Combustion characteristics of non-charring polymer cylinders - experimental and numerical study

Polymeric fuels with a cylindrical shape are widely found as forest combustibles, building components, and electrical cables and wires. Their flammability is commonly assessed using cone calorimetry, despite the fact that the exposed heat flux is well defined only for flat samples. This has led to great difficulties when trying to use the experimental data for calibrating pyrolysis models, which often treat the problem as one-dimensional. This study aims at increased understanding of the combustion of cylindrical fuels in cone calorimeter by carrying out experiments and two-dimensional numerical simulations on black, 20 mm diameter Poly(methyl methacrylate) rods. The solid-phase heat transfer and pyrolysis are modeled using a rectilinear 1 mm mesh, and the reactive flow field is solved by LES and a single-step mixing-controlled combustion reaction. The model is validated with the results of the gasification and flaming experiments with one or five rods under 50kWm−2 irradiation. For the single rod measurements, a steep vertical shrinkage in gasification, and roughly equal vertical and horizontal degradation rates in flaming were observed. Degradation patterns of the five rods experiments consisted of a ∪-shape trend in gasification, and a ∩-shape trend in flaming condition. The numerical simulations reproduce these deformation trends with a favorable accuracy for all cases. The ignition delay time of the five rods case was detected shorter than the single rod case, which is in consistency with the available literature. The model allowed for the extraction of comprehensive thermodynamic information on the surface of the samples. With flaming, the incident heat flux at the top of the sample increased by 15 kWm−2. Flame-induced convective heating is most significant on the sides of the single rod case or on the outermost rods in the five rods case, with a distribution that peaks to about 30 kWm−2. The current framework can be a basis for extension to modelling more complex cylindrical material such as cables and thermal insulations.