Concurrent flame spread over discrete thin fuels
TL;DR: In this article, an unsteady two-dimensional numerical model was used to simulate concurrent flame spread over paper-like thin solid fuels of discrete configurations in microgravity (0,g with 20,cm/s) and in normal gravity (1,g).
About: This article is published in Combustion and Flame.The article was published on 2018-05-01. It has received 25 citations till now. The article focuses on the topics: Flame spread & Solid 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.
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.
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.
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.
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.
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...
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.
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
TL;DR: In this paper, the authors analyzed the upward flame spread over discrete fuels through experiments on vertical arrays of alternating lengths of PMMA and inert insulation board, and found that the fuel coverage was below unity, which indicates that a homogeneous fuel bed approximation is unsuitable for arrays with low fuel coverage.
TL;DR: In this article, the upward flame spread experiments were conducted on long thin composite fabric fuels made of 75% cotton and 25% fiberglass of various widths between 2 and 8.8 cm and lengths greater than 1.5 cm.