Ignition and flame spread over thermal aging electrical wires in subatmospheric pressure

Abstract

Thermal aging affects polymer ignition and flame spread process by changing the polymer kinetic parameters. Polyethylene (PE) with 0.15 mm thickness insulated by copper core of 0.5 mm diameter was used in this experiment. The PE was preheated under different temperature and heating time. Wires which have experienced thermal aging at 130°C for 30 and 200 h display higher crystallinity and pyrolysis temperature. However, the crystallinity and pyrolysis temperature decrease of wires, which experienced thermal aging at 150°C for 30 and 200 h by the results of thermogravimetric analysis and differential scanning calorimetry tests. The ignition experiment results highlight the ignition delay exhibiting “U” type with pressure. Chemical kinetics controls the ignition delay in lower pressure region, and the heat transfer controls the ignition delay in higher pressure region. The region controlled by chemical kinetics is larger for the wire with higher crystallinity and pyrolysis temperature. The flame spread experiment results show that the flame area relays more on flame length for the wires with lower crystallinity and pyrolysis temperatures, while wires with greater crystallinity and higher pyrolysis temperature depend more on flame height.