ABSTRACT In the near future, lean-premixed hydrogen combustion technology for low-emission gas turbine engines is expected to be crucial in the effort to mitigate greenhouse gas emissions, in association with energy system decarbonization. In this study, we examine combustion instabilities in lean fully-premixed hydrogen-air flames in a mesoscale multinozzle array; little is currently known about how these flames respond to acoustic perturbations. Several measurement techniques, including phase-synchronized OH* chemiluminescence imaging, OH Planar Laser Induced Fluorescence, acoustic pressure, and the two microphone method, are used, together with reduced-order acoustic modeling, to identify the key physical properties of lean-premixed hydrogen-air flames, in comparison with lean-premixed methane-air flames. We show that extremely compact lean-premixed hydrogen flames are preferentially coupled to higher eigenmodes of a given system, L3 – L6, including approximately 1 kHz high-frequency instabilities, while the instabilities of methane-air flames are predominantly limited to the first longitudinal mode under the same range of operating conditions. This is attributed to the fact that the dynamics of the methane flames are governed by the collective motion of constituent flames, involving a complex process of the emergence, convection, and interaction of large-scale structures. By contrast, the hydrogen flames in the multinozzle configuration oscillate in isolation within a very short distance and without strong flame-to-flame interactions. This is particularly suitable for accommodating high-frequency heat release modulations. The triggering of intense sound generation from lean-premixed mesoscale hydrogen flames is correlated strongly with a combination of flame surface destruction due to front merging and the flames’ close proximity to a pressure antinode. These results, for the first time, highlight the key features of self-excited combustion instabilities of mesoscale multinozzle hydrogen-air flames in a well-controlled laboratory-scale experiment, and could pave the way for future carbon-neutral gas turbine combustion technology.

中文翻译：

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中尺度多喷嘴阵列中贫完全预混氢-空气火焰的燃烧动力学

摘要在不久的将来，低排放燃气涡轮发动机的稀薄预混氢燃烧技术有望在减少温室气体排放以及能源系统脱碳方面发挥关键作用。在这项研究中，我们在中尺度多喷嘴阵列中检查了贫完全预混氢-空气火焰中的燃烧不稳定性；目前对这些火焰如何响应声学扰动知之甚少。几种测量技术，包括相位同步 OH* 化学发光成像、OH 平面激光诱导荧光、声压和两个麦克风方法，与降阶声学模型一起使用，以确定贫预混氢的关键物理特性- 空气火焰，与贫气预混甲烷-空气火焰相比。我们表明，极其紧凑的贫预混氢火焰优先耦合到给定系统 L3 – L6 的更高本征模式，包括大约 1 kHz 的高频不稳定性，而甲烷-空气火焰的不稳定性主要限于第一纵向模式在相同的操作条件范围内。这归因于甲烷火焰的动力学受组成火焰的集体运动控制，涉及大规模结构的出现、对流和相互作用的复杂过程。相比之下，多喷嘴配置中的氢火焰在非常短的距离内独立振荡，并且没有强烈的火焰与火焰相互作用。这特别适用于适应高频放热调制。稀薄预混中尺度氢火焰产生强烈声音的触发与由于前部合并造成的火焰表面破坏和火焰靠近压力波腹的组合密切相关。这些结果首次在控制良好的实验室规模实验中突出了中尺度多喷嘴氢-空气火焰自激燃烧不稳定性的关键特征，可为未来的碳中性燃气轮机燃烧技术铺平道路。