Experimental and computational study on the glowing ignition of wood

Wildland Urban Interface (WUI) fires are a rapidly increasing hazard. Cellulosic materials play a key role in the spread of WUI fires. The physics controlling the glowing ignition of cellulosic materials is not well understood. In this work, an experimental and computational study of the glowing ignition of wood was performed. Eight wood specimens (Balsa, Red Cedar, Pine, Douglas Fir, Cypress, Redwood, Purpleheart, and Ipe) were tested under a cone calorimeter in the vertical configuration. Non-uniform glowing propagation due to sample-specific surface cracking was observed for all wood samples. The average temperature at the center of each sample was measured using an optical pyrometer. The inflection point in the pyrometer temperature-versus-time curve, which was identified by the maximum peak of the first temperature derivative, was used to identify the onset of glowing ignition. Additionally, a comprehensive model was applied to predict the glowing ignition. The comparisons between model predictions and experimental results showed that the surface temperature, the time to glowing ignition, and the glowing ignition temperature of medium-density wood (rho = 300-500 kg m(-3)) could be reasonably predicted. For lighter (e.g., Balsa, rho = 150 kg m(-3)) and denser wood (e.g., Ipe rho = 960 kg m(-3)), however, significant discrepancies were observed. Hence, further work is needed to understand the influence of wood density on the thermo-physical and thermodynamic properties that can significantly affect glowing.