Measuring lean and rich non-premixed hydrogen flame dynamics in the primary zone of an air-staged combustor

In the pursuit of decarbonizing the aviation sector, hydrogen poses an alternative to kerosene. To facilitate this transition with minimal hardware modifications to existing engines, the air-staged, rich-quench-lean combustion principle is considered for retrofitting. With the importance of the primary zone in this setup in mind, the study examines the thermoacoustic behavior of non-premixed hydrogen flames within the primary zone of an aero-engine prototype combustor under atmospheric, rich and lean conditions. Pairs of rich and lean operating points with similar adiabatic flame temperature are selected for investigation, enhancing the comparability of the pairs. Additional lean operating points are defined to cover a broader range of interest. Stationary flame images are recorded based on OH * chemiluminescence. A non-monotonous dependency between the recorded stationary flame shape and the equivalence ratio is found. The shape of near-stoichiometric and rich flames does not significantly change compared to the observed lean flames. Furthermore, flame-transfer-functions are measured with the multi-microphone-method. Overall, the flame-transfer-function ( FTF ) trends show little sensitivity to the broad range of investigated equivalence ratios, except for the leanest point. Lean, non-premixed hydrogen flames display both an equivalence ratio and frequency dependent behavior. Under near-stoichiometric and rich operating conditions, the equivalence ratio dependency appears dominant.