Citation

Zheng G, Wichman IS, Benard A. Fire Safety J. 2003; 38(3): 229-256.

Copyright

(Copyright © 2003, Elsevier Publishing)

DOI

unavailable

PMID

unavailable

Abstract

A two-dimensional ignition model is examined for two different flow patterns, one with a Navier-Stokes calculation and one with an Oseen approximation. The physical phenomena include channel flow and combustion reaction in the gas phase, pyrolysis and melting in the condensed phase, and radiation heat loss and fuel injection flow at the interface. Ignition is studied by means of an integral energy balance analysis, where various heat transfer mechanisms are evaluated. It is found that the flow pattern has an influence on the ignition process though the qualitative dependence is unchanged except for some isolated (though important) features of the problem. Generally, the Oseen approximation results in a shorter ignition delay. The influence of condensed phase material properties such as latent heat, conductivity, and heat capacity are investigated based on the energy barrier concept. Based on the numerical observations, a simple theory is derived to determine the ignition delay time by employing the energy balance principle. The predicted ignition delay agrees well with the direct numerical results. The external radiation is studied by changing its magnitude over a wide range. It influences the ignition behavior by mainly changing the ignition delay, whose results indicate that the polymer under investigation belongs to in the category of thermally thick polymers. In addition, the surface temperature is observed to increase with increasing external radiation heat flux.