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

K.D. Edwards

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 different mechanisms. Acoustic coupling with the tailpipe produces large-amplitude pressure oscillations which are nonlinear in nature due to interaction with the combustion reaction 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.

Edwards KD (2000). Application of occasional feedback trajectory correction to enhance lean combustion quality in a pulsed combustor. Ph.D. Thesis, University of Tennessee, Knoxville.
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