Droplet-Stream Combustion in the Steady Boundary Layer near a Wall

Abstract

This paper presents a numerical analysis of the thermal-expansion effects on the behavior of healing and vaporizing fuel droplet streams in the flow near a healed flat plate. The gas-phase Navier-Stokes equations are simplified using (he boundary-layer approximation, while the thermal-expansion effect appears as a simplified state equation relating the gas density to its temperature. The main driving force for the thermal expansion is a one-step chemical reaction of the Arrhenius type between the vaporized fuel and the air. In addition, the heating of the gas near Ihe wall contributes to the thermal expansion. The droplets are injected parallel to the wall at a specified streamwise location, and are assumed to remain spherical at all times. The droplet temperature is nonuniform and time dependent. Comparisons of the droplet behavior in terms of trajectories, heating and vaporization rates are made. In all cases, it is predicted that the droplets will be driven away from the hot wall into the cooler gas region, thus increasing their lifelimes. This behavior is more pronounced for smaller and slow-moving droplets.