Rolls-Royce Tests Hydrogen-Powered Jet Engine
 

"The ground test, using a converted Rolls-Royce AE 2100-A regional aircraft engine, used green hydrogen created by wind and tidal power, the British company said on Monday. Rolls and its testing program partner easyJet are seeking to prove that hydrogen can safely and efficiently deliver power for civil aero engines. They said they were already planning a second set of tests, with a longer-term ambition to carry out flight tests. Hydrogen is one of a number of competing technologies that could help the aviation industry achieve its goal of becoming net zero by 2050."


https://www.reuters.com/business/aer...ne-2022-11-28/

Jet engines can almost burn anything, that's easy. The Army even ran a main battle tank on peanut butter once (creamy I presume).

The challenges are:

1. Fuel supply/storage infrastructure. That can solved, at great expense
2. Need actual green power to generate the hydrogen, otherwise it's pointless. That can be solved too. Eventually.
3. Finding the volume onboard aircraft to store the H2 fuel. H2 requires a LOT more volume than Jet A. This is the real hard part, going to need a total redesign of longer-range transport aircraft, basically a blended wing-body or even full flying wing. For short regional flights (like really short) you can use current wing and tube designs.

Yes, H2 is lighter (better specific energy) than jet fuel but the energy density is terrible... the extra aircraft structure to provide the storage volume cancels out any weight benefit, and then some.

Also, keep in mind, with the size of H2 it finds leaks where every other test fluid passes. Water, air, even helium can test good. Then H2 leaks.

Just look at launches scrubbed, at Cape Canaveral, with fuel leaks. They are common.

That part is manageable since airplanes don't need to remain fully fueled for extended periods like days, weeks or months. The ground storage infrastructure would leak a little bit but that would be a cost of doing business.

The big leaks which scrubbed those launches were not caused by H2 molecules, they were caused by mechanical sealing problems which were likely due to cryogenic temps... that would be a technical problem for airplane fuel but I'm sure it can be solved. I think NASA's current problems are caused by NASA, not by H2. Shuttle used H2 for several decades.

Sorry for lack of clarity.

In electrical power plants, H2 is used for cooling the stator of the generator. After all the welding of the metal is complete, pressure tests with Air and then He are done. Any leaks corrected. Then H2 is introduced. Several leaks with H2 are found that were not found with He. This is typical.

In my previous life, I have witnessed this first hand, on the construction site.

H2 lower flammability limit is 4%. It is not how much fuel leak is tolerable, for cost of fuel losses. It is how far away from the leak it can be set off by a spark or other ignition source.

Unlike Jet A, it requires no vaporization. Unlike methane (CH4, natural gas) H2 is much more susceptible to getting out through tiny leaks.

Wonder if an a380 freighter would be viable with the upper deck refitted as a giant fuel tank

Yes H2 will leak... I suspect the only practical solution which could hold up to the rigors of aviation will be a an exterior shell around tanks and probably lines and fittings, which is vented overboard with an appropriate airflow (fan on the ground, ram air when airborne). Not really hard or expensive, but another weight and complexity factor which chips away at the practical utility of H2.

For the freighter, Google says 17 pallets up top, and 28 on main deck. Total cargo volume 1134 m^3.

Rough swag: 17/(17+28) = .38 upper deck volume ratio.

.38 x 1134 = 428 m^3

Assume you could use 80% of upper deck volume for fuel volume after accounting for for fuel tanks, MX access, and associated hardware: .8 x 428 m^3 = 343 m^3

Liquid H2 specific density = 71kg/m^3.

71 * 343 = 24,000kg H2

Liquid H2 energy density = approx 36,000 W*h/kg

24000 * 36000 = 864M W*h worth of energy on our upper deck.

A380 carries 320,000 L of Jet A (energy density 9,800 W*h/L):

320,000 * 9,800 = 3.136 Billion W*h

864M W*h H2 / 3.136B W*h Jet A = 27%.

So not quite 1/3 of the Jet A range. So the math says it's suitable for domestic ops, but not much long haul. Maybe barely transatlantic?

Yes you save some weight since Jet A is a lot heavier than H2 but you're going to use up a lot of that weight savings on the fuel tanks for liquid H2 since (unlike Jet A) it cannot be stored in the aircraft structure directly. You don't save much structural weight by ditching Jet A, since that lives in the wings and fuselage... both of which you still need. You might even need to add ballast to the wings since a heavy fuselage with light wings will result in additional cantilever stress on the wings (that's why we burn center/aft tanks first).


*** Disclaimer: Feel free to check my math, I did not bother.

On electrical power plants, once all the leaks are fixed, they do not have leaks in use. That is the more practical solution. They do not use a secondary containment that is vented, as you suggested as a possible solution. Getting them tested and fixed are a real pain, though. It feels like they are chasing spook dust.

My guess is dynamics of flight would cause small leaks to pop up over time, hence needing a vented containment. Maybe somebody will come up with a leak-proof system which will last 30+ years and 100,000+ airframe cycles.

The containment doesn't need to be high tech, or metal. With sufficient flow, it doesn't need to be perfect either, just prevent more than trace H2 concentrations in the shroud. Old engineering refrain: Dilution is the Solution.

We are just going to disagree on that. Remember, a gas is contained by a pressure vessel, not a tank. Pressure vessels are much thicker. As a result, they are more robust and less prone to impacts of flight dynamics. Metal fatigue is tested for periodically, just like structural integrity metal fatigue of the plane.

I'm looking at four welding tanks that are across the room from me. Pressure Vessel vs tank is semantics.

There are very light pressure vessels, and tanks that will hold insane pressure.

Liquid Hydrogen is kept liquid by keeping it COLD, How cold? Keeping it cold is easier/lighter than keeping it compressed to a pressure where it will have similar energy density. It is practically impossible to compress hydrogen to the density of liquid hydrogen in large quantities in anything light enough to fly. Hence why LH2 is the preffered way to fuel rockets.

Liquid Hydrogen boils at sea level pressure at 20K That's 20 degrees above absolute zero. -423F if you want to put it into Fahrenheit units.
If you aren't going to be using it faster than it boils off, you do need a way to vent it.

What do I know, I just worked with cryogenics for years. Have a fancy degree with letters after my name and before it if that matters.

I would suspect that the more likely source of leaks would be the plumbing not the tanks. But assuming we are talking about liquid H2 it actually doesn't have to be a pressure vessel at all, it could just be a tank that's vented for boil-off pressure relief.

Space launch vehicles tend to use pressure vessels because the pressurized tank is an integral structural component of the rocket. They also use near paper-thin walls, and it only needs to work once (for traditional expendable boosters).


For clarity I've been talking about liquid H2, pressurized gaseous H2 I don't think is practical for large airplanes...

Too little pressure and you can't carry enough. Too much pressure, and the weight of tank becomes impractical. And those points would overlap.

Pressure Vessels vs. Tanks. A lot of lay people say the difference between a jet engine and a piston engine is just semantics. You and I know that is incorrect. Just like gassing up a jet plane is not correct.

Pressure Vessels are most often designed to ASME VIII. They are designed, tested, and stamped for a Maximum Allowable Working Pressure, generally above 15 psig.

Tanks are designed to hold the static head of the liquid and a few inches of water column pressure (a fraction of a psig). They are entirely different design codes.

Big difference. Again, the lay person intersperses words that they think are fine, but are clearly incorrect.

Liquid Hydrogen or Gaseous Hydrogen still has the same size H2. They leak through exactly the same size holes.

Liquid Hydrogen boil off is like LNG boil off. Liquified Natural Gas (LNG) is dropped to -260F in its liquifaction process plants, on shore. It is then moved by ship, long distances. The ships use LNG as boiler fuel. Nothing keeps it cold, other than insulation, once it is in the storage vessels of the ship. As it boils off, the gaseous natural gas is used or is vented. There is nothing to reliquify it, once on board. When more is needed for boiler fuel, they have heat exchangers to use sea water to vaporize the LNG.