Three-dimensional flame propagation above liquid fuel pools

Abstract

Ignition and flame spread above liquid fuels initially below the flashpoint temperature are studied. Opposed air flow to the flame spread due to forced and/or natural convection is considered. Unsteady computations are performed in order to study the ignition event and to describe both uniform and pulsating flame spread. Pools of finite width and length are studied in air channels of prescribed height and width, thereby requiring a three-dimensional space resolution in order to capture the effects at the edge of the pool and at the side walls of the air channel. The effects of variations in surface tension due to surface temperature variations and of buoyancy in both the liquid and gas phases are considered. One-step chemical kinetics, Fickian diffusion, Fourier heat conduction, and laminar flow with variable properties are considered. Boundary layers at the walls and at the liquid/gas interface are resolved. A moving mesh scheme is employed to follow the flame motion. Regions of pulsation are found at both 1 g and 0 g. Average flame speed and pulsation frequency increase with initial fuel temperature. Surface tension can have a major effect, e.g., cause a recirculation. Buoyancy can modify flame speed and flame shape. The flame extends over the edge of the pool producing some clearly three-dimensional effects, such as lateral air motion. The computations are intended to guide and to explain experiments that are being performed at NASA Glenn by H. Ross and F. Miller.