With governments and activists ramping up pressure on airline companies to reduce their greenhouse gas emissions, Michael Nelson explores what innovations are being made to tackle the challenge.

The global economy is reliant on a thriving aviation sector. According to the International Air Transport Association, air transport can provide city-pair connections that serve as virtual bridges, which support the flow of key economic activities between markets. As the only rapid global transportation network, it facilitates links between businesses, governments and people – enabling world trade, investment, tourism and travel among other key economic activities.

Demand for mobility is increasing as wealth grows in emerging economies, and prices for flights are decreasing in response. Studies suggest that these trends could help to double the number of airline passengers to 8.2 billion by 2037.

However, as air travel continues to rise, so does a global focus on understanding the environmental impacts of aviation. The Air Transport Action Group estimates that the aviation industry produces around two per cent of all human-induced carbon dioxide (CO2) emissions, amounting to 915 million tonnes. Aviation is not included in the 2016 Paris Agreement, and has often been cited as an emissions laggard, but improvements may finally be in sight, ushered in by advances in technology and societal expectations.

Reducing emissions through enhancements in aircraft design

One of the reasons why aviation has taken so long to begin implementing sustainable, low-carbon solutions to air travel is because it takes a long time to get new technology into the market.

Obviously, the major area of concern in aviation, from a sustainability point of view, is in the CO2 emissions from burning aviation fuel. New fuels will need to be developed which are sustainable and produce much less CO2.

Tuomo Karppinen, environmental management systems manager for Finnish airline Finnair, says that research and development in aircraft fuel efficiency has been continuous over many decades, and modern aircraft are much more efficient when compared to aircraft from older generations.

“In general, the service life of an aircraft exceeds 25 years, making it a very sustainable transport technology. Many aircraft components are maintained and then recycled rather than being disposed of, meaning that the aviation industry is leading the way in developing a circular economy. For example, in the mid-2000’s, Finnair invested in a number of new-age Airbus aircraft with lower fuel consumption, and only received our first new fleet 11 year later.”

While a lot of action has been taken over the decades to minimise fuel consumption, the real breakthroughs in research and development will come via more technologically advanced planes, and the use of sustainable aviation fuel (SAF).

Mariano Morales, senior and technical account manager in A&D and industrial equipment for engineering simulation company Ansys, says that improvements in aerodynamics can help reduce aircraft emissions in the short-term.

“This physics-based technology allows engineers to uniquely test the planes under any circumstance to reduce the resistance an aircraft may feel as it moves through the air, virtually testing a variety of aircraft frame configurations,” explains Morales. “By reducing drag and air resistance, the industry can save on fuel and emissions, helping with costs, environmental impacts, and meet standards for green aviation.

“Optimising our current aircrafts is not a silver bullet, but until we can comfortably move to sustainable fuels, its impact is crucial. Achieving a zero-emissions aviation sector should be based on a desire to achieve a better, more sustainable industry, and there are many gains that can be obtained in an incremental way. By using simulation, the right answers can be discovered in a fraction of the time, for a fraction of the cost.”

Developments in the sustainable aviation fuel sector

In terms of SAF, Karppinen is sceptical about its application in the near future.

“Currently, SAF is not available on a scale necessary to supply fuel to the global aviation sector, and it can only fill 50 per cent of the fuel tank,” says Karppinen. “The price of SAF is also currently quite high, and we are still uncertain about how much customers are will to pay to account for this. Our assumption is that B2B customers will lead the way and show the example, as sustainability has become a corporate choice, and even shareholders call for environmental actions within a company.”

Issues in supply are beginning to change, however. Fulcrum BioEnergy, a US-based biofuel producer, are in the process of constructing and operating a pipeline of projects in the UK, each of which could convert up to 555,000 tonnes of non-recyclable waste into around 100 million litres of SAF per year.

The Fulcrum process uses a combination of proven technologies, starting with household waste, which has had any recyclable materials removed – called Refuse Derived Fuel (RDF). This is processed to remove further recyclables and other unsuitable materials, which leaves mostly organic material for processing, as well as residual plastics that cannot be recycled.

Gasification technology is used to create a synthesis gas (or ‘syngas’) from the processed RDF, which is then cleaned. The cleaned syngas enters a Fischer-Tropsch process, where hydrocarbons are created which are than further upgraded into a low net-carbon, sustainable aviation fuel.

Their first project in the UK – Fulcrum NorthPoint – will be based at the ESSAR Stanlow Manufacturing Complex in Cheshire. The £600 million facility will convert non-recyclable household and commercial waste in to SAF for use by airlines operating at UK airports. The project will utilise existing pipelines to transport the fuel to UK airports, through the Manchester Jet Line (MJL) and the UK Oil Pipeline network, making Manchester Airport the only airport globally with a direct connection to a SAF refinery once NorthPoint is operational.

Alternative energy technologies and aviation fuels

Morales notes that, as we lead up to the gradual phase-out of emissions from aircrafts, more pressure is being placed upon airlines to use cleaner fuel.

“We have already seen the EU’s plans for a proposal to charge airlines for the pollution produced from their planes as it strengthens its climate policies under the Green Deal. In the longer term, electric and hydrogen technologies will be used more widely as a significant way to reduce carbon emissions. The problem we face today is not a lack of options when it comes to the future of sustainable fuels, it is building the whole infrastructure to produce, transport and store at scale that energy, particularly hydrogen. Hydrogen is a real, sustainable alternative that can and will revolutionise the entire industry. But we are still a long way off from this happening.”

Dr. Jen Baxter is the director of innovation and policy at green hydrogen developer Protium Green Solutions, who work across the three main pillars of aviation, industrial heat, and mobility. She says that, while development of hydrogen as an aviation fuel is a relatively new sector, the company has expanded exponentially since the beginning of 2021, with a sudden increase in projects associated with hydrogen as a fuel.

They have been taking part in the Future Flight Challenge, a project designed to understand the feasibility of sustainable aviation infrastructure. Working with aircraft developer ZeroAvia, Protium have been studying how to supply hydrogen ground infrastructure to airports, alongside testing the possibility of fuelling a 19-seat aircraft with compressed hydrogen.

“The reality is that we want to be flying aircraft [on hydrogen] by 2025, and we are working in the Highlands and Islands with people who live in remote areas,” explains Baxter. “Their thoughts and feelings about aircraft are very different to other people, because aviation brings them everything from food and Amazon Prime deliveries, to visiting relatives, so it is a very different relationship they have with the industry. But they want it to be sustainable, and they do not want to be polluting their environment.”

Despite promising results from the Hydrogen Electric Automated Regional Transport project (Project HEART), part of the Future Flight Challenge, Baxter believes that larger aircraft operators will ultimately transition to SAF as a low-carbon alternative.

“If you think about small aircraft, the majority of air travel is less than 500 miles, which I found staggering,” … Baxter. “When you are travelling sub-regionally or regionally within the UK, for example, smaller aircraft are able to store enough gaseous hydrogen under compression, because the hydrogen does not weigh anything. Once you have worked out how much the storage tank weighs, it is relatively straightforward to calculate how much fuel you need.

“Where it would become really difficult is on larger aircraft: you would either need a large number of tanks, or very large tanks, and you would lose compression over periods of time. While large airliners have been doing research on liquid hydrogen, the challenge there is that you need a lot of energy in order to liquify it and then cool it down, and you are likely to lose some volume through boil off.

“SAF, however, is much easier to use for large airlines because they are effectively producing something that is identical to what is in use already, but it can be made in a net-zero way. All of the storage systems and refuelling systems will stay the same, and, broadly speaking, they would not have to do much to tune their jet engines to use it either.”

What about electrification? Can electricity play a part in powering the aeroplanes of the future?

“A lot of groups who were looking at electrification have now moved over to hydrogen, and the reason for that is that the amount of thrust you need to power an aeroplane is very difficult to achieve from a low-density energy source such as a battery,” concludes Baxter. “The comparison between a lithium-ion battery and hydrogen is absolutely enormous, and when you start to talk about liquified hydrogen, the gap gets even bigger.

“Batteries might work in a very small aircraft, if you do not want to go very far. However, the further you need to go, the more thrust you need and, subsequently, the bigger the battery needs to be and the heavier the aircraft is. Then you get into this vicious cycle of requiring bigger batteries, which increase the weight and increase the amount of thrust you need, meaning you need more batteries. It is completely impractical.

“We have to start thinking about the end results of what we do. While the production of other fuels, compared to electricity, may be less efficient, overall, the result is much more practical and practicable. I think we have to be a little bit more flexible in our thinking around net-zero.”

“Not all air travel is unnecessary”

More efficient aircraft, better aviation infrastructure, and sustainable fuels will all play a role in decarbonising the aviation sector. However, without further research and development, as well as the robust implementation of industry-wide sustainability standards, emissions from aviation will inevitably swell along with passenger traffic.

Despite the obstacles that lie ahead for the aviation sector, Karppinen is keen to challenge the idea that air travel is an unnecessary luxury.

“The pandemic has shown just how important it is to keep supply chains open for essential goods across the world, and airlines have the advantages of speed, reliability, and security. There is also a deep human need to travel and explore the world, and experiencing different cultures helps to reduce the inherent fear we have of something which is different to ourselves. Not all air travel is unnecessary.

“It is important to remember, however, that in aviation, even the smallest things have a big impact. Try to leave one kilogram off from your luggage next time you travel.”

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