An experimental study on coflow diffusion combustion in a pellet-packed bed with different bed lengths

In experimental investigations on axial symmetry, over-ventilated CH4/air diffusion combustion in a packed bed is executed to study the height, shape, and stability of the flame. The combustor is a quartz tube packed with alumina pellets in which a cylindrical fuel stream is surrounded by a coflow air nozzle. The results show that the bed length and pellet diameter have a significant influence on the flame properties. In general, the flame above the pellet surface has axial symmetry, and its shape and color are similar to those of a conventional diffusion flame when the bed length is smaller. The color of the flame front varies with the bed length. The changed color indicates an increased flame-front temperature and that the combustion regime above the bed surface may change from non-premixed combustion to partially premixed combustion or even premixed combustion due to the mix and dispersion effect in the packed bed. In addition, multiple flame behaviors, such as an inclined flame fron...