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Hydrogen fueled aircraft

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Hydrogen fueled aircraft

Old 25th Oct 2021, 19:12
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Hydrogen fueled aircraft

Thereís a lot of talk in the media these days about aircraft being powered by hydrogen in the future, and some practical small scale development is apparently underway. Iím kinda surprised there seems to be no discussion about it on these forums. Perhaps you all - like me - consider it too mad, and a load of window dressing by the airlines and manufacturers. The few formal documents Iíve found online talk about the Hindenburg effect, and the need to make sure the tanks on board are Ďdurableí! Well, if they really think they can engineer a storage tank that will never break open on impact, in an otherwise survivable accident, Iím highly skeptical. Too many people have died in post crash fuel fires with Jet A1, yet now they want us to believe liquid hydrogen can be safely stored - a fuel with a hundred times the explosive flammability of Jet A1.
And then thereís the whole re-fueling infrastructure and ramp safety issue too.
I believe itís a total non runner.
What do you think?
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Old 25th Oct 2021, 19:24
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The problem with hydrogen as an aircraft fuel is - and always will be - storing it on the aircraft. While H2 is very light for it's energy density, it's not dense. So you need to dedicate massive volume to the fuel tanks - and even then you either need it in liquid form (very, very cold) or under extreme pressure. High pressure is viable for ground use (e.g. automobiles) where weight is not critical, but impractical for aircraft.
Problem is liquid H2 isn't much better. You still need very large volume for any appreciable range, near the CG so the aircraft remains controllable as the fuel burns off, and you need a giant thermos bottle to hold it.
Wing storage of the fuel is not longer viable - so unless you want a huge H2 tank in the middle of the fuselage, you'll need massive pods of the stuff on the wings (lots of drag).
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Old 25th Oct 2021, 19:48
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The soviets flight tested a Tu-154 converted to hydrogen. It flew nice however the cabin was mostly filled with H2-tanks.
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Old 25th Oct 2021, 20:07
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There's been an extensive analysis of H2 over at Leeham News: see here for the 34th wrap-up edition of said analysis.

Regarding killaroo's points, a difference between H2 and A1 is that you can more rapidly dump H2, partly because there's nowhere where doing so would cause environmental problems. Possibly one could aim to crash with as little H2 on board as possible.

The explosions at Fukushima were caused by the vented H2 spontaneously exploding as it vented (possibly aided by the O2 that one can surmise was also being vented). I've no idea what happens if you're venting a stream of H2 and some static discharge sets it off; possibly a very impressive "dump and burn" as used to be practised by the occassional SR71 or F111 pilot.
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Old 25th Oct 2021, 20:17
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Take a look on the interweb, at ZeroAvia, who successfully flew a Hydrogen fuel cell powered aeroplane last year at Cranfield. Its based on technology developed by Toyota btw.


And it didn't explode when it had an oops on take off followed by a hard landing either.
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Old 25th Oct 2021, 21:26
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The real issue is producing green hydrogen at an economic cost, until enough electricity is produced to do that hydrogen is not commercial, forget about off peak power that is all going to be used up with storage or charging EV batteries, that is twice as efficient as hydrogen. It may be that a way to produce hydrogen cheaply in the future, until then itís just dreams.
Aviation produces a small part of CO2 emissions, when all surface pollution has been eliminated, the much more difficult aviation solutions will need to be addressed, that will be a very long time in the future
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Old 25th Oct 2021, 22:24
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Although a truly accurate answer would take a detailed 'life cycle' analysis, my suspicion is that - once large amounts of 'green' electricity are available - it would make more sense to 'manufacture' more conventional hydrocarbon fuels - using CO2 extracted from the air and H2 produced by 'green' electricity. The basic technology already exists so no pie-in-the-sky technological breakthroughs required (aside from creating the green electricity). Done properly, this can be 'carbon neutral' (simply removing CO2 from the air then re-releasing it back as turbine exhaust gases). It would bypass all the difficulties of handling and transporting huge amounts of H2 since synthetic hydrocarbon type fuels could be readily handled/transported using the existing infrastructure - and it would eliminate all those nasty issues associated with carrying enough H2 on an aircraft for long range operations.
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Old 26th Oct 2021, 20:16
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The engineering of making kerosene from air, water and solar is mind boggling. The problem is CO2 at 400ppm means the volume of air needing to be filtered is just vast. Using the finest current technology (Carbon Engineering ltd) just to remove the 2019 commercial aircraft emission, about a giga ton of CO2, requires an air intake 8m high, and 5000km long. To power the air induction alone would require 60% of entire electrical energy generated in the USA, and thatís before the CO2 is separated from the air, split up, the H2 is separated from the water and the Kerosene is synthesised.

Just whoís gonna pay for this?

Apologies for the grim facts.

Last edited by Bagheera S; 27th Oct 2021 at 16:59.
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Old 27th Oct 2021, 01:58
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Ammonia as a fuel may be a better bet than straight hydrogen. In ideal circumstances the exhaust would be nitrogen gas and water. Avoiding nitrous oxides will be one of the problems to be solved.
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Old 27th Oct 2021, 03:37
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Re grim facts. Point taken, but.

If you are told to eat a parking lot full of food how would you feel? “Impossible!”
But if someone explained that this is just the amount of food that the average person will eat in their lifetime then the picture changes.
Do we ask every tree if it/he/she will solve the world’s CO2 problems? Those who plant trees with a simple feeling of love and generosity will each help to do their wee bit. Surely every source of CO2 extraction can only be a positive thing?
By the same token, the filthy waters of Tokyo Bay are amazingly cleaned twice daily by millions of shellfish. Do we apologize to them for the grim facts, asking every one of them to think of the bigger picture and the enormity of the task?

Last edited by jolihokistix; 27th Oct 2021 at 04:36.
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Old 27th Oct 2021, 10:22
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Ammonia has been suggested as a practical hydrogen storage mechanism for hydrogen fuel transport via shipping.

Generate Hydrogen at a “green” source - convert it to Ammonia, ship it, then extract the hydrogen from the ammonia at point of consumption.

Toyota is looking at it.

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Old 27th Oct 2021, 14:58
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Ocean water contains around 1000 ppm CO2. Nonetheless, it will be costly to manufacture synthetic kerosine, But installing the infrastructure for any other energy source is equally costly. Perhaps it must be a trade-off between limited synthetic kerosine production and less flying. No more long weekends in New York or Paris.
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Old 1st Nov 2021, 09:56
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National Geograhic has an interesting item on green aviation. Many experts believe, that SAF (synthetic aircraft fuel) is the future, and especially if manufactured from the waste of steel mills. That seems to contain enormeous quantities of carbon di-oxyde. Also, some micro organisms seem to be able to make SAF from various forms of waste. Hm, a germ, producing kerosine? Will that be possible?
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Old 1st Nov 2021, 19:13
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Several years ago I sat in on a presentation about making synthetic jet fuel from algae. It sounded very promising - apparently the algae would consumed stuff such as sewage waste, and the algae could be easily processed to produce a synthetic oil like substance. It didn't take much area to produce large quantities of the algae (far more space efficient than biofuel from conventional crops such as corn or soybean) although it did take large amounts of fresh water. They were working on finding a suitable type of algae that would allow the use of seawater.
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Old 1st Nov 2021, 19:49
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Originally Posted by tdracer View Post
The problem with hydrogen as an aircraft fuel is - and always will be - storing it on the aircraft. While H2 is very light for it's energy density, it's not dense.
Exactly. Airbus hyped a hypothetical hydrogen-powered Mach 4.5 "ultrarapid transport" back in 2015.

Roughly the dimensions of Concorde - but with seating for only 20. The aft 75% of the fuselage was taken up by the liquid H2 tank (and a small O2 tank for a "rocket acceleration/climb phase" in addition to air-breathing turbojet (TO/LNDG) and ramjet (drift-up cruise) flight phases).

I like the idea of H2 fuel, for its flexibility - fuel-cell electric, hot-combustion thrust - as well as no carbon involved. But outside of blimps, it sadly doesn't offer much for aviation anytime soon.
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Old 2nd Nov 2021, 16:45
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I think weíre in the unfortunate gap between desperately needing to reduce/eliminate our fossil fuel usage, and having scaleable battery tech that is acceptably close to a straight swap in terms of energy density. In the interim, closed-cycle hydrocarbon fuel seems like the obvious solution, as we have the infrastructure and engines already (and this covers ships, trains, etc.), rather than having to reengineer everything to hydrogen use then again to electricity.

I wouldnít get too hung up the seeming difficulty of extracting carbon from the environment and making it into fuel; pretty much every living thing does this with ease and with a virtually unlimited energy supply for the processes (sunlight), efficiency is not as important as it might appear. The important bit is to stop digging stuff out of the ground and burning it. Bioengineering, nanotech, enzymes, catalysts, etc. have come a long way and have further to go, and are just waiting for the signal to get on with it. Once a clear signal has been sent that this is whatís going to happen, and at a vast scale, then expect rapid advances, especially if it becomes competitive.
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