistry and scalar transport. The fuel is mostly consumed in the premixed zone to produce CO and H 2 , which are transported to and consumed in the nonpremixed zone. The nonpremixed zone in turn provides heat and H-atoms to the premixed zone. For the range of conditions investigated, the zero-g partially premixed flames exhibit a stable behavior and a remarkably strong resistance to perturbations. In contrast, the corresponding normal-gravity flames exhibit oscillatory behavior at low coflow velocities but a stable behavior at high coflow velocities, and the behavior can be explained in terms of a global and convective instabilities. The effects of coflow and gravity on the flames are characterized through a parameter V R , defined as the ratio of coflow velocity to jet velocity. For V R ≤ 1 (low coflow velocity regime), the structures of both 0-and 1-g flames are strongly sensitive to changes in V R , while they are only mildly affected by coflow in the high coflow velocity regime (V R > 1). In addition, the spatio-temporal characteristics of the 0-and 1-g flames are markedly different in the first regime, but are essentially similar in the second regime. A more significant difference in the first regime between these flames is the presence of a flow instability that manifests itself through the self-excited oscillations of the 1-g flame and the concomitant flickering of the nonpremixed reaction zone. For V R ≤ 1, as the coflow velocity is increased, the oscillation amplitude decreases and the oscillation frequency increases, both of which are in accord with previous experimental and International journal of spray and combustion dynamics · Volume . 1 · Number . 3 . 2009 -pages 339-364 339 1 email: ska@uic.edu computational results concerning 1-g jet diffusion flames. The modified conserved scalar approach is found to be effective in characterizing the flame structure and developing state relationships for both steady and unsteady partially premixed flames. This is demonstrated by the fact that the temperature as well as the major and minor species profiles follow similar state relationships in terms of the modified mixture fraction for the 0-and 1-g flames, even though ...

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Section: Effect Of Coflow Velocity On Flame Structuresupporting

confidence: 93%

Section: Unsteady Partially Premixed Flamesmentioning

confidence: 99%

Section: Comparison Of 1-g and 0-g Flame Structuresmentioning

confidence: 99%

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Structure of Unsteady Partially Premixed Flames and the Existence of State Relationships

Aggarwal

2009

International Journal of Spray and Combustion Dynamics

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“…Its major visible effect was the flickering instability of the top part of the flame [15,16]. These fluctuations did not seem to have a significant effect on the lower part of the flame.…”

Section: Resultsmentioning

confidence: 97%

Structure of laminar coflow spray flames at different pressures

Russo¹,

Gomez²

2002

Proceedings of the Combustion Institute

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Experiments were conducted on laminar spray diffusion flames of ethanol/argon burning in oxygen at pressures of 1 and 3 atm. The flames were physically characterized by measuring droplet velocities and sizes by phase-Doppler anemometry, and gas temperature by thin-filament pyrometry and thermocouples. The flames exhibited a cold core, where little vaporization occurred, surrounded by a primary diffusion flame enveloping most of the droplet cloud. Their structure was strongly influenced by the Peclet number for heat transfer that, by regulating the heat penetrating into the core, and, consequently, the growth of the thermal boundary layer, affected the droplet vaporization history. At pressures above the atmospheric, because of density effects on thermal diffusivity, the boundary layer growth above the burner was reduced and so was the vaporization region. Complete evaporation of the droplets before they reached the primary diffusion flame was ensured if a suitably defined Damkö hler number of evaporation, Da v , was smaller than 1. Conversely, if Da v Ͼ 1, droplets penetrated the flame, ignited by a flame transfer process that was captured photographically, and burned isolated on the oxidizer side. These conditions of internal or partial group combustion prevailed in the lower part of the flame. Farther up in the flame, this combustion regime progressively shifted toward that of external group combustion, with fewer and fewer direct droplet/flame interactions.

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“…The equations have been discretized in a staggered mesh using an explicit quadratic Leith-type of temporal discretization [21]. The solution proceeds in three steps.…”

Section: Numerical Detailsmentioning

confidence: 99%

Identification of local extinction topology in axisymmetric bluff-body diffusion flames with a reactedness-mixture fraction presumed probability density function model

Koutmos

Marazioti

2001

Int. J. Numer. Meth. Fluids

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Preliminary results of a numerical-experimental study of the dynamic structure of a buoyant jet diffusion flame

Cited by 100 publications

References 8 publications

Structure of Unsteady Partially Premixed Flames and the Existence of State Relationships

Structure of Unsteady Partially Premixed Flames and the Existence of State Relationships

Structure of laminar coflow spray flames at different pressures

Identification of local extinction topology in axisymmetric bluff-body diffusion flames with a reactedness-mixture fraction presumed probability density function model

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