Flame Propagation Over Energized Pe-Insulated Wire Under Low Pressure

Flame spread along the energized polyethylene (PE) insulated copper wire under low pressure was investigated experimentally to gain a better understanding of electrical wire fire in aircraft and space habitats. Three types of sample wires, with the same insulation thickness and different core diameters, were used in this research study. First, a simplified model was developed to quantitatively explain the impact of lower pressure on the flame propagation over the energized wires. As with the pressure decreased, both of Grashof number (Gr) and Reynolds number (Re) were decreased and the air-flow diffusion played a gradual and dominant role in the combustion process. Mainly caused by the decrease of natural convention, the heat loss turned to be reduced, resulting in the reduction of oxygen flow and the formation of carbon black was inhibited. Second, several experiments were conducted to investigate the flame spread along the energized wires in a walk-in hypobaric chamber. The experimental results showed that, with the decrease of pressure, the flame height was reduced, the flame shape turned to be spherical, and the blue area showed increased. But the flame shape was reduced gradually along the wire, till extinguished when the pressure set out below a critical value. The accumulation of melt insulation increased and the dripping behavior occurred easily under lower pressure. Moreover, the influence of overload current on the flame spreading velocity was also presented. This work was useful for a further study on the fire risk of electrical wires under low pressure.