I mentioned Hydrogen as an option for aviation. The use of Hydrogen to either power jet engines or to power fuel cells to provide electricity is a real technical option. Although the person I was talking to was engaged in environmental work, they shrugged their shoulders when I mentioned Hydrogen. They were certainly not impressed by these possibilities despite our agreement on the urgent need for de-carbonisation.
I can understand why there’s a level of cynicisms. On my part, it’s like the X-Files[1]. Fox Mulder was the believer and Dana Scully the sceptic. Broadly, I want to believe.
Today’s, liquid fuels can be explosive in certain conditions. However, it takes a considerable effort to create the conditions whereby a devastating explosion can occur. The Boeing 747-100 that was Trans World Airlines Flight 800 (TWA 800)[2] exploded, broke up in the air and fell into the Atlantic Ocean in 1996. This was an example of a worst-case scenario. 230 people were lost in that fatal accident. Now, the ignition of a flammable fuel/air mixture in aircraft tanks is better prevented by design and operational procedures.
If Hydrogen is to be viable in civil aviation such hazardous conditions will be harder to prevent. A flammable hydrogen/air mixture can be ignited much more easily than conventional liquid fuels. Such dangerous situations can be prevented but the measure to do so will require robust design and stringent operational procedures.
Several development programmes are underway, making practical Hydrogen powered aircraft viable. A range of aircraft configurations are possible. From hybrid generator and electric motor set-ups to combustion-based propulsion. This work is moving from academic research into commercial possibilities.
There little read across between the behaviour of conventional hydrocarbon liquid fuels and liquid Hydrogen. This would be evident in any serious incident or accident scenario. Let us imagine the case of British Airways Flight 38, in 2006, a Boeing 777-236 that came down at the end of a runway at London Heathrow[3]. A significant amount of fuel leaked from the aircraft after it came to rest, but there was no fire. There were no fatalities.
The breakup of liquid Hydrogen tanks or plumbing in such a scenario would almost certainly result in a significant fire. The mitigating impact of that fire is the lightness of the gas. Instead of liquid fuel pooling on the ground, Hydrogen would burn upward. However, any explosion could be devastating.
So, for large aircraft design the provisions to protect liquid Hydrogen tanks and plumbing must be extensive and extremely robust. This would have to be maintained, as such throughout the whole operational life of the aircraft. These requirements would be onerous.
Keeping crew and passengers well away from Hydrogen infrastructure will be a must.
POST 1: Crashworthiness doesn’t get much of a look-in. Without it there’s going to be a problem over the horizon. https://www.ati.org.uk/flyzero-reports/
POST 2: At least for eVTOL aircraft some work is being done. https://ieeexplore.ieee.org/document/10011735
[1] https://www.imdb.com/title/tt0106179/
[2] https://www.history.com/news/twa-flight-800-crash-investigation
[3] https://assets.publishing.service.gov.uk/media/5422ec32e5274a13170000ed/S1-2008_G-YMMM.pdf
John Vincent 