Hmmm, "gas station filled with petrol that explodes" vs "gas station filled with hydrogen that explodes".

Being near either one as it explodes would be bad, but I wonder which one looks more impressive movie-effects-wise? :)

In my limited understanding, neither one really explodes. The petrol one would look like a huge impressive fireball that launches a big black mushroom cloud and then just burns like crazy. The hydrogen one, if the hydrogen is fairly pure, would be like a big faint blue wispy fireball, not all that impressive.

If there were an oxidizer in the mix somehow, it would be rather more explosive.

The issue with hydrogen is that it has a fairly wide combustion range (meaning the ratio of fuel/air that can burn), I can't remember the numbers but it's several times greater than other common fuels. The other issue with hydrogen is that the combustion happens VERY fast... if you ignite gasoline vapor/air in an open 5-gallon jug, you have a nice rocket that'll fly 50 feet or so. If you ignite hydrogen/air in the same jug, you have permanent hearing damage and shards of plastic embedded in you.

Cool, thanks. :)

If the hydrogen is fairly pure and the amount is question is small, then sure: combustion will happen at the hydrogen-air interface. If it mixes with air before ignition, then it can burn all a once, and Wikipedia informs me that “the limits of detonability of hydrogen in air are 18.3% to 59% by volume.”. Yes, it will literally detonate with supersonic flame velocity.

I once got to watch some moderately crazy students fill an ordinary party balloon with a stoichiometric mix of hydrogen and oxygen at ambient temperature and pressure. When it was ignited, the result was extremely impressive. No one was injured (because we were all warned to protect our ears and open our mouths and balloons don’t produce significant shrapnel), but the shock wave was not at all subtle.

https://en.m.wikipedia.org/wiki/Hydrogen_safety

Why is having open mouths important?

Less pressure on your eardrums if the shock wave reaches them from both sides.

Ah. So holding my eustachian tubes open (half way through a yawn) would also be a good idea?

My dad did this once. He drained the acid from a car battery and put it in a container with a narrow opening, then dropped in a bunch of zinc galvanized nails. Sulfuric acid + zinc = hydrogen gas. He then stretched balloons over the mouth of the container to inflate them, tied them up, and attached a strip of newspaper to the bottom. Finally, he lit the bottom of the newspaper on fire and let it go. Balloon floats up, makes pretty fireball.

We ran into two problems. First, a number of the flames blew out on their way up. No fireball.

Second, we ran out of balloons pretty fast. So he cast around for ideas, and decided to fall back on a box of condoms. They held a lot more hydrogen than the balloons.

They were also equally likely to go out before blowing up. I always imagined them coming down on someone's lawn, causing no end of confusion.

[DO NOT TRY THIS AT HOME! And if you're tempted, there's one thing I left out that's necessary for it to work properly, and the only thing I'll say about it is this warning: https://sciencenotes.org/add-acid-to-water-or-water-to-acid/ ]

That’s not the same thing, though — your dad forgot the oxygen! A balloon full of approximately pure hydrogen makes a nice fireball but doesn’t really explode — the same group that made the exploding balloon I watched also did one of those.

The stoichiometric premixed balloon is only 2/3 H2 by volume, so it releases 1/3 less energy, but it’s a whole different experience when the energy is released essentially all at once. Interestingly, there was no noticeable fireball from the premixed balloon.

A premixed H2+air balloon probably makes a fine explosion, too :)

> That’s not the same thing, though — your dad forgot the oxygen!

Oh, I'm quite aware. The other fun game we played was with his acetylene welding torch and balloons. It has separately controlled tanks of acetylene and oxygen. Acetylene only = nice big fireball. Acetylene + oxygen = no fireball at all, instead a very loud boom + a bit of a shockwave.

A quick search for higher heating values suggests that acetylene and hydrogen gasses have fairly similar HHV per mole of oxidizer. (H2 needs 1/2 equivalent or O2; acetylene needs 5/2 equivalents, so H2 wins by a bit.)

But H2 takes up most of the space in the balloon, and acetylene is nice and compact, so considerably more total energy should be available with acetylene!

I don’t know whether oxyacetylene will detonate nicely, though, or whether a balloon-sized oxyacetylene mix will merely combust subsonically.

Hydrogen is way worse than gasoline or any hydrocarbon. It has to be stored at very high pressures and there’s no practical situation in which it doesn’t explode.

[delayed]

Neat. I look forward to them rolling out a production model in 2043.

I look forward to them rolling it out downwind.

They can keep making claims to cover up their complete bungling of their market position.

As for the idea itself. Ammonia as fuel fails the first principle of safe design. It’s a poisonous gas. Using it as a fuel is a willingness to trade the safety of people for a cheaper fuel.

The move from cars to SUVs in America was so car manufacturers could skip emissions and safety requirements of cars on the technicality that SUVs are “light truck” chassis[1]. Dan Luu shows that those safety regulations are often a box ticking exercise for manufacturers except Volvo[2]. American stroad design is a particularly bad mix of street and road which is more dangerous for drivers and pedestrians than other designs. And the diesel emissions scandal so many car manufacturers were caught defrauding.

“willingness to trade the safety of people for a cheaper X” is exactly what we should expect car companies (and companies in general) to do, because that’s what they’ve done so often though history.

[1] https://youtube.com/watch?v=jN7mSXMruEo “These stupid trucks are literally killing us” -NotJustBikes

[2] https://danluu.com/car-safety/

It is certainly easier to liquefy, I can't argue that point.

It is important to note that hydrogen, due to the small size of the molecule, is really hard to contain as a gas. Moreover, leaked hydrogen gas is an indirect but potent greenhouse gas via interfering with the degradation of existing methane in the atmosphere. If we leak enough hydrogen, we might not be helping the climate very much.

I was once in a presentation which claimed formic acid to be a better alternative, but I'm not an expert in that field, so I can't comment on its merits.

There were some recent articles suggesting that there may be enough natural hydrogen seeping out of the ground to supply all of humanity’s energy needs. It seems a bit unlikely that leakage of hydrogen from fuel systems would matter much in comparison.

How about radon, is that fissible?

No, it gives off alpha particles and gamma rays. Hypothetically, you could build a device to harvest that energy (along the lines of an RTG), but the energy density and conversion efficiency would be laughable, given the 3.8 day half-life and gaseous state.

To be clear, I’m saying enough hydrogen to power humanity chemically, not by fusion.

Enough hydrogen to power humanity by fusion is readily available anywhere :)

Use compressed air or NOx as oxidizers for delayed combustion in engines. Not only would it provide a means of storing energy for ICEs, but it would also eliminate pumping losses on the intake stroke.

I wonder if this process would be easy enough that “ammonia battery” plants would just synthesize on site when solar power is high. Like charging up a battery with no need to move anything.

Or maybe a regional factory with short pipelines.