Passive control methods are widely used in unsteady combustion systems due to their robustness and convenience. This paper used the upstream microjets method for the first time to control thermoacoustic instability and pollutant NOx emissions in unsteady swirl premixed flame. Three variables of CO₂ microjets flow rate, upstream microjets distance, and microjets number are investigated. Results demonstrate the upstream microjets distance plays a significant role in restraining the thermoacoustic instability and NOx emissions. The smaller the upstream microjets distance, the more completely the thermoacoustic instability is suppressed while the NOx emissions are the opposite, which means a compromise choice needs to be made between them. The damping ratio of pressure amplitude in the chamber can reach the maximum of 81.3%, and the damping ratio of CH* intensity can reach the maximum of 80.2%. Besides, the frequency of pressure and CH* will transit to a lower mode. NOx emissions can realize a maximum reduction of 12.2 ppm. Meanwhile, the flame mode switches from an enlarged Mode-A flame to a shrunk Mode-B flame, and the flame length shows a maximum reduction of 14 mm at the largest upstream distance. However, the specific control mechanism under upstream microjets still needs further study to clarify. This research proved the feasibility of suppressing combustion instability and NOx emissions with upstream microjets in unsteady swirl premixed flame, promoting its practical application in gas turbine systems.

中文翻译：

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上游微射流抑制非定常旋流预混火焰的热声不稳定性和氮氧化物排放

被动控制方法由于其鲁棒性和便利性而被广泛应用于非稳态燃烧系统。本文首次采用上游微射流方法控制非定常旋流预混火焰的热声不稳定性和污染物NOx排放。_{CO 2}的三个变量研究了微射流流速、上游微射流距离和微射流数量。结果表明，上游微射流距离在抑制热声不稳定性和 NOx 排放方面起着重要作用。上游微射流距离越小，热声不稳定性被抑制得越彻底，而NOx排放则相反，这意味着需要在它们之间做出折衷选择。腔内压力幅值阻尼比最高可达81.3%，CH*强度阻尼比最高可达80.2%。此外，压力频率和 CH* 将过渡到较低的模式。NOx 排放量最大可减少 12.2 ppm。同时，火焰模式从放大的Mode-A火焰切换到缩小的Mode-B火焰，火焰长度在最大上游距离处最大减少 14 毫米。但上游微射流下的具体控制机制仍需进一步研究阐明。该研究证明了上游微射流在非定常涡流预混火焰中抑制燃烧不稳定性和NOx排放的可行性，促进了其在燃气轮机系统中的实际应用。