Lean Extinction Characteristics of Kerosene Spray Flames in Porous Media

Abstract

This paper presents an experimental study of lean extinction characteristics of kerosene spray flames in porous media. Two silicon carbide coated carbon-carbon foam porous media with 8 and 25 pores per centimeter both with 87% porosity were used in the experiments. The first (evaporation porous medium) was used to enhance the vaporization rate of liquid fuel. The second (combustion porous medium) was used to stabilize flame on the surface or interior of the porous medium. Aviation grade kerosene was injected upstream of evaporation porous medium with an air-blast atomizer. A Damkohler number-based analysis was developed to study the extinction behavior. Preheating residence time was varied by changing the location of the injector and coflow air velocity. Results show that in interior combustion mode the flame was completely contained within the porous medium and heated it to bright yellow glowing temperature. As fuel flowrate was decreased towards lean extinction limit, a weak transient blue flame appeared on the downstream surface, and immediately extinguished. In surface combustion mode, a decrease of fuel flow rate resulted in a flame partially lifted from the porous medium surface. A further decrease of fuel flow rate resulted in flame extinguishment and a fully lifted flame could not be stabilized. A minimum value of Damkohler number was required to initiate interior combustion. Axial temperature profile and surface temperature uniformity in porous media were also examined near extinction conditions.