3 ms·

If your fuel tank catches on fire you have similar problems, so I don't think these problems with hydrogen are insurmountable.

nitrogen 6y ago
Gasoline is pretty well-behaved until it's vaporized.
- jacquesm 6y ago
  That goes for lots of things including powdered sugar and flour. But that vaporization step usually happens in a relatively controlled environment which makes it manageable.
  - masklinn 6y ago
    Isn't that their point? That gasoline is a pretty well-behaved and easy to work with liquid while hydrogen isn't?
paledot 6y ago
Kerosene burns, hydrogen explodes. And kerosene doesn't actively damage the tank it's stored in, like hydrogen does.[1] Also, while its energy density per kilogram compares favourably to kerosene, its energy density per litre does not. Hydrogen is a great rocket fuel because its specific impulse is second to none, so why isn't it universally used? Because even by rocket fuel standards it's a bugger to work with. There are lots of things that react poorly to being set on fire. That doesn't make them all equally dangerous. [1] https://en.wikipedia.org/wiki/Hydrogen_embrittlement https://en.wikipedia.org/wiki/Hydrogen_embrittlement
- jeffreyrogers 6y ago
  Hydrogen embrittlement depends on the type of tank. It does not occur with every material. Look, I'm not saying hydrogen is great and has no problems. I'm saying the problems are not in theory insurmountable. I have elsewhere made the same point as you with regards to mass vs volume. I'm aware of the drawbacks of hydrogen and am actually pessimistic on its use in aviation, but I think it is worth trying out.
  - jacquesm 6y ago
    Hydrogen is not only in contact with the tank but with other materials en route to the fuel cell as well. And the problems don't need to be insurmountable in theory, they need to actually be solvable and that is a different thing entirely. I'm fine with people trying it out but I'm very skeptical about this ever making it to production. I think this is more of a PR piece than anything substantial.
    - masklinn 6y ago
      > Hydrogen is not only in contact with the tank but with other materials en route to the fuel cell as well. Isn't it also in contact with everything around the tank on account on there being basically nothing which is completely impermeable to hydrogen?
    - jeffreyrogers 6y ago
      I don't think hydrogen powered planes will substantially replace normal planes for reasons having to do partially with safety and partially with performance, but I think the engineering problems are surmountable. There are existing prototypes that have flown using hydrogen fuel cells, and the Tu-155 which ran on liquid hydrogen (used as fuel for its jet engines though, not to power fuel cells). So it's not like this stuff doesn't work. I think you are overestimating the difficulty of dealing with embrittlement. Many materials don't suffer from embrittlement at all, and others (like aluminum) only suffer at high temperatures. Edit: I also wanted to add to the person who made the claim "kerosene burns, hydrogen explodes" that kerosone can explode too, and it obviously is possible to handle hydrogen in a way that explosion is unlikely or it wouldn't be used as rocket fuel (where it is literally combusted with oxygen... combusted, not exploded). I agree that hydrogen is more dangerous than kerosene, but it's not like kerosene is that safe either and the question is whether you can create good enough processes around the storage and handling of hydrogen to offset the risk.
elmo2you 6y ago
It's the huge difference in reaction speed that makes all the difference. Even in their gaseous/vaporized forms, conventional (fossil) fuels react comparatively slowly compared to hydrogen, like a sweet retriever puppy compared to a trained dog of war. It's exactly this difference that makes them relatively safe to use and even still relatively controllable once something goes wrong. With hydrogen, you simply won't get that change. It will be all over in a blink. A very hot and bright one, I might add. Feel free to believe whatever you want, you have every right. But I'm rather sure that your optimism regarding hydrogen is more rooted in ignorance than in knowledge.
- jeffreyrogers 6y ago
  Yeah, I'm actually more familiar with hydrogen than you think. I'm aware of the problems with reaction speed. One advantage hydrogen has is that it escapes very rapidly from its container and goes pretty much straight up due to how light it is. I'm actually not as much of an optimist on hydrogen as you seem to think. I think it is unlikely to be used in aviation in any real sense, for a variety of reasons, some having to do with safety, others with performance. However, I think it is worth investigating, and I do not think the problems around it are insurmountable from an engineering perspective.
  - elmo2you 6y ago
    Fair enough. Thought then I'm sincerely even more surprised you would say that any fuel tank on fire is a (relatively) equal problem. As for hydrogen rapidly escaping and going straight up because of its low density, those properties I would only consider positive in scenarios where the hydrogen isn't reacting (being on fire, to be more precise). When on fire, quite the opposite. Buildup of heat on the ground might still be less of a problem than with heavier fuels (which indeed is a very real problem with those), but not much advantage of that once everything within a certain radius is reduced to the size of matchsticks by a powerful explosion. But if you claim to be (some sort of) an expert, I'll believe you. I certainly am not, that much I admit. I only based my opinion on what I've been told by chemists that I personally trust. They told me rather invariably that the engineering challenges for storing/operating hydrogen are such a bitch, that they are ultimately only a good for when you want something closely resembling a bomb, without actually being one (or just hoping it won't explode before it served its purpose). Like e.g. rocket engines.

nitrogen 6y ago

Gasoline is pretty well-behaved until it's vaporized.

jacquesm 6y ago
That goes for lots of things including powdered sugar and flour. But that vaporization step usually happens in a relatively controlled environment which makes it manageable.
- masklinn 6y ago
  Isn't that their point? That gasoline is a pretty well-behaved and easy to work with liquid while hydrogen isn't?

paledot 6y ago

Kerosene burns, hydrogen explodes. And kerosene doesn't actively damage the tank it's stored in, like hydrogen does.[1] Also, while its energy density per kilogram compares favourably to kerosene, its energy density per litre does not. Hydrogen is a great rocket fuel because its specific impulse is second to none, so why isn't it universally used? Because even by rocket fuel standards it's a bugger to work with. There are lots of things that react poorly to being set on fire. That doesn't make them all equally dangerous. [1] https://en.wikipedia.org/wiki/Hydrogen_embrittlement https://en.wikipedia.org/wiki/Hydrogen_embrittlement

jeffreyrogers 6y ago
Hydrogen embrittlement depends on the type of tank. It does not occur with every material. Look, I'm not saying hydrogen is great and has no problems. I'm saying the problems are not in theory insurmountable. I have elsewhere made the same point as you with regards to mass vs volume. I'm aware of the drawbacks of hydrogen and am actually pessimistic on its use in aviation, but I think it is worth trying out.
- jacquesm 6y ago
  Hydrogen is not only in contact with the tank but with other materials en route to the fuel cell as well. And the problems don't need to be insurmountable in theory, they need to actually be solvable and that is a different thing entirely. I'm fine with people trying it out but I'm very skeptical about this ever making it to production. I think this is more of a PR piece than anything substantial.
  - masklinn 6y ago
    > Hydrogen is not only in contact with the tank but with other materials en route to the fuel cell as well. Isn't it also in contact with everything around the tank on account on there being basically nothing which is completely impermeable to hydrogen?
  - jeffreyrogers 6y ago
    I don't think hydrogen powered planes will substantially replace normal planes for reasons having to do partially with safety and partially with performance, but I think the engineering problems are surmountable. There are existing prototypes that have flown using hydrogen fuel cells, and the Tu-155 which ran on liquid hydrogen (used as fuel for its jet engines though, not to power fuel cells). So it's not like this stuff doesn't work. I think you are overestimating the difficulty of dealing with embrittlement. Many materials don't suffer from embrittlement at all, and others (like aluminum) only suffer at high temperatures. Edit: I also wanted to add to the person who made the claim "kerosene burns, hydrogen explodes" that kerosone can explode too, and it obviously is possible to handle hydrogen in a way that explosion is unlikely or it wouldn't be used as rocket fuel (where it is literally combusted with oxygen... combusted, not exploded). I agree that hydrogen is more dangerous than kerosene, but it's not like kerosene is that safe either and the question is whether you can create good enough processes around the storage and handling of hydrogen to offset the risk.

elmo2you 6y ago

It's the huge difference in reaction speed that makes all the difference. Even in their gaseous/vaporized forms, conventional (fossil) fuels react comparatively slowly compared to hydrogen, like a sweet retriever puppy compared to a trained dog of war. It's exactly this difference that makes them relatively safe to use and even still relatively controllable once something goes wrong. With hydrogen, you simply won't get that change. It will be all over in a blink. A very hot and bright one, I might add. Feel free to believe whatever you want, you have every right. But I'm rather sure that your optimism regarding hydrogen is more rooted in ignorance than in knowledge.

jeffreyrogers 6y ago
Yeah, I'm actually more familiar with hydrogen than you think. I'm aware of the problems with reaction speed. One advantage hydrogen has is that it escapes very rapidly from its container and goes pretty much straight up due to how light it is. I'm actually not as much of an optimist on hydrogen as you seem to think. I think it is unlikely to be used in aviation in any real sense, for a variety of reasons, some having to do with safety, others with performance. However, I think it is worth investigating, and I do not think the problems around it are insurmountable from an engineering perspective.
- elmo2you 6y ago
  Fair enough. Thought then I'm sincerely even more surprised you would say that any fuel tank on fire is a (relatively) equal problem. As for hydrogen rapidly escaping and going straight up because of its low density, those properties I would only consider positive in scenarios where the hydrogen isn't reacting (being on fire, to be more precise). When on fire, quite the opposite. Buildup of heat on the ground might still be less of a problem than with heavier fuels (which indeed is a very real problem with those), but not much advantage of that once everything within a certain radius is reduced to the size of matchsticks by a powerful explosion. But if you claim to be (some sort of) an expert, I'll believe you. I certainly am not, that much I admit. I only based my opinion on what I've been told by chemists that I personally trust. They told me rather invariably that the engineering challenges for storing/operating hydrogen are such a bitch, that they are ultimately only a good for when you want something closely resembling a bomb, without actually being one (or just hoping it won't explode before it served its purpose). Like e.g. rocket engines.