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Accession Number:
ADP011174
Title:
Performance Enhancement of Gas-Turbine Combustor by Active Control of Fuel Injection and Mixing Process - Theory and Practice
Descriptive Note:
Corporate Author:
CINCINNATI UNIV OH DEPT OF AEROSPACE ENGINEERING AND ENGINEERING MECHANICS
Report Date:
2001-06-01
Pagination or Media Count:
10.0
Abstract:
Unstable thermoacoustic modes were investigated and controlled in an experimental low-emission swirl stabilized combustor, in which the acoustic boundary conditions were modified to obtain combustion instability. Axisymmetric and helical unstable modes wore identified for fully premixed combustion These unstable modes were associated with flow instabilities related to the recirculation region on the combustor axis and shear layer in- stabilities at the sudden expansion dump plane. The combustion structure associated with the different unstable modes was visualized by phase locked images of OH chemi- luminescence, The axisymmetric mode showed large variation of the heat release during one cycle, while the helical modes showed circumferential variations in the location of maximal heat release. Two feedback control methods employed to suppress thermoa- coustic pressure oscillations and to reduce emissions reviewed proportional acoustic control and fuel modulations. Microphone sensors monitored the combustion process and provided input to the control systems. An acoustic actuation modulated the airflow and thus affected the mixing process and the combustion. Suppression levels of up to 25 dB in the pressure oscillations and a concomitant 10 reduction of NOx emissions were obtained. At the optimal control conditions It was shown that the major effect of the control system was to reduce the coherence of the vortical structures which gave rise to the thermoacoustic instability. The specific design of the investigated experimental burner allowed testing the effect of different modulated fuel injection concepts on the combustion instability modes. Symmetric and antisymmetric fuel injection schemes were tested. Suppression levels of up to 12 dB in the pressure oscillations were observed. In some cases concomitant reductions of NO and CO emissions were obtained.
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
