Development of the unsteady upward fire model to simulate polymer burning under UL94 vertical test conditions

摘要

In this paper, an unsteady upward burning model for polymers under UL94 vertical test conditions was developed. With this model the simulated mass loss rate of polymethylmethacrylate agreed with experimental data to a certain extent initially, and was over-predicted later but still in the same magnitude as experimental data. It was found that the edge effect was important, and the calculated maximum local mass flux of volatiles increased dramatically at the ignition time to exceed the range of reported critical mass fluxes for ignition. Sensitivity analyses showed that the activation energy and the pre-exponential factor were two most important material parameters. Increasing the char yield shows a significant reduction in the peak mass loss rate (PMLR) but only a slight increase in the ignition time (t_(ig)) and a slight reduction in the afterflame time (t_(af)). Increasing the density or the heat capacity increases t_(ig) and reduces both PMLR and t_(af) Increasing the thermal conductivity increases t_(ig) and decreases t_(af) but has very little effect on PMLR. Increasing the sample thickness reduces both PMLR and t_(ig) but affects t_(ig) less significantly than material properties. Increasing the heat feedback increases both PMLR and t_(af) but has very little effect on t_(ig).