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The mass density of hydrogen is very much negated by the fact that liquefied hydrogen needs to be in a 700 bar pressurised tank whereas kerosene is happy at atm

The mass density of hydrogen is very much negated by the fact that liquefied hydrogen needs to be in a 700 bar pressurised tank whereas kerosene is happy at atmospheric pressure. The more valid comparison is "hydrogen in a hydrogen pressure vessel" to "kerosene in a tank". I know cars are different, but the Toyota Mirai is actually heavier than the Tesla Model 3 even though it only needs a measly 5 kg of hydrogen to go as far as the Tesla.

credit_guy 5y ago
They plan to use liquid hydrogen [1, page 2] "FlyZero has concluded that green liquid hydrogen is the most viable zero-carbon emission fuel with the potential to scale to larger aircraft utilising fuel cell, gas turbine and hybrid systems. This has guided the focus, conclusions and recommendations of the project." [1] https://www.ati.org.uk/wp-content/uploads/2022/03/FZO-AIN-REP-0007-FlyZero-Zero-Carbon-Emission-Aircraft-Concepts.pdf https://www.ati.org.uk/wp-content/uploads/2022/03/FZO-AIN-RE...
zardo 5y ago
I don't see why LH2 would need to be kept at 700bar. The STS LH2 tank was operated at ~1.6 bar.
- nradov 5y ago
  And what happens if ATC directs the airplane to hold on the runway for a few hours? The space shuttle used cryogenic fuel, and after loading they had to continuously replenish the liquid hydrogen due to leakage and evaporation for several hours until launch. That can work for a rocket with a huge operating budget on a dedicated pad but I don't see that working at a busy commercial airport. Jet fuel is much more stable. It can sit in simple fuel tank for months with no special cooling or containment measures.
  - zardo 5y ago
    I suppose they have to flare off the H2. Or the plane itself has the capacity on board to capture and cool boil off.
  - ncmncm 5y ago
    LH2 in tanks boils off and is vented. There will be different procedures for LH2 vehicles on hold than today. That might involve plugging in somewhere for active cooling while on hold. Or, it might just mean you load on enough LH2 to make up for losses while holding. The practical merits of Jet-A fuel will be traded off against the value proposition of LH2 fuel. LH2 will win easily where volume is high and profits are greatest. So, marginal routes and uses will be the last to switch over.
  - ncmncm 5y ago
    The space shuttle, by the way, could not afford insulation on its external LH2 and LOX tank. We may assume that airliners' tanks will have vacuum- or aerogel-insulated tanks.
ncmncm 5y ago
You keep saying this, but nobody keeps LH2 at 700 bar, or even 2 bar. I have to conclude you are just making it up, each time, and after you have been repeatedly corrected.

credit_guy 5y ago

They plan to use liquid hydrogen [1, page 2] "FlyZero has concluded that green liquid hydrogen is the most viable zero-carbon emission fuel with the potential to scale to larger aircraft utilising fuel cell, gas turbine and hybrid systems. This has guided the focus, conclusions and recommendations of the project." [1] https://www.ati.org.uk/wp-content/uploads/2022/03/FZO-AIN-REP-0007-FlyZero-Zero-Carbon-Emission-Aircraft-Concepts.pdf https://www.ati.org.uk/wp-content/uploads/2022/03/FZO-AIN-RE...

zardo 5y ago

I don't see why LH2 would need to be kept at 700bar. The STS LH2 tank was operated at ~1.6 bar.

nradov 5y ago
And what happens if ATC directs the airplane to hold on the runway for a few hours? The space shuttle used cryogenic fuel, and after loading they had to continuously replenish the liquid hydrogen due to leakage and evaporation for several hours until launch. That can work for a rocket with a huge operating budget on a dedicated pad but I don't see that working at a busy commercial airport. Jet fuel is much more stable. It can sit in simple fuel tank for months with no special cooling or containment measures.
- zardo 5y ago
  I suppose they have to flare off the H2. Or the plane itself has the capacity on board to capture and cool boil off.
- ncmncm 5y ago
  LH2 in tanks boils off and is vented. There will be different procedures for LH2 vehicles on hold than today. That might involve plugging in somewhere for active cooling while on hold. Or, it might just mean you load on enough LH2 to make up for losses while holding. The practical merits of Jet-A fuel will be traded off against the value proposition of LH2 fuel. LH2 will win easily where volume is high and profits are greatest. So, marginal routes and uses will be the last to switch over.
- ncmncm 5y ago
  The space shuttle, by the way, could not afford insulation on its external LH2 and LOX tank. We may assume that airliners' tanks will have vacuum- or aerogel-insulated tanks.

ncmncm 5y ago

You keep saying this, but nobody keeps LH2 at 700 bar, or even 2 bar. I have to conclude you are just making it up, each time, and after you have been repeatedly corrected.