About 3 percent of global emissions come from aviation today, and with more passengers and flights expected as the population expands, aviation could be producing three to five times more carbon dioxide emissions by 2050 than it did before the Covid-19 pandemic. Hence to overcome this, electric planes might seem futuristic but they aren’t, at least for short distances. Two-seater Velis Electros are already quietly buzzing around Europe, electric seaplanes are being tested in British Columbia, and larger planes are coming. Air Canada announced on September 15 that it would buy 30 electric-hybrid regional aircraft from Sweden's Heart Aerospace, which expects to have its 30-seat plane in service by 2028.
Analysts at the US National Renewable Energy Lab note that the first hybrid electric 50 to 70-seat commuter plane could be ready not long after that. In the 2030s, they say, electric aviation could take off. That matters for managing climate change.
Aerospace engineer and assistant professor Gokcin Cinar develop sustainable aviation concepts, including hybrid-electric planes and hydrogen fuel alternatives, at the University of Michigan. We asked her about the key ways to cut aviation emissions today and where technologies like electrification and hydrogen are headed.
Why is aviation so difficult to electrify?
Aircraft are some of the most complex vehicles out there, but the biggest problem with electrifying them is the battery weight. If one tries to fully electrify a 737 with today's batteries, he would have to take out all the passengers and cargo and fill that space with batteries just to fly for under an hour.
Jet fuel can hold about 50 times more energy compared to batteries per unit mass. So, you can have 1 pound of jet fuel or 50 pounds of batteries. To close that gap, we need to either make lithium-ion batteries lighter or develop new batteries that hold more energy. New batteries are being developed, but they aren't yet ready for aircraft.
Are hybrids an alternative for electric?
Even though we might not be able to fully electrify a 737, we can get some fuel burn benefits from batteries in the larger jets by using hybrid propulsion systems. We are trying to make that happen in the short term, with a 2030-2035 target for smaller regional planes. The less fuel burned during flight, the fewer greenhouse gas emissions.
How does hybrid aviation work to cut emissions?
Hybrid electric aircraft are similar to hybrid electric cars in that they use a combination of batteries and aviation fuels. The problem is that no other industry has the weight limitations that we do in the aerospace industry. That's why we have to be very smart about how and how much we are hybridising the propulsion system.
Using batteries as a power assist during takeoff and climb is a very promising option. Taxiing to the runway using just electric power could also save a significant amount of fuel and reduce the local emissions at airports.
There is a sweet spot between the added weight of the battery and how much electricity you can use to get net fuel benefits. This optimization problem is at the centre of my research. Hybrids would still burn fuel during flight, but it could be considerably less than just relying entirely on jet fuel. I see hybridisation as a mid-term option for larger jets, but a near-term solution for regional aircraft.
For 2030 to 2035, we're focused on hybrid turboprops, typically regional aircraft with 50-80 passengers or used for freight. These hybrids could cut fuel use by about 10 percent. With electric hybrids, airlines could also make more use of regional airports, reducing congestion and the time larger planes spend idling on the runway.
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What can we expect to see in the near term from sustainable aviation?
Soon we'll see more use of sustainable aviation fuels or SAF. With today's engines, you can dump sustainable aviation fuel into the same fuel tank and burn it. Fuels made from corn, oilseeds, algae, and other fats are already being used.
Sustainable aviation fuels can reduce an aircraft's net carbon dioxide emissions by around 80 percent, but supply is limited, and using more biomass for fuel could compete with food production and lead to deforestation.
A second option is using synthetic sustainable aviation fuels, which involves capturing carbon from the air or other industrial processes and synthesising it with hydrogen. But that's a complex and costly process and does not have a high production scale yet. Airlines can also optimise their operations in the short term, such as route planning to avoid flying nearly empty planes. That can also reduce emissions.
Is hydrogen an option for aviation?
There are two ways to use hydrogen in an airplane: either in place of regular jet fuel in an engine or combined with oxygen to power hydrogen fuel cells, which then generate electricity to power the aircraft. The problem is volume as hydrogen gas takes up a lot of space. That's why engineers are looking at methods like keeping it very cool so it can be stored as a liquid until it's burned as a gas.
Airbus is doing a lot of research on hydrogen combustion using modified gas turbine engines with an A380 platform and aiming to have mature technology by 2025. Australia's Rex airline expects to start testing a 34-seat, hydrogen-electric airplane for short hops in the next few years. By 2050, we could see three to five times more carbon dioxide emissions from aviation than before the pandemic.
(With inputs from PTI)
