Data from: 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 front, isolated reaction zone, and oscillatory motion followed by a pulsating sound with a few Hz in a packed bed, are observed experimentally. The possible reasons for these phenomena are discussed.本研究针对轴对称工况下填充床（packed bed）内过通风甲烷-空气（CH4/air）扩散燃烧开展实验，以探究火焰高度、形貌与稳定性。实验所用燃烧室为填充氧化铝颗粒（alumina pellets）的石英管，圆柱形燃料射流被同轴空气喷嘴（coflow air nozzle）环绕。实验结果表明，填充床床长与颗粒直径对火焰特性具有显著影响。总体而言，当床长较小时，颗粒表面上方的火焰呈现轴对称特征，其形貌与颜色均与常规扩散火焰相近。火焰锋面颜色随床长变化而改变，颜色变化意味着火焰锋面温度升高；且由于填充床内的混合与弥散效应，床面上方的燃烧工况可能从非预混燃烧（non-premixed combustion）转向部分预混燃烧（partially premixed combustion），甚至完全预混燃烧（premixed combustion）。此外，实验中还观测到多种火焰行为：包括倾斜的火焰锋面、孤立反应区，以及填充床内伴随数赫兹脉动声响的振荡运动。本文对上述现象的潜在成因展开了讨论。