A computational approach to flame hole dynamics using an embedded manifold approach

Knaus, Robert; Pantano, Carlos

doi:10.1016/j.jcp.2015.04.037

Cited by 4 publications

(3 citation statements)

References 71 publications

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“…Edge flames have also been studied in other contexts, such as weakly curved premixed flames in stratified mixtures [4][5][6][7] and in strained mixing layers in premixed [8][9][10][11] and nonpremixed [12,13] systems, and have been addressed in a number of model problems [14][15][16]. They are also relevant to studies of turbulent diffusion flames acting as an agent for reestablishing combustion in a hole formed on the flame surface [17]. Although they share some common features with edge flames examined in the present article, the mathematical problems are fundamentally different.…”

Section: Introductionmentioning

confidence: 99%

Anchored and Lifted Diffusion Flames Supported by Symmetric and Asymmetric Edge Flames

Matalon

2023

Symmetry

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Numerous combustion applications are concerned with the stabilization of diffusion flames formed by injecting gaseous fuels into a co-flowing stream containing an oxidizer. The smooth operation of these devices depends on the attachment and lift-off characteristics of the edge flame at the base of the diffusion flame. In this paper, we address fundamental issues pertinent to the structure and dynamics of edge flames, which have attributes of both premixed and diffusion flames. The adopted configuration is the mixing layer established in the wake of a splitter plate where two streams, one containing fuel and the other oxidizer, merge. The analysis employs a diffusive-thermal model which, although it excludes effects of gas expansion, systematically includes the influences of the overall flow rate, unequal strain rates in the incoming streams, stoichiometry, differential and preferential diffusion, heat loss and gas–solid thermal interaction, and their effect on the edge structure, speed, and temperature. Conditions when the edge flame is anchored to the plate, lifted-off and stabilized in the flow, or blown-off, are identified. Two stable modes of stabilization are observed for lifted flames; the edge flame either remains stationary at a specified location or undergoes spontaneous oscillations along a direction that coincides with the trailing diffusion flame.

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Section: Introductionmentioning

confidence: 99%

Anchored and Lifted Diffusion Flames Supported by Symmetric and Asymmetric Edge Flames

Matalon

2023

Symmetry

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“…Moreover, edge-flames are an important aspect of premixed flame stabilization in shear layers [4]. Additionally, edge-flame libraries could potentially extend flamelet models of turbulent combustion, which assume unbroken flame surfaces, to conditions involving local quenching [5].…”

Section: Introductionmentioning

confidence: 99%

Propagation and extinction of premixed edge-flames

Clayton

Suk

Ronney

2019

Proceedings of the Combustion Institute

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The propagation rates (Uedge) of edge-flames in premixed hydrocarbon-oxygen-inert mixtures were measured as a function of global strain rate (σ), mixture strength, and (by changing fuel and inert type) Lewis number (Le). Using a counterflow slot-jet burner with electrical heaters at both ends to anchor the flame edges, both advancing (positive Uedge) and retreating (negative Uedge) edge-flames were characterized. Results are presented for both twin (premixed gas against premixed gas) and single (premixed gas against cold inert gas) edge-flames in terms of the effects of a non-dimensional strain rate (e) and non-dimensional heat loss (k) on a scaled propagation rate. Uedge showed a strong dependence on Le and flames images show that high (low) Le lead to weaker (stronger) edge-flame burning intensity. Uedge for single edge-flames scaled with the square root of the unburned to burned gas density ratio in a manner similar to nonpremixed flames whereas for premixed flames Uedge scaled linearly with density ratio. Edge-flames exhibited two extinction limits corresponding to a high-σ strain induced limit and a low-σ heat loss induced limit; a simple description of the low-σ limits was proposed and found to correlate well with experiments in twin-premixed, single-premixed, and nonpremixed edge-flames over more than a two-decade range of k. Results are in good qualitative and reasonable quantitative agreement with simple theories except that retreating twin edge-flames in high-Le mixtures are predicted theoretically but were not observed experimentally.

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“…Local extinction has been also a topic of numerical studies. A number of studies reported the importance of the scalar dissipation rate on the local extinction [10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Local extinction and reignition mechanism in a turbulent lifted flame: A direct numerical simulation study

Karami

Talei

Hawkes

et al. 2017

Proceedings of the Combustion Institute

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Local extinction and reignition is studied in a direct numerical simulation (DNS) dataset of a turbulent lifted flame [1]. Extinction holes are identified as regions on the stoichiometric surface which have a product mass fraction less than a critical value. Using this criterion, thirty individual holes are identified and tracked in time. It is observed that large outwardly pushing structures caused compressive strain rates normal to the mixture-fraction iso-surface. These high strain rates caused high dissipation rates and the initiation of the extinction process, leading to the initial creation of holes. Extinction, i.e. hole growth, then occurs in two phases. In the first phase, the edge-propagation velocity is initially negative and the fluid dynamic tangential strain rate on the hole surface is positive, leading to rapid hole growth. Subsequently, in the second phase, local compressive strain rates at the flame edge relax, and the edge-flame propagation velocity switches to positive. However, in this second phase, the hole continues to expand because of positive tangential strain rate on the hole's surface, which dominates over the healing effect of positive edge-flame propagation velocities. When reignition starts, the edge-propagation velocity is mainly affected by the product-mass fraction displacement speed and shows a dependency on curvature and scalar dissipation rate, similar to what is expected in edge-flame propagation. An analysis of thermal diffusion on the unburned portion of the mixture-fraction iso-surface shows that the edge-flame propagation mechanism dominates turbulent engulfment during reignition in this study. AbstractLocal extinction and reignition is studied in a direct numerical simulation (DNS) dataset of a turbulent lifted flame [1]. Extinction holes are identified as regions on the stoichiometric surface which have a product mass fraction less than a critical value.Using this criterion, thirty individual holes are identified and tracked in time. It is observed that large outwardly pushing structures caused compressive strain rates normal to the mixture-fraction iso-surface. These high strain rates caused high dissi-* pation rate, similar to what is expected in edge-flame propagation. An analysis of thermal diffusion on the unburned portion of the mixture-fraction iso-surface shows that the edge-flame propagation mechanism dominates turbulent engulfment during reignition in this study.

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A computational approach to flame hole dynamics using an embedded manifold approach

Cited by 4 publications

References 71 publications

Anchored and Lifted Diffusion Flames Supported by Symmetric and Asymmetric Edge Flames

Anchored and Lifted Diffusion Flames Supported by Symmetric and Asymmetric Edge Flames

Propagation and extinction of premixed edge-flames

Local extinction and reignition mechanism in a turbulent lifted flame: A direct numerical simulation study

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