Thermal runaway effect of the centerbody on boundary layer flashback in a swirl-stabilized gas turbine burner operated with hydrogen

The effect of centerbody heating by the flame on flashback propensity is experimentally investigated. The burner is technically premixed with 100% hydrogen as fuel under atmospheric pressure. The centerbody temperature was monitored by thermocouples revealing a thermal runaway of the centerbody temperature at the onset of flashback. Post-processed OH*-chemiluminescence imaging data of the flame show an increase in OH*-chemiluminescence intensity during thermal runaway indicating either less quenching or auto-ignition events of hydrogen/air mixtures being in contact with the heated centerbody surface. The authors recorded the formation of an auto-ignited flame kernel upstream of the flame front. An analytical model involving an auto-ignition Damköhler number Da_AI, the Reynolds number Re and the normalized burner pressure drop Δp_bur/Δp_burref is introduced predicting whether thermal runaway takes place under certain operating conditions. Experimental data from two different burners are applied to the model's safety map and good agreement is found.