Submitted by je97 t3_z7wnkt in UpliftingNews
UnCommonSense99 t1_iya6yat wrote
Unfortunately nobody can design a practical hydrogen fuel tank to fit inside an aircraft wing.
Reasons to do with fundamental constraints of engineering and physics.
I mean you could make a tank with insufficient fuel in it or you could make a tank which was extremely heavy, but nobody wants either of those things.
If you want a fly thousands of miles on a jet plane and be green you need to run on biodiesel; This stuff about hydrogen is basically green washing.
bustervich t1_iyaf1bu wrote
The real problem with future propulsion is about energy density. Find something as energy dense as petrochemicals* and you’ll be the next bazillionaire.
*No I don’t mean nuclear powered planes.
Quixophilic t1_iyahvjp wrote
>nuclear powered planes
Ah yes! Every plane crash a mini-Chernobyl!
Master_Bayters t1_iyaos3a wrote
Actually a plane would never use a bwr reactor like Chernobyl. So a lot of measures could be implemented to seal the core and prevent meltdown... Mass production of small nuclear reactors never advanced due to the bad reputation nuclear has, not because it's impractical. We would have solved the energy crysis and reach carbon zero a.long time ago. Not to mention saving 5 million lifes due to air pollution reduction.
bustervich t1_iyb0u2n wrote
Designing a plane that could fly on nuclear power has been tried before early in the nuclear age. I don’t know if technology exists today to make it practical, but making it safe in the event of a crash is another story.
People generally think of black boxes on planes as indestructible, and they are pretty tough. But they’re good for protecting a few memory chips from impact and thermal forces. But even though the boxes are in the tail and designed so that the entire front of the plane acts as a crumple zone, there have been crashes where the black boxes were never found, even though the crash location was known and on land. Now imagine trying to build a containment vessel for some sort of reactor that can keep a plane crash from turning into a dirty bomb while also being light enough to be flown on a plane that also has to carry passengers and cargo.
Master_Bayters t1_iyca84x wrote
We lost almost 40 years of comercial nuclear study due to the fear mongering that happened after Chernobyl. Some is understandable. I was just stating it wasn't impossible, but the industry went on a completely different path. And yes, to seal a core from impacts would be a pain in the *ss
dustofdeath t1_iyafyit wrote
It would have more than enough energy density for all domestic flights.
UnCommonSense99 t1_iyet61t wrote
You are technically correct..... But given a choice between having some small fuel tanks full of biodiesel or some much larger and heavier fuel tanks full of hydrogen; what do you think will work best?
( I assume you realise that it's much easier to run a jet engine on diesel than it is to run it on hydrogen)
dustofdeath t1_iyexm6x wrote
Hydrogen is 2.8x more energy dense than kerosene for the same unit of mass. But needs four times more volume.
Meaning you actually need less fuel - so it almost negates the increased volume issue. Especially if the efficiency of fuel to thrust is better than fossil fuels.
I believe AirBus is already planning a commercial plane by 2035. So there likely have been developments on how to properly store liquid hydrogen (that eliminates the volume issue). The ZEROe.
3O3- t1_iycl90b wrote
Very cold take, H2 as approximate 3x the energy density of kerosene (120 vs 40 MJ/kg)
The problem is the size required to store it, not the mass, which is a completely separate technological issue (compression)
QVCatullus t1_iycntuk wrote
It still goes exactly to what the post you're responding to said. They didn't claim that hydrogen had a low energy density, they said that a hydrogen tank that fit on a plane would either not have enough fuel (like, not even remotely enough -- the volumetric "energy density" of hydrogen is on the order of 1/3000 that of kerosene per atmosphere the hydrogen is stored at, so even with a high-pressure 700 bar tank you need 4ish times the fuel storage), or would have to be rated to such high pressures/low temperatures (for cryogenic storage, which is maybe not a good choice for air travel in any kind of near future) that it would be impractically heavy.
In other words, it seems like your comment is calling out a mistake in the post you're responding to, when really you're just restating it, since precisely the problem at hand the PP was referencing was the compression issue.
3O3- t1_iyezs2w wrote
It does not at all, since the mass, not space (implied by the original post), is the limiting factor for flight. Imagine a standard commercial plane but 1/2 the seating space is now a fuel tank. There, you already have the 4x space, with no innovation in design, and with 1/3 of the fuel mass. As the original post pointed out however, what is currently limiting the application of H2, is in the mass (and general impracticality) of the current fuel compression technology.
There is definitely room for improvement in storage technology, and there are certainly no “fundamental constraints of physics and engineering” that limit to the mass of containers which store hydrogen to precisely what is currently available.
Simply, planes can be made much bigger (to accommodate the space needed to store the hydrogen even in the absence of significant advances in fuel compression technology) without being unviable (demonstrated categorically by the presence of huge commercial jets), which is already partly offset due to the huge mass savings thanks to very high MJ/kg of hydrogen.
If only The original commenter were working for Rolls Royce, they could have warned them it was useless due to the fundamental laws of physics and engineering, theyd have saved millions, and we would all have been spared this “greenwashing”
danielv123 t1_iycnhqx wrote
Generally, by energy density we mean volumetric energy density. Specific energy is the common term for gravimetric energy density.
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