Blow-off characteristics of a premixed methane/air flame response to acoustic disturbances in a longitudinal combustor

Abstract In this work, we conducted systematic studies on a premixed methane/air flame response to acoustic disturbances in a longitudinal combustor with emphasis on the blow-off characteristics. Both experimental and numerical studies are performed to shed lights on the premixed flame-acoustics interaction in an acoustic resonant combustor. It is experimentally found that the flame separation and flame height increment are captured during the blow-off process. The vortices on the unburnt gas are revealed by the schlieren images, which suggest that the flame height increment is significantly affected by the evolution of the vortices in the unburnt gas. The blow-off sound pressure level is shown to be decreased significantly under an excitation frequency of 260 Hz. In this case, our PIV tests suggest that a weaker pressure disturbance can induce velocity fluctuations with a larger amplitude. To better understand the acoustics resonant dynamical response of the combustor and blow-off characteristics, numerical simulation is performed to investigate the combustor's acoustic modes. According to the acoustic modes of the combustor under various excitation frequencies, the flame is located in a low sound pressure region when the excitation frequency is 260 Hz, where the velocity amplitude is larger than that in other regions. The easily induced blow-off behavior of the flame at 260 Hz is caused by the critical velocity amplitude in this region. In general, the present work sheds light on the fundamental physics of a premixed flame response to acoustic disturbances.