Experimental study of combustion in a double-layer burner packed with alumina pellets of different diameters

The combustion performance in a double-layer burner packed with alumina pellets of different diameters was experimentally studied. The effects of the diameter of the alumina pellet on the flame stability limits, flame temperature, pressure drop, and pollutant emissions were examined. The 3. mm diameter alumina pellets were located in the upstream, while the 6, 8, 10, and 13. mm diameter alumina pellets were located in the downstream. A single-layer burner packed with 3. mm diameter pellets was also investigated as a reference. The flame can be more effectively stabilized near the interface between the two sections of double-layer burner. The flame stability limits could apparently be extended in the double-layer burner compared with the single-layer burner. The flame and surface temperatures increased more evidently with increased flame speed for the single-layer burner than for the double-layer burner. The flame temperature decreased with increased alumina pellet diameter, whereas the surface temperature was insensitive to the pellet diameter. An optimal pellet diameter corresponding to the lowest NO. _x emissions was found. The CO emissions of the double-layer burner were lower than those of the single-layer burner at a low velocity range (S<. 35. cm/s) and was almost identical for pellets of different diameters at a high velocity range (S>. 35. cm/s). The unburned hydrocarbon emissions decreased with increased alumina pellet diameter within the entire experimental velocity range.