Alternative fuels like hydrogen are presently discussed as one possibility to reduce carbon dioxide emissions from gas turbines. Premixed lean combustion is a current standard to minimize nitrogen oxide emissions. However, the early mixing of fuel and oxidizer upstream of the combustion chamber opens up the possibility of upstream flame propagation, referred to as flame flashback. Flame flashback in gas turbines has to be prevented as it leads to immediate engine shut down or even structural damage. Due to high burning velocities and low quenching distances, flashback is especially critical in premixed hydrogen flames. In particular, the low velocity region near the burner wall promotes flashback. Diluting the mixture near the wall by fluid injection is one approach to counteract this phenomenon and to enhance the safe operating range of a gas turbine burner.
This article presents an experimental study on the effect of air injection on flame flashback investigated at a channel burner configuration. Different injection mass flow rates, positions and angles are compared to a reference case without injection regarding their flashback limits. The effectiveness of the injection increases with the injected mass flow rate. The resulting flashback limits can be correlated with the equivalence ratio at the wall by concepts taken from film cooling. However, the fluid injector is a source of boundary layer disturbances leading to an initial penalty regarding flashback resistance. This penalty increases the closer the injector is located to the burner exit. Furthermore, the penalty increases for lower injection angles as the area of the injector and the corresponding boundary layer disturbances increase.