The aviation industry is rushing to decarbonize and reach jet zero, and right now, the leading decarbonization solution seems to be using sustainable jet fuel as an alternative to the fossil fuel-based option.
The reason sustainable aviation fuel (SAF) is taking off is that it has wide commercial potential for large aircraft, and electric planes, unlike electric cars, have been slow to lift off because, to date, only small all-electric planes have gotten off the ground.
The reason is that currently, the only motors that exist as ones that generate hundreds of kilowatts, and according to engineers at the Massachusetts Institute of Technology (MIT) megawatt-scale motors are needed to electrify larger, heavier jets.
To prevent the worst impacts of climate change, scientists have determined that global CO2 emissions must reach net zero by 2050, and by the same year, the commercial aviation industry has committed to reaching net zero emissions.
The industry has a tall order to fill, because as the International Energy Agency reports, in 2021 aviation accounted for over 2% of global energy-related CO2 emissions, having grown faster in recent decades than road, rail, and shipping.
In 2023, the IEA confirms the industry is not on track to meet its goals.
According to Zoltan Spakovszky, the director of the Gas Turbine Laboratory at MIT, who is leading the project, meeting these goals will require “step-change achievements” in the design of unconventional aircraft.
“There is no silver bullet to make this happen, and the devil is in the details,” Spakovszky said in a statement, emphasizing that this feat is “hard engineering.”
The reason it’s so difficult is that individual components need to be co-optimized while “maximizing overall performance.”
“To do this means we have to push the boundaries in materials, manufacturing, thermal management, structures and rotordynamics, and power electronics,” he said.
Pushing these boundaries opens up a Pandora’s box of other engineering conundrums. The way an electric motor works is that it uses an electromagnetic force to generate motion. A good example of this is the motor that powers the fan in the laptop on which this article is being written. That fan uses electric energy from a battery supply to generate a magnetic field, typically through copper coils.
However, bigger appliances and vehicles require bigger copper coils and magnetic rotors, leading to heavier machines. Plus, the more power an electrical machine generates, the more heat it produces which requires more components to keep it cool in the sky, thus making it even heavier.
“Heavy stuff doesn’t go on airplanes,” Spakovszky said in a statement. “So we had to come up with a compact, lightweight, and powerful architecture.”
So to push the limits, the MIT research and engineering team is working on a motor it envisions could be paired with a source of electricity such as a battery or a fuel cell, a cell that converts the chemical energy of a fuel into electrical energy.
The team says it could also be paired with traditional jet engines to create a hybrid plane, that provides electric propulsions during certain phases of the flight. When coupled with the electrical machine the motor also allows effective air cooling.
But the central question remains. Despite solving all the other problems: is the motor light enough?
According to the team, the MIT electric motor and power electronics are each designed to be about the size of a checked suitcase weighing less than an adult passenger.
Spakovszky believes this is the “first truly co-optimized integrated design.”
This week, Spakovszky and members of his team, along with industry collaborators, will present their work at a special session of the American Institute of Aeronautics and Astronautics – Electric Aircraft Technologies Symposium (EATS) at the Aviation conference in San Diego, California.
These MIT scientists aren’t the only ones tinkering with electric planes. This aviation giant Airbus might be the biggest commercial aerospace company working on electric and hybrid-electric propulsion and like MIT the company theorizes electrical sources for its motors could come from batteries or fuel cells which convert hydrogen into electricity.
The company has been preparing for the energy transition, creating an electric plane for well over the last decade, and it will be demonstrating its hybrid plane at the Paris airshow next week.
Another company, Cosmic Aerospace is also working on an electric plane, but its ambitions lie on fully electric models that they say can fly 20-30 passengers for just over 600 miles without any emissions. By 2025 the Cosmic team aims to have its first flight demonstration and by 2028 enter production.
For context, Cosmic's ambitions are close to the average flight which is
around 500 miles. While a flight from NYC to LA is just under 2,500 miles, most flights are a fourth of that. Still, the MIT team is targeting the longer haul flights too, which produce more emissions.
Once the MIT team can demonstrate the design as a whole, they’re confident the megawatt-scale motor can both power regional aircraft as well as be a companion to traditional motors for hybrid planes. Eventually, they also believe that the one-megawatt design could be scaled up to multi-megawatt motors, to power larger passenger planes.
“I think we’re on a good trajectory,” Spakovszky said. Spakovszky himself is not an electrical engineer by training, but is instead a professor of aeronautics. However, he says “addressing the 2050 climate grand challenge is of utmost importance.”
“Working with electrical engineering faculty, staff, and students for this goal can draw on MIT’s breadth of technologies so the whole is greater than the sum of the parts.
So in addition to reinventing the electric motor, Spakovszky said “we are reinventing ourselves in new areas.”