An experimental investigation of self-excited combustion instabilities in a high pressure, lean premixed natural gas jet flame is presented. The combustor is designed with optical access and is instrumented with high frequency pressure transducers at multiple axial and circumferential locations. OH*-chemiluminescence measurements performed at a frequency of 50 kHz were temporally synchronized with the acoustic measurements recorded from the pressure transducer array during the test. Two representative test conditions are analyzed in detail: Flame 1 (F1) that presents longitudinal mode dynamics $(p^{\prime }/p_c=3\%)$ and Flame 2 (F2) that presents high amplitude transverse instabilities $(p^{\prime }/p_c=15\%)$. Singular Spectrum Analysis (SSA) and Dynamic Mode Decomposition (DMD) analysis indicate a strong correlation of both instabilities to flame-vortex interactions. Longitudinal mode instabilities are correlated with axisymmetric vortex shedding about the combustor axis that result in periodic axial variations in heat release at the 1L frequency. Transverse mode instabilities correspond to asymmetric vortex shedding pattern that drive transverse variations in heat release at the fundamental 1T frequency of the combustion chamber. The phase relationship of the flame emission intensity and the chamber head-end pressure measurement at the 1T frequency indicates presence of a non-stationary transverse mode that rotates about the chamber axis at 55 Hz.

提出了在高压，稀薄的预混天然气射流火焰中自激燃烧不稳定性的实验研究。燃烧室设计为具有光学通道，并在多个轴向和圆周位置装有高频压力传感器。在测试期间，以50 kHz频率执行的OH *化学发光测量与从压力传感器阵列记录的声学测量在时间上同步。详细分析了两个代表性的测试条件：火焰1（F1），显示纵向模式动力学$（p^{\prime }/p_C=3％）$ 火焰2（F2）表现出高幅度的横向不稳定性 $（p^{\prime }/p_C=15％）$。奇异频谱分析（SSA）和动态模式分解（DMD）分析表明，两种不稳定性都与火焰涡旋相互作用密切相关。纵向模式的不稳定性与绕燃烧器轴的轴对称涡流相关，导致在1L频率下热量释放的周期性轴向变化。横向模式不稳定性对应于非对称涡旋脱落模式，该模式驱动燃烧室的基本1T频率的热量释放产生横向变化。在1T频率下，火焰发射强度与腔室前端压力测量的相位关系表明存在一个非平稳横向模式，该模式围绕腔室轴以55 Hz的频率旋转。