In this study, we investigate the flame stabilization behavior in hydrogen-enriched stratified swirl flames after the flame flashes back into an annular mixing tube with an axial swirler of swirl number 0.9. Two different modes of flame stabilization, namely intermediate stabilization and flameholding, are identified. For 80% or higher hydrogen enrichment of the fuel, the flashback is found to result in flameholding. Acetone-PLIF measurements are used to assess the equivalence ratio distribution in the mixing tube. It is shown that the flow inside the mixing tube has intermittent presence of fuel-rich pockets. Furthermore, high speed laser diagnostic and simultaneous chemiluminescence imaging was carried out to understand the transition of flame propagation from the center-body boundary layer to the outer wall boundary layer. With the help of time-resolved images and simultaneous velocity fields, four different stages of flashback-to-flameholding transition were identified. It was noted that the bright flame kernels formed due to the flame's interaction with fuel-rich pockets, impose significant deflection on the approach flow in the vicinity of the outer wall boundary layer. Acute-tipped narrow flame structures were found to anchor the flame on the outer wall. These flame structures were found to accelerate upstream upon reaching the fuel-rich regions in the outer wall boundary layer.

在这项研究中，我们研究了富氢分层涡流火焰在火焰闪回具有涡流数 0.9 的轴向涡流器的环形混合管后的火焰稳定行为。确定了两种不同的火焰稳定模式，即中间稳定和火焰稳定。对于 80% 或更高的氢富集燃料，发现回火会导致火焰稳定。丙酮-PLIF 测量用于评估混合管中的当量比分布。结果表明，混合管内的流动间歇性地存在富燃料袋。此外，还进行了高速激光诊断和同步化学发光成像，以了解火焰传播从中心体边界层到外壁边界层的转变。在时间分辨图像和同步速度场的帮助下，确定了闪回到火焰保持过渡的四个不同阶段。值得注意的是，由于火焰与富含燃料的口袋相互作用而形成的明亮火焰核对外壁边界层附近的引流造成了显着的偏转。发现尖尖的窄火焰结构将火焰固定在外壁上。发现这些火焰结构在到达外壁边界层中的富含燃料的区域时向上游加速。对外壁边界层附近的引流施加显着偏转。发现尖尖的窄火焰结构将火焰固定在外壁上。发现这些火焰结构在到达外壁边界层中的富含燃料的区域时向上游加速。对外壁边界层附近的引流施加显着偏转。发现尖尖的窄火焰结构将火焰固定在外壁上。发现这些火焰结构在到达外壁边界层中的富含燃料的区域时向上游加速。