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Experiment investigation of the effects of hydrogen content on the combustion instability of methane/hydrogen lean premixed swirl flames under different acoustic frequency ranges

Experimental study on combustion instability of lean premixed swirl flame was conducted for methane-hydrogen mixtures, and the influence mechanism of hydrogen content (0%, 10%, 20%, and 40%) on the combustion instability under different acoustic frequencies (110–240 Hz) was investigated. A forced acoustic field created by a loud speaker was to simulate the complex and variable acoustic environment of unstable combustion. The flame transfer function was used to characterize the combustion instability. The morphologies of the flame, the evolution of vortex in the flame flow field, intensity of OH* chemiluminescence of flame front structure, and the degree of local thermo-acoustic oscillation of flame were also investigated to facilitate this study. The results show that the increase in hydrogen content weakens the combustion instability of lean premixed swirl flame in the acoustic frequency ranges of 170–240 Hz, while the combustion instability is enhanced for the acoustic frequency ranges of 110–160 Hz. The main reason for this phenomenon is the increase in the hydrogen content changes development of the vortex in the flame flow field, the evolution of the flame surface and the intensity of OH* chemiluminescence of flame front structure. This study provides an important reference for mastering the mechanism of the combustion instability of mixed gas flames and for developing technologies to inhibit combustion instability.