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Theoretical and numerical analysis of oscillating diffusion flames

Published on Nov 1, 2016in Combustion and Flame4.12
· DOI :10.1016/j.combustflame.2016.08.023
Milan Miklavčič13
Estimated H-index: 13
(MSU: Michigan State University),
Indrek S. Wichman22
Estimated H-index: 22
(MSU: Michigan State University)
Source
Abstract
Abstract A novel method is presented for solving the forced transient diffusion flame in the exit region of a coflow burner. Streamwise diffusion is eliminated, which produces the Burke–Schumann model. A mathematical transformation renders the transient, forced convection problem equivalent to a steady-state convection problem. The transformation differs from previous approaches because its use does not require a priori restriction to small perturbations. For this reason, flow fluctuations that are large fractions of the initial flow field may be described exactly and features of nonlinear response can be examined without recourse to detailed numerical simulation. The method is applied to study flame evolution and oscillation for two physically separated coflow slot burner flames as they merge.
  • References (16)
  • Citations (3)
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References16
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A plane fuel jet bifurcated into two streams of jets by a V-shaped bluff-body burner with co-flowing air streams was studied. The flame behavior, length, and temperature distributions of the bifurcated jets were experimentally examined. Flame behavior was characterized by flame visualization and instantaneous photograph. The flame length characteristics was obtained by using the long-exposure flame images. The temperatures distributions were measured by using a finewire thermocouple. Three chara...
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Experiments to determine the limiting distances for flame merging of multiple pool fires are presented. As model substances n-heptane and di-tert-butyl peroxide are used. Laboratory scale tests with a diameter d = 6 cm and relative distances between the pools of 0.08 ≤ D/d ≤ 4 are described and complemented with field experiments with a diameter d = 1.5 m and relative distances between the pools of 0.17 ≤ D/d ≤ 1. Three regions for flame merging are observed and limiting distances are determined...
8 Citations
#1Nicholas Magina (Georgia Institute of Technology)H-Index: 4
#2Dong-Hyuk Shin (Georgia Institute of Technology)H-Index: 11
Last. Tim Lieuwen (Georgia Institute of Technology)H-Index: 42
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This paper describes the dynamics of non-premixed flames responding to bulk velocity fluctuations, and compares the dynamics of the flame sheet position and spatially integrated heat release to that of a premixed flame. The space–time dynamics of the non-premixed flame sheet in the fast chemistry limit is described by the stoichiometric mixture fraction surface, extracted from the solution of the -equation. This procedure has some analogies to premixed flames, where the premixed flame sheet loca...
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#2H. SantoshH-Index: 2
Last. Tim LieuwenH-Index: 42
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�c and � � s ,forcurvatureand hydrodynamic strain, respectively. Unsteady curvature effects on the flame surface area become significant when j� � c jSt 2 2 � O� 1� and are responsible for the experimentally observed reduction in the flame front wrinkle size in the flow direction [referred to as “filtering” by Bourehla and Baillot (Bourehla, A., and Baillot, F., “Appearance and Stability of a Laminar Conical Premixed Flame Subjected to an Acoustic Perturbation,” Combustion and Flame,
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Flame shape is an important observed characteristic of flames that can be used to scale flame properties such as heat release rates and radiation. Flame shape is affected by fuel type, oxygen levels in the oxidiser, inverse burning and gravity. The objective of this study is to understand the effect of high oxygen concentrations, inverse burning, and gravity on the predictions of flame shapes. Flame shapes are obtained from recent analytical models and compared with experimental data for a numbe...
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Abstract The heat release response of a two-dimensional (2-D) co-flow diffusion flame is theoretically investigated for the mass fraction fluctuations of reactant concentration at the inlet boundary and for time-varying spatially uniform flow velocity field in the domain. The present work is an extension of the Burke–Schumann steady flame model to an oscillatory situation, but in a 2-D framework. The governing equation of the problem is the scalar advection equation for the Schwab–Zel'dovich var...
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Abstract The unsteady characteristics of oscillating methane diffusion flames in coflowing air diluted with CO 2 in earth gravity have been studied experimentally and computationally. The measured frequency of flame flickering due to buoyancy-driven large-scale vortices was bi-modal; it jumped from ≈11 Hz to ≈15 Hz with an increase in the air velocity (at ≈11 cm/s). As CO 2 was added into coflowing air gradually, the base (edge) of the flame detached from the burner rim, oscillated at half the f...
33 CitationsSource
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#2Richard I. Masel (UIUC: University of Illinois at Urbana–Champaign)H-Index: 46
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Abstract We examine the cellular instabilities of laminar non-premixed diffusion flames that arise in a polycrystalline alumina microburner with a channel wall gap of dimension 0.75 mm. Changes in the flame structure are observed as a function of the fuel type (H 2 , CH 4 , and C 3 H 8 ) and diluent. The oxidizer is O 2 /inert. In contrast to previous observations on laminar diffusion flame instabilities, the current instabilities occur in the direction of flow above the splitter plate, and only...
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Experimental study was carried out to understand the flame merging behavior from multiple fire sources placed in 2 arrays consisted of three separate fire sources within each array (2 by 3 configuration) without external winds. The sand burner with a diameter of 0.2m was used as an unit burner and LPG was employed as a fuel. The distances between two arrays, Sy, and between fire sources separated, Sx, in each array were changed systematically to characterize the flame height and merging behavior...
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Characteristics of lifted flames in laminar axisymmetric jets of propane with coflowing air have been investigated experimentally. Approximate solutions for velocity and concentration accounting virtual origins have been proposed for coflow jets to analyze the behavior of liftoff height. From the measurement of Rayleigh scattering to probe the concentration field of propane, the validity of the approximate solutions was substantiated. From the images of OH PLIF and CH chemiluminescence and the R...
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Abstract This paper reports simulation results of oscillatory cool flame burning of an isolated, submillimeter sized n-heptane (n-C7H16) droplet in a selectively ozone (O3) seeded nitrogen-oxygen (N2-O2) environments at atmospheric pressure. An evolutionary one-dimensional droplet combustion code encompassing relevant physics and detailed chemistry was employed to explore the roles of low-temperature chemistry, O3 seeding, and dynamic flame structure on burning behaviors. For XO2= 21% and a rang...
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Abstract This paper reviews current understanding of the manner in which non-premixed jet flames respond to flow disturbances, and compares these characteristics to premixed flames. Disturbances in flow velocity excite wrinkles on non-premixed flame sheets and perturbations in heat release. These disturbances convect axially along the flame at the local flow velocity and decay in amplitude. Sufficiently large disturbance amplitudes cause opposing sides of the flame to merge and pinch off, leadin...
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#1Milan Miklavčič (MSU: Michigan State University)H-Index: 13
#2Indrek S. Wichman (MSU: Michigan State University)H-Index: 22
ABSTRACTA method for mathematically solving the oscillatory infinite reaction rate diffusion flame is extended to the case where the oscillating convective coflow is either inside of, or adjacent to, a viscous vortex. The neglect of streamwise diffusion coupled with the restriction to infinite rate chemistry produces a Burke-Schumann boundary layer flame. The mathematical transformation, which does not require a priori restriction to small coflow oscillations, renders the transient oscillatory p...
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