Effects of porous media on partially premixed combustion and heat transfer in meso-scale burners fuelled with ethanol

Porous media (PM) have the potential to enhance the flame stability and improve thermal performance in a micro/meso-scale burner. In this work, zirconia foam and high-porosity nickel foam are used in the meso-scale burners and partially premixed submerged combustion of liquid ethanol is achieved. An experimental investigation of the effects of foamed PM on flame structure, detailed temperature distributions, emissions, and thermal performance is undertaken. A blue flame can be observed in the nickel foam and the transient features of flame front is obtained. The flame front propagates intermittently when the combustion zone moves upstream. The maximum instantaneous flame speed in the PM is 6.519 mm/s and the average flame speed is 0.225 mm/s. The foamed PM in the meso-scale burners are shown to significantly improve the heat transfer efficiency. The burner in submerged combustion has a lower reaction zone temperature (806 °C vs. 1721 °C), lower exhaust gas temperature (419 °C vs. 1227 °C) and higher wall temperature than that with free flame. The heat transfer efficiency of the submerged flame is about twice that of the free flame.