Development of a Lean Direct Fuel Injector for Low Emission Aero Gas Turbines

Abstract

CFD Research Corporation has developed a promising lean direct fuel injector for application to all sizes of aero gas turbine engines. The patented injector design utilizes a bifurcated flow pattern structure that produces low NOx emissions at full power conditions and low CO, UHC and smoke emissions at low power. The design consists of three swirlers and two fuel circuits, and a flow splitter that divides the airflow into two airstreams. Two concentric fuel circuits fuel the two airstreams, producing two distinct flames: a pilot flame and a main flame. This unique flame structure allows separate control of two flame regions, but still allows them to interact. A large percent of combustor airflow enters through the injector. At low power (idle and approach), only the pilot circuit is fueled. The pilot fuel flows into the pilot airstream, and a flame is anchored in the bifurcated recirculation zone. Lean blowouts at idle conditions as low as an injector equivalence ratio of 0.04 have been realized. Low CO, UHC and smoke emissions have been demonstrated at these conditions. For power settings above approach, the fuel flow through the pilot is reduced, and the main is fueled. At cruise to max power conditions, only 10% of the fuel goes through the pilot and 90% goes through the main to achieve both low NOx and good stability. At max power conditions, the injector equivalence ratio is approximately 0.60–0.65, and the flame is blue and non-luminous, resulting in reduced heat loads to the liner. NOx emission levels have been measured in single-injector tests that show this injector has the potential to reduce the Landing/Takeoff (LTO) NOx levels by 60–70% compared with 1996 ICAO standards. This paper presents an overview of how the fuel injector works and how overall performance was achieved. The most difficult aspect of injector performance, i.e. achieving low lean blowout (LBO) fuel-air ratio, is described at the end of the paper, including LBO data for a range of configurations.