Investigating Boundary Layer Flashback of a High Turbulence Intensity Jet Flame at Gas Turbine Conditions

Hydrogen derived from non-fossil sources is an attractive candidate to replace carbon based fuels in gas turbines, as it is inherently carbon free. Yet the unusual combustion properties of hydrogen requires some care to successfully use it in gas turbines. To attain the lowest NOx emissions, uniformly low reaction temperatures must be assured thus the reactants must be well mixed. This is accomplished in low emission gas turbines by mixing the reactants within a pre-mixer section prior to entry into the combustor. With the addition of hydrogen into the fuel, certain issues arise such as higher flame speeds compared to carbon based fuels. Flashback is a phenomena that occurs when the flame no longer propagates downstream of the injector but instead retracts and propagates upstream towards the pre-mixer and injector. Flashback occurs when the flame speed exceeds the local flow velocity. In the present work, studies are conducted under different levels of turbulence intensity. Higher turbulence intensity is known to increase turbulent burning velocity, hence the question of how flashback propensity is affected is raised. Studies are conducted at pressures from 3 to 8 atm. with preheated reactants up to 750 K utilizing hydrogen as the fuel. The results show that even with significantly different turbulence intensities (ratio of flow centerline turbulence to centerline axial velocity) boundary layer flashback is not strongly affected. This is attributed to the role of the quenching distance in connection with the boundary layer. Core flow flashback or other flashback mechanisms may be affected differently