Active control of combustion instability with on-line system identification

In this study, an adaptive control system is developed for suppressing pressure oscillations in a generic combustor, where the unsteady flowfield associated with the combustion instability is described by a nonlinear inhomogeneous wave equation. The control system consists of a pressure sensor, the controller, and an auxiliary fuel injector. The influence of the controlled fuel injection is modeled as a distributed array of time-delayed combustion sources. Controller performance is examined in terms of robustness against plant parameter changes (especially unknown factors involved in the injector performance), pressure oscillation convergence speed, and control fuel mass expenditure. A proportional-plus-integral (PI) controller studied previously by Fung et al. (Y.T. Fung, V. Yang, and A. Sinba, Combust. Sci. and Tech. 78:217-245 1991) is used to compare with the adaptive controller. The comparison shows that the adaptive controller is more robust with respect to system uncertainties. Also, first order estimates for controller convergence speed and control fuel consumption are established for application to a realistic scenario.