Originally published at: Beyond Aero Concludes Hydrogen Aircraft Design Review
The company said it is targeting certification under transport-category standards for its hydrogen jet program.
To my mind, this seems to be a significant improvement over batteries. Refilling is much faster than recharging and the energy density of hydrogen is much higher than batteries. Of course, a tank capable of safely carrying a gas pressurized to 700 bar is going to be heavy (eating into the energy density calculation), there are probably safety concerns around hydrogens transparent flame, and I’m sure that somebody will share the multitude of issues I’ve missed. Regardless, even with the well earned skepticism that comes from decades of broken promises in aviation, this brings me a little happiness.
Interesting concept with some advantages, and also real world disadvantages. Handling of gaseous hydrogen is tricky, and refueling won’t be done by regular fuel jockeys. At over 10,000 psi, containment and handling of a gas with such tiny molecules can be problematic. A leak can spontaneously combust at those pressure. Ever see hydrogen burn? No, because you can’t. Perhaps it may be a future reality with advancing technology.
The high pressure storage and hydrogen’s negative Joule-Thomson coefficient (heats on expansion leading to spontaneous ignition) are indeed problems. The work of compression to 700 bar is about 1/6 of the energy content.
Even so, a great deal of work has been done on fuel cell electric vehicles. Such vehicles have been well received by those who have been able to lease them with one exception, the cost and availability of the fuel. The technical challenge of refueling was not a problem among early adopters.
Fuel cost and refueling infrastructure will be problems for aviation too, though there are fewer numbers of refueling locations and greater cost tolerance in aviation.
Tank geometry is the problem for aviation. You need cylindrical or spherical tanks at this pressure. The don’t fit well in thin wings. The tanks are generally carbon fiber wound over a thin aluminum (to stop hydrogen permeation) bladder making them reasonably light weight. Volumetric energy density is a bigger problem. Even at pressures over 10,000 psi or 700 bar the volumetric energy density is only about 10% that of Jet-A. Fitting the tank aspect ratio within the cross-section of an aircraft is problematic.
SAF has its own set of problems including cost and potential feedstock limitations, but the energy density of SAF makes it a better solution. That and the fact that it fits into existing infrastructure and fleets. The solution to the feedstock issue is eSAF or power to fuels which use CO2 and hydrogen to produce synthetic SAF. CO2 sources are more abundant than other SAF feedstocks. This pushes the resource limitation to power needed to produce hydrogen. Ironically (to me at least) the solution to that will be nuclear energy which will see a resurgence to power AI datacenters. As that need is met the use of nuclear power in eSAF production will address a significant fraction of the cost reduction and production capacity needed for SAF to be a real solution.
Batteries, are an intermediate source of final electric power. Alternators, sized for the power loads, will keep an aircraft in flight until something fails; or a very, very long time. Hydrogen has never been an acceptable source of aircraft power. Most of the flying public has seen the explosion of the Hindenburg airship on videos and would not fly anything operated on Hydrogen. Hydrogen, like Natzism, is personna not grata! Gone from humanity for ever! And you know people will be willing to waste their money on anything just for the sake of supposed newness; but not in the case of hydrogen power because humanity has already had one very bad dose of a hydrogen powered airship(s)!
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