In this study, we examine the effectiveness of microjet air injection as a means of
suppressing thermoacoustic instabilities in a swirl-stabilized, lean-premixed propane/air
combustor. High-speed stereo PIV measurements, taken to explore the mechanism of
combustion instability, reveal that the inner recirculation zone plays a dominant role in the
coupling of acoustics and heat release that leads to combustion instability. Six microjet
injector configurations were designed to modify the inner and outer recirculation zones with
the intent of decoupling the mechanism leading to instability. Microjets that injected air into
the inner recirculation zone, swirling in the opposite sense to the primary swirl were
effective in suppressing combustion instability, reducing the overall sound pressure level by
up to 17 dB within a certain window of operating conditions. Stabilization was achieved near
an equivalence ratio of 0.65, corresponding to the region where the combustor transitions
from a 40 Hz instability mode to a 110 Hz instability mode. PIV measurements made of the
stabilized flow revealed significant modification of the inner recirculation zone and
substantial weakening of the outer recirculation zone.
LaBry Z, Shanbhogue S, Speth R, Ghoniem A (2010) Instability Suppression in a Swirl-Stabilized Combustor Using Microjet Air Injection. 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition. Available: http://dx.doi.org/10.2514/6.2010-1524.
The authors would like to acknowledge the King Abdullah University of Science and Technology for their support of this research. This work was funded by the KAUST grant, number KUS-110-010-01.