Electric Propulsors for Zero-Emission Aircraft: Partially superconducting machines

Be it through combustion in a turbine or via direct conversion with fuel cells, hydrogen electric is considered the most attractive path toward a future with zero-emission aircraft. An internal combustion engine, with hydrogen as the fuel, results in very low amounts of nitrogen oxide emissions, providing an attractive option for a turboelectric propulsion system. Additionally, new lean combustion strategies show promising results to further minimize these emissions. On the other hand, a fuel cell-based electrical architecture, with no direct emissions, can be used to power a fully electric propulsion system. Whichever method is used, electric machines play a key role in hydrogen-powered aircraft as it is the unit that efficiently converts electrical power to mechanical power. With promising trends pointing toward hydrogen as the key to electrification of large transport aircraft, efficient and “flightweight” megawatt (MW)-class motors and, in some cases, tens of MW are needed. NASA’s Advanced Air Transport Technology (AATT) program anticipated this and launched several NASA Research Announcements, leading to the continued development and availability of enabling technologies. Other agencies are also stepping up to the challenge with integral R&D, such as thermal management-related work supported by Advanced Research Projects Agency–Energy. In this article, we discuss technology options, developments, challenges, and trends toward an electric propulsor that will power the future of aviation.