Innovators at the NASA Armstrong Flight Research Center have developed a compressor-generator-motor turbojet design concept that integrates the generator with the aerodynamic blade structures of the compression section of turbomachinery. This reduces weight and volume compared with conventional turbine generator arrangements in which the turbojet or turbofan drives a separate shaft-driven generator. All conventional turbomachinery designs suffer from some type of system inefficiencies: Conventional side-mounted generators add the weight of a 90-degree gearbox; a rear-mounted generator is difficult to cool. The Armstrong design improves existing configurations with a flight-weight electromagnetic turbo-generator that is suitable for application to distributed turboelectric systems on aircraft, and aids in cooling the system. This technology may enable new aircraft configurations and future TurboElectric Distributed Propulsion (TeDP) aircraft designs.
The innovation uses the rotating blades of the compressor section to act as structural support for the generator. Since the compressor is the coolest part of the engine, there would be no adverse effects to the degradation rate or the overall lifetime of the magnetics, Curie points, or insulation systems. The configuration proposed by the Armstrong design is an axial magnetic flux permanent magnet generator or motor. The electrical/mechanical interface could serve to deliver power to the shaft of the turbojet/fan or to extract power from the shaft. This axial electromagnetic flux design is more efficient than radial designs because of the volumetric aspect ratio of the compressor section. Since the blades are aerodynamic, they will serve to cool the coils and magnets of the electromagnetic device.
Applications include TeDP aircraft designs, N+3 vehicle concepts, large-class cargo transports, and commercial and private aircraft. Other applications include turbo-electric generation systems that would provide more compact onboard ground restart systems that would be more volumetrically efficient than existing turbo-compressed air-start systems.