Active control of combustion instabilities using real time identification of unstable combustor modes

The theoretical foundation and performance of an active control system that rapidly characterizes and damps combustor instabilities whose characteristics are not known in advance are presented. The heart of this control system is an observer that uses, for example, a measured combustor pressure to determine the frequencies and amplitudes of the combustor modes in real time. This information is input into a controller that provides each mode with a gain and a phase shift prior to sending a signal to an actuator that injects an oscillating fuel stream into the combustor. The paper uses numerical simulations to demonstrate the capabilities of the developed controller. First, it is shown that the developed observer can determine the frequencies and amplitudes of oscillating modes without having any prior knowledge about their characteristics. Next, it is shown that this controller can identify and control instabilities involving several modes in linearly unstable systems. Finally, the ability of the developed controller to rapidly damp a nonlinear, shock-wave like, instability in a rocket combustor by controlling the fundamental mode and its harmonics is demonstrated.