Swirl-stabilised hydrogen combustion has great potential in the aviation industry since emissions can be significantly reduced compared to fossil fuels. However, a major drawback is a high proneness to flashback. This could be overcome with non-swirling axial air injection (AAI) on the centre-line of the mixing tube. The effect of this concept on the effective Swirl number and flashback propensity was investigated for a radial- and axial swirl generator by Computational Fluid Dynamics (CFD) simulations and cold flow Particle Image Velocimetry (PIV) experiments on a custom-designed combustor model. Acquired results indicate that with increasing amount of AAI the Swirl number reduces due to both inertial and viscous effects. The flashback propensity also reduces as the axial velocity on the centre-line increases by AAI. For equal Swirl numbers the axial swirl generator was found to have a lower flashback propensity compared to the radial swirl generator, suggesting safer operation. ... Read more