Suppression Mechanisms of Stratified Jet-in-Crossflow on Thermoacoustic Instability and NOx Emissions in Premixed Combustors

The premixed combustion of a gas turbine is prone to thermoacoustic oscillation, which affects the safety of combustion systems. This study experimentally investigated the suppression mechanism of a stratified jet-in-crossflow on the thermoacoustic instability and nitrogen oxides (NOx) in an unstable lean-premixed combustor. Two key parameters of the jet-in-crossflow—gas density and jet flow rate—were investigated to elucidate their effect on momentum ratios. The results reveal that the stratified jet-in-crossflow reduces the maximum amplitude of combustion oscillation by 58%, while the NOx concentration exhibits a high damping ratio of 48.8%. Higher jet flow rates and gas densities enhance the suppression of combustion thermoacoustic oscillations and NOx emissions. The distribution of flame radicals indicates that an increase in the jet flow rate reduces the intensity of the flame heat release rate, thereby reducing the flame thermoacoustic instability. As the argon/helium volume ratio increases, the mode of thermoacoustic oscillation shifts. As the argon/helium volume ratio gradually increases from 0%/100% to 100%/0%, the main frequency of thermoacoustic oscillations gradually decreases from 267 to 121 Hz. Notably, the transient amino-group radicals in the flame increase with the increasing argon/helium volume ratio, indicating that the jet suppresses NOx generation. The changes in peak temperature and flame shape after jetting further confirm that the stratified jet-in-crossflow alters the flame structure within the combustion chamber. The effect of the momentum ratio on the suppression of thermoacoustic instability is studied for the first time. This study provides a promising method for suppressing the thermoacoustic oscillations and NOx emissions in premixed flames, contributing to a safer operation and cleaner emissions in lean-premixed combustors.