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1469. Experimental study of the burning behavior and key parameters of gasoline pool fires with different ullage heightsJinlong Zhao, Xinjiang Li, Zhenqi Hu, Rongxue Kang, Grunde Jomaas, 2023, original scientific article Abstract: Pool fires with different ullage heights are a common type of fire accident. A series of gasoline pool fire ex- periments with two sizes (D = 40 cm, 60 cm) and six ullage heights (h = 0, 0.2D, 0.4D, 0.6D, 0.8D, 1.0D) are conducted. The burning process, axial temperature profile, radiative heat feedback, and burning rate are measured and analyzed. The result shows that the fuel vapor layer and the down-reaching flame layer are distinguished based on the axial temperature profile for the steady burning stage. Meanwhile, the down-reaching flame length (Ldown) increases more profoundly for large tank diameters under the same ullage height. Subse- quently, the dimensionless down-reaching flame length (Ldown* = Ldown/D) increases exponentially with the dimensionless ullage heights (h* = h/D). Finally, based on the classical burning rate model for the low ullage height and the heat transfer process from the flame to the fuel surface, a correlation with different ullage heights is established to calculate the burning rate, which is then validated against the experimental data in the paper and literature values. The results are of importance to understand the burning rate and the radiative heat feedback to the fuel surface for pool fires with different ullage heights.
Keywords: pool fires, ullage height, down-reaching flame, flame radiative heat feedback, burning rate correlation
Published in DiRROS: 08.01.2024; Views: 334; Downloads: 65
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1470. The effect of duct size, sample size, and fuel composition on concurrent flame spread over large cellulose samples in microgravitySandra L. Olson, Gary A. Ruff, Paul V. Ferkul, Jay C. Owens, John Easton, Ya-Ting T. Liao, James S. T'ien, Balazs Toth, Grunde Jomaas, A. Carlos Fernandez-Pello, Guillaume Legros, Augustin Guibaud, Osamu Fujita, Nikolay Smirnov, David L. Urban, 2023, original scientific article Abstract: Concurrent flame spread data for thermally-thin charring solid fuels are presented from Saffire and BASS experiments performed in habitable spacecraft for three duct sizes, five sample sizes, two materials, and two atmospheres. The flame spread rates and flame lengths were strongly affected by duct size even for the relatively large ducts (> 30 cm tall). A transient excess pyrolysis length (i.e., flame length overshoot) was observed for the cotton fabric that burned away, which indicates that the transient excess pyrolysis length phenomenon is caused by more than just the flame moving into the developing boundary layer thickness as was the case with the SIBAL sample. A burnout time, defined as the pyrolysis length divided by the flame spread rate, normalized the pyrolysis length histories into a single curve with a steady burnout time of 22 s for the SIBAL fabric. The transient excess pyrolysis length is hypothesized to be a post-ignition flame growth transient for the essentially two-dimensional flames where the burnout time becomes very long until the preheat and pyrolysis lengths develop. The three-dimensional flames over narrow samples have lateral thermal expansion and lateral oxygen diffusion which allows them to transition to a steady state length without the transient excess pyrolysis length. Surface temperature profiles, nondimensionalized by the pyrolysis length, indicate that the temperature profiles exhibit the same shape across the pyrolysis zone. A surface energy balance calculation in the preheat region revealed that the heat flux increased rapidly at the pyrolysis front to near the critical heat flux for ignition. An estimate of the acceleration of the inviscid core flow in the duct due to thermal expansion and developing boundary layers on the duct walls and the SIBAL sample surface seems to explain the observed spread rate trends across three duct sizes and multiple sample sizes.
Keywords: concurrent flame spread, microgravity, duct size, sample size, cellulose fabrics
Published in DiRROS: 08.01.2024; Views: 273; Downloads: 51
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