Simplified modelling of transient upward flame spread on combustible element

Abstract

This paper presents the development and validation of a simplified model to simulate upward fire growth and flame spread on vertical surface with combustible materials. The model consists of the following main sub-models: a one-dimensional combined heat and mass transfer model perpendicular to the vertical surface to compute gaseous fuel production due to decomposition and combustion of the combustible material, a simplified model to calculate surface heat flux, and a transient flame growth model based on an existing steady state flame model that takes into account transient heat feedback due to combustion. Validation of the model is checked by comparison of the predictions of this model against FDS (Fire Dynamic Simulator) simulation results and experimental results wherever available, including the following: flame growth with variable heat release rates of solid materials under various levels of external irradiation, temperature distribution through thickness of the wall, and propagation of the pyrolysis front. To demonstrate capability of the new model, vertical burning and upward flame spread on 2.4 m high panels of wood and 5.0 m high panels of PMMA are carried out and compared with FDS simulations. The new model calculation results, including propagation of the pyrolysis front, total heat flux and heat release rate are in good agreement with FDS simulation results. However, the new model requires a fraction (a few minutes of CPU time) of that for carrying out the corresponding FDS simulation (CPU time of 2 days).