Premixed combustion in a porous burner with different fuels

This study investigated the premixed combustion of fuel/air in a packed bed burner. The burner was packed with alumina (Al₂O₃) beads with upstream and downstream diameters of 3 mm and 8 mm, respectively. Methane was selected as fuel, whereas propane and hydrogen were taken as alternative fuels. The effects of fuel on flame stability, axial temperature profile, flame temperature, pressure drop of cold and reaction flows, and concentration levels of pollutants were investigated. The equivalence ratio for methane or propane/air and hydrogen/air, respectively, varied in the range from 0.55 to 0.70 and 0.25 to 0.35. Results showed that the flame stability limits of methane, propane, and hydrogen expanded with increasing equivalence ratio. The flame stabilization region of hydrogen/air was the largest among those of the three fuels because of higher mass diffusion and heat release through combustion. The flame temperature strongly depended on flame speed, equivalence ratio, and fuel type. Carbon monoxide emissions were mainly dependent on flame temperature and were significantly reduced below 50 ppm when the temperature was above 1400°C. The unburned hydrocarbon emissions were sensitive to the equivalence ratio and fuel type. The nitrogen oxide levels of propane were higher than those of methane and remained fairly constant for a given equivalence ratio.