Experimental Investigation on Thermoacoustic and Structural Dynamics in a Premixed Arrayed Micro-Tube Hydrogen Combustor

Thermoacoustic instability remains a major challenge in the development of hydrogen micromix combustors. This study presents the design of a full-scale premixed-array microtube hydrogen combustor. Jet-in-crossflow micromixing technology was employed, resulting in relatively uniform mixing within each injector tube. Subsequently, the thermoacoustic dynamics were investigated. A low-order thermoacoustic model was used to characterize the experimentally observed longitudinal acoustic oscillations, with a deviation of 1.6% in the predicted modal frequency. After the onset of thermoacoustic instability, intermittent high-amplitude burst oscillations emerged amid low-amplitude combustion noise at moderate equivalence ratios, as quantified using recurrence quantification metrics. As the equivalence ratio increased further, the bursts gradually dominated the pressure fluctuations, eventually leading to an intense limit-cycle oscillation above 1800 Pa. Collective synchronization among individual flames was a key factor in distinguishing intermittent from limit-cycle oscillations. The phase difference between the heat-release fluctuations of different flame elements was nearly fixed during limit-cycle oscillation, whereas intermittent oscillation showed weaker phase synchronization. Finally, the structural vibration induced by thermoacoustic oscillations was found to be spatially anisotropic and to exhibit a linear amplitude relationship. The derived proportional coefficient was 8.5 m⋅(s²⋅kPa)⁻¹, which facilitates quantitative evaluation of the strength of thermoacoustically induced vibration. The structural dynamics exhibited a significant response gain in the high-frequency regime. This study sheds light on understanding the instability and broadening the operability of the hydrogen combustor.