Adaptive 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. Control action is achieved by injecting auxiliary liquid fuel, and is modeled as an array of time-delayed combustion sources. The adaptive controller employs on-line system identification (SID) for robustness with respect to transient operating states, modeling uncertainties, external disturbances, and additional modes of instability that may arise in the course of control. Comparisons are made between the adaptive controller and a previously developed proportional-plus-integral (PI) controller, in terms of performance (degree of oscillation suppression, and speed with which oscillations are damped), robustness against plant parameter changes (particularly unknown factors of the auxiliary characteristics), and control-fuel mass expenditure. The adaptive controller exhibits good performance with a clear advantage over the PI controller in robustness. Also, the adaptive controller with on-line SID stabilizes the pressure oscillations without exciting additional mode(s).