Experimental investigation of the effect of mechanical vibration on the laminar premixed flame

Energy conversion from heat to acoustics remains one of the major challenges in high-performance propulsion systems. It has been found that structure vibration may lead to combustion instability, though the mechanism behind this is still unknown. In this paper, the impact of axial mechanical vibration on a premixed methane flame is studied experimentally, using an electromagnetic vibration exciter to drive the flame burner. The burner's movement is measured by the accelerometers. The flame morphology is captured by a high-speed camera with an image intensifier via long exposure times, and the local unsteady heat release rate is measured by a photomultiplier tube. The flame transfer functions are analyzed at various equivalence ratios and mean flow velocities. The results indicate that the mechanically induced vibration leads to a clear bandpass filtering effect on the premixed flame across different equivalence ratios and flow velocities without altering the peak frequency. In addition, as the vibration amplitude increases, the flame response saturates and the flame tips become wrinkled, especially when the driving frequency aligns with the response peak.