Dual-fuel, dual-swirl burner for the mitigation of thermoacoustic instabilities in turbulent ammonia-hydrogen flames

In this paper, a novel dual-fuel, dual-swirl burner is presented and its potential to mitigate thermoacoustic coupling for ammonia-hydrogen-air flames is explored. The key feature of this burner is that the extent of mixing between ammonia and hydrogen before injection into the combustion chamber can be tuned by recessing an inner dividing tube. Non-reacting, 1-D Raman measurements confirm that recessing the dividing tube changes the radial profile of fuel composition at the injector's outlet. Time-averaged flame imaging shows that this modifies, in turn, the flame morphology. Specifically, the more stratified is the fuel, the least compact is the flame. In the most stratified case, a “blue” flame, predominantly burning hydrogen, pilots another “orange” flame, predominantly burning ammonia, further downstream. Acoustic measurements show that the least stratified (most compact) flame exhibits intrinsic thermoacoustic modes (ITA), while these modes are not featured for the most stratified (least compact) flame. Consequently, this study demonstrates that the thermoacoustic behavior of this carbon-free burner can be altered by tailoring the injection of ammonia and hydrogen while keeping the thermal power (7.4 kW), global equivalence ratio (0.64), and fuel flow rates strictly constant. This lays the foundation for the development of future practical burners in which the extent of mixing between ammonia and hydrogen upstream of the flame would be actively controlled to mitigate thermoacoustic coupling.