EXPERIMENTAL 3D ANALYSIS OF FLAME PROPAGATION IN A LEAN-PREMIXED SWIRL BURNER OPERATED WITH HYDROGEN

Highly reactive fuels increase the flashback propensity in stationary gas turbines when operated under lean premixed conditions. This leads to undesired events such as flame propagation and flame anchoring. In this study, the flame propagation as well as the propagation to anchoring transition is experimentally investigated for a premixed burner with centerbody and fuel injection in the swirler. The burner is operated with 100% hydrogen as fuel under atmospheric pressure. The preheat temperature corresponds to engine conditions. The flame behavior at different bulk flow velocities is analyzed by means of OH* - chemiluminescence high speed imaging. A 360^◦ optical measurement technique was established to identify the flame propagation to anchoring transition characteristics. The experimental results reveal that the flame propagation through the burners mixing tube exhibits three phases; (1) transition from unconfined to confined state, (2) upstream propagation of the flame up to an intermediate stabilization within the mixing tube and, (3) flame propagation to anchoring transition. Depending on the bulk flow velocity, the three phases take place independently of each other at/along the centerbody or at/along the mixing tube boundary layer. Two modes of flame structure are observed during the flame propagation to anchoring transition for the propagation along the centerbody. Furthermore, the 360° view imaging data reveals that the flame shows a symmetrical propagation behavior for the propagation along the centerbody and an asymmetry of the flame when propagating along the mixing tube wall.