The influence of forced flow on opposed flame spread

Abstract

Opposed flow flame spread under forced flow conditions has been the subject of many studies in the flammability literature. Previous studies have presented findings such as the transition between a thermal and kinetic regime through the Damköhler number (Da). While Da scaling has been successfully used to observe the increasing influence of finite rate kinetics in the gas phase, this characterization lacks explicit measurements of the solid and gas-phase heat transfer under various flow conditions. Experiments were conducted using a range of forced flow rates (0–3 m/s) and oxygen concentrations (21–40%) to quantify the thermal conditions in the solid ahead of the flame front. Solid-phase temperature measurements provide the thermal profile, and heat transfer conditions through the solid, ahead of the flame front. These measurements are paired with CH∗ chemiluminescence measurements to explicitly define the flame structure and position relative to the fuel surface. The combination of these measurements provide novel insight into opposed flow flame spread, illustrating the increasing influence of solid-phase heat transfer at high flow rates in air (21% O₂) and the increasing influence of gas-phase heat transfer in the thermal regime for oxygen rich environments (e.g., 40% O₂).