Glowing and piloted flaming ignition of vertical wood exposed to power-law thermal radiation

Fire hazards are dangerous to human life and property safety. Fire accidents occur frequently in wood-frame villages all over the world. In this paper, glowing and flaming ignition of vertical wood heated by five power-law heat fluxes (HF) is experimentally studied using a self-built apparatus. Comparative ignition tests with and without piloted ignitor were performed, and some crucial variables were collected, encompassing surface and in-depth temperatures, mass loss rate, and ignition time. A 1D numerical model was developed to simulate experimental results and determine temperature-dependent thermodynamics of wood by inverse modelling. The results showed that ignitor induced flaming ignition, whereas absence of ignitor enabled only glowing ignition. Flaming ignition was preceded by flash ignition. Surface temperatures of flaming ignition were well predicted by numerical model. However, the predictive accuracy declined when modelling in-depth temperatures due to cracks in char layer. Three stages were identified in both ignition modes: a preheating stage, a water evaporation stage, and a pyrolysis stage. The numerical model underestimated mass loss rates due to additional heating contributed by flash ignition and char cracks. Critical temperature and critical mass flux were comparatively analyzed, and the former was used in assessing ignition time. Measured ignition times were well estimated by an analytical correlation. The numerical model accurately predicted flaming ignition times but overpredicted glowing ignition times due to char cracks. The proposed model can contribute to the fire safety retrofitting of historic buildings and minimize human casualties and property damage.