The transition of thermo-acoustic oscillations in a turbulent bluff-body syngas combustor is analyzed experimentally in the present work. The analysis was carried out for three syngas compositions using simultaneous, unsteady pressure measurement and OH* chemiluminescence across the variation of Reynolds number, Re, over 2289–8009 range. It is observed that across the variation of controlled parameters, the system undergoes series of dynamical states having different nonlinear oscillations. In this paper, we investigate the seldom observed transitions from low-frequency instability to high-frequency instability through two-scale oscillations, and finally, it attains the combustion noise state in response to the variation in Re. To identify the nature of these thermo-acoustic oscillations, time-series analysis based on wavelet transformation, phase portrait, and a novel wavelet-based measure is performed. Based on the results of time-resolved OH* chemiluminescence, the distinct flame behavior is observed in response to the change in Re. It is observed that syngas combustion instability is driven by small-scale structures due to flame stabilization and modulation in the shear layer. Further, the wavelet-based analysis also tracks the evolution of the dynamical state by quantifying the stable state and other non-stable states to be composed of continuously varying phase shifts resulting in stable/quasi-stable combustion.

在本工作中，通过实验分析了湍流钝体合成气燃烧器中热声振荡的转变。使用同时，非恒定压力测量和OH *化学发光对三种合成气成分进行了分析，整个过程的雷诺数Re在2289–8009范围内变化。可以看出，在受控参数的变化范围内，系统经历了一系列具有不同非线性振荡的动力学状态。在本文中，我们研究了很少观察到的通过两级振荡从低频不稳定性到高频不稳定性的转变，最后，它响应于Re的变化而达到了燃烧噪声状态。。为了识别这些热声振荡的性质，进行了基于小波变换，相位肖像和新颖的基于小波的测度的时间序列分析。根据时间分辨的OH *化学发光的结果，观察到独特的火焰行为响应Re的变化。可以看出，由于剪切层中的火焰稳定和调制，合成气燃烧的不稳定性是由小规模的结构驱动的。此外，基于小波的分析还通过量化稳定状态和其他不稳定状态（由连续变化的相移组成）来跟踪动态状态的演变，从而导致稳定/准稳定燃烧。