Can aviation get the carbon out of flying? For short flights in small, personal aircraft, battery power and electric motors certainly work – Airbus’s one-man E-Fan crossed the Channel as long ago as 2015 – but while the subsequent half-decade has seen dozens of companies experiment with battery power to chase the dream of zero-emission urban air taxis, none has yet entered service.
Commercial aviation’s higher power requirements also demand a different strategy. Airbus and Rolls-Royce appeared to have opted for a series hybrid solution when they launched the E-Fan X demonstrator programme in late 2017, backed up by Siemens (whose electric power division was subsequently acquired by R-R).
The plan was to mature the technologies required for hybrid propulsion by modifying a BAE Systems Avro RJ100 regional jet, replacing one of its four Honeywell gas turbines with a 2MW electric fan motor powered by batteries charged by an inboard AE 2100 gas turbine. Originally set for flight testing this year, come April and the project was cancelled altogether.
At the time, both Airbus and Rolls-Royce were already reeling from the Covid-19 shutdown of aviation, so it was no surprise to hear both sides citing costs among other reasons. As R-R chief technology officer Paul Stein put it then, much had already been learned from the project but “flight testing would have cost tens of millions and we have both decided that we would prefer to save that money.”
The hard truth appears to be more fundamental than even money. As Airbus zero emissions technology vice-president Glenn Llewellyn told a 25 June webinar titled “Path to clean aviation in a new world”, while E-Fan X illuminated some interesting technologies that will someday be used in commercial aircraft: “As a combination in a serial hybrid-electric configuration it was not giving us the disruptive – and I really mean disruptive – level of [emissions] reductions that we need to make over the next years.”
Llewellyn could perhaps be forgiven despair, but sees a solution: hydrogen.
Hydrogen can be burnt directly in an engine or feed an electricity-producing fuel cell, in either mode emitting only water vapour. Hydrogen can be used to make synthetic fuels, it is well-understood because it is already widely used in the chemical industry, has been extensively researched as an automotive fuel and is a mainstay propellant in space rockets, where combining liquid hydrogen and liquid oxygen delivers massive thrust. And, of course, it is wildly abundant – seawater, after all, is H2O. Hydrogen, reckons Llewellyn, could yield half of the carbon dioxide (CO2) reduction needed; as a fuel, it would even slash another great health hazard of aviation, nitrous oxide (NOx) emissions. Hydrogen should even scale up and eventually be able to power the large aircraft familiar to Airbus.
Ultimately, hydrogen as a prospective solution leaves the outside observer wondering why aviation has ever been interested in batteries. Of course, as with any technology shift there is much devil in the practical detail, and Llewellyn readily cites challenges of weight, reliability and infrastructure, which is a massive issue at airports. Safety is another big concern, and he underscores the need to develop a system that is at least as safe as using kerosene on and around aircraft.
But on balance, he says: “It looks like there are ways to make hydrogen really feasible for commercial aircraft applications.”