Rolling Bombs

The big problem with using hydrogen for fuel is that it’s a gas. The combustibility of the gas is of little matter when it comes to using it as a transportation fuel. The problem is that in order to have enough of it to get anywhere, you have to liquefy it. There are two ways to do this, temperature and pressure.

The space shuttle uses liquid hydrogen as a fuel source, but stores it cryogenically, which is why the fuel tank has to be insulated with foam that likes to occassionaly fly off and damage the heat shielding. Cryogenic storage is expensive and impractical for use in earth bound transportation. It’s really impractical and too expensive for rockets too, but the alternatives kind of suck.

The other option is to pressurize the hydrogen to such a degree that it becomes a liquid at normal atmospheric temperatures. The first trade off in this kind of scheme is that it takes about 30% of the energy stored in the hydrogen to get it to a liquid state. The other major disadvantage to storing hydrogen in liquid state is that it has to be stored at about 10,000 psi, which is essentially bomb. And not just any bomb, a bomb that will spew cryogenic liquid everywhere.  There’s also the issue with the tank material needing to stand up to wide temperature fluctuations as you start to draw off hydrogen, thus cooling the liquid down to a cryogenic state.

The other solution is to store it as a gas a very high pressures. This still has the problem of creating a bomb. It’s not the combustibility of the gas that’s a problem, it’s the energy stored up as pressure.

13 Responses to “Rolling Bombs”

  1. Hence why the X-33 failed (could not create a tank light enough, and the composite materials they used could not withstand the cold or the pressure).

    This is also why a good deal of research is being done in storing Hydrogen in a structural matrix, much like how a sponge can store water.

  2. SandH says:

    Oh come on man. The Hindenburg was just a one-time thing. It’s not like cars are going to be crashing into each other or anything. Sheesh, you talk like it could be another Pinto or something. ;-)

  3. Sebastian says:

    Hindenburg was actually the material they used to paint the fabric, rather than the hydrogen. A hydrogen fire tends to burn upward.

  4. Weer'd Beard says:

    As a SCUBA diver I’m always VERY cautious when transporting my tanks. Dive circles are ALWAYS filled with stories of gas bottles that tip over or are cracked and suddenly become VERY destructive ballistic missles. And a SCUBA cylender is only pressurized to around 3000 PSI.

    VERY scary shit. Also how heavy would said tank need to be to keep a freeway pile-up from creating a crater…

  5. Alcibiades McZombie says:

    Since trains follow a set path, they could just use overhead wires like most commuter trains do…

    Maybe we could just electrify the interstate and force all cars onto “rails”. That’s still kind of crazy, but less so.

    I’m fairly sure that “thermite paint” is a myth. It did exist, but it wasn’t the sole cause for the burning (the hydrogen did most of that work). (I’m not talking about ignition, just burning.)

  6. Sebastian says:

    Yeah, you’re right about that it seems. There’s a paper out there that discredits the paint theory.

  7. vinnie says:

    Hydrogen could be safer than gasoline. spill a gallon of each on the sidewalk and come back the next day with a match. A hydrogen leak self corrects quickly.
    As for the high pressure, If the French can build a car that runs on compressed air why can’t we get some of that energy back in our vehicle?

  8. Sebastian says:

    The French car that runs on compressed air is also a bomb on wheels. Gasoline is nice because its energy is stored up as a liquid at room temperature that’s merely combustible if ignited.

    Once you put gas, any gas, under extreme pressure, the vessel that holds it will explode violently if it fails.

  9. gattsuru says:

    More people died when the helium-filled USS Akron hit the ground than when the Hindenberg went boom. Hydrogen fires aren’t particularly dangerous at 1 ATM. There’s energy there, but not nearly as much as people expect.

    As for hydrogen vehicles, pressurized air vehicles are a well-established field. They can’t get nearly the same range as hydrogen, but they’ve shown that pressured gases can be used without making life too dangerous.

    Bulk transportation to the actual problem, but there are better methods than simple pressurization. There are a lot of things hydrogen combines with; while it’s not free to remove from (for example) borax, it’s relatively cheap, and extremely dense.

  10. Alcibiades McZombie says:

    I thought gasoline evaporated fairly quickly. It probably won’t stay on the sidewalk for long.

    Well, the Akron crashed into the ocean at speed. The argument is that a catastrophic failure is more likely with hydrogen over helium. If the Hindenburg had caught on fire 2500 feet in the air, everyone would have died.

    Of course, there seemed to be a hell of a lot of structural failures in all those airships, so it’d be hard to tell the difference.

  11. Blackwing1 says:

    Back in the early ’80’s I did an engineering study for a hydrogen-fueled vehicle using metal hydride beds as the storage mechanism. I found out that the US Army did some testing with hydride beds, attempting to ignite them with armor-piercing incendiary rounds. They not only failed to blow up, they failed to ignite for more than a few seconds…the oxygen in the atmosphere (necessary to burn) poisons the hydrides.

    Unfortunately, the weight penalty of carrying around several hundreds of pounds of finely powdered nickel alloys was enormous, and rendered the entire concept moot.

    I experimented extensively with metal hydrides for hydrogen storage, and can state quite explicitly that hydrogen fires burn:
    A) EXTREMELY hot, and
    B) Almost invisibly.
    You typically notice it when something starts to melt…

    Gasoline in liquid form is impossible to ignite, since it’s the vapors that burn. Diesel fuel is even harder. Try pouring a small pool of diesel in a metal pan (outdoors, of course) and try to ignite it. Use a blowtorch, and you’ll be standing there heating up the entire pool until enough vaporizes to start burning. It’s slightly easier to vaporize gasoline, but you can still toss a lit cigarette into a pool of it…and put out the cigarette.

  12. Blackwing, did you do work with any other hydrogen storage mediums?

  13. Dan_P says:

    Well, I had a 31 year career in automotive safety.
    Not just, how to make the cars just “safe and legal”.
    But, how to help our vehicle occupants survive.
    When either “they”, or their “opponents” did something REALLY stupid.
    So, I will lay claim to having “a modest amount of expertise”.

    And, I just have to say:
    Hydrogen is MUCH harder to “make safe” than gasoline.
    Gasoline is way more than “hard enough”.
    Ask the Pinto engineers/marketing idiots.

    No, I did not work for Ford.
    But, “our competive testing” early on showed they had a “real problem”.
    And, it took them way too long to address “their customer problem”.
    It was not just the Pinto, it was their entire fuel system design philosophy. $$$

    Hydrogen makes solving the “Pinto problem” look like a piece of
    cake. “We” knew how to solve the Pinto and all of their other similar designs from our very first tests of their “sh_t”.

    Money. A very small amount of money. A change in their philosophy,

    Put a “few hydrogen examples” out on the road, no problem.
    Make “the entire fleet” hydrogen, “OH, MY GOD” ! ! !