An engineering model for the pyrolysis of materials

Abstract

Accurately representing the time dependent heat release rate of fuels is critical to performance-based design in fire safety applications. Existing simplified models either use average pyrolysis rates at different heat fluxes or do not account for the change in burning behavior at higher heat transfer rates. This paper presents the theoretical basis of a scaling-based pyrolysis model, S-Pyro. The model is based on the concept of maintaining the shape of a reference heat release rate per unit area curve but scaling the magnitude and time based on a dynamic thermal exposure. The model has been implemented in the computational fluid dynamics software Fire Dynamics Simulator (FDS). The model is validated with solid-phase only and multi-phase simulations of cone calorimeter experiments. The solid-phase simulations evaluated the capability of the model to predict the heat release rate per unit area of 149 materials tested at heat fluxes other than the reference flux. Multi-phase simulations of bench-scale fire experiments with a single material, Canada Pine and Spruce plywood, were used to evaluate the performance of the pyrolysis model in FDS. The model uncertainty was lower for high heat release rate materials, with the model uncertainty approaching the experimental uncertainty at higher burning rates.