Application of occasional feedback trajectory correction to enhance lean combustion quality in a pulsed combustor

The behavior of a laboratory-scale pulsed combustor is characterized over a wide range of operating conditions. The behavior of the combustor is shown to be driven by two differ- ent mechanisms. Acoustic coupling with the tailpipe produces large-amplitude pressure oscillations which are nonlinear in nature due to interaction with the combustion reac- tion and turbulent mixing. Due to the highly nonlinear nature of the combustion reaction at lean conditions, the system dynamics undergo a bifurcation as the equivalence ratio approaches the lean flammability limit which introduces low-frequency combustion instabilities that are superimposed upon the acoustically driven pressure oscillations. Rapid consumption and slow restocking of the available fuel inventory leads to poor-quality combustion events, misfire and, eventually, unrecoverable flameout.

A control algorithm is presented which monitors the peak pressure during each cycle to detect when the available fuel inventory has been consumed and the pulsed combustor begins to experience poor-quality combustion events while the fuel inventory is restocked. The controller then injects a small pulse of supplemental fuel to hasten the restocking process and drive the system back toward a more stable mode of operation. The control strategy is shown to be effective at dampening the combustion instabilities which results in lower unburned-hydrocarbon emission levels and allows the operating regime of the combustor to be extended further toward the lean flammability limit.