Mitigating combustion instability and NO_x emissions with annular oxyfuel jets into the flame shear layer region

Abstract

The shear layer is a region between the internal and external recirculating zone of the flame, which is critical for combustion stabilization and emission. This study experimentally studied the effects of oxyfuel (CO2/O2) shear layer injections on combustion dynamics and pollutant emissions of a model gas turbine combustor. To evaluate the damping performances of ‘Oxy’ CO2/O2 shear layer jets on unsteady combustion and pollutant formation processes, four variables of the CO2/O2 shear layer injection system are studied—the flow rate, the inner diameter, the injection angle and the oxygen ratio. Experimental results show that thermoacoustic instability and NOx emissions can be suppressed with the ‘Oxy’ CO2/O2 shear layer injection method. The minimum inner diameter cases could achieve better control effectiveness of 80%, with the sound pressure amplitude drops from 27 to 5.4 Pa. The maximum inner diameter case could achieve better control effectiveness of 59.2%, with the concentration of NOx emissions drops from 25 to 10.2 ppm. Flame oscillation modes experienced shifting and switching under different shear layer angles and oxygen ratios. There exist extreme points that can be selected for a better control effect. The CO2/O2 shear layer injection splits the inner and outer recirculation zones of the flame. As the oxygen ratio of CO2/O2 varied from 36% to 46%, a flame flapping phenomenon emerged. The ‘Oxy’ CO2/O2 shear layer injection method could eliminate combustion instability and NOx emissions at a relatively lower cost and complexity, which will promote the development of high‐performance burners.