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I'm surprized hydrogen fueled flight isn't looked into more. Hydrogen can be produced using electrolysis and it's packs significantly more energy per weight eve
by ginko 7y ago
I'm surprized hydrogen fueled flight isn't looked into more. Hydrogen can be produced using electrolysis and it's packs significantly more energy per weight even than kerosene.
The main drawback is the low density which would require larger fuselages, but that should be offset by the significantly lower weight.
- wlesieutre 7y agoTo store enough hydrogen to be useful you probably need it in liquid form like rockets use. Hydrogen is energy dense by mass, but not by how much space it takes up compared to liquid fuels. Otherwise you'll have a really giant bag of gaseous hydrogen which does help your bouyancy, but then you've made an airship instead of a plane and a spark accidentally turns it into the Hindenburg.
- afiori 7y agoIs it so much less energy dense per liter to offset the gain in weight? In a plane energy per weight is rather important afterall
- wlesieutre 7y agoAs a gas at 1 atmosphere, wikipedia says 0.011 MJ/L, compared to jet fuel at 35 MJ/L. You'd save weight (it weighs less than air so this would make you float) but need 3000x as much space if it's not compressed. Compressed at 690 bar (about 680 atmospheres) it goes all the way up to 5 MJ/L, only 7x as much volume of fuel required compared to jet fuel. But the tanks to pressurize something that much are presumably very heavy and not a reasonable solution in an airplane. Liquifying it gets that up to 10 MJ/liter and I don't think you need as much pressure to store that (as long as you keep it very very cold). Per weight instead of volume you beat jet fuel (by 3-4x), so that aspect is a win. Having enough volume to store it and keeping the storage equipment light are the challenges.
- Tade0 7y agoCounterintuitively enough liquid ammonia packs more hydrogen than liquid hydrogen per unit volume - also it condenses at -33C (-27.4F), so it actually wouldn't require cooling once in the air. It can be burned in a gas turbine, but for now the NOx emissions are pretty horrible.
- jandrese 7y agoAlso, it's horribly corrosive and poisonous.
- usrusr 7y agoThe penalty for more volume is rising with higher speed, whereas the penalty for more weight is staying pretty much constant. In a fast plane, volume is just as important as weight, if not more.
- wlesieutre 7y agoAlso liquid fuel tanks in planes are usually out in the wings. They can be shaped pretty much like whatever as long as the fuel keeps flowing. Pressure vessels though, you're better off making them round.
- hfkajshfaks 7y agoIts so bad that only the largest space rockets use liquid H2. All the others use kerosene or the like. Either way, the Soviets tried gaseous fuels in the 80s - See Tu-155. They ran on liquid H2, CNG. If I recall, the weight increase didn't make it practical. On the other hand it was a turbine powered plane. It might work out with fuel cells (although you'd need a big and heavy compressor to run it)
- mannykannot 7y agoLiquified is the only option, I think. Compressing it into cylinders or storing it as a metal hydride is probably way too much weight. Until recently, making hydrogen by electrolysis was not a benefit, environmentally, as a lot of the electricity would have come from fossil fuels. I think decomposition of methane is an option that would allow the carbon to be sequestered.
- black6 7y agoTupolev made the one-off Tu-155 using liquid hydrogen and liquefied natural gas as fuel for its turbines.
- ginko 7y agoYeah, I've found this Russian video about the Tu-155 when looking into it: https://www.youtube.com/watch?v=yvgOLapNubI https://www.youtube.com/watch?v=yvgOLapNubI
- alex_young 7y agoThe main source (95%) of hydrogen fuel in the US is a by-product of Natural Gas extraction (https://www.energy.gov/eere/fuelcells/hydrogen-production-natural-gas-reforming https://www.energy.gov/eere/fuelcells/hydrogen-production-na...). What problem are we solving by moving to hydrogen?
- semi-extrinsic 7y agoWhen you do steam methane reforming to produce hydrogen, separating out the CO2 is a necessary step in the process. Then it's just a matter of storing it underground, rather than just emitting it.
- alex_young 7y agoAre there any commercial examples of carbon sequestration? We've heard that line for decades now, if it's real there should be plenty of production sites by this point.
- mmaurizi 7y agohttps://en.wikipedia.org/wiki/Carbon_capture_and_storage#Industrial-scale_projects https://en.wikipedia.org/wiki/Carbon_capture_and_storage#Ind...
- nightwing 7y agoTrying to make simpler and cheaper planes, not everything has to be about CO2.
- TheSpiceIsLife 7y agoThere’s probably some limits to how big a reasonably swift aircraft can be due to drag. This charge seems to indicate liquid hydrogen would require something like three times the volume as jet fuel / kerosene/ diesel. https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/Energy_density.svg/2000px-Energy_density.svg.png https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/En...
- NickM 7y agoYeah I have wondered about this option as well. Hydrogen fuel cell cars make very little practical sense for a lot of reasons, but most of those reasons don't seem to apply so much when you're dealing with air travel: - It'll be a long time before fuel cells are cost competitive with gas or electric cars, but for planes the cost of fuel and operation is much more significant than with a car, so the upfront cost for building the plane seems less significant in comparison - Refueling infrastructure is much easier to implement at a (relatively) small number of airports than it is to build many small consumer refueling stations everywhere - Space is more important than weight in a car, but the opposite may be true for a plane - Crash safety is a much bigger problem for cars than planes - plane crashes are rare, and if a plane crashes there's a good chance everyone dies anyway, but if you're designing a car you're going to have to be really careful to make sure every other fender bender doesn't result in a hydrogen explosion Of course there's the issue that most hydrogen today is created from fossil fuels, but perhaps there are ways to generate it sustainably and still remain competitive with the cost of jet fuel? Electric cars can be a very competitive alternative to gasoline cars, but electric batteries are not yet energy-dense enough to make long-distance air travel viable, so it feels like hydrogen planes might be the least bad solution if we want to get off of fossil fuels.
- rootusrootus 7y ago> if a plane crashes there's a good chance everyone dies anyway That's actually not the case. Overall your odds of surviving an accident in a plane are something like 95%. Still above 50% for "serious" incidents. Sure, if the plane drills the ground everyone is going to die, but planes crash somewhat regularly with most/all surviving.
- base698 7y agoTo further the above point, here is a searchable database provided by the NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx
- tomatocracy 7y agoAlso one of the most dangerous places to be in a plane, statistically, is on the ground. A surprisingly large proportion of historic fatalities in air accidents have been crashes on the taxiway or runway between two aircraft (eg plane lands on top of another or taxis across a live runway when it shouldn't do).
- mrfusion 7y agoHow about using carbon atoms to store your hydrogen? May I suggest methane.
- nradov 7y agoHydrogen is hardly ever produced by electrolysis. It's very inefficient. https://en.wikipedia.org/wiki/Hydrogen_production https://en.wikipedia.org/wiki/Hydrogen_production
- rootusrootus 7y agoBut the three alternative methods for production are fossil fuel based. Kinda defeats the point.
- AtlasBarfed 7y agoHydrogen production is either not carbon neutral (from ?natural gas?) or isn't particularly efficient to produce once you tack on transport with electrolysis losses.
- gambiting 7y ago1kg of kerosone can be kept in a plastic tank that weighs nothing. 1kg of hydrogen has to be kept in a pressurized, pure-lead 70kg bottle, and even then hydrogen will diffuse through it in just few weeks. So to take 1kg of hydrogen with you you're taking a lot of weight in the tanks too.
- ggreer 7y agoSome rockets use hydrogen and their pressure vessels aren't so heavy as to keep them stuck on the ground. You only need to contain the hydrogen for hours, not weeks.
- hfkajshfaks 7y agoFew though, and only the largest ones and they have incredibly complicated and long (and dangerous - imagine having to deal with refueling a cyrogenic liquid after every leg) fueling. Most rockets use hydrocarbons for this very reason.
- rbanffy 7y agoThe relative weight of the tank decreases with volume and the aircraft doesn't need to hold the fuel for more than the duration of the flight. The idea is not without merit. Shape will be more interesting - storing the fuel within the wings is not a very bright idea in this case.
- marcosdumay 7y ago> hydrogen will diffuse through it in just few weeks This one is a non-problem. I don't think there is any civilian airport with enough fuel storage for two weeks. (But the tank weight, well that is a problem.)
- tomatocracy 7y agoVery many are supplied by pipelines though to avoid that need.
- 7y ago
- pjc50 7y agoRather than mess around with hydrogen, with the proper mandates a lot of jets could switch over to renewable jet fuel. One of the main leaders here is, surprisingly, the US Navy: http://www.altenergy.org/new_energy/seawater-into-jet-fuel.html http://www.altenergy.org/new_energy/seawater-into-jet-fuel.h... directly from seawater and nuclear energy from a ship's reactor, or various other biofuel initiatives.
- hfkajshfaks 7y agoThe Navy does a lot of this. They funded a program to make biofuels from algae. But don't forget that the stated purpose of funded research is often a lie[0] and this is not necessarily viable outside the lab. [0] You get other benefits from the research including subsidizing your national industry, training your workforce, doing research you're interested in with a more politically palpable purpose.
- gnode 7y agoIt would be much harder to engineer: you'd need a hefty tank; cryogenic fuel handling to increase density and lower tank weight. Safety is critical on aircraft. Hydrogen is difficult to contain, and has very low viscosity due to its small molecules. It burns with an almost invisible yet very hot ultraviolet flame. It easily mixes with air to form an explosive mixture and has a very low minimum ignition energy (about a tenth of gasoline). Combustion of hydrogen in a heat engine for propulsion would be very inefficient compared to a battery electric. Fuel cells are in between, at about 40-60% efficiency, but have a substantial weight cost.
- Gibbon1 7y agoMy dad worked at a company that was researching hydrogen (probably for scram jets). Problem he said with hydrogen is the size of the fuel tanks starts negatively impacting the amount of payload you can carry.
- emanuensis 7y agoHow 'bout Ammonia fuel cells?
- dredmorbius 7y agoVery bad news in event of loss of fuel containment.
- emanuensis 7y agoHaha, not so bad as loss of H2 containment (as seen IRL in Norway) ... and of course farmers deal with it every day.
- dredmorbius 7y agoAmmonia is deadly of itself. Even before it explodes.
- emanuensis 7y agoWell to increase safety one can use a fuel like ~methanol with a regular ICE, no need for electric conversion or reformation, just a new carburetor! i was suggesting NH3 because it is much more dense and involves NO carbon at all. Like i said farmers regularly deal with NH3 ... so it can be safely handled. ~methanol Renewable CO2 recycling and synthetic fuel production in a marine environment https://www.pnas.org/content/early/2019/05/28/1902335116 https://www.pnas.org/content/early/2019/05/28/1902335116
- russdill 7y agoliquefied methane/natural gas would be a much better choice. The energy density per volume is about 2/3rds that of jet fuel and higher per weight. It's slightly less efficient to produce from electricity than hydrogen.