Flame spread over electric wire in sub-atmospheric pressure

Flame spread along the single wire harness (thin-metal wire with coating of polyethylene film) in sub-atmospheric pressure has been examined experimentally to gain better understandings of the electric fire ill the aircraft and space habitats. Two kinds of sample Wires, made by nickel-chrome (NiCr) and iron (Fe) as core metal, are used in this study. Ambient gas is fixed as air and total pressure is varied from atmospheric to sub-atmospheric (100-20 kPa). As the pressure decreases. flame shape changes from typical teardrop to oval and flame becomes less-luminous irrespective of the materials of the wire. It turns out that the dependence of the spread rate on pressure varies with the materials of the wire: when the pressure decreases, the spread rate of NiCr-harness monotonically increases, whereas that of Fe-harness mostly remains as constant. From the simple thermal-length analysis, it is proposed that there are two modes in the spread depending oil the controlling factor: one is wire-driven mode (the spread is mainly governed by the thermal input through the wire) and the other is flame-driven mode (the spread is mainly governed by the thermal input from the flame). observed two cases (NiCr- and Fe-harness) would be categorized to the latter and former modes, respectively. (c) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.