Opposed flow flame spread over thermally thick solid fuels: buoyant flow suppression, stretch rate theory, and the regressive burning regime

Hossain, Sarzina; Wichman, Indrek S.; Miller, Fletcher; Olson, Sandra L.

doi:10.1016/j.combustflame.2020.05.001

Cited by 17 publications

(2 citation statements)

References 30 publications

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“…At the downstream side of the sample (with respect to the opposed oxidizer inflow), a 28‐gauge Kanthal wire connected to a DC power supply was used to ignite the sample. For improved ignition the trailing edge was machined into a pointed shape, as discussed previously 12,13 and as seen in Figure 2B,C. Each test started with supply air entering the NCA regulated by a mass flow controller.…”

Section: Experiments Description and Image Acquisitionmentioning

confidence: 99%

“…At the downstream side of the sample (with respect to the opposed oxidizer inflow), a 28-gauge Kanthal wire connected to a DC power supply was used to ignite the sample. For improved ignition the trailing edge was machined into a pointed shape, as discussed previously 12,13 and as seen in Figure 2B,C After the samples had cooled to room temperature it was possible to analyze the hardened (frozen) sample bubble distribution, the sample shape and other quantities related to the material response. Procedures related to the bubble distribution are described below.…”

Section: Flame Spread Facility and Testsmentioning

confidence: 99%

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Experimental study of molten bubble layer growth and bubble size distribution in post‐flame‐spread PMMA samples

et al. 2022

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Although thermoplastics possess many desirable traits as solidified materials, they are combustible and burn readily. Post burning samples of polymethylmethacrylate (PMMA) are the focus of this study. During flame spread, PMMA forms a bubble containing molten surface layer that influences the spread rate and the surface mass efflux. This study examines the formation and distribution of bubbles inside a PMMA sample that has previously been subjected to flame spread and then re‐hardened into its solid state. Experiments discussed herein were conducted in a Narrow Channel Apparatus (NCA), which reduces the influences of gravitation (buoyancy) on flame spread. Bubble sizes and counts were determined using digital image analysis (DIA). The burnt samples were analyzed by dividing sample images into eight equal area sections. Frequency distributions of bubble size (area) were compared. Distribution functions were fitted against the empirical probability density function (PDF) for the bubble size distribution. The log‐normal distribution predicts the bubble size distribution for all segments. The bubble distribution function can be used to describe physical processes inside the polymeric material as it undergoes thermal transformation by the spreading flame.

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Section: Experiments Description and Image Acquisitionmentioning

confidence: 99%

Section: Flame Spread Facility and Testsmentioning

confidence: 99%

Experimental study of molten bubble layer growth and bubble size distribution in post‐flame‐spread PMMA samples

et al. 2022

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Flame Spread Transition to Regression of Thick Fuel in Oxygen-Limited Concurrent Flow

et al. 2023

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Effects of Confinement on Opposed-Flow Flame Spread over Cellulose and Polymeric Solids in Microgravity

Sharma,

Li,

Liao

et al. 2024

Microgravity Sci. Technol.

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Opposed-flow flame spread over solid materials has been investigated in the past few decades owing to its importance in fundamental understanding of fires. These studies provided insights on the behavior of opposed-flow flames in different environmental conditions (e.g., flow speed, oxygen concentration). However, the effect of confinement on opposed-flow flames remains under-explored. It is known that confinement plays a critical role in concurrent-flow flame spread in normal and microgravity conditions. Hence, for a complete understanding it becomes important to understand the effects of confinement for opposed-flow flames. In this study, microgravity experiments are conducted aboard the International Space Station (ISS) to investigate opposed-flow flame spread in different confined conditions. Two materials, cotton-fiberglass blended textile fabric (SIBAL) and 1 mm thick polymethyl methacrylate (PMMA) slab are burned between a pair of parallel flow baffles in a small flow duct. By varying the sample-baffle distance, various levels of confinement are achieved (H = 1–2 cm). Three types of baffles, transparent, black, and reflective, are used to create different radiative boundary conditions. The purely forced flow speed is also varied (between 2.6 and 10.5 cm/s) to investigate its interplay with the confinement level. For both sample materials, it is observed that the flame spread rate decreases when the confinement level increases (i.e., when H decreases). In addition, flame spread rate is shown to have a positive correlation with flow speed, up to an optimal value. The results also indicate that the optimal flow speed for flame spread can decrease in highly confined conditions. Surface radiation on the confinement boundary is shown to play a key role. For SIBAL fabric, stronger flames are observed when using black baffles compared to transparent. For PMMA, reflective baffles yield stronger flames compared to black baffles. When comparing the results to the concurrent-flow case, it is also noticed that opposed-flow flames spread slower and blow off at larger flow speeds but are not as sensitive to the flow speed. This work provides unique long-duration microgravity experimental data that can inform the design of future opposed-flow experiments in microgravity and the development of theory and numerical models.

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Opposed flow flame spread over thermally thick solid fuels: buoyant flow suppression, stretch rate theory, and the regressive burning regime

Cited by 17 publications

References 30 publications

Experimental study of molten bubble layer growth and bubble size distribution in post‐flame‐spread PMMA samples

Experimental study of molten bubble layer growth and bubble size distribution in post‐flame‐spread PMMA samples

Flame Spread Transition to Regression of Thick Fuel in Oxygen-Limited Concurrent Flow

Effects of Confinement on Opposed-Flow Flame Spread over Cellulose and Polymeric Solids in Microgravity

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