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Abstract

Flame transfer function is a widely used strategy for characterizing the forced response of flames and predicting the occurrence of thermo-acoustic instability. Characteristics of flame transfer function under symmetric conditions and combustion instability under asymmetric conditions were investigated in a dual-nozzle CH4/H2 gas turbine combustor. The H2 composition was set to the main parameter in both symmetric and asymmetric conditions. In symmetric flames, the H2 addition induced short and compact flame structure, and it subsequently affected the degree of flame-vortex interaction, which decreased the local maximum FTF gain in high H2 compositions. In asymmetric flames, strong combustion instability occurred at 0% H2 condition. However, when the H2 composition of the upper nozzle was increased, combustion instability became weak and totally diminished. The difference in axial flame position in asymmetric flames induced the phase difference, and it acted as the main damping source of combustion instability. Consequently, in both symmetric and asymmetric flames of a dual-nozzle combustor, changes in the flame structure due to H2 addition played an important role in determining characteristics of FTF and combustion instability.