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Journal ArticleDOI

Experimental study of upward flame spread over discrete thin fuels

01 Dec 2019-Fire Safety Journal (Elsevier)-Vol. 110, pp 102907
TL;DR: In this article, an array of 10 1.5 cm-long 5 cm-wide filter papers is uniformly distributed on a vertical sample holder subjected to double-sided burn, and the distance between the samples was varied from 0 to 4 cm.
About: This article is published in Fire Safety Journal.The article was published on 2019-12-01. It has received 18 citations till now. The article focuses on the topics: Flame spread.
Citations
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Journal ArticleDOI
01 Apr 2021-Fuel
TL;DR: In this paper, the combined effect of inclination angle and array fuel bed width on flame spread over discrete fuel arrays was investigated. But, the authors did not consider the effect of the angle of inclination on the upward flame spread.

18 citations

Journal ArticleDOI
TL;DR: In this paper, a group of birch rods with different lengths (denoted by l within 60-100mm) and spacings (S, 1-9mm) were analyzed experimentally and theoretically.

17 citations

Journal ArticleDOI
TL;DR: In this paper, the authors performed microgravity experiments to study concurrent-flow flame spread over an array of thin cellulose-based fuel samples, using NASA Glenn Research Center's 5.18-s drop tower.

11 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the upward flame spread over a homogenous PMMA plate and an array of discrete thermally thin PMMA elements, and the experimental results showed that the flame spread rate peaks in the case of discrete PMMA element with a fuel coverage around 80% rather than 100% (the homogenous case).
Abstract: Experiments and theoretical analysis were conducted to investigate the upward flame spread over a homogenous PMMA plate and an array of discrete thermally thin PMMA elements. In the experiment, a digital video camera was used to record the flame spread process. An electronic balance and thermocouples were adopted to monitor the mass loss and pyrolysis front position, respectively, as a function of time. In the theoretical analysis, the mass loss rate of PMMA was correlated to the heat transfer during flame spread. The experimental results show that the flame spread rate peaks in the case of discrete PMMA elements with a fuel coverage around 80% rather than 100% (the homogenous case) because the gap with an appropriate spacing between neighboring elements accelerates the flame spread. However, the flame cannot spread over an array of discrete fuels at a coverage of 50% or smaller where the gap is too large to allow effective heat transfer required for flame spread. A smaller coverage of PMMA results in a larger mass loss rate per area since the gaps between elements can entrain more air to promote the burning. A logarithmic relation, that can well describe the mass loss rate as a function of PMMA coverage, was proposed based on the theoretical analysis and the fitting of experimental measurements.

11 citations

Journal ArticleDOI
TL;DR: In this article, a stagnation point flow model based on the mass transfer B-number was adapted to approximate the heat flux and time to ignition of dowel arrays subject to forced convection flame spread.

10 citations

References
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Journal ArticleDOI
01 Jan 2013
TL;DR: In this article, a thermally thick slab of polymethyl methacrylate was used to study the effects of the inclination angle of a fuel surface on upward flame spread and the influence of buoyancy-induced flows in modifying heat-flux profiles ahead of the flame front, which controlled flame spread, and in affecting the heat flux to the burning surface of the fuel.
Abstract: A thermally thick slab of polymethyl methacrylate was used to study the effects of the inclination angle of a fuel surface on upward flame spread. While investigation of upward spread over solid fuels has typically been restricted to an upright orientation, inclination of the fuel surface from the vertical is a common occurrence that has not yet been adequately addressed. By performing experiments on 10 cm wide by 20 cm tall fuel samples it was found that the maximum flame-spread rate, occurring nearly in a vertical configuration, does not correspond to the maximum fuel mass-loss rate, which occurs closer to a horizontal configuration. A detailed study of both flame spread and steady burning at different angles of inclination revealed the influence of buoyancy-induced flows in modifying heat-flux profiles ahead of the flame front, which control flame spread, and in affecting the heat flux to the burning surface of the fuel, which controls fuel mass-loss rates.

123 citations

Journal ArticleDOI
01 Jan 1973
TL;DR: In this paper, a two-dimensional upward flame spread over cotton fabrics was found experimentally to be an accelerating process that acquires a turbulent character after a brief laminar period.
Abstract: Two-dimensional upward flame spread over cotton fabrics was found experimentally to be an accelerating process that acquires a turbulent character after a brief laminar period. With the fabric inclined with respect to the vertical, the heat transfer from the bottom flame was found to control the spread rate. Mass-burning rate m ˙ b ″ , and mass-heating rate m ˙ f ″ had constant values of 19.6 and 57.9 g/m2s, respectively, independent of angle of inclination, relative humidity, and fabric mass per unit area. The transport processes that control upward flame spread were simulated in a steady-stategas-burner experiment that permitted measurement of mass- and heat-transfer rates for various burner orientations. In agreement with the fabric-burning experiments, a semiempirical analysis, based on the gas-burner data, showed that the accelerating spread rate asymptotically attains a steady state that normally cannot be reached, however, with practical dimensions of the test fabric. The asymptotic spread rates computed from the experiments depended strongly on angle of inclination and moderately on ambient relative humidity, varying between 0.20 and 0.45 m/s.

91 citations

Journal ArticleDOI
TL;DR: In this article, experiments on wind-aided firespread across an array of very small-diameter (1.3-4.4mm), discrete fuel elements were carried out in a specially designed wind tunnel.
Abstract: Laboratory-scale experiments on wind-aided firespread across an array of very-small-diameter (1.3-4.4-mm), discrete fuel elements were carried out in a specially designed wind tunnel. The rate of firespread, ty, is inferred from the output of streamwise-disiributed, near-bed-surface thermocouples. The fuel consists of an array of identical, regularly arranged, wooden, toothpick-like Tuel elements, positioned upright in shallow holes drilled in a ceramic substrate. Adoption of this well-defined fuel bed facilitates repetition. Extensive testing suggests that νy ∼ (U/m)1/2 over a wide range of the uniform ambient wind speed U and the fuel-mass distribution m (fuel, per unit planform area of the bed, consumed with firefront passage). The effects on the firespread rate of other parameters investigated and reported include the type of wood species; fuel-element length; fuel-element diameter; fuel-bed width, including streamwise-varyjng width; enhanced moisture content of the substratum and/or fuel; sm...

88 citations

Journal ArticleDOI
TL;DR: In this article, a set of laboratory burn experiments in artificial fuel beds where gap structure, depth, and slope were controlled were conducted to investigate threshold spread behaviors, and the results revealed that fire spread was limited by gap distance and that the threshold distance for spread was increased for deeper fuel beds and steeper slopes.
Abstract: Many fuel beds, especially live vegetation canopies (conifer forests, shrub fields, bunch-grasses) contain gaps between vegetation clumps. Fires burning in these fuel types often display thresholds for spread that are observed to depend on environmental factors like wind, slope, and fuel moisture content. To investigate threshold spread behaviours, we conducted a set of laboratory burn experiments in artificial fuel beds where gap structure, depth, and slope were controlled. Results revealed that fire spread was limited by gap distance and that the threshold distance for spread was increased for deeper fuel beds and steeper slopes. The reasons for this behaviour were found using a high-speed thermal camera. Flame movements recorded by the camera at 120 Hz suggested fuel particles experience intermittent bathing of non-steady flames before ignition and that fuel particles across the gap ignited only after direct flame contact. The images also showed that the flame profile within the fuel bed expands with height, producing greater horizontal flame displacement in deeper beds. Slope, thus, enhances spread by increasing the effective depth in the uphill direction, which produces wider flames, and thereby increases the potential flame contact. This information suggests that fire spread across discontinuous fuel beds is dependent on the vertical flame profile geometry within the fuel bed and the statistical properties of flame characteristics.

73 citations

Journal ArticleDOI
TL;DR: In this article, experimental observations were presented on flame propagation along uniform, linear, horizontal arrays of vertically oriented matchsticks, and the necessary conditions for flame propagation, linear rates of flame propagation and char angle.
Abstract: Experimental observations are presented on flame propagation along uniform, linear, horizontal arrays of vertically oriented matchsticks Matchstick height and spacing between matchsticks are varied Reported results include necessary conditions for flame propagation, linear rates of flame propagation, and char angle—the angle between the horizontal and a photographically recorded line of incipient char formation on the face of the matchstick array Theoretical explanations for the experimental observations are offered on the basis of a model which employs an ignition temperature and uses previously determined flame shapes for individually burning cellulosic cylinders The remarkably good agreement between theory and experiment supports the contention that convective effects are of primary importance in flame propagation at matchstick size scales

62 citations