K.D. Edwards, C.E.A. Finney, K. Nguyen
University of Tennessee
Knoxville TN 37996-2210
Oak Ridge National Laboratory
Knoxville TN 37932-6472
A feedback control strategy is applied to enhance the performance of a laboratory-scale pulsed combustor operating near the lower flammability limit. As with many combustion processes, at lean conditions, combustion instabilities develop which result in complex, low-frequency fluctuations in fuel concentration and lead directly to misfire and flameout. The control strategy exploits the highly nonlinear relationship between equivalence ratio and reaction rate at lean operating conditions to dampen the instabilities via high-speed injection of supplemental fuel. Timing of the control perturbations is determined by monitoring the combustor pressure for characteristic mediating trajectories which lead to misfire. The nonlinear nature of the system allows combustion stabilization to be achieved with relatively small injections of supplemental fuel. The control scheme is shown to be effective in reducing unburned-hydrocarbon emission levels and extending the practical operating limit of the pulsed combustor towards the lower flammability limit.
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