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SomeDEGuy t1_iy8l90q wrote

Reply to comment by kukukele in Rolls-Royce successfully tests hydrogen-powered jet engine by je97

Noise shouldn't be a huge difference, as its still burning material to force an object through air at speed.

Hydrogen is more energy dense per pound, but has some storage issues that would have to be figured out for safety. Storing a compressed gas like hydrogen is significantly more dangerous than the same mass of jet fuel. It's a good test, though, and helpful to explore new methods.

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Fearlessleader85 t1_iy8wznr wrote

Not to mention nearly all metals and some other materials suffer "hydrogen embrittlement" which causes them to fail catastrophically after extended exposure.

Hopefully it works out, but there are still significant engineering challenges to overcome before this is commonplace.

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Dangerous_Dac t1_iy9588s wrote

Significant is an understatement. More like "need to develop whole new levels of material science to even begin to consider this viable" levels of engineering challenges.

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Fearlessleader85 t1_iy965pz wrote

We have materials that can hold hydrogen well, and it's trivially easy to make an effectively impermeable coating on something like a compressed gas cylinder. But doing the same for a full plane is less simple.

And we have some promising materials for that, like some graphene based stuff. It's not as far out as you suggest. It's just a long way from cheap.

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CrosshairLunchbox t1_iy97a8w wrote

Slap a bit of gold plating on and you're good up to 1000-2000 PSI Hydrogen last I recall from materials engineering.

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Fearlessleader85 t1_iy9869t wrote

Gold might not be a bad material for it, especially on tubes and engine parts, but I don't know enough about gold playing to know if it's adherence is good enough in a thin film application to coat something like a turbine.

Another problem is hydrogen's flame temp is absolutely insanely hot. Gold has a fairly high melting temp for such a soft metal, but it will need excellent cooling. It's conductivity could help a bunch with that though.

Damn, i wish i was in engine r&d sometimes. All my fiddling with engines is on 4-bangers in my shop. And i don't even have a cnc.

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brcguy t1_iy9zed5 wrote

It’s more about the storage than the turbine tho. The tanks and fuel lines are the problem way before the combustion chambers. Those need to handle more heat, but shouldn’t be in major danger of hydrogen embrittlement as it’s on fire and mixing with air by then. (I could be wrong it’s been a while since I’ve messed with turbines).

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Fearlessleader85 t1_iy9zzsb wrote

I mean, you could be right, but with the lifetimes we're demanding of aircraft, i think it would behoove us to keep everything from hydrogen embrittlement. Injectors might be the main trouble spot, though.

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brcguy t1_iya0urx wrote

Yeah plus I think storing a suitable volume might be a problem too. Just need to make a super efficient electric turbine and then build the whole airframe out of batteries lol.

Who are we kidding - the climate crisis will only be solved by the climate crisis killing half of us. Now I’m sad.

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EmperorArthur t1_iyecwwv wrote

> then build the whole airframe out of batteries

Nuclear!

Actually skip the electric engine, just use the fuel to heat the air.

90% sure the US dreamed up a plane like that in the 60s.

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Statertater t1_iya0ynb wrote

What about ceramic?

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Fearlessleader85 t1_iya1ctf wrote

I'm no expert on hydrogen containers, but i do believe some of our better options emply ceramic coatings, but they can't generally be pure ceramic, because they can't handle the hoop stress. Also, i think most ceramics still leak a significant amount of hydrogen.

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mces97 t1_iyad5r6 wrote

I'm more concerned about what happens if they need to make an emergency landing, if landing gear don't work? Cause if that tank isn't 100% tested against the type of damage that could make it explode, I would be very concerned getting on a plane.

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moofunk t1_iya75dw wrote

Considering how long it takes the FAA to certify unleaded fuel, which is supposed to be done by 2030, I can't imagine how long it would take to certify a hydrogen powered plane.

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Fearlessleader85 t1_iya7b89 wrote

I certainly wouldn't plan on buying tickets on such a plane any time soon.

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Dt2_0 t1_iyb7oi7 wrote

Yea it's looking more like the airline industry will transfer to biofuels and work to be carbon neutral than go for non carbon fuels.

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MrJoyless t1_iy8xhwa wrote

>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.

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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.

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_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!

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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. 😋

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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.

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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

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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.

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jg727 t1_iydu28q wrote

Yes, you're right. But I was referring to the obvious plumes of off gassing

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kr0kodil t1_iybuxan wrote

Yes, you’d 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 you’d need to constantly vent off excess hydrogen when tank temperatures rise.

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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.

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1funnyguy4fun t1_iycvvjq wrote

Speaking of the containment issue, I read a comment from an engineer that said, “Hydrogen won’t work out because it is a slippery little bastard that is hard to contain and a general pain in the ass to work with.” 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.

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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.

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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.

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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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Bagellord t1_iy8x75u wrote

What would make me nervous is keeping it stable and leak free in an airplane, over their service lives. Not to mention the infrastructure on the ground.

To be clear, I think it's a great thing, if the benefits are there. But there's a ton of work to be done beyond a functioning engine.

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ThellraAK t1_iy90bxo wrote

Don't really need it to be leak free, just need to manage it so leaking doesn't make things explode.

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itsbicycle_repairman t1_iy98pri wrote

If that was the case, you'd need to know at what rate it leaked to work out how much fuel you need for a flight, and if the leakage was a "standard" rate over every aircraft. And if it was a linear equation too, but I'd hazard a guess that more pressure = more loss at a higher pressure.

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Sinister-Mephisto t1_iybznnv wrote

Couldn’t it be stored as a liquid ?

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EmperorArthur t1_iyedb0t wrote

Unfortunately not. Hydrogen is so tiny it has to be stupidly cold or under insane pressure to be a liquid.

We do it for rockets, but even through all the insulation ice still forms. That killed seven people...

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