Forced forward smoldering propagation in horizontally oriented flexible polyurethane foam

A series of experiments was conducted in a small-scale wind tunnel to investigate the effect of forced flow on forward smoldering propagation in flexible polyurethane foam material located horizontally. In the wind tunnel, the air at a flow rate in the range of 0.01-1.5 m/s passed over the foam layer surface. Foam samples of different lengths with the same cross-sectional area were studied. From the experimental results, it is seen that the foam length has no clear influence on the smolder propagation velocity. With an increase of air flow rate, firstly, the smolder propagation velocity increases and reaches a maximum at an air flow rate of around 0.8 m/s due to the increased mass transfer of oxygen into the smolder reaction region. It decreases with further increase of air flow rate as heat losses becomes dominant compared to the positive effect of the increase of oxygen transfer into the reaction zone. The variation of the steady smoldering temperature with the air flow rate follows the same trend as that of the smolder propagation velocity. In this paper, a simple analysis is also presented to analyze the co-effect of the mass transfer of oxygen to the smoldering reaction region and the heat loss to the surrounding on the smolder propagation under our current experimental conditions.