Experimental study and asymptotic analysis of horizontally forced forward smoldering combustion

An experimental study and asymptotic analysis were conducted to investigate smoldering propagation in a horizontally oriented layer of flexible polyurethane foam. Experiments were done in a small-scale wind tunnel, where the air current is flush with the upper surface of the foam layer. The activation energy asymptotic approach was applied to analyze smoldering propagation. The experimental results show that increasing the air flow over the foam's surface not only enhances the mass transfer of oxygen to the smoldering reaction zone, but also increases the heat loss to the surroundings. The maximum smoldering propagation rate was observed at medium flow rates of air. The variation of the steady smoldering temperature with the flow rate followed the same trend as that of the smoldering propagation rate. Both adiabatic and non-adiabatic conditions were considered in the asymptotic analysis. For the adiabatic case, it is shown that the smoldering propagation rate and the smoldering temperature both increase with the flow rate of air. Results from the adiabatic analysis show that an increase in the density of the porous material lowers the smoldering propagation rate. Increasing the concentration of ambient oxygen, the porosity of the porous material or the mass transfer coefficient of the air stream increases the smoldering propagation rate. Results from the nonadiabatic analysis show a similar trend. Consistency is observed between the analytical results and the experimental measurements.