# Rolls-Royce, EasyJet fire up first hydrogen-fueled jet engine

An aviation first has been reached in the UK, with Rolls-Royce and easyJet saying they have conducted the "world's first run of a modern aero engine on hydrogen."  While the test was ground based, Rolls-Royce said the successful firing of a Rolls-Royce AE 2100-A regional aircraft engine converted for hydrogen power was a major …

1. #### Batteries != energy

Even if the weight issue with batteries was solved, it still wouldn't be viable since you'd need to generate >1GWh for cross-Atlantic/cross-Pacific airliners.

1. #### Re: Batteries != energy

I'm not sure what your point is - whether it's 1GWh of energy stored as hydrogen, or 1GWh of energy stored in a battery, I can guarantee it involved an expenditure of greater than 1GWh of electricity at some point prior to take-off to charge the store. Unless we're talking gray hydrogen of course, in which case it's just another fossil fuel.

1. #### Re: Batteries != energy

Hydrogen can be produced en masse in a constant stream either on site or centralised somewhere (or a mix), electricity can't since changes in demand require ramping up and down of the fuel source. Remember, that's only 1GWh per plane (given my very fuzzy calculations). If an airport needs to refuel say 5 trans-Atlantic flights per hour that's 5GWh. The largest nuclear plant in the world is ~7GWh max and it's about the size of an airport.

1. #### Re: Batteries != energy

Ah, you're arguing that hydrogren is useful for this application because it can be moved at a higher ... I think the word I want is "current" - than charging a battery on a plane? Yes, I agree with you on that.

2. #### Re: Batteries != energy

I'm sorry - I can't take seriously the back of a napkin maths of someone who doesn't distinguish between energy and power.

1. #### Re: Batteries != energy

Actually it's pretty simple. I estimated the equivalent energy required for a Boeing 737 engine to be ~50MW. For a London to New York flight it would require about 600 MW of energy for a 5 hour flight plus some extra for safety, and to recharge that in half an hour would require ~1.2GWh to be competitive with the roughly 20 minute refuel time of kerosene.

If you're talking about the title, batteries store energy, getting that energy in the form of power is more cumbersome than liquid fuels.

1. #### Re: Batteries != energy

And then claim that you can measure a power plant in MWh...

1. #### Re: Batteries != energy

I said their maximum output was in GWh (7GW in an hour), not their capacity. My whole argument is about the time requirement of refueling a plane. The hour part is pretty relevant here wouldn't you say? I'm all for being a nitpicky a-hole, but try to consider nuance first.

1. #### Re: Batteries != energy

7GW in an hour doesn't mean anything.

7GW means 7GJ per second

You could say a 7GWh per h but that's a bit silly

1. #### Re: Batteries != energy

A GW is indeed a GJ per second. a GWh is a GJ per second per hour. That's actually a pretty widely accepted concept.

1. #### Re: Batteries != energy

No, it's actually a GJ per second for an hour. It's the difference between multiplication and division, which is a pretty big and fundamental difference. It's a unit of energy, not a unit of power; the total amount of energy stored in a big storage system would be measured in GWh (or, more simply, in GJ), and the rate of consumption in GW. In the same way, your electricity meter measures KWh as the amount of energy you have used, not the rate you are using it.

1. #### Re: Batteries != energy

It's a colloquialism for crying out loud. I thought I escaped this kind of pedantic behaviour when I left Twitter. Does it have any bearing on my initial argument that batteries for airliners cannot be charged effectively in an airport?

1. #### Re: Batteries != energy

If you're trying to make a technical point, it's hardly pedantic to question your working when you're using the wrong units, because what you wrote doesn't mean what you think it does, and others aren't going to read it and get the meaning you meant to impart, if that's not what you said...

1. #### Re: Batteries != energy

I didn't use the wrong units. I said an airliner would need >1GWh, that's how much energy would be needed to drive the 50MW engines. Which part of that is wrong?

1. #### Re: Batteries hold energy and deliver power

As a third party to this argument, let me rework the math as actual math:

Power consumption = energy consumption rate (or flow) = 50 MW / engine * 2 engines = 100 MW (plane) or 0.1 GW

Battery capacity requirement = 5 hour flight * 120% = 6 hours capacity (extra hour covers taxiing, boarding/deplaning, holding patterns, etc.)

Total battery energy = 100 MW * 6 hours = 600 MW-hr or 0.6 GW-hr or 2160 GJ

Recharge time = 0.5 hour

Recharge RATE (power) = 600 MW-hr / 0.5 hr = 1200 MW = 1.2 GW

The original numbers were correct; however, the final calculation has time units on both sides of the division, so it falls out.

Is everyone happy now?!?

1. #### Re: Batteries hold energy and deliver power

1.21GW? Great Scott!

2. #### Re: Batteries hold energy and deliver power

Ah, now I get why they were being so nitpicky. I wasn't writing an equation, I was making a point about the time constraint of charging a battery.

3. #### Re: Batteries hold energy and deliver power

"Is everyone happy now?!?"

I doubt it. This is ElReg.

4. #### Re: Batteries hold energy and deliver power

With numbers like that, it may be better the change, rather than charge the battery. Then you can take as long as you like to charge it before putting it back in a plane.

1. #### Re: Batteries hold energy and deliver power

Or, we could install overhead electrical lines for airplanes. You only would have to equip existing airplanes with pantographs, and that's it...

2. #### Re: Batteries != energy

"I thought I escaped this kind of pedantic behaviour when I left Twitter."

TehIntraWebTubes were built on pedantry, alas. Makes a certain class of commentard feel important. Welcome to ElReg.

"Does it have any bearing on my initial argument that batteries for airliners cannot be charged effectively in an airport?"

No. At least not until each airport has a multi-tens-of-megawatts nuke plant devoted solely to charging aircraft. Which ain't going to happen, ever.

3. #### Re: Batteries != energy

Use of electric aircraft is growing in the GA sector, especially in some schools. The approach taken there is hot-swappable batteries - you charge a large number of batteries (particularly overnight) then swap batteries in and out between flights rather than refueling.

I think aircraft would also have longer than 20 minutes in which to charge - the technical limit on turnaround time for most aircraft is not how long it takes to refuel (many regional flights don't refuel at every stop anyway) but how long it takes the brakes to cool down enough to allow you to take off (they have to be cool enough that they won't catch fire if you need to use heavy braking to reject a take off), which is usually between 45 and 60 minutes.

2. #### Re: Batteries != energy

"You could say a 7GWh per h but that's a bit silly"

No sillier than metres per second per second.

1. #### Re: Batteries != energy

GWh = GW × h

Therefore GWh per h = GW × h ÷ h = GW.

Acceleration = m ÷ s² = m ÷ s ÷ s

Do you see the difference?

2. Hydrogen seems to be more a viable future for planes (also) than batteries.

Well done Rolls Royce, you beat CFM in the hydrogen race

== Bring us Dabbsy back! ==

1. The real problem for hydrogen that still needs to be solved is a reliable and safe way of storing it either under very high pressure or in a liquid form. Because the molecular size of hydrogen is so small, it can escape from a hole that is literally too small to detect with current scanning technology. Adding to that is the fact that escaped hydrogen, when combined with atmospheric oxygen, is an explosion just waiting for a very, very small spark to happen.

NASA and other space agencies have been trying to solve the hydrogen storage problem for decades, and they are still no nearer to a solution.

1. Yup. NASA know it'll leak, so they have procedures and designs of kit and spaces to cope with that. Witness the postponements of the Artemis 1 mission due to H2 leaks.

Aircraft design will become a lot more interesting if they are forced to use a fuel, H2, which is totally unsuited for that use.

1. #### Plane fuel

Instead of Hydrogen, react it with CO2 and make synthetic fuels.

Most of the problems are solved.

1. #### Re: Plane fuel

You need to get rid of the O2 in the reaction, which is somewhat hard. If you don't the fuel weight contains the oxygen atoms which won't contribute to the burn, since they are already bound to the C and are thus deadweight. There are compounds with C and O in where they aren't bound together, and so they can react together to contribute to the energy output. However these compounds are generally used as explosives...

2. #### Re: Plane fuel

"Instead of Hydrogen, react it with CO2 and make synthetic fuels."

There is a group at Stanford looking to do just that ... making Gasoline out of atmospheric CO2, with the help of a ruthenium catalyst. If they are successful, and it can be done in bulk at low cost, running ICE engines on it will be carbon neutral.

Here's a link to an article on the subject. (WARNING! Minimal technology content!).

Naturally, the Greenaholics will try to ban it if Stanford can get it to work.

3. #### Re: Plane fuel

> react it with CO2 and make synthetic fuels

Not green.

And doesn't use blockchain.

Seriously, the point is to be "green". Large scale synthetic fuel production already worked during WWII, so I guess it's not the technical issues which would prevent it almost a century later.

1. #### Re: Plane fuel

"Seriously, the point is to be "green". Large scale synthetic fuel production already worked during WWII, so I guess it's not the technical issues which would prevent it almost a century later."

Primarily, it's the cost and effort of making it compared to pumping it out of the ground. Wind and solar have the potential to make it manufacture of syngas more economic. It'll never be cheaper than drilling and pumping in terms of cash spent per KWh, but it's has the potential to be much cleaner. The real problem is you can't really run the entire worlds energy needs just on wind and solar (and hydo where possible)

2. Hydrogen also occupies a big volume. I saw somewhere that there's enough space in a long haul airliner to store the hydrogen required, as long as you remove the passengers and luggage!

1. I saw somewhere that there's enough space in a long haul airliner to store the hydrogen required, as long as you remove the passengers and luggage!

Simple. Just make bigger aircraft! Doesn't really scale for battery powered aircraft though. However, you could solve* the H2 production cost by carrying that as fuel. So TiH2 as an example, because titanium and hydrogen are both lighter than batteries. Then all the aircraft would need is to heat the TiH2 to release the H2 and feed that to the engines. I think this would be especially suited to hypersonic aircraft because friction would supply the heat. Or it could be combined with space-based solar and microwave beams, assuming those could track the aircraft.

Best thing is it's entirely sustainable because the spent titanium fuel could be recharged using free solar heat and Green hydrogen. With a few billion in funding, I'm certain Eel Industries could have a prototype ready to fly 33.500 lobbyists to COP30.

*By solve, I mean by glossing over a few minor points, a powerpoint could be created to sell it to our gullible politicians. I mean they've wasted trillions already on pre-industrial and pointless 'Green' tech already. Plus there's a fair pile of cash already sloshing around the 'hydrogen battery' space doing pretty much this. And it looks fine, as long as you don't look too closely at the physics, engineering or economics.

3. "Because the molecular size of hydrogen is so small, it can escape from a hole that is literally too small to detect with current scanning technology."

At least it's bigger than He since H likes to exist as H2 and He is happy being alone.

Embrittlement, fire risks, HP tanks that need changing every couple of years and all sorts of other issue still gives liquid fuel the gold medal.

The lower hanging fruit is doing better with ground transportation. If the US had a better, more useful passenger rail system, it would get used more. High speed rail isn't always the answer. A train that goes slower but allows enough time for a sleep, breakfast and a shower is much like the trip taking no time at all. I'd love to board a train in the late evening after dinner, have a G&T or two and then stretch out to awake to a fresh cup of coffee, some nibbles or even a full breakfast and be at my destination at 8-9am. Flying is too much hurry up and wait with intervals of being groped by people I might be tempted to cross a street to avoid in another setting. I've never been good at packing light either.

If flying was mainly for crossing oceans (as there aren't any liners anymore), there would be less of a need for them.

4. https://www.hybridairvehicles.com/our-aircraft/airlander-10/

Scale this up and more travel time has to be a compromise/reality check … and you are there.

With the benefit the lift a Helium Airship brings much of the power required to literally keep several tons of inanimate airframe in the sky goes away and all you need is the lower energy to move from A to B.

A transatlantic-grade A321XLR maximum take off weight is 101T/223,000lb)… though a lot of that weight is fuel…. as some reference.

1. Airships have their own problems, which is why they were eventually phased out. Obviously Hindenburg-scale fireworks come to mind, but even Helium-filled airships had their spectacular and career-ending accidents (IIRC USS Akron and USS Shenandoah were destroyed in storms, and USS Macon suffered a spontaneous disassembly). And it's not just the US ones, AFAIK most airships worldwide eventually met a sticky end (usually in a storm).

Fixed-wing aircraft are a lot faster, sturdier, storm-resistant, and more cost-efficient; The only advantage of airships is their great fuel efficiency.

(For the record I do like airships, but I doubt modern travelers will accept 3-4 day long transatlantic flights in 21st century comfort standards, i.e. crammed together like sardines on uncomfortable seats, surviving on eye-wateringly expensive salted peanuts, and having to queue to use the only lavatory...)

1. So long as they don't forget to load the lemon-soaked paper napkins before departure, I'm sure it'll be just fine...

5. Hydrogen is already used in commercial cars, so I guess there are solutions for tanks.

Those are on roads every day, and I didn't hear about one exploding yet.

'In properly designed systems these very small leaks do not present a problem as the tiny amount of hydrogen released will not be enough to cause a flammable mixture in air. Only when hydrogen gas can accumulate over time in a confined area will a risk of a flammable mixture or asphyxiation arise.'

Batteries can be unsafe too.

== Bring us Dabbsy back! ==

1. Not sure I'd trust it. I've had a facefull or two of LPG from "failsafe" quick release LPG fillers on cars and they're fairly low pressure systems.

2. Those are on roads every day, and I didn't hear about one exploding yet.

I did! Think it was in Germany, over a decade ago. H2 leaked into the car, ignited and the driver just suffered some mild flash burns. That got me thinking about making a 'green' yacht using hydrogen fuel cells. Fuel, and especially fuel vapors being rather hazardous at sea, especially when that vapor is denser than air and pools inside a convenient closed hull. If* H2 did leak, it would be less hazardous because it loves to escape. We managed to get Volvo interested to the point where we had some tests done, so what would happen in an H2 explosion, and those generally didn't lead to other stuff catching fire. Still the overpressure challenge, but those were more manageable. Biggest challenge was learning some naval architecture, and why ripping out or moving mass around in a yachy kinda buggered up it's handling, safety etc. So that would have made it challenging to retrofit into ICE-powered yachts. And of course the usual problem of H2 fuelling points in harbours/docks/marinas.

*Ok, no if, but when. Or how quickly.

3. Tiny fuel tanks.

I mean, really, really tiny fuel tanks.

And batteries are substantially safer than say, an internal combustion engine.

6. The real problem for hydrogen that still needs to be solved is a reliable and safe way of storing it either under very high pressure or in a liquid form.

There is some very interesting work being done on "solid state" hydrogen storage where a solid medium is used to absorb the hydrogen under pressure, which then expels when you release the pressure. The vessels only operate at ~70bar rather than 700bar, no cryogenics required. You still have a tank full of solid absorption medium though, which is quite heavy. It's being proposed for freight trains where a heavy "fuel" wagon on a train of 100+ wagons is of no consequence. A couple of Canadian companies are trialling it on a converted "switcher" locomotive.

Storage solutions exist, but aren't necessarily a good fit for aviation, or indeed cars - it's useful for static storage or in a low-friction environment (like rail).

For aviation, syngas or biofuels seem like they might be easier to handle/store than raw hydrogen.

7. Is that why the tests were done in the Orkneys?

One small spark and one less Orkney...

8. To go off on a tangent, in the early 80's Convair were looking at the feasibility of launching a spaceplane off the back of a 747. The idea was to store the hydrogen for the spaceplane inside the 747, so that it could be fuelled up in-flight (avoiding problems with leaks, or at least moving the problems). To add extra performance to the 747, they then planned to modify the jet engines to add hydrogen fuelled afterburners, to launch the spaceplane as high and fast as possible.

Oh, and just to add to the fun, they were looking at using fluorine as the oxidiser in the spaceplane's engines.

I just love the whole concept :)

source

1. Anyone considering using fluorine as an oxidiser should be required to read Ignition.

And then to explain very, very, carefully why there is no other option...

3. #### I suspect this is most useful as PR

I think hydrogen is going to have a hard time competing with synthetic hydrocarbons because of the storage problems. Even liquid hydrogen requires much bigger storage tanks. Then you've got the weight and size of the insulation. If you don't liquify it, you've got to compress it, which again requires heavy tanks. Then you've got the much higher risks from leaks, especially during refueling.

Long distance flight must eventually become net-zero carbon, but I doubt that Rolls Royce would be doing this if EasyJet weren't paying for it, probably from their PR budget.

1. #### Re: I suspect this is most useful as PR

It all comes down to cost. I'm with you, in that synthetic fuel can be a drop-in replacement for ordinary jet fuel, requiring no new infrastructure or aircraft designs, while hydrogen requires a lot of new infrastructure, and pretty much requires radical new designs to accommodate the tanks, so the former would seem to be much more likely. But if all the green hydrogen production being planned results in very cheap hydrogen, and synthetic fuel remains expensive, then hydrogen might still end up being worth it.

2. #### Re: I suspect this is most useful as PR

It's pretty obvious that hydrocarbon fuels are the winner in energy density and ease of storage and use, as well as having current technologies that use them. The end game is going to be the production of synthetic hydrocarbons from carbon-neutral feedstocks (e.g. carbon dioxide and water in, hydrocarbons and oxygen out). From a chemical point of view, it's actually not very easy to do, because carbon-carbon and carbon-hydrogen bonds are relatively weak compared to carbon-oxygen and hydrogen-oxygen bonds, which is why energy is released when you burn them. You have to pump energy in to break those carbon-oxygen and hydrogen-oxygen bonds, and then force it to make carbon-hydrogen bonds instead, without the energetically favourable recombination of carbon dioxide and hydrogen. In nature, the formation of hydrocarbons happens in a multi-step process, which starts with photosynthesis (the energy input here being sunlight), then various biological processes that produce things like fatty acids, burial, and prolonged temperature and pressure causing the oxygen to be removed to form hydrocarbons from that organic material.

If that nut can be cracked synthetically, with a decent energy efficiency, then we could have factories that use electrical energy to pull carbon dioxide and moisture from the air and turn it into fuel that is a drop-in replacement for existing fuels without all the storage headaches of hydrogen, or weight, and life-cycle issues of batteries. Anyone who can solve that will either be a billionaire overnight, or will be murdered.

1. #### Re: I suspect this is most useful as PR

Anyone who can solve that will either be a billionaire overnight, or will be murdered.

Hopefully the latter, and swiftly, and consider it self-defence. Consider the quantity of hydrocarbons used annually, then how much CO2 we'd need to remove from the atmosphere to produce synfuel equivalents. And then what happens when atmospheric CO2 levels drop too much.

1. #### Re: I suspect this is most useful as PR

I can't see how the CO2 needed to create synfuel could possibly be greater than the amount of CO2 release by the subsequent burning of that synfuel, so if we were suddenly able to switch from fossil fuels to synfuels I expect the net effect would be a slow shift of atmospheric CO2 levels from 400ppm back to 300ppm.

1. #### Re: I suspect this is most useful as PR

I expect the net effect would be a slow shift of atmospheric CO2 levels from 400ppm back to 300ppm.

And what effect would that have on crop yields? Especially after cunning plans, like the Netherland's nitrogen taxes, and offering to compulsory purchase farms to build housing. Which will presumably house vegetarians, who will require more farmland so vegetables can eat vegetables.

But you're making an assumption. Like we went from 300ppmv to 400ppmv exclusively due to burning hydrocarbons. Reality is anthropogenic CO2 is a teeny fraction of the total CO2 (or methane) emisisons because nature dominates. You can see this here-

https://en.wikipedia.org/wiki/Keeling_Curve

Especially in the seasonal variation. Surely winter should be higher than summer because that's peak heating season when we burn all those hydrocarbons. So anyway, we ban fossil fools (I wish) I mean fuels. No more anthropogenic CO2. No more CO2 for it's many industrial uses, so no artificially carbonated drinks or CO2 pumped into greenhouses to raise crop yields.. Which with no nitrogen just increases food poverty as well. Or we decide that it's a brilliant idea to extract it from the atmosphere. Current industrial demand is for around 230 million tons annually. Currently, it's assumed (very crudely) that anthropomorphic CO2 emissions are in the order of 30bn tons annually. Because this is all (allegedly) 'fossil' CO2 due to isotope ratios..

We'd need to increase CO2 production. A lot. And not use hydrocarbon or hydrocarbon-derived energy to do so.

So sure, we could maybe drop CO2 levels to 300ppmv. But every summer, they'd drop a little further. And then keep dropping. And when it gets below 200ppmv, everything starts to die. Even the militant vegetarians, vegans and Extinction Rebellion fuckwits. Unless of course their real objective is extinction, or they're just too dumb to realise that's the inevitable outcome of their policies. Except that as our population dies off due to starvation, or other poverty related deaths, the CO2 extraction machines would stop anyway.

Well, they should stop long before then because the fundamental flaw behind most 'Green' dreams is energy, or lack thereof. See-

https://gridwatch.co.uk/wind

Today: minimum: 0.329 GW maximum: 1.707 GW average: 0.827 GW

1. #### Re: I suspect this is most useful as PR

Careful, actual science is against most social media TOS.

2. #### Re: I suspect this is most useful as PR

Yup, plants thive the most at 1200ppm, or 0.12 percent CO2. Greenhouses will even buy CO2 bottles to increase the amount of CO2 inside the greenhouse to encourage healthier plants. Our atmosphere's current 400ppm, or 0.04 percent CO2, is close to the equivalent of suffocation for plant life. Think someone put a plastic bowl over your head, sealed to your neck, then put a 1 inch diameter hole in front of your mouth. Barely enough fresh air to survive. 150ppm, or 0.015 percent CO2, is where plant death occurs. When the plants die, Earth becomes a barren rock with nothing alive on it, not even in the ocean. Or, when someone tapes the hole shut

CO2 and temp doesn't even have that much of a relationship anyway. Venus is only about 700 degrees hotter than Earth, but has a 97 percent CO2 atmosphere as opposed to Earth's 0.04 percent, is 93 Bar as opposed to Earth's 1 Bar atmosphere, and it's 67.2MM miles from the Sun instead of 93MM miles away. Solar irradiance is 2601.3 watts per square meter as opposed to Earth's 1361.0 watts per square meter, or almost twice as much energy. That the AGW alarmists converted to PPM from percent says a lot, because they wanted it to be more alarming than it is. 400 parts per million sounds scary to the low intelligence group as it has hundreds and millions, but even they understand that 0.04 percent is nothing.

2. #### Re: I suspect this is most useful as PR

"I can't see how the CO2 needed to create synfuel could possibly be greater than the amount of CO2 release by the subsequent burning of that synfuel"

If the process requires energy to produce the fuel (making and/or heating cayalysts, using industrial plant etc) that energy has to come from somewhere and is in addition to theoretically zero emission syngas CO2 cycle. Even if all power input is based on wind and tidal and solar generation, production is certainly not net-zero. This process could reduce CO2 emissions, perhaps significantly so, but wouldn't stop them.

1. #### Re: I suspect this is most useful as PR

Note that we weren't discussing whether or not the creation of such synfuels could be made carbon neutral, rather whether the use of atmospheric CO2 as a feedstock could lead to a dangerous depletion of said gas from the atmosphere or whether the subsequent use of the synfuel would simply return most/all of the feedstock back into the atmosphere such that the net effect (ignoring any contributions from the creation process itself) would be essentially nil.

2. #### Re: I suspect this is most useful as PR

"If that nut can be cracked synthetically, with a decent energy efficiency"

In your first paragraph you outlined why using Hydrogen is problematic from the standpoint of needing to break molecular bonds. That places a theoretical maximum efficiency on the process that isn't that great to start with. The way nature accomplishes switching around atoms takes loads of time, pressure and heat to accomplish. What is required for commercial applications is something that takes very little time. Using more energy as a substitute for time makes it all fall apart. If that nut could be cracked, I think there would also be very nice genetically engineered trees that grow very straight to a harvestable height in one year.

3. #### Re: I suspect this is most useful as PR

"Long distance flight must eventually become net-zero carbon"

Why? I think that if the bulk of travel was done on the ground where there are more options for reducing the energy required for travel, there would be less need for air travel or its price could rise to where it's not the first choice except for getting across oceans.

I don't see Hydrogen as being a good storage medium. On Earth it's tied up tightly in molecules and breaking those bonds is never going to be an efficient use of the energy used to do it. Even if there is energy lying around being wasted, something like running protein folding simulations would return better value than chopping apart a tank of water.

4. #### Gravy train

Who cares if tech is not viable if you can spend years "researching" it and milking tax payer subsidies.

It's for Net Zero after all, so it can't be criticised.

1. #### Re: Gravy train

"Who cares if tech is not viable if you can spend years "researching" it and milking tax payer subsidies."

So is back to the old saying "If you can't be part of the solution, you can make lots of money extending the problem"?

5. #### Revert back to airships?

Hydrogen's nice and light, but needs three times the volume as aviation fuel if stored as liquid (very cold). Six times the volume if stored as 700bar pressurised gas.

So planes will significantly need bigger fuel tanks, but will save energy by not having to carry as much fuel weight around.

Batteries, with current technology, aren't as energy-dense as liquid hydrogen. But easier to handle.

Volumetric energy capacity:

- Petrol/aviation fuel: around 34 MJ per litre

- Compressed hydrogen (700 bar): 5.6 MJ per litre (fuel tanks six times larger)

- Liquid hydrogen: 10.1 MJ per litre (fuel tanks three times larger)

1. #### Re: Revert back to airships?

Hmm. 700 bar fuel tanks will need to be robust and therefore, probably, heavy. Also compressed H2 heats up on expansion (depending on the initial temperature) so the tanks and plumbing will have to cope with significant temperature changes during the flight. I think we'll need a new design of plane rather than retrofitting into an existing fleet of A320s.

1. #### Re: Revert back to airships?

Wrong way round, gases cool down on expansion, and heat up on compression. You're going to get some very cold plumbing if you use liquified hydrogen.

1. #### Re: Revert back to airships?

gases cool down on expansion

Mostly true but not for H2. See; https://en.wikipedia.org/wiki/Joule%E2%80%93Thomson_effect

We sometimes used to refill small H2 cylinders from larger ones (outside, of course) when we needed to 'hydrogenate' something for a lab experiment. We had to monitor the temperatures of the cylinders to guard against thermal shock.

1. #### Re: Revert back to airships?

So, if I'm reading that right, when squeezing those gases through a small aperture, you get a heating effect that outweighs the cooling you get from adiabatic expansion, essentially a "friction" effect. Presumably, that only happens when the aperture is small, and the heat that is generated comes from somewhere (energy isn't free), so whilst the aperture is heated, presumably, the gas is cooled?

1. #### Re: Revert back to airships?

I knew of the effect from practical experience and dire warnings from my supervisor at the lab during a between school and university year working. I do recall that the larger cylinder would get warm and that had to be moderated. If the outside of the cylinder is warming up then the gas inside is even hotter. I didn't actually remember what the effect was called until I DDG'd it a few hours ago. Here's another link which might explain it better https://profound-answers.com/why-does-hydrogen-get-hot-when-it-expands/. From a skim read I don't think it's actually a friction effect.

I changed career from lab work to IT after about seven years (which was an age ago).

1. #### Re: Revert back to airships?

I'm intrigued. Does this happen when going from a higher pressure to a lower one (like filling a small cylinder from a larger one), so the change in pressure is relatively minor in the main cylinder? Where does the heat come from? Energy must be conserved, so if the pipe heats up, something else must be cooling down.

Presumably, when you are using liquid hydrogen as a fuel source, and it is changing phase when going through the pipes, that cooling effect outweights this one? You're always going to have to deal with the phase change heat (going from a liquid to a gas uses that heat, of course), and it's typically much higher than the specific heat required to raise the temperature in the gas phase.

2. #### Re: Revert back to airships?

There's a gentleman in New Zealand who took this to its logical conclusion and used gaseous expansion to cool beer. And of course, the best way to expand gas quickly? Burn it in a jet engine:

https://www.asciimation.co.nz/beer/

2. #### Re: Revert back to airships?

"- Liquid hydrogen: 10.1 MJ per litre (fuel tanks three times larger)"

Boil-off becomes an issues unless you have well insulated tanks (bigger and heavier) and bring enough extra to compensate for losses or a refrigeration plant to keep the LH2 cold. Not only do the tanks need to be insulated, there must also be mitigation to keep ice from forming on the aircraft anywhere that could be 0° or less. It's a big issue with rockets since they can gain a significant amount of mass through water condensing and freezing on them.

6. #### Hydrogen?!

Hydrogen is dangerous. It leaks through everything, and it is flammable. The mass of something able to contain enough hydrogen to feed an engine for a long trip is not something an aircraft wants to carry around. The Hindenburg disaster is a hint that when things go bad with hydrogen, they go bad very enthusiastically. To quote NASA, "Liquid hydrogen must be stored at minus 423°F and handled with extreme care. To keep it from evaporating or boiling off, rockets fueled with liquid hydrogen must be carefully insulated from all sources of heat, such as rocket engine exhaust and air friction during flight through the atmosphere." Gaseous hydrogen needs a very strong container, or something that can adsorb or absorb the hydrogen - then release it. Both are heavy.

NASA uses liquid hydrogen (with great precautions) mostly in UPPER stages. Dealing with liquid hydrogen in a main stage only makes all the problems bigger. The Shuttle engines used liquid hydrogen, but they threw the fuel tank away before they reached orbit. Wouldn't want the leftover fuel close to the shuttle and its crew and cargo for the entire trip. Wouldn't want airplane passengers sitting on it either.

The only place I can see hydrogen being really useful in transportation is for a train, where weight is far less significant.

1. #### Re: Hydrogen?!

Trains do derail, and run into vehicles on level crossings.

1. #### Re: Hydrogen?!

There is a lot of difference between handling liquid hydrogen and compressed hydrogen gas.

Liquid oxygen is incredibly dangerous to handle but we still let people use oxygen masks in hospital

1. #### Re: Hydrogen?!

If oxygen masks used liquid oxygen, those hospitals would be more concerned with treating the freeze-burns of the victims. IIRC, the boiling point of oxygen is about -180°C.

You're right about liquid oxygen being dangerous though. One of the main dangers of using cryogenically cooled moisture-traps on vacuum-lines in chemistry labs (cooled by liquid nitrogen) is that if you open the line to the atmosphere and suck air through it, liquid oxygen will collect in the trap, and if you've got anything organic that has also condensed in there, it will try to blow you up.

2. #### Re: Hydrogen?!

I did mention that the containers for hydrogen gas had to be extremely sturdy, and were heavy. You might get by with an airship, where the hydrogen is (mostly?) not compressed, IF you are very very careful. Helium works in an airship, but we're having a helium shortage and really shouldn't be throwing it away in balloons (or ballonets). Reliable storage for a lot of hydrogen gas would probably weigh as much as the rest of the plane put together.

Hydrogen doesn't belong free in the air unless it is very dilute.

2. #### Re: Hydrogen?!

"Trains do derail, and run into vehicles on level crossings."

I see accidents at level crossings as the car/truck committing suicide. Sometimes it's complete stupidity like recently when a cop parked across the tracks and put somebody they had detained into the back of the car. I hope they did a drink/drug test on that cop.

2. #### Re: Hydrogen?!

Yes, but when hydrogen leaks, it doesn't continue to lurk as a potentially explosive cloud, but immediately exploits all the remaining defects and pores to mix with our atmosphere.

1. #### Re: Hydrogen?!

"Yes, but when hydrogen leaks, it doesn't continue to lurk as a potentially explosive cloud"

That wasn't the case at the TEPCO Fukushima power plants. H2 collected at the top of the building and went bang.

1. #### Re: Hydrogen?!

Nor was it the case at the Cambridge Electron Accelerator in 1965. I wasn't there when it happened, fortunately, but earlier (before filling) I'd been crawling around the LH2 bubble chamber. That thing was sturdy.

http://washuu.net/cea-bang.htm

3. #### Re: Hydrogen?!

"The Hindenburg disaster is a hint that when things go bad with hydrogen"

It certainly demonstrated that containing the H2 within a bag coated with Thermite was a really bad idea. That and the importance of electrical grounding safety.

4. #### Re: Hydrogen?!

"The only place I can see hydrogen being really useful in transportation is for a train"

Trains are the lowest hanging fruit for electrification. The tracks are fixed and installing overhead lines right next to them is not that difficult. A battery tender car could allow the train to bridge gaps where overhead lines would be difficult such as existing low tunnels and stations where many tracks criss cross each other.

7. #### Syngas sin

The first, conducted at the Swiss Federal Institute of Technology, found that synthetic gas (or syngas, a mixture of hydrogen and carbon dioxide) can be generated using only moisture and CO2 gathered from the ambient air and reformed in a high-performance solar radiation condenser.

Not quite. Syngas is hydrogen and carbon monoxide. Carbon dioxide is one of the feedstocks, and one of the products you get from burning it (along with water vapour), making it overall carbon-neutral (assuming the energy input is from a carbon-free source). Not quite as "clean" as burning pure hydrogen, as you can still potentially get soot if you burn too lean, but it does have the advantage that you can actually see the flame (pure hydrogen fires are invisible to the naked eye, which makes for them being a tad dangerous). Of course, breathing a mixture of hydrogen and air won't kill you like CO will either, so safety goes both ways. In general, it's probably best to keep using it as a chemical feedstock in industrial plants, rather than as a commodity fuel.

8. #### Syngas

Is H2 and CO (carbon monoxide). Could not find the link for corrections, sorry!

1. #### Re: Syngas

Previously known as Coal Gas. There's lot's of practical experience with handling that stuff.

9. #### Synthetic Kerosene is already 0.1% of the fuel being used in current aviation engines

A brief summary of "Germany opens world's first green kerosene plant", dwm dot com.

E-kerosene is a type of Sustainable Aviation Fuel (SAF) that can be blended with conventional jet fuel to bring down flight emissions - currently SAFs are mainly biofuels made from sustainable feedstocks, such as waste products or agriculture residues. Current engines can technically run on up to 50% sustainable fuel, but that's far from being a reality right now. SAF production is currently about 0.1% of the total aviation fuel consumed globally, according to the IATA.

The Atmosfair plant in Emsland, Germany, is aiming to produce carbon-neutral synthetic kerosene by combining hydrogen generated by renewable electricity (from nearby wind turbines) and sustainable carbon dioxide — captured from the air and biomass.  (Note: the electricity could just as well come from nuclear, and still be carbon neutral.).

E-kerosene is currently four to five times more expensive than conventional jet fuel. It's also energy-intensive to produce, requiring large amounts of green carbon dioxide and green hydrogen. Just powering domestic flights with e-fuels would require more renewable energy than Germany is currently able to produce. About 40% of the electricity Germany produces still comes from fossil sources; 45% comes from renewables, but much of that is diverted to help other sectors decarbonize.

However, the fact that "Just powering domestic flights with e-fuels would require more renewable energy than Germany is currently able to produce", even though renewables are 40% of current electric power supply, raises a question - To what extent is it because flying requires a huge amount of energy, and to what extent is it because the manufacture of SAF is inefficient?

Is the advantage of the described pure hydrogen engine that it greatly improves total efficiency relative to SAF?

10. Sadly all this hydrogen-from what nd.or waves is all a bit of nonsense: the energy density of waves or wind is ver y ver ylow compared to break oxygen-hydrogen bonds. So this means we need to build ridiculous qualities of wind farms (dumb because w eneed wind for other things like blowing pollen about to fertize crops, e.g. wheat and baey). What about waves? Argh: these are needed to oxygenate the shore line, so we have fewer dead zones. So hydrogen sounds good, but the production is awful. So we need ... nuclear, the only green power source with sufficiently high energy density to cut it.

This is the usual green-wash withering in that gives environmentalism a bad name.

1. Couldn't agree more. It's like all the graphs you see showing the increase in wind/solar energy over the last few years. What is it now, 20-something percent? People assume we just need to isntall more and this line will continue to increase. WHat they forget is that getting to 20% is not so difficult as that is about the percentage of the time these generation sources are producing. However, you cannot just extrapolate the curve forever upwards, as the wind and sun are not there a lot of the time.

As this gentleman says, nuclear is the only viable option. No emissions, 24/7/365 operation so extremely efficient with resources, including transmission line infrastructure utilisation, and extremely safe (safer than wind). Nuclear waste issue completely exagerated (need nuclear isotopes anyway for medical etc) and wwell contained. New generation of molten salt Thorium reactors surely need to be pushed agressively - much cheaper to construct, cheaper than coal to run and intrinsically safe (no possibility of meltdown, no danger of radiation leaks, no risk of explosions, no proliferation risk as doesn't produce plutonium) and can actually be used to burn the existing nuclear waste we have, including the UKs vast plutonium stockpile.

Solar and wind sound nice, but when you look into the detail both have huge flaws in terms of solving our need for CHEAP clean energy.

No one even questions what will happen to all the "solar panel waste". How will all the heavy metals and toxic chemicals from those be dealt with when they reach end-of-life? And yet people extol the virtues of that and won't even consider nuclear, and in particular the "new" variants of nuclear that solve the issues

Watch this https://youtu.be/N-yALPEpV4w

1. Most of the numbers supporting wind and solar are cherry picked from the best case scenarios and usually heavily averaged. Very sunny summer weekends when industrial use is low, very windy nights where overall use is low and averaging that skips over the glitches caused by patchy clouds. There are times when my solar drops 70-80% in a matter of seconds when a cloud goes over.

At least wind has some mechanical inertia. There should have been a requirement for even basic storage for any grid scale solar installation to aid with the sudden drops and peaks.

11. #### hydrogen as jet fuel

wouldn't helium be safer?

1. #### Re: hydrogen as jet fuel

And easier to detect if theres a leak... 'cos all the passengers will start squeaking.

2. #### Re: hydrogen as jet fuel

"wouldn't helium be safer?"

Sure! All you have to do is safely heat it up enough to push it out the back really, really fast.

12. #### Hydrogen is a pretty s**t energy store, unless you're a chemist

Either you chill it to -253c (yes that is very cold) or compress it to 5000psi (about 34MPa). BTW the USAF range safety teams rate any pressure vessel with multi 1000psi pressure in terms of lbs of TNT equivalent (that pressure alone stores a lot of energy, even if it didn't explode).

Roughly speaking however much the H2 stores it will take 3x that to a)Compress it b)Cool it.

And if you choose to make it from methane you increase CO2 emissions over just burning the regular dino juice. That option is total greenwash.

This does not bother chemists but engineers will know it's a massive PITA.

Technically the first jet engine (in Germany in 1938) was also the first H2 fuelled jet engine. The next generation was in the 1970s in the US. They are right that doing it with a modern engine is an impressive engineering achievement (given the vast difference in O:F ratio)

13. #### What about the nitrogen?

Burning hydrogen at high temperatures in the atmosphere is surely going to produce Nitrogen oxides, otherwise known as acid rain. This is not green.

If hydrogen is to be used to fuel aeroplanes, would it not be better to generate electricity from fuel cells, and power the propellers that way?

1. #### Re: What about the nitrogen?

Only if you burn it in your Mr Fusion™

2. #### Burning hydrogen at high temperatures in the atmosphere is surely going to produce Nitrogen oxides,

That's NOx

Or "Laughing gas"

OTOH burning Sulphur will produce sulphuer compounds that will cause "Acid rain"

BTW (specifically for H2) Reaction Engines solved the issues of low NOx combustion during the LAPCAT project about 17 years ago.

The trick (roughly) is to do a staged combustion, a very little hot, then the rest to produce a colder flame.

Alan Bond couldn't believe his team had managed it but the combustion simulation team assured him it was correct.

1. #### Re: Burning hydrogen at high temperatures ::snip for length::

NOx, a mix of NO (nitric oxide) and NO2 (nitrogen dioxide) is most definitely not N2O (nitrous oxide, or "laughing gas"), not by any stretch of the imagination.

1. #### Re: Burning hydrogen at high temperatures ::snip for length::

Yup, nitrogen and oxygen like to party together in various different ways. IIRC, nitrogen can happily form oxidation states from -3 (ammonia) right up to +5 (dinitrogen pentoxide). For most of these gases, you will not be laughing if you breathe them.

Nitrogen dioxide, for example, will react readily with water to form nitric and nitrous acid. Get any amount of that in your lungs, and there's no coming back.

1. #### For most of these gases, you will not be laughing if you breathe them.

Well, it's been a very long time since I've been in a chemistry lab.

I just know it as green house gas.

However my point stands.

Reaction Engines solved the NOx combustion issues for H2 in the LAPCAT programme in the context of a M5 commercial aircraft (The German entry promised M8 with keroscene using SCramjets. They couldn't make it work). The Reaction design countered the no-fly areas for >M1 (whose problem is IMHO greatly exaggerated once you look at the test conditions the USAF used for the original tests) by having a 20 000 Km range at subsonic speeds.

Reaction are also involved in a company to build the heat exchanger for a system to partly crack ammonia into an ammonia/H2 blend that is much easier to burn, with a view to both ship and aircraft engines, rescuing "stranded" assets that would be unusable otherwise.

When it comes to moving big lumps of stuff (IE container ships from China) batteries won't cut it and LH2 at -253c (or GH2 at 5000psi) is absurd.

For commercial aviation the big plane makers and the big airlines are going to need to make a choice because the regulations for dino-juice powered aircraft are going to tighten up.

14. #### No. Problem!

Liquid hydrogen takes up too much space and hasn't the energy density to get anywhere near jet-A and the like. Absent an entirely unexpected breakthrough in battery technology - well, physics trumps technology, so It's either 'sustainable aviation fuels' (problematic in their own right) or we need to pack in 95% of mass aviation. Or the earth is doomed. My money's on doomed, TBPH.

.

15. Hydrogen...blah blah blah...batteries...blah blah blah...renewable...blah blah...carbon neutral...blah blah blah...1.21 Jiggawatts...blah blah.

Whatever. When do I get my flying car? Flying cars were PROMISED, hydrogen-fuelled or battery-powered jetliners are just nice-to-haves. Can we set some priorities and focus, people? And maybe work on making the Dick Tracy watches not suck so much?

16. #### Burning hydrogen in a gas turbine is the easy bit!

Surely the problem here is not modifying a jet engine to be able to burn hydrogen instead of Jet-A. I have a camping stove that can do the same thing.

The big issue is the storage of the gas on a practical airplane. That is a problem of the extremely low volumetric energy density of hydrogen compared to Jet-A which means a suitable airplane what have to have enormous tanks. Plus also the fact that the tanks would need to be constructed to contain the liquid hydrogen, which means huge pressures and very low temperatures. Hence the impact of the tank construction will largely outweigh the mass advantage of hydrogen.

So, what has been done is the really easy bit. The hard bit remains, and may be impractical. A bit like fusion?.....

17. #### Not the First

This was done before in TU-155 (https://en.m.wikipedia.org/wiki/Tupolev_Tu-155). The problem with hydrogen is that it diffuses through solid metal. Because of this it can't be safely stored.

18. #### Not much of a first

The first stock turbojet to run on liquid hydrogen was in 1957 during Project Suntan.

See https://history.nasa.gov/SP-4404/ch8-3.htm (and Wikipedia)

19. "As for other recent green aviation moves, last year the UK government awarded a meager £700k (\$836k) to airports for future-proofing efforts."

More than outdone by allowing a 3rd runway at Heathrow

Boris promised he is going to be laying in front of the bulldozers to prevent that... oh no, he's jetted off on another holiday

20. #### £700k (\$836k) to airports for future-proofing efforts

like changing some bulbs to LEDs? Can't think what else they could use this staggering amount of cash on?

1. #### Re: £700k (\$836k) to airports for future-proofing efforts

Sea walls, and raising runways?

Most airports are on flat land, for some reason. And for some other reason, a lot of flat land tends to be low-lying (admittedly not all).

I suspect sea-level rise is a significant risk for some of these.

1. #### Re: £700k (\$836k) to airports for future-proofing efforts

You won't get many feet of seawall for 700,000 nicker

You won't even get a design study to lift a runway for that.

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