Acoustic sensitivities of lean-premixed fuel injectors in a single nozzle rig

An experimental and numerical investigation into the attenuation of combustion induced pressure oscillations in a single nozzle rig was undertaken at the United Technologies Research Center. Results from these investigations indicated a high combustor exit Mach number, similar to that used in a gas turbine engine, was required to correctly simulate the combustor dynamics and evaluate acoustic characteristics of lean premixed fuel injectors. Comparisons made between aerodynamically stabilized and bluff-body stabilized nozzles and the use of premixed and diffusion pilots showed that small levels of diffusion piloting behind a bluff-body yielded the best acoustic/emission performance. Their success is due to increased flame stabilization (superior anchoring ability), which reduced flame motion and thermal/acoustic coupling. For cases where diffusion piloting was not present, both designs exhibited similar dynamical behavior. Increases in the combustor exit Mach number and reductions in the inlet air temperature were shown to degrade acoustic performance of both nozzle designs. The bluff-body configuration with small levels of diffusion piloting, however, was found to be less sensitive to these changes when compared to its aerodynamic counterpart.