Analysis of Combustion Instability of Hydrogen Mixed Retrofit Gas Turbine Nozzles

This study analyzed the combustion instability characteristics of retrofit and original nozzles in hydrogenmixed gas turbines using a 1D thermoacoustic model.Experiments were conducted on a laboratory-scale test rig at hydrogen mixing ratios of 0%, 30%, and 50%.Both nozzles exhibited frequency shift phenomena with increasing hydrogen content, but showed opposite trends in dynamic pressure amplitude.The original nozzle showed decreased dynamic pressure amplitude with increasing hydrogen ratio, while the retrofit nozzle exhibited increased dynamic pressure amplitude.Analysis of experimentally measured flame transfer functions revealed that the retrofit nozzle exhibited longer time delay than the original nozzle under the same conditions.Root locus analysis confirmed that this difference in time delay is the key factor determining system stability.It was identified that the center cooling air in the retrofit nozzle induces flame lift-off, increasing the time delay.