Climate change, carbon offsetting, and green technology and receiving increasing attention across industries and from governments. As a fuel and emissions heavy industry, aviation is understandably a top focus area. The aviation industry has set a goal of halving net carbon dioxide emissions by 2025 (based on 2005 levels)
Green changes so far have mostly affected aircraft and engine design. The next shift will be in aviation fuel and propulsion. We take a look here at some of the most significant changes.
More efficient aircraft
As aviation developed in the early days, performance, speed, and capacity played a key role. Operating economics went along with this, but efficiency less so. In the past decades, though, there has been a growing focus on efficiency. New generations of aircraft, large and small, have focussed on engine and aerodynamic improvements. And this will continue.
Commercial narrow bodies have seen major improvements with the A320neo (new engine option) and the 737 Next Generation and MAX aircraft. While larger widebodies have had clean-sheet designs with efficiency a top priority – such as the 787 and A350.
Improved efficiency has been a similar focus for business jets. As just one example, consider the Falcon 900. A major focus of later variants like the 900LX has been engine and winglet improvements to aid efficient operation and making flight planning easier.
Use of sustainable aviation fuel (SAF)
It’s not just aircraft and engine design that has become greener; fuel has as well. Kerosene-based jet fuel is being supplemented with Sustainable Aviation Fuel (SAF) in an effort to reduce full lifecycle carbon emissions.
SAF is an alternative hydrocarbon fuel that comes from renewable sources (feedstock). This includes cooking oil, plant materials, or household waste. This feedstock is collected, processed, and mixed with traditional jet fuel. The key here is ensuring the fuel has the same properties and can be used as a replacement in existing engines.
The uptake of SAF is low but growing (some estimates are that it accounts for only around 0.01% of aviation fuel use currently). Cost is a significant factor too, with SAF presently running at 3 to 5 times more expensive than traditional jet fuel. This should change as adoption picks up and legislation increases.
Longer-term, the aviation industry is looking at the possibilities of moving away from hydrocarbon fuels entirely. Using electric engines with stored battery power is one such possibility.
Battery technology, in particular size and weight, is a significant limitation, though. Much more space is needed for battery storage compared to fuel. And unlike liquid fuel, a battery weighs the same for the whole flight – a significant change to aircraft operating economics.
We have seen some early work with smaller aircraft and with hybrid engines. The 9-seat Cessna eCaravan (powered by a magniX electric engine) is currently the largest flying but only for very short ranges. Looking slightly further ahead, Rolls-Royce is working with Scandinavian airline Widerøe to develop an electric commercial jet by around 2026. This could take capacity up to 11-12 passengers, but still for short flights. Midsize and large aircraft – especially with a long-range – are a long way off.
Switching to hydrogen propulsion
Hydrogen power presents a more promising new alternative, especially for midsize and large aircraft. Hydrogen can either be used directly as an engine fuel or used as part of a fuel cell to produce electricity for engine power. Hybrid use is also possible.
Engine and fuel cell technology for hydrogen already exist and are in use in other industries. This is transitioning over to aviation but remains experimental. UK company Zero Avia has flown a Piper M-Class hydrogen aircraft on test flights and hopes to get this working for short-range flights.
For larger aircraft, Airbus is the furthest ahead. It launched a project in 2020, known as ZEROs, to get a hydrogen-powered aircraft in service by 2035. It is still to confirm the design for this, but it is likely to be similar to a regional turboprop or small jet aircraft.
Fuelling and airport infrastructure remain a major challenge though. For aircraft manufacturers to move to hydrogen, they will need confidence that it can be sourced at enough airports. Increased collaboration will likely be needed to make the necessary changes. One early move in this area has been seen in Paris. Airbus, Air France-KLM and Paris airports are planning to work together to create a hydrogen hub. More schemes like this could build the confidence for at least early stage adoption by manufacturers and operators.
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