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Carmignani, L., Garg, P., Thomsen, M., Gollner, M. J., Fernandez-Pello, C., Urban, D. L., et al. (2022). Effect of sub-atmospheric pressure on the characteristics of concurrent/upward flame spread over a thin solid. Combust. Flame, 245, 112312.
Abstract: The variation of ambient pressure is a potential tool for studying the driving parameters of fire dynamics and heat release in low-pressure environments such as high-altitude locations, aircraft, and spacecraft. The study of upward flame spread over a solid fuel has direct implications on material flammability and fire development, and low pressure environments have recently gained more attention for the possible comparison with the reduced gravity conditions encountered during space missions. In this work, we consider upward spreading flames over thin acrylic sheets in ambient pressures between 30 and 100 kPa. A forced flow velocity of 20 cm/s is added to the naturally-driven buoyant flow, creating a mixed flow field (natural and forced) that varies with pressure. Flame characteristics such as spread rate and standoff distance are measured from the video analysis of the experiments. It is observed that the former decreases with pressure while the latter increases. The larger flame stand-off distance at low pressures partially explains the decrease of the flame spread rate since the convective heat flux from the flame to the solid decreases. Additionally, volumetric concentrations of the combustion products are measured during the experiments. The results show lower O-2 consumption and CO2 production rates at lower pressures. Based on these rates, we could calculate the heat release rate from upward spreading flames at low pressure, providing fundamental information for better understanding pressure-gravity correlations. According to the results, the volumetric heat release rate is proportional to pressure, which is consistent with previous studies on pressure modeling of fires. This suggests that chemical kinetics is not a constraint for the conditions tested in this study, which could help make future flammability tests comparable to low gravity ones.
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Thomsen, M., Carmignani, L., Rodriguez, A., Scudiere, C., Liveretou, C., Fernandez-Pello, C., et al. (2022). Downward Flame Spread Rate Over PMMA Rods Under External Radiant Heating. Fire Technol., 58(4), 2229–2250.
Abstract: There are multiple situations in which fires may occur at environmental conditions that are different than standard atmospheric conditions. Changes in ambient pressure, oxygen concentration, flow velocity, the presence of an external heat source or gravity may change the flammability and fire dynamics of materials. The objective of this work is to study the effect of external radiant heating on downward flame spread over cylindrical samples of polymethyl methacrylate (PMMA). In this work, experiments under normal gravity and atmospheric ambient conditions are conducted using a variable heat flux with peak values up to 13.2 kW/m(2). A forced flow of air with a mass-mean velocity of 10 cm/s is used during the experiments. Flame spread rates were measured from video processing of the experiments at different conditions. Results show that the flame spread rate measured depends strongly on the amount of radiant heating provided. An analysis is presented to correlate the flame spread rate with the energy applied to the surface of the sample and the surface temperature. The results provide a baseline for comparison with future microgravity experiments to be performed by NASA as part of the SoFIE/MIST project aboard the International Space Station. It is expected that the results will provide insight for what is to be expected in different conditions relevant for fire safety in future space facilities.
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