Thierry Dubois Far-reaching progress in fuel efficiency and hydrogen transition should be accompanied by swift fleet replacement, says Clean Aviation executive.
Thierry Dubois
The European Partnership for Clean Aviation came into force in late November, and the first statements by Axel Krein, executive director of the related joint undertaking (JU), show the project is strengthening Europe’s drive to increase its use of hydrogen power.
Clean Aviation follows on the Clean Sky 2 private-public initiative, which has structured a large part of the European aerospace industry’s research and technology effort since 2014. The actual start of Clean Aviation is 11 months late due to protracted negotiations among European institutions. The first call for proposals is scheduled to be issued in March 2022.
The additional time may have helped Clean Aviation’s promoters clarify their objective. Hydrogen should be the fuel of the next generation of commercial aircraft, they assert. Early studies have given Airbus confidence the goal is attainable.
“Short-to-medium-haul flights, below 4,000 km [2,150 nm], account for two-thirds of global emissions,” Krein stresses. This reinforces the case for developing a hydrogen-fueled narrowbody such as Airbus’ ZEROe concepts. Technological roadblocks would make it difficult to design a hydrogen system in a long-range aircraft, too.
“Liquid hydrogen is by far the most promising energy carrier,” Krein continues. It eliminates CO2 emissions and solves the problems created by nitrous oxides and contrails, he says. The debate, however, continues between those who contend using hydrogen does not emit the condensation that create nuclei contrails and those who anticipate the increased amount of water vapor will generate clouds anyway.
Hydrogen may be used on the same aircraft in a fuel cell, a turbine engine or both. This will be one of Clean Aviation’s two main areas of focus, Krein emphasizes: “We will fly demonstrators by the end of the decade ,” he says. “The demonstration program should start by 2027-28 to leave enough time before entry into service in 2035 . . . [F]or a medium-range aircraft, the target is realistic.” The dates are aligned with Airbus’ preliminary schedule.
The other main focus will be cutting fuel burn. “Whatever the source, we are taking energy demand away,” says Krein. He partly disapproves of the use of synthetic fuel, as it requires electric energy to combine hydrogen with other substances. However, sustainable aviation fuels—including synthetics—may be the way to go for long-range aircraft until 2045 at the earliest, he says.
Clean Aviation’s objective is a 30-50% reduction in fuel consumption by 2050. This will entail replacing 75% of the global fleet in 2035-50. “We need to focus on technologies suitable for mass production,” Krein notes.
The Aviation Week Network 2022 Commercial Aviation Fleet & MRO Forecast projects that there will be about 42,000 commercial aircraft (from regional turboprops to widebodies) in the global fleet in 2031, the furthest year in the forecast. Factoring in growth and replacement rates, replacing three-quarters of the fleet in 15 years beginning in 2035 means, roughly speaking, doubling production.
The Clean Aviation JU probably will have fruitful links with its air traffic management counterpart, the Single European Sky ATM Research 3 Joint Undertaking, which is in charge of improving ATM. Giving crews the freedom to choose flightpaths is part of a trend toward fine-tuning operations. In a search for the optimal way of operating, more autonomy could be given to pilots of an aircraft, Krein suggests. The right handover between the aircraft’s systems and the air traffic controller’s instructions will have to be found, he says.
In addition, Clean Aviation is hoping for synergy with the Fuel Cells and Hydrogen Joint Undertaking. “Some of their work could be directed to air transport, such as creating aviation-grade stacks for fuel cells,” Krein points out. “They have competencies we want to benefit from.” Similarly, working with the new European Batteries partnership, dubbed Batt4EU, may help, he says.
Such cooperation also is aimed at mitigating the €4 billion ($4.5 billion) budget, lower than the hoped-for €5 billion. The €4 billion number is stable compared to the budget for the ongoing Clean Sky 2 project, and the EU is contributing €1.7 billion. Clean Aviation will have to be even smarter in terms of organization, Krein stresses: “We need to fly in formation.”
Clean Sky 2 involves 950 entities, from universities to small family companies and large OEMs. The project thus is rooted deeply in the aviation industry. Its results are encouraging. An evaluation conducted last May showed research and technology work already achieved would enable a 17-26% reduction in CO2 emissions for a short-to-medium-range aircraft. The precise percentage would depend on the entry-into-service year. The objective is 20-30%, and another three years of work are allowed under Clean Sky 2.