A further Note on Active Control of Combustion instabilities Based on Hysteresis

Abstract

Hysteretic behaviour, as found in the dump combustor facility at GALCIT, allows nonlinear active control of the instability, demonstrated recently by Knoop et al. (1996). As in that work, pulses of secondary fuel, based on a simple on/off control law, have been successfully used to drive the transition between the two modes present in the hysteretic region, thereby reducing the amplitude of the pressure oscillations with minimal use of fuel. In order to clarify the origin of the phenomenon, high speed shadowgraph images of the flowfield during the transition between 'unstable' and stable burning have been taken, showing distinctive features that may help in modeling the observed behaviour. A preliminary parametric study (type of injector, duration of pulses, type of secondary flow) has also been conducted, showing that the transition can be obtained over a broad range of conditions.