The effect of mixing tube length (partial premixing level) on the amplitude of coherent structures and acoustics, and stability of partially premixed flames (PPFs) of methane off a concentric flow conical nozzle (CFCN) swirl burner is experimentally investigated. The flowfield inside the quartz confinement is documented using particle image velocimetry (PIV), and coherent structures are captured using proper orthogonal decomposition (POD) technique. Acoustics measurements are performed using Bruel & Kjaer type 4189 microphone. Additionally, high-speed imaging and quantitative light sheet (QLS) techniques are used to qualitatively investigate the flow mixing characteristics. The results reveal that increasing partial premixing level significantly enhances flame stability. Compared to traditional dump burner/combustor, the present burner configuration promotes flame divergence with no outer recirculation zone (ORZ) and larger homogeneous and isotropic turbulent zone. More importantly, the results show that, in contrast to the traditional dump combustor, the use of a swirl in a CFCN burner makes it possible to sustain stable flame under ultra-lean conditions.

实验研究了混合管长度（部分预混合水平）对相干结构和声学振幅的影响以及同心流锥形喷嘴（CFCN）旋流燃烧器中甲烷的部分预混合火焰（PPF）的稳定性。使用粒子图像测速（PIV）记录了石英禁闭区内的流场，并使用适当的正交分解（POD）技术捕获了相干结构。使用Bruel＆Kjaer 4189型麦克风进行声学测量。此外，高速成像和定量光片（QLS）技术用于定性研究流动混合特性。结果表明，增加部分预混合水平显着增强了火焰稳定性。与传统的自燃式燃烧器/燃烧器相比，当前的燃烧器结构在没有外部再循环区（ORZ）和更大的均质和各向同性湍流区的情况下促进了火焰的扩散。更重要的是，结果表明，与传统的倾卸式燃烧器相比，CFCN燃烧器中使用涡流可以在超稀薄条件下维持稳定的火焰。