nfluences of acoustic instabilities on turbulent-flame propagation

Influences of acoustic instabilities on premixed turbulent-flames have been studied experimentally in a Taylor–Couette (TC) combustor for downward flame propagation in a turbulent flow-field generated in the annulus between two cylinders. Flow-field velocities were measured at a fixed location upstream of the propagating flame using laser-doppler velocimetry, while flame speeds were determined from video-recorded images. It is found that the existence of pre-ignition turbulence in the combustor (generated by rotation of the combustor-cylinder walls) does not eliminate acoustic instabilities, however as the level of pre-ignition turbulence is increased the influence of the secondary acoustic instability on the turbulent-flame speed becomes insignificant. For low intensities of pre-ignition turbulence the flame is found to accelerate during the latter stages of flame propagation, while for high levels of pre-ignition turbulence the flame propagates at a statistically constant speed, even though velocity fluctuations have been substantially amplified by the time the flame reaches the bottom end of the combustor as a result of acoustic instability.