Combustion in a Meso-Scale Liquid-Fuel-Film Combustor with Central-Porous Fuel Inlet

Abstract

Utilizing a metal-porous medium for a liquid fuel film combustor is an effective method to increase the contact surface area and conduction heat transfer for liquid fuel vaporization and flame stabilization. Based on this concept, a meso-scale liquid fuel film combustor with a central porous inlet is developed and tested. The effects of porous material type and bead size on the flame structures and combustion characteristics are examined. Porous media made of stainless steel and bronze are tested in the meso-scale combustor with different fuel and air flow rates, equivalence ratios, and bead sizes. The flame structure and its corresponding stabilization mechanism are different between the stainless steel and the bronze porous media combustor. In the stainless steel case, the high specific heat capacity enhances fuel vaporization and fuel-air mixing, and the flame anchor locates on the surface of the porous cap. In the bronze case, due to its low heat capacity, the flame is swept downstream where the recirculation zone above the porous cap offers a low velocity field to help anchor the flame. The flame structure and stabilization mechanism in the chamber can be related to a tribrachial flame. Chemiluminescence measurement and Abel deconvolution are performed to verify the flame structure in the vicinity of the porous cap. In addition, temperature measurements and exhaust gas analysis highlight the differences in combustion characteristics between the two kinds of porous media. As regards bead size effects, results indicate that there is no obvious difference in flame structure and flame anchoring position, but the stable operating ranges of a porous combustor decrease with decreasing bead size due mainly to the concomitant increase in thermal conductivity.