Airbus A380 hydrogen engine flying test bed

[Stan]

This is obviously being taken seriously.

[Moxi]

Not sure it is being taken seriously - the amount of money being thrown into this is miniscule in "big oil" terms.

No matter what they do, they cannot ignore physics and the fact that hydrogen is NOT an energy dense fuel, thus (and roughly speaking) your average 737 carries 26 cubic meters of kerosine fuel. The same plane with hydrogen would only carry around 4.3 cubic meters. Significantly lighter by around 22 tonnes BUT not only a volumetric range reduction but also an energy range reduction because where Kerosine has an energy density of 34.69MJ/Litre, Hydrogen only has 5.6MJ/Litre so a further massive range reduction on energy yielded. Burning Kerosine and Hydrogen in air is relatively similar with a max efficiency of around 25%.

So to put it another way, the energy content of 1 Nm³ hydrogen gas is equivalent to 0.34 Litre Kerosene, 1 Litre liquid hydrogen is equivalent to 0.27 Litre Kerosine and 1 kg hydrogen is equivalent to 2.75 kg Kerosene (approximate).

Compressed hydrogen is the answer we may hear some say? Yes, you can compress Hydrogen but its a cryogenic operation and therefore prohibitively expensive and I cannot see anyone building the infrastructure needed to provide the worlds cryogenic aviation fuel without them wanting a return on their investment, making flying the realm of the wealthy once again.

All that aside and assuming cryogenic hydrogen fuel becomes readily available can you imagine the bang if a fully fuelled hydrogen plane ever crashed?

Moxi

[dan_b]

Here's an idea on decarbonisation of aviation -

For short-haul flights, replace routes with high speed rail, BEVs and small EV planes.

For long-haul, meanwhile, focus on fully electrifying the land transport fleet with BEVs

Then divert the biofuel that currently goes into petrol blends for the now non-existent petrol car fleet demand, and use that to replace fossil-derived kerosene.

And ensure all ground service equipment is fully electric.

THe idea of powering passenger jets with H2 is just beyond idiotic.

[Oldgreybeard]

The Toyota Mirai runs its storage tanks at 700 bar. At that pressure a 1m³ tank can hold about 42kg of hydrogen, so just under about 1.4MWh per m³ of storage volume.

A 1m³ tank of Jet A1 holds about 808kg on average (density varies a bit for Jet A1 from batch to batch) and that gives about 9.6MWh of potential energy.

If they are serious about hydrogen for aviation fuel then even if they increased the efficiency of whatever propulsion system they use so it was 100% efficient at converting potential energy into kinetic energy there is still a massive shortfall.

[Countrypaul]

What are they actually looking at when using hydrogen propulsion they are testing? Research often starts with very inefficient approaches, but once something is working it can oftem be make more efficient quite rapidly. Often the outcome of research is not predicted especially by those not directly involved and can have bebeficial side products.

A normal jet engined plane appears to use 100% power for take off, but <50% for cruising, and almost nothing for landing. The takeoff phase lasts 5-15 minutes, where as the cruising can last hours.
If using batteries / fuel cells electric motors to largely power a plane, then using hydrogen jets to aid take off, allowing smaller electric motors and batteries/fuel cells might be a step forward. Using an A380 as a test bed may largely to check how a hydrogen powered jet engine performs and look at aspects that have not been / can not be tested except in the air.

The testing with an A380 should be viewed as research and not as tying to produce a hydrogen powered A380 no matter how uch we would like to see that.

[Oldgreybeard]

Not sure about other types, but a twin turboprop I used to fly cruised at MCP (maximum continuous power) and take off/go around power was maybe 15% more. My single engine light aircraft used to cruise at around 80% of full power. I would guess that 50% as a most economic cruise power is significantly lower than the vast majority of commercial aircraft operate at. The high cruise power requirement is one of the major issues with hybrid aeroplanes being a bit of a non-starter, as unlike cars aeroplanes just don't have that very ratio between average cruise power and peak acceleration power. Not surprising, as drag uses almost all the power from an aircraft engine, and drag is at its highest at cruise speed.

[Paul_F]

Umm.... so I work for one of the companies involved in this (in a different but not-unrelated project), so I'm going to have to be a bit careful what I say here:

• It's using cryogenic hydrogen, not compressed or held as a hydride. That's vastly lighter than other technologies, and also has immense system benefits in some architectures.
• Don't focus too much on volumetric energy density. Current jets are optimised for very dense fuels, changing the design to carry less weight of a bulkier fuel around isn't all that hard. Essentially you end up with less induced drag and a bit more friction drag - if you do your sums right you come out ahead.
• Hybridisation is being looked at in parallel to hydrogen burning, on different aircraft testbeds. The open fan engine being tested with the same partners on another A380 is a hybrid. There are significant fuel burn savings from hybridisation, even if you don't carry any batteries on board.
• Light aircraft and turboprops have different throttle settings to jet airliners - for them the maximum power us usually defined by airport noise abatement. That's actually rarely used (compare taking off at London City to Heathrow), but is essentially the sizing point for the engine and thus has impacts on cruise efficiency. Hybridisation means you don't have to rely on the thermal core for peak take-off power.