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•DOI•

Effects of finite sample width on transition and flame spread in microgravity

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W.E. Mell¹, T. Kashiwagi²•Institutions (2)

University of Utah¹, National Institute of Standards and Technology²

01 Jan 2000

TL;DR: In this paper, three-dimensional and two-dimensional simulations of flame spread were performed on a thermally thin cellulosic sample, where the sample was bounded by an inert sample holder.

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Abstract: In most microgravity studies of flame spread, the flame is assumed to be two-dimensional, and twodimensional models are used to aid data interpretation. However, since limited space is available in microgravity facilities, the flames are limited in size. It is important, therefore, to investigate the significance of three-dimensional effects. Three-dimensional and two-dimensional simulations of ignition and subsequent transition to flame spread were performed on a thermally thin cellulosic sample. Ignition occurred by applying a radiant heat flux in a strip across the center of the sample. The sample was bounded by an inert sample holder. Heat loss effects at the interface of the sample and the sample holder were tested by varying the thermal-physical properties of the sample holder. Simulations were also conducted with samples of different widths and with different ambient wind speeds (i.e., different levels of oxygen supply). The width of the sample affected both the duration of the flame transition period and the post-transition flame spread rate. Finite width effects were most significant when the ambient wind was relatively small (limited oxygen supply). In such environments, the velocity due to thermal expansion reduced the net inflow of oxygen enough to significantly affect flame behavior. For a given sample width, the influence of thermal expansion on the net incoming oxygen supply decreased as the ambient wind speed increased. Thus, both the transition and flame spread behavior of the three-dimensional flame (along the centerline) tended to that of the two-dimensional flame with increasing ambient wind speed. Heat losses to the sample holder were found to affect the flame spread rate in the case of the narrowest sample with the slowest ambient wind.

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26 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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Journal Article•DOI•

Flame Spread Over Thin Solid Fuels

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P. J. Pagni¹•Institutions (1)

University of California, Berkeley¹

01 Feb 1975-Journal of Heat Transfer-transactions of The Asme

15 citations

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

...…flame lengths are shorter due to strong convective transport of heat and mass. Effect of Opposed Free-Stream Velocity The effect of free-stream velocity in the direction of opposing flame spread has been studied extensively both experimentally (Olson and Miller, 2009) and numerically (Kumar, 2004)....
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...The effect of free-stream velocity in the direction of opposing flame spread has been studied extensively both experimentally (Olson and Miller, 2009) and numerically (Kumar, 2004)....
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...In normal-gravity environments the flame is characterized by large induced buoyant velocity (Kumar, 2004)....
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