Hydrogen Cools Well, but Safety Is Crucial
power-eng.com
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1. H2 is still expensive. Most fuel cells require very pure H2 (five nines; 99.999%), or else it can damage the internal membrane. This pure H2 is not very affordable outside of a limited number of fuelling stations.
2. The rules around H2 use and transportation are still fuzzy. Despite being around for so long, regulations are still lacking or unclear.
3. H2 is light weight but takes up a lot of volume, limiting the usefulness of small-scale applications. Compressing it to liquid takes a lot of energy.
4. Fire/explosion risks, as you mentioned.
5. Fuel cells are expensive. If you look at financial statements for most fuel cell companies, they are selling them at a loss, meaning most fuel cells sold today are subsidized by government grants and investors.
6. The oil/gas industry is still pushing "grey" and "blue" hydrogen, which uses natural gas and emits carbon to produce H2.
I think H2 will play an important role, especially in decarbonizing steel making and large transportation applications, but people need to be aware of the limitations and longer timelines required for widespread adoption of green H2.
https://www.linkedin.com/pulse/clean-hydrogen-ladder-v40-mic...
My understanding is that H2 is seeming to standardize upon 300-bar (aka: 4500ish PSI).
There's liquid and a few other more difficult storage (700-bar / 10,000 PSI for example). But 300-bar is where a lot H2 stuff is standardizing today.
Its not quite as dense as in liquid form, but it starts to be usable at 300-bar. Of course, the thicker and heavier steel needed to hold H2 at this pressure makes it unsuitable for say... drones. But its more than usable for H2 Forklifts and other smaller vehicles.
Kilmartin should spend more time around rocket scientists. After hearing a few tales of some of the stuff they've come up with in the name of performance - like a Hydrogen/Lithium/Fluorine(!) tripropellant engine (but you get an Isp of 542s!!!) - using Hydrogen for cooling will sound positively tame, and easily controlled.
Getting the peak of performance sounds cool when you ignore costs, but in the real world with limited budgets, building a rocket twice as large is easily worth it if it means you never have to touch liquid hydrogen.
Exodus seems a bit of an overstatement. Other than spacex who else has or is planning to develop a methane engine? And other than SSME and Vulcain which other widely used engines used H2?
It is very hard for a hydrogen-fueled rocket to be cost-competitive against a methane-fueled one. Not strictly because of the cost of the fuel, but because of the cost of everything else that LH requires that LCH4 doesn't.
BO's New Glenn first stage, RocketLab's Neutron, and Relativity Space's Terran 1/Terran R, are all/will all be methane.
> which other widely used engines used H2?
Ariane 5 and 6, and the upper stages of previous Ariane rockets
https://en.wikipedia.org/wiki/Rocket_propellant#Current_cryo...
Edit: Long March 9 will be mostly methane, with hydrogen upper stage.
In practice, hydrogen cars are quite safe. They're just not worth the cost in infrastructure and lack of efficiency compared to BEVs.
Two words: Attached Garage
Don't BEVs weigh more than hydrogen cars, given the same model and range? That would give at least some incentive to use hydrogen over BEV, as it decreases road wear, which reduces the costs associated with the operation of that car.
Additionally, hydrogen cars could be considered safer once they've gotten into an accident, as risk of battery thermal runaway wouldn't usually be an issue for extended periods of time in hydrogen cars, whereas several car carrier ships have been lost due (in part or in full) to battery fires.
Gas still has the infrastructure, but batteries are closer to having what they need than hydrogen for critical adoption.
Unless you're in the upper Midwest and your car is one of those stuck at a charger unable to fast charge because it's too cold and you didn't have an hours worth of time and energy to preheat it.
You also have the problem where it is "too hot". Higher battery wear and all. Part of me feels the BEV revolution only considered half the northern hemisphere.
I think cold is a harder problem to solve, I think your delta T of environment temps and operating temps are much greater in cold weather.
I've worked in areas where they were developing hydrogen fuel cell vehicles at major auto makers. The facilities are equipped with collectors, detectors, and alarms, and everyone knows to GTFO if the alarm goes off. Hydrogen leaks indoors are extremely dangerous.
Encouraged by this I filled one of those grocery store vegetable bags with H2 + O2 from the same electrolysis setup (combine both outputs this time). Stoichiometric mixture! The boom was so loud I thought it was going to break my windows from about 20 feet away.
Possibly what you're trying to say is that it's easier to get the air in? Or that it's stored under pressure?
Add in a minuscule spark energy and H2 is no joke
Hydrogen has zero of those safety virtues.
[1] https://www.history.com/news/the-hindenburg-disaster-9-surpr...
I'm all for bringing back H2 blimps, but let's be honest about H2 - it's crazy dangerous.
Lower spark energy Broader range of combustibility Faster detonation speed (? [1])
It's only positive is it dissipated quickly, but that's not that great because it goes boom boom at 5% H2 -air. Everyone I know who has worked on combustion problems (I haven't myself, but colleagues have) give H2 a lot of respect.
[1] this one is an educated guess on my part based on the thermo.
But not at the same time. That is important because H2 has such a wide ignition range. At the lower end of concentration it isn't much easier to ignite than other things. A readable discussion:
* https://h2tools.org/bestpractices/hydrogen-compared-other-fu...
https://www.youtube.com/watch?v=jVeagFmmwA0
(Edit: added Toyota's test where they shot an hydrogen tank, you can see the fibers and the gas dispersion)
But a hydrogen / air mixture is explosive from 4% hydrogen to 74% hydrogen, Americans love their attached garages, and most attached garages feature a perfectly-placed electric spark detonator...er, I mean electric garage door opener...which is triggered daily.
The low viscosity is the reason the energy needed to transport hydrogen by pipeline is only slightly higher than natural gas, even though the combustion energy per molecule is considerably lower.