Megawatt-scale motor could help electrify commercial airlines

The potential reduction of aviation’s carbon footprint through electrification could be significant. However, the development of large-scale electric propulsion systems for commercial airliners has been limited so far. To address this challenge, a team of engineers from MIT is currently working on the creation of a 1-megawatt motor that could serve as a crucial step towards electrifying larger aircraft. Extensive testing and computational analysis have been conducted on the motor’s major components, demonstrating its ability to generate one megawatt of power while remaining competitive in terms of weight and size with existing small aero-engines.

In the context of all-electric applications, the team envisions the motor being paired with a power source such as batteries or fuel cells. This motor would then convert electrical energy into mechanical work to drive a plane’s propellers. Additionally, the electrical machine could be combined with a traditional turbofan jet engine to operate as a hybrid propulsion system, offering electric propulsion during specific flight phases.

Zoltan Spakovszky, the T. Wilson Professor in Aeronautics and the Director of the Gas Turbine Laboratory at MIT, who leads the project, emphasizes the significance of megawatt-class motors as a vital component in greening the aviation industry, regardless of the energy carrier used, such as batteries, hydrogen, ammonia, or sustainable aviation fuel.

The team from MIT, consisting of faculty, students, and research staff from the Gas Turbine Laboratory and the Laboratory for Electromagnetic and Electronic Systems, will present their findings at a special session during the American Institute of Aeronautics and Astronautics—Electric Aircraft Technologies Symposium (EATS) at the Aviation conference in June. The project is sponsored by Mitsubishi Heavy Industries (MHI), and industry collaborators have also contributed to the research and development efforts.

Heavy stuff

In order to effectively combat the impacts of human-induced climate change, it is crucial to achieve net-zero global carbon dioxide emissions by 2050. Within the aviation industry, meeting this target will necessitate significant advancements in various areas such as unconventional aircraft design, intelligent and adaptable fuel systems, advanced materials, and safe and efficient electrified propulsion systems. Many aerospace companies are currently focused on developing electrified propulsion technologies and designing lightweight, high-powered electric machines capable of propelling passenger aircraft.

Zoltan Spakovszky emphasizes that there is no one-size-fits-all solution to achieve these goals, and the key lies in paying attention to intricate details. The process involves complex engineering, requiring the co-optimization of individual components to ensure compatibility and maximize overall performance. It entails pushing the boundaries in various areas such as materials science, manufacturing techniques, thermal management, structural design, rotordynamics, and power electronics.

Fundamentally, an electric motor employs electromagnetic force to generate motion. In devices like laptop fans, electrical energy from a battery or power supply is utilized to create a magnetic field through copper coils. This magnetic field interacts with a nearby magnet, causing it to rotate in alignment with the generated field, ultimately driving a fan or propeller.

Electric machines have been in existence for over a century and a half, and traditionally, larger appliances or vehicles required larger copper coils and magnetic rotors, resulting in increased weight. Moreover, higher power generation by electrical machines leads to greater heat production, necessitating additional cooling mechanisms. All of these factors contribute to a heavier and bulkier system, posing challenges for aviation applications where weight reduction is crucial.

Spakovszky emphasizes that aircraft design demands compact, lightweight, and powerful architectures. As a result, the team had to devise innovative solutions to overcome these challenges and develop a motor that meets these requirements.

Good trajectory

The MIT electric motor and power electronics have been designed to be compact, with each component roughly the size of a checked suitcase and lighter than an adult passenger. The motor consists of several key elements, including a high-speed rotor with an array of magnets of varying polarity, a compact low-loss stator housing intricate copper windings, an advanced heat exchanger for cooling, and a distributed power electronics system comprising custom-built circuit boards. The power electronics system precisely controls the currents flowing through the stator’s windings at high frequency.

Zoltan Spakovszky describes this design as the first truly co-optimized integrated approach, achieved through an extensive exploration of the design space. Factors such as thermal management, rotor dynamics, power electronics, and electrical machine architecture were considered holistically to find the optimal combination for achieving the required specific power at one megawatt.

The motor is designed to ensure minimal transmission loss by closely coupling the distributed circuit boards with the electrical machine. This arrangement allows for effective air cooling through the integrated heat exchanger. The high-speed rotation of the machine is facilitated by the rapid movement of magnetic fields, made possible by the circuit boards switching at high frequency.

To mitigate risks, the team has individually built and tested each major component, confirming their ability to perform as designed under conditions surpassing normal operational demands. The researchers plan to assemble the complete electric motor and commence testing in the coming months.

Phillip Ansell, director of the Center for Sustainable Aviation at the University of Illinois Urbana-Champaign, commends the MIT team’s design for its combination of conventional and cutting-edge methods in electric machine development. He highlights its robustness and efficiency, making it suitable for future aircraft needs.

Once the team demonstrates the complete electric motor, they envision its application in regional aircraft and as a complement to conventional jet engines for hybrid-electric propulsion systems. Furthermore, they propose that multiple one-megawatt motors could power distributed fans along the wings of future aircraft designs. The foundation of the one-megawatt motor design could potentially be scaled up for multi-megawatt motors, suitable for powering larger passenger planes.

Spakovszky expresses confidence in the project’s trajectory and acknowledges the interdisciplinary nature of the research. While his background is not in electrical engineering, he recognizes the significance of addressing the climate challenge by collaborating with experts in the field. MIT’s broad range of technologies allows for reinvention and exploration in new areas, ultimately contributing to the overarching goal.

Source: Massachusetts Institute of Technology

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