Closed-loop control in a flame and a dump combustor

A closed-loop control system was constructed to control the lift-off height of a premixed flame at the lean flammability limit. Control authority was obtained by forcing the initial shear layer of the fuel-air mixture, thus generating small scale vortices which improved the flame stability. An AM controller was developed using the open-loop frequency as a carrier signal. Bode and Nyquist analyses showed that the flame is stable only in a limited range due to convective time lag, related to the convection time of the vortices. The application of lead and lag compensations was studied to extend the stability margins. The control system response to changes in operating conditions was superior to that of the open-loop control operation. The same actuation technique investigated in the flame experiments is used, in conjunction with a different control strategy, for active combustion control in the dump combustor. Parameters affecting the efficiency of the various methods for active combustion control were studied. The effectiveness of the acoustic shear-layer excitation on the combustion characteristics was evaluated.<
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