Flame spread across liquid pools with very low-speed opposed or concurrent airflow

The consequences of forced airflow on flame spread over liquids is to a large extentunexplored, especially for low air speeds on the order of that due to buoyant convection driven by the flame. Yet small gas flows can influence heat and mass transfer ahead of the flame and alter its spreading characteristics. In this paper we present results from normal and microgravity experiments on flame spread over 1-butanol with either an opposed or a co-current forced airflow ranging from 5 to 30 cm/s. A small flow duct was used to control the air flowing over a laboratory-scale fuel tray. Video flame imaging was used to determine the flame shapes and spread rates, and Rainbow Schlieren Deflectometry (RSD) and infrared thermography of the liquid surface were employed to measure the liquid thermal fields during spread. Large differences in the liquid temperature field were noted depending on the flow direction, and for some concurrent flow rates, the initial flame spread rate was affected. Slow opposed airflows serve mainly to alter the flame pulsation frequency, while small concurrent flows eliminate the pulsations in agreement with numerical modeling that indicates a gas-phase recirculation cell is necessary for flame pulsations. In microgravity the flame spreads slowly and uniformly for higher opposed velocities, and a lower bound of between 10 and 20 cm/s is found below which the flame begins to spread and then extinguishes.