How can intrinsic flame instabilities influence the retrofit of GT brownfield units to burn hydrogen?

Modern gas turbine (GT) manufacturers face the challenge of designing advanced premixers and combustors capable of safely combusting fuels with high hydrogen content, up to 100%, under high-pressure ratio conditions. However, hydrogen combustion presents significant challenges, particularly under such high-pressure conditions, as it can promote the onset of thermo-diffusive instabilities. These instabilities lead to changes in the flame morphology enhancing the flame displacement speed[1] and ultimately promoting phenomena like the flashback or triggering the pressure pulsation. Lower compressor discharge temperatures further promotes the onset of intrinsic flame instabilities[2], linking their occurrence to the gas turbine’s thermodynamic cycle. Decarbonizing the oil and gas industry also pivots on retrofitting existing GTs to burn hydrogen and hydrogen-natural gas blends. These older turbines typically operate at lower pressure ratios and discharge temperatures, raising the question: do these conditions favour hydrogen combustion compared to modern GTs? To address this question, this study provides the linear stability analysis of hydrogen flames under operating conditions representative of older and newer GT cycles. This analysis identifies the smallest unstable wavelengths and most excited modes, providing insights into conditions that promote thermo-diffusive instabilities. These findings aim to enhance the understanding of hydrogen combustion dynamics across different thermodynamic cycles and inform the design and retrofit strategies for gas turbines in the transition toward decarbonized energy systems.