Aviation has yet to end its 70-year addiction to the highly polluting hydrocarbon cocktail known as jet fuel, but several initiatives are propelling the industry towards a cleaner future. These are focused on sustainable aviation fuel (SAF), liquid hydrogen and electric power, both pure and hybrid.
SAFs can be obtained from a range of renewable sources – for example, forestry waste, used cooking oil, food packaging and even disposable coffee cups that would otherwise be destined for landfill. Since much of the renewable biomass used in its production absorbs carbon from the atmosphere, SAF has “the potential to reduce greenhouse gas emissions by up to 80% compared to conventional jet fuel” , according to Shell.
Many airlines have committed to adopting SAF. For example, BA’s owner, International Airlines Group, has pledged to fuel 10% of its flights with this fuel by 2030. In May, it took delivery of a batch of SAF produced at the Lincolnshire refinery from the American oil company Phillips 66. to add to the pipeline infrastructure that supplies airports in the United Kingdom.
Similarly, United Airlines has agreed to buy up to 52.5 million gallons of SAF from Finnish refiner Neste over three years to power its services from Amsterdam’s Schiphol Airport.
United Airlines’ Director of Sustainability, Lauren Riley, reports that “customer demand to limit their in-flight emissions is growing exponentially. This agreement means that customers flying from Amsterdam and potentially other airports will be partners in our sustainability efforts.
The search for a sustainable alternative
Despite these headline examples, more concerted action is still needed to ensure industry-wide adoption, according to Simon Burr, director of engineering and technology for Rolls-Royce’s civil aerospace arm. Barriers to the widespread use of SAF remain, he says. Chief among them is its current lack of “availability, scalability, and affordability.” We therefore need global action in forums such as the General Assembly of the International Civil Aviation Organization. It is vital that governments agree on a long-term decarbonization goal.
Promoting the use of SAF is a key part of Rolls-Royce’s sustainability strategy. The company has successfully tested several of its engines for fuel compatibility. Its next-generation engine demonstrator, UltraFan, is expected to undergo similar testing.
“Through rigorous testing, we know our engines can run on SAF,” says Burr, who adds that, if production can be scaled up enough, “adoption will improve affordability and create an environment where more airlines will be able to adopt SAF as part of their own flight to net zero.
Liquid hydrogen is another cleaner alternative to kerosene that has appeared on the industry radar. The UK government is injecting £27.2million into a program led by GKN Aerospace to develop a hydrogen propulsion system for small planes that could be scaled up. The H2Gear project aims to enable flights by 2026, using a system that converts hydrogen into electricity using a fuel cell system. The process does not emit COof them.
Partners in the initiative include Aeristech, Intelligent Energy and the universities of Birmingham, Manchester and Newcastle, while easyJet will provide information on operational requirements and options for flight demonstrations.
“Technology is a key driver in achieving our decarbonisation goals, with hydrogen propulsion being a frontrunner for short-haul airlines like ours,” says easyJet Director of Flight Operations David Morgan. His airline is optimistic that it “could start flying customers on aircraft powered by hydrogen combustion, hydrogen-electricity or a hybrid of the two by the mid to late 2030s. “.
Make old machines green
While the arrival of new hydrogen planes will create a new category of cleaner air travel, another approach is to retrofit existing planes with the technology.
ZeroAvia’s HyFlyer II project is developing hydrogen engines for demonstration on a 19-seater plane that it hopes will fly next year. The Anglo-American company will work with the Canadian group MHIRJ Aviation to design and equip regional jets (planes designed to carry less than 100 people on short-haul flights) with a 600 kW powertrain.
At the World Economic Forum’s annual summit in Davos in May, ZeroAvia Founder and CEO Val Miftakhov said the hundreds of regional flights that take place daily across North America “can and should be zero emissions as well before the end of this decade. This agreement is a giant step in the supply of hydrogen electric engines to the regional aircraft segment. »
The company has obtained experimental aviation safety certificates for its prototype aircraft from UK and US airworthiness authorities, passed significant flight tests and established partnerships with original equipment manufacturers and global airlines. It is on track to start commercial operations in 2024.
ZeroAvia is also developing a 5 MW modular powertrain for 40- to 80-seat turboprop aircraft – a project with backers such as Alaska Air and United Airlines.
As urban road networks struggle to accommodate commuter traffic, the only way is up. This is the rationale for the evolution of a new category in aviation: advanced air mobility – a mix of urban air mobility (flying taxis) and commuter aircraft.
“These planes will introduce all-electric, quieter and more efficient flight, which will allow us to significantly reduce journey times,” says Matheu Parr, customer commercial director at Rolls-Royce.
The company plans to introduce all-electric and hybrid-electric engines for the service by the mid-2020s. For this, it uses next-generation demonstration aircraft, including the Spirit of Innovation. Powered by a 400kW unit, it can claim to be the world’s fastest all-electric vehicle, having topped 387mph in a test flight.
Rolls-Royce has also worked with manufacturers Tecnam and Rotax to complete flight testing of a hybrid-electric aircraft powered by parallel-hybrid propulsion – a technology that could be applied to larger planes.
The data from the tests is already applied in the urban air mobility market. A Rolls-Royce unit has been chosen by Vertical Aerospace for its all-electric VX4 aircraft, designed to carry one pilot and four passengers, emission-free, for 100 miles at 200 mph. The Bristol-based company aims to achieve certification of the VX4 in 2025 and has secured conditional orders and pre-order options for up to 1,350 planes from players including American Airlines and Virgin Atlantic.
Electric aircraft versus sustainable aviation fuel
Regardless of which alternative energy source becomes the predominant choice, one certainty is that tomorrow’s skies will feature a wider range of vehicle types. This represents an opportunity for disruptors to shape the future of energy-efficient propulsion technology.
Bedford-based SME Blue Bear Systems Research is leading a seven-member consortium developing “a quiet, efficient, high-power-density propulsion module with zero tailpipe emissions.” The design can be adjusted for general aviation aircraft, large cargo drones, air taxis and regional planes.
Co-funded by the government program of the Institute of Aerospace Technology, the Integrated Flight Control, Energy Storage and Propulsion Technologies for Electric Aircraft (Inception) project focuses on optimizing the conversion of electrical energy into thrust.
The project began in January 2021 and production of the completed design is underway, with wind tunnel testing expected to begin shortly. The plan is to install the module on an aircraft platform, aiming for airworthiness certification in 2026.
The industry needs to place more faith in disruptive new entrants if it is to have a greener future, says Blue Bear CEO Dr Yoge Patel.
“The UK is one of the most inventive countries, attracting a lot of investment – and Blue Bear has had excellent government support,” she says. “But how do you get that brand credibility when you’re a startup?”
The next big challenge, once you have a foothold in aviation, is staying in the game, says Patel. And the third is to grow your business, whether organically or through investments, without losing the culture of innovation that “keeps you sharp, keeps you from getting complacent, and keeps you from being focused.” on the processes.
His company, for example, “set out to become an agile systems integrator. It was also important to create an agile culture and not be dependent on any of the big companies”.
Vertical integration was crucial for the Inception project. In addition to producing the engine, Blue Bear also provides all the testing and evaluation infrastructure.
“We are not dependent on a third party for this. We also do our own certification and assurance,” says Patel. “We have verticals that we’ve brought together to allow us to move from an idea to delivering flight-tested products.”
This level of control is unusual for an SME. And, while this has given the company freedom, there is one crucial factor over which it has no control: regulating the next generation of energy-efficient engines that will serve many forms of aviation, potentially sharing the same airspace.
“Rules and procedures are going to change,” says Patel. “The way the industry provides evidence of airworthiness must also change if we are to do it faster and more thoroughly. With funding, it’s an absolute hurdle.