Abstract Modern, lean and premixed gas turbine combustion concepts for low NOx emissions are prone to combustion instabilities. In a previous work it was shown that laser interferometric vibrometry (LIV) can be used to record global as well as local heat release fluctuations in swirl-stabilized premixed methane flames quantitatively, if other effects influencing density are small. In this work a newly developed camera-based full-field LIV system (CLIV) was applied to a lean, confined, premixed and swirl-stabilized methane flame under atmospheric conditions. Instead of time-consuming pointwise scanning of the flame, CLIV records full-field line-of-sight density fluctuations with high spatio-temporal resolution. With a recording rate of 200 kHz, CLIV enables the visualization of highly unsteady processes in fluid dynamics and combustion research. As an example for an unsteady process, the propagation of the flame front through a lean, premixed gas volume is visualized during an ignition process. A discussion of algorithms and assumptions necessary to calculate heat release oscillations from density oscillations is presented and applied to phase-averaged data recorded with CLIV for this type of flame. As reference, OH* chemiluminescence data were recorded simultaneously. While density gradients travelling with the flow are recorded by LIV and CLIV, chemiluminescence imaging will show nothing in the absence of chemical reaction. Graphic abstract a Time-averaged density gradient within the combustor in lateral direction. b Density fluctuations along line-of-sight 7 ms after ignition. c Phase-averaged and local heat release fluctuations at 225 Hz perturbation frequency

中文翻译：

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用全场激光干涉测振仪定量测量密度波动

摘要 用于低 NOx 排放的现代、稀薄和预混燃气轮机燃烧概念容易出现燃烧不稳定性。在以前的工作中表明，如果影响密度的其他影响很小，激光干涉测振法 (LIV) 可用于定量记录旋流稳定预混甲烷火焰中的全局和局部放热波动。在这项工作中，新开发的基于相机的全场 LIV 系统 (CLIV) 应用于大气条件下的稀薄、受限、预混合和旋流稳定的甲烷火焰。CLIV 不是对火焰进行耗时的逐点扫描，而是以高时空分辨率记录全场视线密度波动。CLIV 具有 200 kHz 的记录速率，可实现流体动力学和燃烧研究中高度不稳定过程的可视化。作为非稳态过程的一个例子，在点火过程中，火焰前锋在稀薄的预混合气体体积中的传播是可视化的。讨论了从密度振荡计算放热振荡所需的算法和假设，并将其应用于使用 CLIV 记录的此类火焰的相位平均数据。作为参考，同时记录 OH* 化学发光数据。虽然 LIV 和 CLIV 记录了随流移动的密度梯度，但在没有化学反应的情况下，化学发光成像将什么也没有显示。图形抽象了燃烧器内横向的时间平均密度梯度。b 点火后 7 ms 沿视线的密度波动。c 225 Hz 扰动频率下的相位平均和局部放热波动