Key factors and control methods of combustion instability under axial staging combustion

The axial staging combustion for industrial gas turbines significantly widens the power regulation range and effectively reduces NO_x emissions. However, the impact of secondary nozzle parameters on the combustion instability requires further investigation. To address this, a three-dimensional theoretical model is developed to consider the coupling of multiple nozzles with the perforated liner, in order to analyze the effects of axial staging combustion on combustion instability and the control mechanisms of the perforated liner. Results show that the flame response of the primary nozzle has a notable effect on the first-order axial modes, while the parameters of the secondary nozzle mainly affect the first-order azimuthal modes. Furthermore, when the secondary nozzle is located at the acoustic pressure antinode of the first-order axial mode, i.e., near the inlet and outlet of the combustion chamber, its effects on frequency and growth rate become more important. When the circumferential angular difference between the two secondary nozzles is π/2, the combined effects of their flame responses on the nondegenerate azimuthal modes are relatively weak. In contrast, when the circumferential angular difference is π, the combined effects of the secondary nozzles' flame responses on the nondegenerate azimuthal modes become more significant. In addition, the presence of the secondary nozzles leads to an axial sound pressure distribution for the first-order azimuthal mode, allowing the perforated liner positioned close to the secondary nozzle to effectively suppress the combustion instability.