Ammonia (NH3) has been widely considered as a promising carbon-free energy and hydrogen carrier for various applications. The large-scale direct utilization of NH3 as fuel in gas turbine engines is currently attracting significant interest, with strong focuses on improving the efficiency and stability of the system and reducing the emissions of pollutants. The present study experimentally examined the impacts of swirl intensity on combustion stability and emissions in an NH3-enriched premixed swirl-stabilized CH4/air combustor under a wide range of equivalence ratios. Simultaneous high-speed OH* chemiluminescence and particle image velocimetry measurements suggested that increasing swirl intensity resulted in more compact flame shapes and expanded the recirculation zone, which promoted flame stability at higher NH3 ratios. However, under specified conditions, enhancing swirl intensity could increase the instability frequency and amplitude of pressure oscillations. The flame dynamics exhibited different behaviors depending on the swirl intensity. At high swirl intensity, the flames underwent high-frequency, small-amplitude periodic motion. At low swirl intensity, the flames oscillated axially with large amplitude and low frequency. For flow dynamics, the stability of the vortex at high swirl intensity contrasted with the periodic vortex shedding at low swirl intensity. Furthermore, the two-dimensional Rayleigh index indicated that the dominant positive thermoacoustic coupling regions were located near the flame shear layers and flame tail at low and high swirl intensities, respectively. Finally, the experimental results showed that swirl intensity affected pollutant emissions by influencing the temperature of combustion chamber and gas mixing efficiency. The pathway of fuel-type NOx was found to be dominant in the NOx emission of the NH3/CH4/air flames.

中文翻译：

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旋流强度对富氨甲烷/空气燃烧器中燃烧动力学和排放的影响

氨（NH3）被广泛认为是一种有前景的无碳能源和氢载体，适用于各种应用。目前，在燃气涡轮发动机中大规模直接利用NH3作为燃料引起了人们的极大兴趣，重点是提高系统的效率和稳定性以及减少污染物的排放。本研究通过实验检验了在各种当量比下，旋流强度对富 NH3 预混旋流稳定 CH4/空气燃烧器中燃烧稳定性和排放的影响。同时进行的高速 OH* 化学发光和粒子图像测速测量表明，增加旋流强度可导致更紧凑的火焰形状并扩大再循环区，从而促进较高 NH3 比例下的火焰稳定性。然而，在特定条件下，增强旋流强度会增加压力振荡的不稳定频率和幅度。根据旋流强度，火焰动力学表现出不同的行为。在高旋流强度下，火焰进行高频、小幅度的周期性运动。在低旋流强度下，火焰轴向振荡，振幅大，频率低。对于流动动力学，高涡流强度下涡流的稳定性与低涡流强度下的周期性涡流脱落形成对比。此外，二维瑞利指数表明，在低旋流强度和高旋流强度下，主要的正热声耦合区域分别位于火焰剪切层和火焰尾部附近。最后，实验结果表明，旋流强度通过影响燃烧室温度和气体混合效率来影响污染物排放。研究发现，燃料型 NOx 的途径在 NH3/CH4/空气火焰的 NOx 排放中占主导地位。