Some commentators such as Gryf have concerns about the practicality of hydrogen in airports and aboard planes, so it will be interesting to see how this develops, and whether they hit any gliches.

@sd,
Hydrogen is very practical for commercial aircraft:
1... weighing 1/3 as much as Jet fuel means that much higher payload capacity per BTU of fuel burned.

2... The fuel can be stored in the tail section of the aircraft and that will ensure that the fuel tank will remain intact after a crash, thus avoiding deadly flames that engulf the aircraft to kill most people on board.

3.... LH2 cannot burn because it is so cold. By the time it evaporates, it will fly upward like a homesick angel and won't stick around to engulf the occupants. Talking "The Incredible Lightness of Being" here !

4... To avoid taking up internal space of existing airliners, the LH2 could be in multiple long cylindrical shapes to be mounted underneath existing airliners, thus taking up no internal space. Fire and H2 leak sensors will be employed to detect fire and H2 leakage in order for the tank on fire or leaked to be ejected, just like drop tanks in military aircraft.

5... Green LH2 will one day be incredible cheap, due to continual dropping in prices of RE, Nuclear, and of electrolyzers. We now have Solar panel with record efficiency of 33%, which will result is much cheaper Solar electricity. It is projected that H2 will eventually cost $1,5 per kg in compressed form, and around $2 for liquid form.

Thus, be prepared for much cheaper air travel, (and much safer from fire hazard) from doubling of fuel efficiency per lb of payload due to very light fuel, to very cheap to produce Green H2.

Hi sd!

As the genuine Davemart, although I have not found anything to rule out hydrogen, I am way less certain than Roger about it, but OTOH my knowledge base is minimal, including about the certification process.

Zero Avia apparently reckon that they can significantly shorten certification as they are converting existing aircraft, so it is primarily the new propulsion system which needs fresh certification.

A bit here about how they are approaching the hydrogen containment vessels:

https://www.compositesworld.com/articles/zeroavia-advances-to-certify-za600-in-2025-launch-za2000-with-liquid-hydrogen-in-2027

' We’re designing some initial applications, probably for the end of the decade, with LH2 tanks that can be swapped in and out when needed. This can’t be done every cycle due to potential for damage and inspection requirements, so we need tanks that can be in place for as many cycles as possible. Eventually, I think we’ll need to match the capability of the existing jet fuel tank technology, which is again, roughly 50,000 cycles.”'

I tend to like pragmatic one step at a time approaches, rather than giant leaps, so am keen on going for lower life and frequent inspections initially.

Presumably a frequent inspection cycle makes certification easier.

Thank you, Davemart, for the update.
I believe that mounting LH2 tanks on the bottom of the fuselage that can be individually ejected in case of fire or leakage would make it the safest and most acceptable and certifiable. Sensors will be needed along the lower fuselage border to detect early fire or leakage.
In this way, the wings can still be used to store liquid Jet A fuel in case LH2 fuel is not available, and the engine designed to burn both LH2 and JetA fuel in order to fast-track the adoption of green LH2 fuel.

Mike has not got around to/doesn't seem to fancy this one either, which if it can be scaled is of major, major importance:

https://www.pnas.org/doi/10.1073/pnas.2301206120

So ammonia can be produced with very small energy imputs, just spraying water in the presence of an earth abundant catalyst!

' Water (H2O) microdroplets are sprayed onto a magnetic iron oxide (Fe3O4) and Nafion-coated graphite mesh using compressed N2 or air as the nebulizing gas. The resulting splash of microdroplets enters a mass spectrometer and is found to contain ammonia (NH3). This gas–liquid–solid heterogeneous catalytic system synthesizes ammonia in 0.2 ms. The conversion rate reaches 32.9 ± 1.38 nmol s−1 cm−2 at room temperature without application of an external electric potential and without irradiation. Water microdroplets are the hydrogen source for N2 in contact with Fe3O4. Hydrazine (H2NNH2) is also observed as a by-product and is suspected to be an intermediate in the formation of ammonia. This one-step nitrogen-fixation strategy to produce ammonia is eco-friendly and low cost, which converts widely available starting materials into a value-added product.'

They talk about it in relation to replacing present ammonia production for fertiliser etc, but if it works at scale presumably huge amounts of ammonia can be produced, which means plentiful hydrogen without massive solar and wind farms and electrolysis.

I find this staggering.

Hi sd.

You argued:

' Yes, we currently use a lot of hydrogen. So, if we can make low cost green hydrogen, why not first use it to replace the existing steam reformed hydrogen? Sort like grabbing the low hanging fruit.'

That is perhaps the sort of calculation which would work, or at any rate be applied, in a top down command economy.

For capitalist systems, then opportunity cost rules, where initially you go for premium products, or ones where it is most difficult to reduce emissions, not the high volume inputs at low margin to the petro chemical industry.

So in my link, already given above:

https://www.compositesworld.com/articles/zeroavia-advances-to-certify-za600-in-2025-launch-za2000-with-liquid-hydrogen-in-2027

' “This is a higher margin market versus automotive,” says Miftakhov. “We see it as similar to the market for fuel cells. For typical light-duty automotive vehicles using a standard internal combustion engine [ICE], the cost of power delivered is about $30 per kilowatt. For typical aviation turbine engines, it’s closer to $800-1,000 per kilowatt, ranging from small turbines to large ones. So, you have an order of magnitude price differential for aviation, which makes it easier to have a profitable fuel cell company, for example. We think there’s going to be a similar dynamic for composite LH2 tanks, with margins and pricing that will hopefully drive the supply.”

The same argument would appear to me to apply to the hydrogen in the tanks as to the tanks themselves.

For a start, liquifying hydrogen is an expensive business, so the difference in a perhaps initially more expensive process using green hydrogen and bog standard grey hydrogen is proportionately less.

Of course, if the thing is going to work big time, then at some stage green hydrogen would have to be cost competitive with grey, and hopefully it will, althouth it should be noted is that any lack of competitiveness against grey hydrogen or fossil fuels is largely due to the real costs of use being externalised, ie, fossil fuels are not charged for the damage they do.

This is politics, not capitalism or economics.

But the soft target for green hydrogen is in premium uses such as substituting for jet fuel, not going head to head as you suggest.