Injector-Induced Effects on Hydrogen Flame Dynamics in Coaxial Swirl Burners

To meet the European Green Deal 2050 targets, hydrogen is gaining increasing attention as a carbon-free fuel for aviation. However, its high reactivity and flame temperatures pose significant challenges regarding flashback propensity and NOx formation, particularly in premixed configurations. This work experimentally investigates the role of injector configuration in a dual swirl, co-axial partially premixed burner operated with 100% hydrogen. Tests were conducted at a constant thermal power of 12 kW and a global equivalence ratio (𝜙𝑔𝑙𝑜𝑏𝑎𝑙) of 0.25, focusing on the comparison between co-swirling and counter swirling configurations. The analysis specifically evaluates how the injector head recess (IHR) and inner swirl direction influence flame morphology and stability. Results indicate that the swirl configuration has a measurable impact on flame morphology and overall stability. In the explored conditions, the counter-swirl arrangement is associated with reduced stability margins compared to the co-swirl configuration. Consistent with available literature, these trends appear to be linked to shear layer dynamics between the two coaxial flows: the rapid decay of the tangential velocity component in the counter-swirl configuration negatively affects hydrogen mixing and weakens flame anchoring mechanisms compared to the co swirl case. The IHR was also found to significantly affect the stability limits. This suggests that while an extended premixing region can favor mixing effectiveness, concurrent modifications to the local flow field may also influence the stability envelope. Although direct measurements of the flow field are not available, these findings suggest that hydrogen flames may be sensitive to both local flow structures and the overall morphology of the injector-induced flow. This interpretation is consistent with expected flow-flame interactions, but further investigation is needed to confirm the relationship.