A numerical model for simulating pyrolysis and combustion behaviors of multilayer composites

A modified 1D numerical solver concerning the pyrolysis and combustion of a multilayer structure is reported in this study to better understand the unique thermal response of this composite. Complex pyrolysis reaction schemes, including multicomponent, parallel or consecutive or hybrid high order reactions, and thickness regression are considered in each layer. Predictive capability of the established model was first validated by comparison with experimental results of a three-layer PC(Polycarbonate, 1 mm)-PE(Polyethylene, 40 mm) foam-PC (1 mm) composite under 35, 40 and 50 kW/m² heat fluxes. Despite some minor deviations, the numerical model successfully captured the shape, magnitude and locations of the two peaks of the measured MLR curves and surface temperatures. The evolutions of total thickness regression, in-depth temperature and density, normalized mass and MLR of each component in each layer were demonstrated. Subsequently, the extrapolation capability of the model was further verified by simulating the pyrolysis and combustion of a PVC(Polyvinyl chloride, 2 mm)-Kydex(polymethyl methacrylate-polyvinyl chloride alloy, 2 mm)-wood (20 mm) composite. Two reaction schemes of wood with different complexities were incorporated, and both pyrolysis and oxidation reactions were involved to identify their contributions. The results show oxidation reactions would significantly accelerate the decomposition and thickness regression processes. The total char yields of wood using the two pyrolysis reaction schemes are 31% and 17%, respectively. Oxidation of raw components in wood considerably impact the simulated thickness, density, surface and in-depth temperatures and total MLR. Furthermore, the contribution of each reaction to the total MLR is thoroughly examined.