A Computational Study on Opposed Flow Flame Spread Over Thin Solid Fuels with Side-Edge Burning

doi:10.1080/00102201003694842

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A Computational Study on Opposed Flow Flame Spread Over Thin Solid Fuels with Side-Edge Burning

Journal Article•DOI•

A Computational Study on Opposed Flow Flame Spread Over Thin Solid Fuels with Side-Edge Burning

Chenthil Kumar¹, Amit Kumar¹•Institutions (1)

Indian Institute of Technology Madras¹

18 Aug 2010-Combustion Science and Technology (Taylor & Francis Group)-Vol. 182, Iss: 9, pp 1321-1340

TL;DR: In this article, a steady-state flame spread model has been used to study the effect of side-edge burning on flame spread over thin solid fuel strips of finite width, and simulations have been carried out for fuel strips with both inhibited (by metallic strips) and uninhibited side edges.

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Abstract: A steady-state flame spread model has been used to study the effect of side-edge burning on flame spread over thin solid fuel strips of finite width. Simulations have been carried out for fuel strips with both inhibited (by metallic strips) and uninhibited side edges. The effect inhibition on both normal- and microgravity flame spread along with several intermediate gravity levels has been investigated. Such a study is important for understanding the physiochemical processes controlling the flame spread in low gravity where human experience is limited. Although simulations have shown an overall increase in spread rate for uninhibited cases for both normal- and microgravity flames, some effects such as flame spread variation with external imposed velocity and flame extinction limits show different behavior for microgravity and normal gravity flames. The heat and mass transport processes in the flame have been discussed in detail to explain the observed trends.

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Journal Article•DOI•

Solid combustion research in microgravity as a basis of fire safety in space

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Osamu Fujita¹•Institutions (1)

Hokkaido University¹

01 Jan 2015

TL;DR: In this paper, the authors introduce fire safety standards for flammability evaluation of solid material intended for use in a spacecraft habitat, and the difference between the limiting value in microgravity and the indices given by the standard test methods on the ground is discussed.

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Abstract: This paper introduces fire safety standards for flammability evaluation of solid material intended for use in a spacecraft habitat. Two types of existing standards include material evaluation by pass/fail criteria corresponding to Test 1 of NASA STD 6001B and evaluation by a flammability index such as maximum oxygen concentration (MOC) corresponding to the improved Test 1. The advantage of the latter is the wide applicability of the MOC index to different atmospheres in spacecraft. Additionally, the limiting oxygen index (LOI) method is introduced as a potential alternative index for the evaluation using the improved Test 1 method. When criteria based on an index such as MOC or LOI are applied for material screening, the discrepancy of the index to the actual flammability limit in microgravity such as minimum limiting oxygen concentration (MLOC) is essential information for guaranteeing fire safety in space because material flammability can be higher in microgravity. In this paper, the existing research on the effects of significant parameters on material flammability in microgravity are introduced, and the difference between the limiting value in microgravity and the indices given by the standard test methods on the ground is discussed. Finally, on-going efforts to develop estimation methods of material flammability in microgravity according to normal gravity tests are summarized.

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74 citations

Journal Article•DOI•

Experimental Study of the Effects of Side-Edge Burning in the Downward Flame Spread of Thin Solid Fuels

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Bruna Comas, Toni Pujol

13 Mar 2012-Combustion Science and Technology

TL;DR: In this paper, a comparison between the downward flame spread rate for thermally thin samples with one or two inhibited edges is done in multiple situations, and the effects of atmospheric composition as well as the width and thickness of a cellulosic-type fuel are tested experimentally.

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Abstract: A comparison between the downward flame spread rate for thermally thin samples with one or two inhibited edges is done in multiple situations. The effects of atmospheric composition as well as the width and thickness of a cellulosic-type fuel are tested experimentally. We have found that the normal velocity to the inclined flame front in a side-edge burning is very similar to the downward flame front speed when the sample is inhibited by both edges. Also, the effect of locating a sidewall close to the free edge of the sample is investigated. All these results may be important in order to validate or refute possible models of downward flame spread that take into account side effects.

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27 citations

Cites background or methods or result from "A Computational Study on Opposed Fl..."

...Although the above data may suggest that the extinction limit for the one inhibited edge case occurs at lower XO2, Kumar and Kumar (2010) found that by doing simulations with and without side-burning, the extinction point is at XO2¼ 20% for the inhibited case and XO2¼ 20.5% for both uninhibited…...
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...D simulations carried out by Kumar and Kumar (2010) both using cellulosic type fuels with width w¼ 2 cm (see other sample details in Table 1)....
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...D model have recently revealed the importance of lateral oxygen supply for the free-edge burning condition (Kumar and Kumar, 2010)....
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...Although the above data may suggest that the extinction limit for the one inhibited edge case occurs at lower XO2, Kumar and Kumar (2010) found that by doing simulations with and without side-burning, the extinction point is at XO21⁄4 20% for the inhibited case and XO21⁄4 20.5% for both uninhibited sides cases, although the velocity at the extinction point is higher in the uninhibited case. Unfortunately, we have not been able to experimentally confirm such behavior due to experimental difficulties found near the extinction point. In addition, the angle h measured from the vertical side edge to the inclined pyrolysis front was obtained after analyzing the recorded data in the uninhibited cases. These are reported in Figure 5 as a function of the oxygen concentration level XO2 where we also include results obtained from the w1⁄4 2 cm and w1⁄4 6 cm cases. In Figure 5, we also show how our results are consistent with the experimental angles obtained by Vedha-Nayagam et al. (1986) (see Table 1) and the one extracted from the 3-D simulations carried out by Kumar and Kumar (2010) both using cellulosic type fuels with width w1⁄4 2 cm (see other sample details in Table 1)....
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...More recently, Kumar and Kumar (2010) studied the effect of side-edge burning in normal gravity and in microgravity using computational methods with a steady 3-D model....
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Journal Article•DOI•

Downward flame spread over extruded polystyrene: Effects of sample thickness, pressure, and sidewalls

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Weiguang An¹, Weiguang An², Huahua Xiao¹, K.M. Liew², Lin Jiang¹, Weigang Yan¹, Yang Zhou¹, Huang Xinjie³, Jinhua Sun¹, Lijing Gao⁴ - Show less +6 more•Institutions (4)

University of Science and Technology of China¹, City University of Hong Kong², Anhui University of Technology³, Chiba Institute of Science⁴

01 Feb 2015-Journal of Thermal Analysis and Calorimetry

TL;DR: In this article, the effects of sample thickness (d), sidewalls and atmospheric pressure (p) on the flame spread of extruded polystyrene (XPS) are studied.

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Abstract: An experimental study on the characteristics of downward flame spread of extruded polystyrene (XPS) is presented. The parameters investigated include average mass loss rate per unit of thickness ( $$ \dot{m}^{'} $$ ), average flame height (H f), average flame spread rate (v f), and mass growth rate ( $$ \dot{m}_{1} $$ ) of molten XPS. The effects of sample thickness (d), sidewalls and atmospheric pressure (p), and the combined effects of these factors on the flame spread are studied. The larger sample thickness corresponds to larger $$ \dot{m}^{'} $$ and higher flame upon most occasions. As d rises, v f and $$ \dot{m}_{1} $$ increase under all conditions; v f and d follow the equation: $$ {\text{v}}_{\text f} = A ( 1- {\text{exp(}} - {\text{Cd))}} $$ . The dimensionless heat release rate: $$ \dot{Q}^{*} \propto { \exp }( - 0. 3d) $$ . $$ \dot{m}^{'} $$ , v f , and $$ \dot{m}_{1} $$ obtained without sidewalls are higher than those with sidewalls. $$ \dot{m}^{'} $$ , v f, and H f obtained on the plain (p = 100.8 kPa) are larger than those obtained on the plateau (p = 65.5 kPa). $$ \dot{m}_{1} $$ obtained on the plain is lower than that on the plateau. In most cases without sidewalls, $$ \dot{m} \propto p^{{\text n_{0}} } $$ , where 1.9 < n 0 < 2, and $$ H_{\text f} = a + \mu p^{{\text n_{0} }} $$ . H f obtained in the cases without sidewalls is larger than that with sidewalls when the sample thickness is small, while the opposite is true for thicker samples. When sidewalls are absent, on the plain, with a rise in thickness, the increase of v f is significant for thin samples while the variation is not considerable for thick samples; on the plateau, this increase is significant for all thicknesses tested. The experimental results agree well with the theoretical analysis.

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21 citations

Cites result from "A Computational Study on Opposed Fl..."

...The phenomenon confirms the numerical simulation result of Kumar and Kumar [24]....
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...The experimental conclusion verifies the simulation results of Kumar and Kumar [24]....
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Journal Article•DOI•

Experimental study of the channel effect on the flame spread over thin solid fuels

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Bruna Comas, Adria Carmona, Toni Pujol

01 Jan 2015-Fire Safety Journal

TL;DR: In this article, the speed of the flame front when it propagates within a narrow channel (closed cross section), within a channel with lateral walls only and through a free cross section (plain case) was investigated.

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Abstract: We experimentally burn thin solid fuels and obtain the speed of the flame front when it propagates (1) within a narrow channel (closed cross section), (2) within a channel with lateral walls only and (3) through a free cross section (plain case). The latter configuration is the classical one and it has been extensively studied with analytical, numerical and experimental methods by other authors. Our experiments have been carried out at different geometrical configurations and angles of inclination of the sample and also at several values of oxygen molar fraction. All experiments are restricted to purely buoyant flow. Our main results are as follows: (1) sidewalls reduce the flame spread rate in a non-monotonous trend when varying its height; (2) in horizontal flame spread, two simultaneous flame fronts that propagate at different velocities may arise in the channel case at high oxygen levels. The fastest flame front speed may be higher than that obtained in the plain case; (3) in upward flame spread, the channel effect configuration produces the highest flame front speed. We finally analyze the correlation of the downward flame front speed data in terms of the Damkohler number.

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18 citations

Journal Article•DOI•

Numerical study of horizontal flame spread over PMMA surface in still air

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A.I. Karpov¹, Oleg P. Korobeinichev¹, Artem A. Shaklein¹, A. A. Bolkisev¹, Amit Kumar², Andrey G. Shmakov³, Andrey G. Shmakov¹ - Show less +3 more•Institutions (3)

Russian Academy of Sciences¹, Indian Institute of Technology Madras², Novosibirsk State University³

05 Nov 2018-Applied Thermal Engineering

TL;DR: In this paper, a coupled model of heat and mass transfer describing the feedback between gas-phase flame and solid fuel has been defined by non-stationary two-dimensional elliptic equations applied both for gas phase and liquid fuel.

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Abstract: Flame spread over the horizontal surface of polymethyl methacrylate (PMMA) has been studied numerically by a coupled model of heat and mass transfer describing the feedback between gas-phase flame and solid fuel Mathematical formulation has been defined by non-stationary two-dimensional elliptic equations applied both for gas phase and solid fuel The computational procedure is based on modification of the OpenFOAM open-source code Results of predictions have been compared with the data of comprehensive experimental investigation of the thermal and chemical structure of PMMA flame Good agreement has been obtained for the detailed gas-phase and the solid fuel temperature and species concentrations profiles, as well as for the macroscopic parameters: the flame spread rate, the total mass regression rate and the length of the pyrolysis zone Based on the analysis of thermal degradation of methylmethacrylate in inert surrounding, the concept of reduced molar weight for gaseous products of PMMA pyrolysis has been proposed, which provided better agreement for fuel distribution in the gas phase

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17 citations

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Journal Article•

Flame spreading over a thin solid in low-speed concurrent flow- Drop tower experimental results and comparison with theory

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G. D. Grayson¹, Kurt R. Sacksteder², Paul V. Ferkul², James S. T'ien•Institutions (2)

Case Western Reserve University¹, Glenn Research Center²

01 Jul 1994-Microgravity Science and Technology

TL;DR: In this article, a 5.18 s drop tower was used to investigate flame spread over thin paper samples in low-speed concurrent flow and compared with a theoretical model describing concurrent flame spread on thin solids in low speed flows.

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Abstract: Flame spread over thin paper samples in low-speed concurrent flow is experimentally investigated in a 5.18 s drop tower. In the experiment, the oxygen molar percentage is varied from 30% down to the flame extinction limits and the forced flow velocity from 5.29 cm/s down to the quenching limits. Motion pictures are taken to observe flame shape, color, size, and spread rates. These quantities are compared with a theoretical model describing concurrent flame spread over thin solids in low-speed flows. The paper also discusses the similarity and difference between concurrent-flow and opposed-flow flame spread in microgravity and between low-speed and high-speed concurrent-flow flame spread. Finally the limitations of using a drop tower for flame spread research is assessed.

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47 citations

"A Computational Study on Opposed Fl..." refers background in this paper

...The right side of the figures shows the reaction rate contour corresponding to value, 10 4 g=cm3=s, which represents the visible flame (Grayson et al., 1994) and the fuel mass flux vectors....
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...The right side of the figures shows the reaction rate contour corresponding to value, 10 4 g=cm(3)=s, which represents the visible flame (Grayson et al., 1994) and the fuel mass flux vectors....
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Journal Article•DOI•

Buoyant downward diffusion flame spread and extinction in partial-gravity accelerations

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Kurt R. Sacksteder¹, James S. T'ien²•Institutions (2)

Glenn Research Center¹, Case Western Reserve University²

01 Jan 1994

TL;DR: In this paper, the authors describe experimental observations of downward, opposed-flow flame spreading made under partial gravity conditions aboard NASA research aircraft, for effective acceleration levels ranging from 0.05 to 0.6 times normal earth gravity (1 g ).

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Abstract: This paper describes experimental observations of downward, opposed-flow flame spreading made underpartial-gravity conditions aboard NASA research aircraft. Special apparatus and techniques for these tests are described, including schlieren imaging of dim near-limit flames. Flame-spreading and flammability limit behaviors of a thin cellulosic fuel, 1×10 −3 g/cm 2 tested at 1 atm of pressure in oxygen/nitrogen mixtures of 13–21% oxygen by volume, are described for effective acceleration levels ranging from 0.05 to 0.6 times normal earth gravity (1 g ). Downward-burning flammability increases in partial gravity, with the limiting oxygen fraction falling from 15.6% oxygen in 1 g to 13–14% oxygen in 0.05–0.1 g . Flame-spread rates are shown to peak in partial gravity, increasing by 20% over the 1- g value in air (21% oxygen). Partial-gravity flame-spreading results, corrected for fuel density and thickness, are consistent with results obtained at acceleration levels above 1 g in a centrifuge. The results compare qualitatively with predictions of flame spreading in buoyant flow by models that include finite-rate chemical kinetics and surface and gas-phase radiative loss mechanisms. A correlation of experimental buoyant downward flame-spread results is introduced that accounts for radiative heat losses using a dimensionless spread rate, V f o , a radiation/conduction number. S R , and the Damkohler number, Da , as parameters. The correlation includes data from 0.05 g to 4.25 g and oxygen/nitrogen mixtures from 14% to 50% oxygen.

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44 citations

"A Computational Study on Opposed Fl..." refers result in this paper

...This behavior is also consistent with experimental observations (Sacksteder and Tien, 1994) and computations in the previous section....
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...This behavior is consistent with low-gravity experimental observations (Sacksteder and Tien, 1994) and computations in the preceding section....
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The Effect of Microgravity on Flame Spread over a Thin Fuel

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Sandra L. Olson¹•Institutions (1)

Glenn Research Center¹

01 Dec 1987

TL;DR: In this article, a flame spreading over a thermally thin cellulose fuel was studied in a quiescent microgravity environment, and two different extinction limits were found in microgravity for the two thicknesses of fuel.

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Abstract: A flame spreading over a thermally thin cellulose fuel was studied in a quiescent microgravity environment. Flame spread over two different fuel thicknesses was studied in ambient oxygen-nitrogen environments from the limiting oxygen concentration to 100 percent oxygen at 1 atm pressure. Comparative normal-gravity tests were also conducted. Gravity was found to play an important role in the mechanism of flame spread. In lower oxygen environments, the buoyant flow induced in normal gravity was found to accelerate the flame spread rate as compared to the microgravity flame spread rates. It was also found to stabilize the flame in oxidizer environments, where microgravity flames in a quiescent environment extinguish. In oxygen-rich environments, however, it was determined that gravity does not play an important role in the flame spread mechanism. Fuel thickness influences the flame spread rate in both normal gravity and microgravity. The flame spread rate varies inversely with fuel thickness in both normal gravity and in an oxygen-rich microgravity environment. In lower oxygen microgravity environments, however, the inverse relationship breaks down because finite-rate kinetics and heat losses become important. Two different extinction limits were found in microgravity for the two thicknesses of fuel. This is in contrast to the normal-gravity extinction limit, which was found to be independent of fuel thickness. In microgravity the flame is quenched because of excessive thermal losses, whereas in normal gravity the flame is extinguished by blowoff.

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41 citations

"A Computational Study on Opposed Fl..." refers background or result in this paper

...Experimental study on flame spread over thin solid fuels is generally carried over a finite-width fuel strip with the edges inhibited (Hirano and Saito, 1994; Frey and Tien, 1976; Olson 1987b)....
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...In most experiments in opposed=downward flame spread (Frey and Tien, 1976; Hirano and Saito, 1994; Olson, 1987a) over thin fuel, the edges of sample are inhibited either by chemical treatment or by using a metal support strip....
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...This is consistent with the previous studies (Olson, 1987b)....
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Journal Article•DOI•

Fire spread phenomena: the role of observation in experiment

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T. Hirano¹, K. Saito¹•Institutions (1)

University of Kentucky¹

01 Jan 1994-Progress in Energy and Combustion Science

TL;DR: In this article, a review of recent experimental findings of fire spread phenomena is presented, focusing on the importance of observation in experiments, which is the source of imagination and successful modeling.

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Abstract: Summarized are recent experimental findings of fire spread phenomena. This review covers flame spread over solids (including melting solids and metals), large-scale spread through discrete fuels (such as fire brands and fire whirls), and scale modeling techniques applied to flame spread study. Emphasis is placed on the importance of observation in experiments which is the source of imagination and successful modeling.

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38 citations

"A Computational Study on Opposed Fl..." refers background in this paper

...Experimental study on flame spread over thin solid fuels is generally carried over a finite-width fuel strip with the edges inhibited (Hirano and Saito, 1994; Frey and Tien, 1976; Olson 1987b)....
[...]
...In most experiments in opposed=downward flame spread (Frey and Tien, 1976; Hirano and Saito, 1994; Olson, 1987a) over thin fuel, the edges of sample are inhibited either by chemical treatment or by using a metal support strip....
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Journal Article•DOI•

Flame Spread Along Free Edges of Thermally Thin Samples in Microgravity

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William E. Mell¹, Sandra L. Olson², Takashi Kashiwagi³•Institutions (3)

University of Utah¹, Glenn Research Center², National Institute of Standards and Technology³

01 Jan 2000

TL;DR: In this article, the effects of imposed flow velocity on flame spread along open edges of a thermally thin cellulosic sample in microgravity were studied experimentally and theoretically, and the results showed that the upstream and downstream edge flame spread rates were faster than the central flame spread rate for up to 5 cm/s.

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Abstract: The effects of imposed flow velocity on flame spread along open edges of a thermally thin cellulosic sample in microgravity were studied experimentally and theoretically. In this study, the sample was ignited locally at the middle of the 4 cm wide sample, and subsequent flame spread reached both open edges of the sample along the direction of the flow. The following flame behaviors were observed in the experiments and predicted by the numerical calculation, in order of increased imposed flow velocity: (1) ignition but subsequent flame spread was not attained, (2) flame spread upstream (opposed mode) without any downstream flame, and (3) the upstream flame and two separate downstream flames traveled along the two open edges (concurrent mode). Generally, the upstream and downstream edge flame spread rates were faster than the central flame spread rate for an imposed flow velocity of up to 5 cm/s. This was due to greater oxygen supply from the outer free stream to the edge flames and more efficient heat transfer from the edge flames to the sample surface than the central flames. For the upstream edge flame, flame spread rate was nearly independent of, or decreased gradually with, the imposed flow velocity. The spread rate of the downstream edge, however, increased significantly with the imposed flow velocity.

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29 citations

"A Computational Study on Opposed Fl..." refers background or methods in this paper

...In studies by Mell and Kashiwagi (2000a) and Mell et al. (2000b), because both the experiments and simulations were carried out on a small specimen size (4 cm 10 cm) a steady flame spread may not have been achieved....
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...This flame shape for free edge burning sample has been observed in experiments (Creeden and Sibulkin, 1976; Mell and Kashiwagi, 2000a; Mell et al., 2000b; Vedha-Nayagam et al., 1986)....
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...In the recent work of Mell and Kashiwagi (2000a) and Mell et al. (2000b), which comprised both experiment and three-dimensional numerical simulation, the fuel was ignited at the middle of the sample and at sufficient imposed flow velocity the flame grew and subsequently reached the free edges....
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