Pyrolysis and piloted ignition of PVC-insulated wire arrays exposed to time-dependent thermal radiation
摘要
Pyrolysis and ignition of wire arrays using commercial PVC-copper wires with three different diameters were experimentally studied under five time-dependent heat fluxes. Surface temperature, mass loss rate (MLR), ignition time (tig), and ignition criteria were collected. A numerical model involving condensed and gaseous phases was developed to simulate experimental measurements. Thermogravimetric analysis (TGA) tests at 15 K min−1 and 20 K min−1 heating rates were conducted to extract pyrolysis kinetics of PVC. The results showed that pronounced melting, multiple flash, stochastic large bubbles, and small jet flames occasionally emerged before ignition. Higher heat flux shortened tig and resulted in a thinner and more discrete char layer. Measured surface temperature and MLRs were well predicted despite some minor deviations. Measured critical temperature and critical MLR were 526.3 K and 2.5 g m−2 s−1, respectively. Under fixed heating condition, ignition of sample with intermediate wire diameter was easier. Both thinner PVC layer and thicker copper core facilitated thermal sink effect of copper core and delayed tig. Experimental tig were estimated numerically and analytically using measured ignition criteria. Critical transient heat flux at tig varied in the range of 13.15–20.62 kW m−2. Meanwhile, simulated temperature, pyrolyzate concentration, and velocity field evolutions at gas phase were analyzed.