Surface Roughness Effects on Flame Stability in an Additively Manufactured Fuel Injector

This paper describes the impact of surface roughness inherent in the metal additive manufacturing (AM) process on the flow and flame characteristics of a swirl-stabilized injector for gas turbine applications. The laser powder-bed fusion (L-PBF) method of AM offers a new design space for injectors but raises concerns over hydraulic, thermal, and structural integrity due to relatively rough surfaces compared to cast components. In this work, the impact of region-specific surface roughness for a swirl injector on flame stability is demonstrated using Reynolds-averaged Navier–Stokes simulations to capture the trends in flame structure and stability limits with varying roughness values for blends of natural gas and hydrogen. Results show that increasing the surface roughness shortens the flame because the roughness changes the flow profile in the injector. Further, the injector with AM surface roughness has wider flame static stability limits, particularly for high-hydrogen fuel blends. The simulations are complemented with experiments that compare a traditionally manufactured injector with an L-PBF injector. Similar trends in flame shape are observed both in simulations and experiments. The two sets of results are synthesized to better understand the impact that AM roughness can have on flame behaviors.