Forward smolder of Polyurethane foam in a forced air flow

An experimental study is conducted of forward smolder of polyurethane foam. Air is used as oxidizer, and is forced in the direction of smolder propagation under conditions that produce approximately one-dimensional forward smolder propagation. The objective of the study is to provide further understanding of the mechanisms controlling forward smolder and verification of theoretical models of the problem. Upward and downward forward smolder are compared to also observe the effect of buoyancy on the process. Measurements of the temperature histories at several locations throughout the foam sample are used to infer the characteristics of the smolder process, and to calculate the smolder propagation velocity along the sample length as a function of the air flow velocity and gravitational orientation. It is found that as the flow velocity is increased, there is a transition in the smolder characteristics from a smolder process that is characterized by the propagation of a single exothermic oxidation (smolder) reaction to one characterized by the propagation of two reactions, an oxidative smolder reaction preceded by an endothermic pyrolysis reaction. Buoyancy is observed to affect this mode of smolder at very low air velocities, or when the smolder front approaches the sample end. The smolder velocity data are correlated well in terms of a nondimensional smolder velocity derived from previously developed theoretical models of forward smolder. The good agreement between theory and experiments verifies that the smolder controlling mechanisms and simplifying assumptions implicit in the models are appropriate at least for the present experimental conditions.