Regime and morphology of polyhedral bunsen flames

Weng, Yue; Potnis, Aditya; Saha, Abhishek

doi:10.1016/j.combustflame.2022.112585

Cited by 4 publications

(2 citation statements)

References 46 publications

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“…This behavior is consistent with physical intuition derived from the classical dispersion relation for free flat flames, where the destabilizing role of differential diffusion at small scales makes the critical wavenumber relatively large for Le < 1 [5,12]. Unlike the qualitative wavenumber scalings that follow from the analytic dispersion relation for a flat flame (for example, see the recent analysis of Weng et al [22,Fig. 5a]), however, the present model enables quantitative predictions of which azimuthal wavenumbers may be unstable for a conical flame associated with a given set of parameters.…”

Section: Polyhedral Flamessupporting

confidence: 87%

“…Polyhedral Bunsen flames were first reported by Smithells and Ingle [16] in rich benzene, pentane, and hexane mixtures and subsequently described and analyzed in progressively greater detail in a variety of experimental circumstances featuring sub-unity Lewis numbers [17,18,19,20,21,22]. Unlike free flat or spherical flames, Bunsen flames experience significant heat losses to the burner and are strained by local velocity gradients that induce negative stretch (compression) near the flame tip and positive stretch near the flame foot.…”

Section: Introductionmentioning

confidence: 99%

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Flash-back, blow-off, and symmetry breaking of premixed conical flames

Douglas,

Polifke,

Lesshafft

2023

Combustion and Flame

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Section: Polyhedral Flamessupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Flash-back, blow-off, and symmetry breaking of premixed conical flames

Douglas,

Polifke,

Lesshafft

2023

Combustion and Flame

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Structures of Laminar Lean Premixed H2/CH4/Air Polyhedral Flames: Effects of Flow Velocity, H2 Content and Equivalence Ratio

Shi,

Breicher,

Schultheis

et al. 2024

Flow Turbulence Combust

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Polyhedral Bunsen flames, induced by hydrodynamic and thermo-diffusive instabilities, are characterized by periodic trough and cusp cellular structures along the conical flame front. In this study, the effects of flow velocity, hydrogen content, and equivalence ratio on the internal cellular structure of premixed fuel-lean hydrogen/methane/air polyhedral flames are experimentally investigated. A high-spatial-resolution one-dimensional Raman/Rayleigh scattering system is employed to measure the internal scalar structures of polyhedral flames in troughs and cusps. Planar laser-induced fluorescence of hydroxyl radicals and chemiluminescence imaging measurements are used to quantify the flame front morphology. In the experiments, stationary polyhedral flames with varying flow velocities from 1.65 to 2.50 m/s, hydrogen contents from 50 to 83%, and equivalence ratios from 0.53 to 0.64 are selected and measured. The results indicate that the positively curved troughs exhibit significantly higher hydrogen mole fractions and local equivalence ratios compared to the negatively curved cusps, due to the respective focusing/defocusing effect of trough/cusp structure on highly diffusive hydrogen. The hydrogen mole fraction and local equivalence ratio differences between troughs and cusps are first increased and then decreased with increasing measurement height from 5 to 13 mm, due to the three-dimensional effect of the flame front. With increasing flow velocity from 1.65 to 2.50 m/s, the hydrogen mole fraction and local equivalence ratio differences between troughs and cusps decrease, which is attributed to the overall decreasing curvatures in troughs and cusps due to the decreased residence time and increased velocity-induced strain. With increasing hydrogen content from 50 to 83%, the hydrogen mole fraction and local equivalence ratio differences between troughs and cusps are amplified, due to the enhanced effects of the flame front curvature and the differential diffusion of hydrogen. With increasing equivalence ratio from 0.53 to 0.64, a clear increasing trend in hydrogen mole fraction and equivalence ratio differences between troughs and cusps is observed at constant flow velocity condition, which is a trade-off result between increasing effective Lewis number and increasing curvatures in troughs and cusps.

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Assessing Local Statistics of a Premixed Turbulent Bunsen Flame

Weng,

Potnis,

Unni

et al. 2024

AIAA Journal

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The local interactions between the flame-front and turbulence control the dynamics, morphology, and propagation of a premixed turbulent flame. To investigate such complex dynamics of a flame–turbulence interaction, we present an experimental exposition of a premixed turbulent Bunsen flame. Several quantities have been evaluated to assess the flame–turbulence interaction. We first measured the statistics of the flowfield adjacent to the flame and compared it with the cold flow. This allowed us to evaluate the effect of the flame on the upstream turbulence. Subsequently, we performed statistical analyses of the local values of various stretch rates and quantified how their distribution changes with turbulence intensity and flame temperature. We also evaluated the pairwise relation among various stretch rates to assess their dependence on each other. Finally, we used flame particles to evaluate the Lagrangian evolution of stretch rates conditioned on flame-fronts. All the analyses presented in this work point out Karlovitz number as a key factor in determining the flame–turbulence interaction. Specifically, we observe a stronger influence of turbulent eddies on flames with increasing Karlovitz number, as evidenced by the reduced effect of flame on upstream flow, wider probability distribution functions of stretch rates, and increased persistence timescales for stretches.

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Regime and morphology of polyhedral bunsen flames

Cited by 4 publications

References 46 publications

Flash-back, blow-off, and symmetry breaking of premixed conical flames

Flash-back, blow-off, and symmetry breaking of premixed conical flames

Structures of Laminar Lean Premixed H2/CH4/Air Polyhedral Flames: Effects of Flow Velocity, H2 Content and Equivalence Ratio

Assessing Local Statistics of a Premixed Turbulent Bunsen Flame

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