MrJoyless t1_iy8xhwa wrote
Reply to comment by SomeDEGuy in Rolls-Royce successfully tests hydrogen-powered jet engine by je97
>Hydrogen is more energy dense per pound,
True, but not by volume. That's why you see hydrogen tanks for rocket launches taking up a huge % of the total launch vehicle volume vs the oxidizer. Also the extra insulation required really offsets hydrogen's main weight saving benefit.
I'm not sure if there really is a good or safe way to transport or store hydrogen for air travel. Thermal issues would abound, especially with the temperature differentials airplanes experience at cruising altitude. That's not even mentioning the storage issues that occur since hydrogen is so damn small it can leak through seemingly solid containment vessels.
Stenthal t1_iy9b2k0 wrote
> True, but not by volume.
Generally weight is the bottleneck for aircraft, not volume. If we could trade weight for volume, we'd just make fatter planes.
> I'm not sure if there really is a good or safe way to transport or store hydrogen for air travel.
This is a bigger problem.
_toodamnparanoid_ t1_iyas0xp wrote
> fatter planes
Aaaaaaaaare you gonna take me home tonight?
Aaaaaaaaah, down beside red PAPI lights
Aaaaaaaaaaare you gonna let those flaps hang out?
Fat bottomed planes you make the turbine world go round!
jesset77 t1_iyald09 wrote
>Generally weight is the bottleneck for aircraft, not volume. If we could trade weight for volume, we'd just make fatter planes.
We already tried this though, Blimps have not been terribly successful. Especially the ones kept in the sky via hydrogen. đ
Dangerous_Dac t1_iy95kem wrote
And even with all that volume and insulation, they're still constantly topping off the tanks until t-0, and all that gas you see billowing out from rockets on the pad is boiloff from large amounts seeping out from various junctions and connections because keeping that shit in one place is hard.
jg727 t1_iy9abwl wrote
A lot of that is intentional release of hydrogen and oxygen.
They cryogenic fuels in rockets, stored at their freezing point. As they slowly warm up/boil off the liquids, the tanks have to hav a way to vent the excess pressure
Prophet_of_Entropy t1_iydg0az wrote
hydrogen also leaks out or most seals and will even infiltrate metals and make them brittle, hydrogen isnt the new new miracle fuel.
jg727 t1_iydu28q wrote
Yes, you're right. But I was referring to the obvious plumes of off gassing
kr0kodil t1_iybuxan wrote
Yes, youâd run into the same issues with hydrogen-powered jets. You need to compress and refrigerate the hydrogen in order to store it in liquid or supercritical form, and youâd need to constantly vent off excess hydrogen when tank temperatures rise.
Pesto_Nightmare t1_iy9evb8 wrote
Isn't the extra insulation specifically for liquid hydrogen? I would expect an airplane to be more like a hydrogen powered car and take compressed gas, not liquid.
1funnyguy4fun t1_iycvvjq wrote
Speaking of the containment issue, I read a comment from an engineer that said, âHydrogen wonât work out because it is a slippery little bastard that is hard to contain and a general pain in the ass to work with.â Seems to be the general consensus from what I have read. In theory, hydrogen as a fuel solves a lot of problems. In practice, you end up creating a lot more problems than you fix.
EmperorArthur t1_iyec9e0 wrote
It's why SpaceX is looking at Methane. It's just not something that sounds "Green" since almost all methane we use on Earth is from wells.
groveborn t1_iyaf1bx wrote
It depends on how the fuel is used. If it's being burned then it needs to be done in an elemental state (h2 gas or liquid), but if we just need electricity to run the engines, then the hydrogen can be bonded with a metal for easy and safe storage. Just add water to fizz it out.
I suspect the first, rather than the second.
Isosceles_Kramer79 t1_iychmtt wrote
Using that energy to make a carbon neutral synfuel like butanol would make more sense honestly.
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