Hydrogen Embrittlement[1] is not discussed in the link, an effect where hydrogen diffuses into metals and causes them to become brittle and crack. Many aerospace materials are especially vulnerable: high strength steels, nickel and titanium alloys, etc. Fueling a disposable balloon or rocket with hydrogen is one thing, but a vehicle that can safely be refilled with hydrogen over and over for decades is quite another. (Recall how the rust red Space Shuttle External Tank was not recycled like the white SRBs were and was the only large expendable component each launch.)
Real economies are made by saving even 8.5% of the cost of an airship's gas. That's real money. Plus, that hydrogen won't escape the vessel over time, so that's a percentage you don't have to keep refilling.
It got me wondering if the increase lift capacity would be added factor, but quick calculation shows that it would only gain an extra ~1% of lift. So it would really just be a cost question: https://en.wikipedia.org/wiki/Lifting_gas
Until I got to the last line I assumed this was about safer transmission of hydrogen, not lift gas. Of course it would be uneconomic for pipelines to have 91.5% inert carrier gas but I wonder if you could use an inert refrigerant gas to make "non-flammable hydrogen mix" within piping that runs to consumers through non-zone-rated or even residential areas, and then refrigerate the gas at point of use, to leave a pure hydrogen stream? The refrigerant would just go around in a mostly-closed loop.
Incidentally, using 8.5% hydrogen as lift gas will make a gnat's fart of difference; the lift force is proportional to the difference in density between air and lift gas - both helium and hydrogen are way less dense than air.
Key line: "Are the cost savings by using a 8.5% mixture of hydrogen worth all the trouble and effort it will take to convince your customers that the mixture is safe, as opposed to avoiding the safety questions altogether by using 100% helium?"
Stoichiometric mixture is only loosely connected to flamability.
You can have a stoichiometric mixture that will not be flammable because both reagents would be in right proportions but very diluted in the inert gas.
And a mixture that is very non-stoichiometric can still be very flammable, no problem. The extra gas most of the time performs the same role as inert gas -- dilutes the reagents and takes away energy from the reaction. There are exceptions, though, where you can have different results depending on the mix (for example your burning producing CO rather than CO2 because of abundance of carbon relative to oxygen in the mix).
This article popped up on HN a few months ago advocating 100% hydrogen airships for 'crew-less' cargo shipping
https://www.thecgo.org/benchmark/bring-back-hydrogen-lifting...
Anyone thought about using aerogel infused by pure hydrogen, wrapped in plastic? In case the wrap is breached it should make mixing with air slow, preventing explosion. (I am aware that aerogel is absurdly expensive in needed quantity. Just a thought experiment.)
Let us ignore the Helium shortage.
ITS NON-FLAMMABLE HELIUM https://www.youtube.com/watch?v=KsjQZ2eXTxE
That MSDS sheet saying 8.5% is, I assume, for pressurized hydrogen. I wonder if the non-pressurized lifting gas (roughly atmospheric pressure) would allow higher concentration with it still considered inert?
This is making me curious about hot air balloons combined with hydrogen/helium. I don’t know whether the heat would affect the balloon lift in a meaningful way, but would be nice to have control.
Hydrogen is non-explosive. If you prevent oxygen from mixing in, then it's also not going to rapidly deflagrate.
The original question was wrong, airships have never used this mixture.
You will get a ~8% reduction of cost, but you get other large costs like dealing with hydrogen onsite and dealing with contaminated helium. How does that re-compress? How do you make sure your mixture stays at the right percentage.
What is the purpose here?
Venting helium is expensive, but venting hydrogen is not. You can't do this with a mix but you could vent hydrogen if it's in separate internal bags. That's a possible use, but again you'd need to look at total costs.
Read up properly here for this mixing idea, but there seems little purpose -
Flammability limits of hydrogen-diluent mixtures in air https://prism.ucalgary.ca/bitstream/handle/11023/164/ucalgar... (2012)
"Hydrogen-helium mixtures fail to propagate a flame at 92% helium in the fuel mixture under atmospheric pressure (Calgary, 89k Pa) and ambient temperature. Therefore, only a small percentage of the helium in dirigibles can be safely offset with hydrogen. This is in agreement with previously reported data.
The lean flammability limits of hydrogen binary mixtures with argon, carbon dioxide, and nitrogen diluents in air for upward flame propagation appear to be very close to the limits predicted using the adiabatic flame temperature concept"
Charge the hull, ionize the gas, minimize loss by forcefield. Needs current carrying hull though. Graphene?
I did t read the article. Are hydrogen and helium miscible or do they separate out. I definitely think they would because of the difference in density.
Interesting! Living in Friedrichshafen (Germany) the birthplace of the Zeppelin, I'm wondering if this would be a valid option, because the Zeppelin NT that is used here in the summer uses only Helium AFAIK. The Zeppelin NT has an emergency drain that would essentially mean releasing 7.400 m³ worth of helium. I will definitely ask a family member that works at Zeppelin what he thinks of this research!