MIT's New Hybrid-Electric Plane Could Reduce Aviation Pollution 95 Percent

The concept takes its cue from emissions-control systems already used for ground transportation vehicles, according to the MIT blog post. Numerous heavy-duty diesel trucks house post-combustion systems to control the emission of pollutants like NOx, which inspired the MIT team to suggest a similar design for the aviation industry, with an electric edge.

UPDATE Jan. 14, 5:15 PM EST: Typical planes can't add emissions-control, engine thrust interference

Modern-day planes use jet engines to propel themselves through the sky (which is why we see their high-altitude contrails on clear blue days). Each engine is typically hoisted on the bottom of either wing, and inside the engines, a gas turbine powers a propeller which moves the plane forward through the air while the exhaust fires out of the back of the turbines.

This schema has prohibited the use of emissions-control devices because they would interfere with the thrust the engines create, and thus reduce the lift of the wings on the plane.

UPDATE Jan. 14, 5:25 PM EST: Hybrid-electric plane concept integrates gas turbine into cargo-hold

However, MIT's new hybrid-electric (also called "turbo-electric") design switches this design up — integrating the gas turbine into the plane's cargo hold. Instead of directly powering propellers or fans, the gas turbine can drive a generator — also within the hold — to generate electricity.

This can then provide electrical power to the plane's wing-mounted, electrically-powered propellers, or fans, according to the MIT blog post. The emissions produced from the gas turbine could then flow into the emissions-control system — basically akin to those found in diesel vehicles — effectively eliminating the exhaust before ejecting it into the atmosphere.

UPDATE Jan. 14, 5:30 PM EST: Net-zero aviation is a colossal engineering challenge

"This would still be a tremendous engineering challenge, but there aren't fundamental physics limitations," said Professor of Aeronautics and Astronautics Steven Barrett of MIT, in the blog post. "If you want to get to a net-zero aviation sector, this is a potential way of solving the air pollution part of it, which is significant, and in a way that's technologically quite viable."

The design's specs include several analyses of the hybrid-electric plane's potential fuel cost and health effects, and the new paper's co-authors are Raymond Speth, Sebastian Eastham, Prakash Prashanth, and Jayant Sabnins — all of whom are members of MIT's laboratory for aviation and the environment.

UPDATE: Jan. 14, 5:40 PM EST: Hybrid-electric innovation seeded from emissions scandal

The early planning for the hybrid-electric plane took seed amid Barrett and his team's work with the Volkswagen diesel emissions scandal. Back in 2015, environmental regulators learned the German auto manufacturer had intentionally manipulated its cars' diesel engines to activate onboard emissions-control systems only while undergoing lab tests.

This allowed the automaker's cars to meet NOx emissions requirements without losing real-world driving performance — at a dangerous cost of emitting up to 40 times more NOx outside of a testing environment.

UPDATE Jan. 14, 5:50 PM EST: Barrett's semi-electrified plan

While Barrett looked at the wider health impacts of Volkswagen's emissions gambit, he also familiarized himself with diesel vehicles' emissions-control systems more broadly. At roughly the same period, Barrett was researching concepts for a large, all-electric aircraft.

"The research that's been done in the last few years shows you could probably electrify smaller aircraft, but for big aircraft, it won't happen anytime soon without pretty major breakthroughs in battery technology," said Barrett in the blog post. "So I thought, maybe we can take the electric propulsion part from electric aircraft, and the gas turbines that have been around for a long time and are super reliable and very efficient, and combine that with the emissions-control technology that's used in automotive and ground power, to at least enable semielectrified planes."

UPDATE Jan. 14, 5:55 PM EST: Minimal extra weight added to plane, 0.6 percent more fuel to fly

Barrett's concept avoids the potential cons of emissions-control reducing the jet engines' stream of thrust with a novel approach, separating the thrust-producing propellers from the power generating gas turbine. In this case, the propellers or fans would receive a direct power supply from an electric generator — which itself would receive power from the gas turbine.

The new concept calls for "folding up" the emissions-control system — like an accordion — in the plane's cargo hold. This would isolate it from the thrust-creating propellers.

In the paper, the researchers found such a hybrid-electric system would add extra weight, but this would only call for roughly 0.6% more fuel to fly the plane.

"This would be many, many times more feasible than what has been proposed for all-electric aircraft," said Barrett. "This design would add some hundreds of kilograms to a plane, as opposed to adding many tons of batteries, which would be over a magnitude of extra weight."

UPDATE Jan. 14, 6:05 PM EST: Net-zero aviation

As of writing, the MIT team is furthering designs for a "zero-impact" airplane capable of flying without emitting any NOx — or other chemicals, including the climate-changing CO2.

"We need to get to essentially zero net-climate impacts and zero deaths from air pollution," said Barrett in the blog post. "This current design would effectively eliminate aviation's air pollution problem. We're now working on the climate part of it."

The future is terrifying, and we're living in it. But it's in the most uncertain times that human ingenuity strives to grasp new ways to carry on its way of life. After half a century of jet-powered flight, grounding the aviation industry indefinitely for climate and health reasons would change the global community for keeps, not to mention the economy. Lucky for us, Bennet and his MIT team are inventing ways around both problems, and no one can blame us for dreaming of hitching a ride on a zero net-climate hybrid-electric plane.