Abstract An experimental study on the compact lean premixed flames stabilized on a bluff-body and swirl burner is performed. The flames are featured with a strengthened Inner Recirculation Zone (IRZ). The objective is to identify the critical causes of blow-off near the lean limit. Meanwhile, the effects of hydrogen addition on the flame stabilization are also examined. Premixed CH4/H2/air mixtures are adopted with varied hydrogen fractions up to 80%. Flames far from and close to the blow-off conditions are both obtained for comparison. Simultaneous PIV/OH-PLIF measurements are performed, and flow-flame dynamics are analyzed. Results show that the flow straining near the flame root is dominant to induce the root extinction and initiate the blow-off. The strain is observed to mainly result from the shear deformation. The weakened root burning intensity is demonstrated with the CH* chemiluminescence. With hydrogen addition, the flame root is strengthened due to the enhanced resistance to the strain. The increased burning velocity and temperature with hydrogen are also beneficial for the flame stabilization. The inner shear layer vortices are anticipated to promote the blow-off by convecting cold unburned mixture into the IRZ.

中文翻译：

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在稳定和接近吹气条件下具有稀薄预混 CH4/H2/空气混合物的紧凑旋流火焰的实验研究

摘要 对钝体旋流燃烧器上稳定的致密稀薄预混火焰进行了实验研究。火焰具有强化的内部再循环区 (IRZ)。目标是确定在稀薄极限附近发生放气的关键原因。同时，还研究了氢气添加对火焰稳定性的影响。采用预混合的 CH4/H2/空气混合物，氢气含量高达 80%。获得远离和接近吹气条件的火焰以进行比较。同时进行 PIV/OH-PLIF 测量，并分析流动-火焰动力学。结果表明，火焰根部附近的流动应变占主导地位，导致根部灭绝并引发吹灭。观察到应变主要由剪切变形引起。CH* 化学发光表明根部燃烧强度减弱。加入氢气后，火焰根部因应变抗力增强而得到加强。用氢气增加的燃烧速度和温度也有利于火焰的稳定。预计内部剪切层涡流会通过将冷的未燃烧混合物对流进入 IRZ 来促进吹出。