Experimental and simulation investigation on overload ignition of XL-ETFE insulation material in low-pressure environments

• Overload ignition of flame-retardant XL-ETFE wire in low pressures was explored. • A unique “core-forced ignition” mode for XL-ETFE insulated wire was observed. • A 3-D numerical model considering the insulation detachment effect was developed. • Practical guidance for fire safety engineering in low pressures are provided. The overload ignition of flame-retardant cross-linked ethylene-tetrafluoroethylene (XL-ETFE)-insulated wires under low-pressure conditions presents a critical challenge for stable energy transmission and fire-safe material design in extreme operational environments (e.g., aerospace, high-altitude power systems). This work experimentally and numerically investigates the pyrolysis and ignition behaviors of overloaded XL-ETFE wires under low pressures (25 to 101 kPa), with a particular focus on solid-phase role that is commonly overlooked. A three-dimensional numerical model was developed based on solid-phase thermodynamic parameters and gas-phase finite-rate combustion chemistry. Results reveal a unique “core-forced ignition” mode driven by the insulation detachment. As overload current and pressure decrease, such insulation detachment effect becomes more significant. Ignition delay time (IDT) decreases with increasing applied current (heating rate) due to the shorter core exposure time and shorter chemical time, while it slightly increases with decreasing pressure mainly due to the reduced thermal feedback to fuel–air mixture under the stronger detachment effect (longer chemical induction time), and the suppressed chemical reaction (longer chemical reaction time). Ignition energy follows a “U”-shaped trend with IDT at higher pressures, while it increases monotonically at lower pressures. The minimum ignition energy (MIE) is higher in low pressures, and the overload current corresponding to MIE coincides with the threshold current to identify whether the insulation detachment is completed at the ignition moment. This study facilitates the understanding of fundamental ignition mechanisms of insulation materials and may offer practical guidance for fire safety engineering in low-pressure environments, so as to ensure the stable operation of power system.