Ignition Delay of Fluorinated Ethylene Propylene Wire Insulation in a Forced Flow Field in Microgravity
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Ignition Delay of Fluorinated Ethylene Propylene Wire Insulation in a Forced Flow Field in Microgravity K. Wanga , J. Fanga , J.-W. Wanga , S.-M. Zhenga , J.-F. Guanb , H. R. Shaha , J.-J. Wanga , and Y.-M. Zhanga
UDC 536.46
Published in Fizika Goreniya i Vzryva, Vol. 56, No. 4, pp. 46–55, July–August, 2020. Original article submitted January 9, 2020; revision submitted February 19, 2020; accepted for publication February 19, 2020.
Abstract: Fluorinated ethylene propylene (FEP) wire insulation ignition is investigated in a forced flow field in microgravity and normal gravity with a continuous current. First, FEP insulation melts and decomposes, causing jet bursting in both normal gravity and microgravity. Second, the forced flow and gravity produce minor effects on the core heating and bursting time, while the pyrolysis time increases slightly with increasing air velocity. Third, the positively stretch rates in terms of the velocity gradients are higher in microgravity. Both the forced flow and gravity have significant effects on the induction time, which is dependent on the stretch rate and Damk¨ ohler number. The induction time increases with increasing air velocity, and it is higher in microgravity. Finally, the ignition delay time is dominated by the core heating and bursting time, while its bigger value and faster increase in microgravity with increasing air velocity are dominated by the induction time. Keywords: microgravity, ignition, FEP wire insulation, bursting jet, stretched flow. DOI: 10.1134/S0010508220040048
INTRODUCTION A number of theoretical and experimental studies have been conducted on the ignition characteristics of solid materials in microgravity [1]. Previous research was focused on the piloted ignition of PMMA and thin cellulosic sheets heated by an external heat flux [2–5]. In spacecraft, one potential cause of fires is the combustion of insulation, beginning with shortcircuiting or overloading of the enclosed wires. The insulation of thin wires has a large curvature. When the wire is overloaded, spontaneous ignition of the insulation proceeds differently compared to the piloted ignition of these materials in planar geometries. An ignition-to-spread model of electrical wires was developed to systematically explain the ground pilot ignia
University of Science and Technology of China, State Key Laboratory of Fire Science, Hefei, Anhui, P. R. China, [email protected]. b Tsinghua University, Hefei Institute for Public Safety Research, Hefei, Anhui, P. R. China.
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tion and the following transition to spread by Huang et al. [6]. Pioneering and extensive research into the spontaneous ignition of wire insulation in microgravity was conducted in [7–10], using mostly polyethylene (PE)coated wires, to understand various aspects of the ignition mechanism, including the ignition limit, the minimum ignition energy, and the effect of the oxygen concentration and air pressure. However, rather than regular insulation materials such as PE, fire-resistant materials such as poly (etheneco-tetrafluoroethylene) (ETFE
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