Influence of Variable Fuel Staging on the Flow Structures in a Multi-Jet Burner Operated on Lean-Premixed Hydrogen

Abstract Hydrogen facilitates the decarbonization of gas turbines but presents engineers with one of the most significant challenges in recent decades, particularly when fuel flexibility is also considered. The transition from natural gas to hydrogen induces substantial changes in chemical properties. Swirl-stabilized combustion strategies struggle to manage hydrogen’s high reactivity under dry, lean-premixed conditions, which are necessary for low NOx emissions. To ensure the required flashback safety, jet flame-stabilized combustion systems with high axial flow velocities offer a promising design solution. In this study, particle image velocimetry (PIV) measurements and OH*-chemiluminescence flame imaging are used to investigate the impact of radial fuel staging on the global flow structures of a multi-jet burner operated with 100% hydrogen and natural gas under atmospheric conditions. Individual control of the fuel mass flow for each jet flame allows for separate staging of the equivalence ratio in the two coaxial jet flame rings that compose the burner. To evaluate the impact of fuel reactivity on the flow structures, cases with pure hydrogen are compared to those with natural gas at technically relevant global flame temperatures of 1900–2000 K. Fuel gas-dependent inner and outer recirculation zones are identified and the influence of the flame position on these structures is analyzed. Flow field statistics for both fuel gases are examined to characterize the effects of fuel staging. Velocity measurements over a wide region of the combustion chamber reveal significant modifications in the flow field as fuel is shifted towards the combustor wall. The resulting flame structures for different fuel stagings are assessed using OH* chemiluminescence images.