Mechanism of flashback in horizontal smoldering of polyurethane foam: A numerical study

Abstract

Smoldering of polyurethane foam continues to attract the attention of the fire community because of its potential of causing severe fire hazards. Our previous work observed a unique flashback phenomenon denoting the reversal spread of horizontal smoldering front. This work further develops a one-dimensional model of foam smoldering via Gpyro to examine the flashback mechanism. The model adopts a 6-step reaction scheme consisting of two pyrolysis and four oxidation reactions based on thermogravimetric analysis. Comparison with the experimental results indicates that the computational model successfully reproduces the flashback phenomenon and explains the flashback mechanism. From the view of chemical kinetics, the initial pyrolysis of foam is followed by the oxidation of β-foam during the 1st stage with a lower peak temperature and limited oxygen supply, and the flashback in the 2nd stage is mainly dominated by char oxidation, which results in more heat releases and a higher peak temperature. The rapid temperature rise at the end of the 2nd stage, causing the maximum temperature in the whole smoldering process, is attributable to the oxidation of α-char (secondary char oxidation).