Effect of pyrolysis kinetic parameters on the overload ignition of polymer insulated wires in microgravity

The overload ignition of polymer insulated wires in microgravity was investigated as basic information for space fire safety. This paper focuses on the effect of pyrolysis kinetic parameters of the insulation material on the ignition characteristics. A two-dimensional numerical model calculation under varied pyrolysis model was carried out to simulate the overload ignition, and microgravity experiments have been conducted for the model validation. With the help of thermogravimetric analysis, the original pyrolysis model of the polyethylene insulation used for wire ignition experiments was obtained. Three groups of varied pyrolysis models were proposed by changing the activation energy (E), pre-exponential factor (A) from the original model. Numerical simulations were conducted with the varied pyrolysis models. The simulated results employing the original pyrolysis model showed a good agreement with the microgravity experiments for ignition delay time with continuous current and the minimum ignition energy (MIE) with short-term current, respectively. From the simulation results with continuous overloading, the independent variation of A and E in the pyrolysis model has a limited effect on the ignition delay time but a significant effect on ignition modes in microgravity. Such effects are mainly reflected by changing the pyrolysis temperature during overloading, which determines the ease of spontaneous ignition. With a constant pyrolysis temperature, the change of mass loss rate in the pyrolysis model may affect the transition point from the “spontaneous ignition” to the “wire assisted ignition” when the current increases. Finally, for short-term current supply in microgravity, the single change of A or E showed higher MIE than the original pyrolysis model.