Model-based control of combustion instabilities

Model-based active controllers are designed for two laboratory combustion systems exhibiting a combustion instability, a simple Rijke tube and an atmospheric pressure combustion rig. The unstable open-loop transfer functions (OLTFs) of both are measured experimentally using an actuator signal which is comprised of two components; a control signal from an empirically obtained controller, and a wide-bandwidth signal for identification of the transfer function. This method of measuring the OLTF could be applied equally well at full scale. Robust model-based controllers are designed for both systems using linear Nyquist techniques, and are implemented experimentally. Both sets of controllers stabilise their system (even from within the limit cycle resulting from instability), with a reduction of 80 dB at the Rijke tube microphone and a reduction of approximately 40 dB at the combustion rig pressure transducer. In addition, both sets of controllers are demonstrated to control the system beyond the operating conditions which they were designed for, demonstrating the advantages of robust model-based controllers.