Heat Loss and Kinetic Effects on Extinction and Critical Self-Sustained Propagation of Forced Forward Smoldering
This work studied the forced forward smoldering mechanism of foam by a transient one-dimensional numerical model. A three-step reaction scheme, including foam oxidation and pyrolysis, char oxidation was adopted. Based on the first principles of mass, mome
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Jiuling Yang, Haixiang Chen, and Naian Liu
Abstract
This work studied the forced forward smoldering mechanism of foam by a transient one-dimensional numerical model. A three-step reaction scheme, including foam oxidation and pyrolysis, char oxidation was adopted. Based on the first principles of mass, momentum, and energy, the mass fractions of solid and gas species as well as temperature evolutions in self-propagation regime were examined. Foam oxidation and pyrolysis fronts were found to be ahead of char oxidation front where oxygen is not completely consumed. The critical kinetic parameters for self-sustained smoldering were determined. It was found that pyrolysis endothermic reaction, heat losses, and limited kinetics of char oxidation are favorable for smoldering extinction. Especially, smoldering extinction is more sensitive to kinetic parameters of char oxidation reaction than that of other two reactions. The halfway quenching of smoldering is mainly due to the weakening of char oxidation reaction, which cannot offset the pyrolysis endothermicity and heat loss to environment. Keywords
Smoldering Extinction Self-propagation Kinetic effects Heat losses
85.1
Introduction
Smoldering is a kind of heterogeneous combustion reaction taking place at the phase interface between a porous fuel and oxygen [1]. Smoldering can self-sustain in oxygen-starved environment for a very long time, and once it transits to flaming combustion, human life and property security would be threatened. So it is imperative to study the factors that influencing smoldering extinction and self-sustained propagation. Besides the experimental investigations, the numerical model is essential for a better understanding of smoldering mechanisms. Based on the smoldering experiments
J. Yang H. Chen (*) N. Liu State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China e-mail: [email protected]
conducted in the space shuttle flights [2–5], a transient one-dimensional model in microgravity with a three-step reaction was put forward [6], in which the smoldering velocity was predicted to be linear with the airflow once selfsustaining propagation was supported. Afterward, Rein et al. expanded this model to five-step reaction [7] and successfully captured every reaction structure in both forward and opposed smoldering combustion with the same kinetic parameters extracted from thermogravimetric data by genetic algorithms [8]. Dodd et al. also examined the two-dimensional cone structure of the smoldering front with a seven-step reaction mechanism [9]. These studies promote the development of numerical smoldering propagation models. Most of numerical studies on smoldering focus on the propagation, rather than extinction of smoldering. Two extinction mechanisms including blowoff and quenching extinction are reported in literature. The former extinction is caused by the strong convective cooling effect due to
# Springer Science+Business Media Singapore 2017 K. Ha
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