An experimental and theoretical study on smoldering combustion in horizontally oriented flexible polyurethane foam layer was conducted. The research covered experimental investigation of smolder initiation, smoldering propagation and transition from smoldering to flaming and theoretical analysis of smoldering propagation via activation energy asymptotic approach....[ Read more ]

An experimental and theoretical study on smoldering combustion in horizontally oriented flexible polyurethane foam layer was conducted. The research covered experimental investigation of smolder initiation, smoldering propagation and transition from smoldering to flaming and theoretical analysis of smoldering propagation via activation energy asymptotic approach.

Fire retarded foam and non-fire retarded foam were selected to study the phenomena of smoldering combustion. Foam length and ignition power were found to have key effects on the smolder initiation. Fire retardants with phosphorus and bromine showed positive and negative influence on restricting the smolder initiation under different ignition powers. Triggering of the transition from smoldering to flaming was revealed to significantly depend on exothermic oxidation of the residual char and the availability of oxygen inside the foam layer. Effects of foam length, ignition power, moisture content and fire retardants in the foam on the transition were also explored. Propagation of horizontally oriented forced forward smoldering was found to be controlled not only by oxygen supply rate to the reaction zone but also by the heat loss to the surroundings. It was found that the smoldering propagation rate firstly increases with air flow rate and decreases after reaching a maximum at the air flow rate of around 0.8 m/s.

Through asymptotic analysis, it was shown that for the adiabatic case, the smoldering propagation rate and smoldering temperature increase with the air flow rate. Furthermore, they are larger than the corresponding values under the stoichiometric condition. Analysis also showed that the density and porosity of the foam, ambient oxygen concentration and mass transfer coefficient have effects on the smoldering propagation rate. Under nonadiabatic condition, the variation tendencies of the smoldering propagation rate and smoldering temperature were suggested to be similar to the experimental results. The analytical results are consistent with the experimental data.

Keywords: Forward Smoldering Combustion, Flexible Polyurethane Foam, Smolder Initiation, Smoldering Propagation, Transition from Smoldering to Flaming, Steady Smoldering Temperature, Activation Energy Asymptotic Approach