Effects of Noise and Time Delay Upon Active Control of Combustion Instabilities

To improve the performance of practical active control system (ACS) for unstable combustors, the effects of system noise and ACS time delay upon combustion instabilities and the ACS performance were studied. Experimental and theoretical studies of an uncontrolled liquid fueled combustor showed that...

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Bibliographic Details
Main Authors: Zinn, Ben T, Neumeier, Y, Lubarsky, E, Johnson, C E, Lee, J
Format: Report
Language:English
Subjects:
COMBUSTION
Combustion and Ignition
COMBUSTORS
CONTROL SYSTEMS
DELAY
OSCILLATION
PRESSURE
WHITE NOISE
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Summary:To improve the performance of practical active control system (ACS) for unstable combustors, the effects of system noise and ACS time delay upon combustion instabilities and the ACS performance were studied. Experimental and theoretical studies of an uncontrolled liquid fueled combustor showed that the presence of noise apparently causes the 'beating' phenomenon and 'phase jumps' exhibited by the unstable pressure oscillations. Next, experiments in which the ACS was operated in open loop showed that the delay between the command signal to the ACS actuator and the response of the combustor pressure is of the order of two cycles of the oscillations. Subsequent simulations showed that this large time delay adversely affects the ACS performance. Furthermore, simulations and experimental studies of the ACS performance when operated in closed loop showed that the 'beating' phenomenon depends upon the complex relationship between the noise and the process that drives the instability, they poorly attenuate the random component of these oscillations, which is related to the magnitude of the RMS of the pressure oscillations. The combined effects of the long time delay in the control loop cause this.