Leeham News and Analysis
There's more to real news than a news release.
Leeham News and Analysis
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- Boeing 2024 Proxy Statement: Executive Compensation includes retirement gifts for Calhoun, Deal; housing support for Ortberg, Pope, and other stuff March 17, 2025
- Bjorn’s Corner: Air Transport’s route to 2050. Part 13. March 14, 2025
Bjorn’s Corner: Air Transport’s route to 2050. Part 10.
By Bjorn Fehrm
February 21, 2025, ©. Leeham News: We do a Corner series about the state of developments to replace or improve hydrocarbon propulsion concepts for Air Transport. We try to understand why the development has been slow.
Last week, we reviewed the present fallout of lower emission projects that have not reached their goals and where investors, therefore, have decided not to invest further.
There is a well-known project failing every month at the present pace. Some recent ones: Universal Hydrogen’s ATR conversions, Volocopter and Lilium’s bankruptcies, Airbus freezing the CityAirbus eVTOL (Figure 1) and pushing out the ZEROe hydrogen airliner, hibernation of the Alice battery aircraft, etc. There will probably be more in the coming months.
Airbus’ way forward
Some of these projects stopped because batteries did not evolve as fast as expected. Still, most did so because their assumptions about the use and cost of present batteries and what was needed in terms of energy for operational flights were just naive.
There is no point in taking an airline flight of 100-150nm unless you live in an archipelago. More is not possible with present batteries when all factors are considered (bad weather, headwind, safety reserves beyond the legal ones, etc.).
The one technology that can enable longer flights is the exchange of the kerosene fuel for hydrogen, as the hydrogen has three times the energy content per weight unit (and aircraft are hypersensitive to weight). We looked at the Hydrogen Fuel Cell option in Part 8 and concluded that while it has true zero emissions (producing water), it has limitations in engine size and power.
I was at the Airbus 2024 results conference earlier in the week, and there, Airbus CEO Guillaume Faury said that it had chosen the Fuel Cell path instead of Hydrogen burn for its ZEROe airliner project. At the same time, he said that the present technology (including Airbus’s own fuel cell project) would not produce a commercially viable aircraft with present technology. With that, he meant that the air transport performance would be too low in relation to its operating costs.
The technological development inside Airbus around fuel cells for aircraft applications will now continue for another 10 years, with a plan to produce a viable aircraft using fuel cells to drive electric motors and propellers on the far side of 2040.
Hydrogen Burn
Airbus has concluded that the hydrogen burn alternative, where a turbofan’s core is converted to burn hydrogen instead of Jet-A1, is an alternative that Airbus will not pursue further. Why was not given.
It could be because hydrogen burning in a gas turbine core produces NOx emissions, though at a lower rate than for a Jet-A1 burning core.
It could also be that Airbus realizes it’s prudent to start a hydrogen-fueled airliner project outside the hot single-aisle segment, where about 2,000 aircraft per year will be delivered in the 2040s. A fuel cell machine will come in at about a 100 seater Turboprop in size and performance, well different from the A320 series and its successor in size and speed.
Introducing an alternative propulsion architecture in the segment that pays the bills of the industry, can lead to major disruption and confusion. Such an aircraft can’t be ramped to scale anytime soon after its introduction, but it can upset programs running at 50 to 75 units/month (i.e., two to three aircraft produced per day), and that is not what OEMs want to happen.
We will probably not find out anytime soon what the real deciding factor behind Airbus’s decision to go for fuel cells is. But it’s a bit of an irony that as Airbus decides on fuel cells, the hydrogen burn alternative announces its most interesting development in 10 years: the US Department of Energy’s ARPA-E sponsored Pratt & Whitney HySIITE project.
HySIITE is a long-term project that changes how hydrogen is burned in a gas turbine. Such a process produces a lot of water (more than the Jet-A1 burn process), which has, to date, been expelled with the gas turbine’s exhaust.
HySIITE changes this. It uses the water to improve the hydrogen burn process in a major way. How we will cover in nexts weeks Corner.
Bjorn; do fuel cells obey the same rules as gas turbine engines in that the hotter they run and the higher their internal pressure then the more their thermal efficiency?
That might explain Airbus’ decision to abandon hydrogen propulsion in a gas turbine. Being less energetic per unit volume than kerosene, perhaps they need much higher efficiency to get the volume of the hydrogen tank down.
No, that’s not the case with proton exchange membrane fuel cells. They don’t follow the brayton cycle.
One intricacy is that they like to be at their optimum temperature, and so cooling becomes an important consideration.
The main problem with hydrogen is the process to produce Green hydrogen at scale. This require processes outside Airbus domain, like massive wind power parks at sea with hydrogen production and pipelines to end users with processes to make LH2, consuming lots of electrical power. So Airbus can wait for the heavy truck industry to solve those problems. To burn hydrogen in converted gas turbines is much easier.
Hydrogen production by electrolysis at large scale seems to be a very big problem ,despite everyone saying how incredibly easy it is.No one seems to be willing or able to explain why it hasn’t happened
It’s not lack of demand,because it would be able to easily act as a battery using existing technology and it is being expensively produced from gas at the moment
Lots of work by top universities in catalysers to reduce energy for hydrolysis, still no windmills at sea that produce H2 in volume and feed pipelines. For natural gas pipelines above a certian class mixing in H2 is not a problem like in the US Hyblend project. Some development in “H2 Extraction from Hydrogen-Enriched Natural Gas (HENG) using Membrane Technology” that would make H2 supply to airports easier. You can design windmills just to produce H2 and not care about frequency/power matching and have electrolysis that can use the windmill max power at strong winds. Without government help nobody want to go first and loose money until the market and technology is there for the banks to jump in.
There is a lot of work on using ammonia is a hydrogen carrier. You can have direct combustion of ammonia in engines and gas turbines although that requires a lot more R&D. Production can be done at scale and transport is known. But the big problem is toxicity. You need almost perfect combustion for the exhaust gasses to be non toxic and leaks are also a big issue. The long distance shipping industry has this as a high priority even though the fuel volume increases by a factor of 4 compared with heavy diesel.
Toluene is also a promising hydrogen carrier, but unlike ammonia you need to ship the depleted carrier back to the H2 generation location.
I see this a a circular situation where there is no escape from the loop.
Its the tyranny of Hydrogen storage and that assumes all the other problems with procuring hydrogen are solved (making hydrogen, transporting it, storing it on site). Unlike Jet A, there are losses and costs in keeping it chilled (a Jet A pipeline cost is the pump).
Fuel cells are interesting and in the right application, can work.
But you have the issue of requiring an Alternator and while not huge, add in the Converters to make that electrical power useful.
The larger your electric drive motors (at least two if not 4 for safety) the bigger the generator (alternator).
Said generator can be supplemented by battery but that is a large fixed weight.
And the on board Hydrogen storage problem does not go away and it requires a tube and doomed ends as well as insulation. Only place to put it is the fuselage.
This is a good read on using LNG in ships. The offsets have to work for the economics as the tank takes a lot of space out of your build, ie, it has to be bigger for the same size transport of containers.
https://gtt.fr/sites/default/files/container_shipping_and_trade_-_cma_cgms_newbuilds_feature_integral_bunker_tanks.pdf
And that is a direct drive ICE system
What about Eve and their evtol ? They’re on Target for prototyping and first flight, along with an ecosystem softwares for ATC. Sure this is for short distance flights, but yet, electric driven with thousands already ordered.
Maybe they know something nobody knows & will succeed delivering all the eVTOL’s ordered. Or maybe not.
All of them were on Target for prototyping and flight, some actually flew (until they crashed financially).
Frankly the one I am impressed with is an anathema to the issue, aka Boom.
they flew a private jet at over Mach 1. Never been done. Of course their prototype looks nothing like what they propose.
Stay tuned
Collier Trophy stuff, still the big Overture with brand new own developed engines is of a different scale engineering- and money-wise to get certified. Just getting the engine inlets working efficiently and safely over all flight conditions is a multi million dollar adventure without own wind tunnel.
Actually a Global 7500 flight test aircraft exceeded Mach 1 during several flight tests a few years ago as part of the Global 8000 development program (per the following article it was in a shallow dive and Mmo will be 0.94M but the aircraft was intentionally flown supersonic nonetheless):
https://www.ainonline.com/aviation-news/business-aviation/2022-05-23/bombardier-global-8000-takes-speed-range-crowns
Based on what is known of the Global 8000, the flight test aircraft was fully representative of the final product 😉
Do agree that Boom has achieved an impressive milestone but they are a very long way from certifying, manufacturing, delivering and supporting a commercial airliner!
For boom, the issue is the entire airframe is different, engine location, shape.
I have to wonder if the test article was just to prove they could do Mach + as opposed to any transfer to a Mach 1.7 or whatever the current goal is.
Maybe the control laws transfer. Kind of multi aspects as pre transonic, transonic and then sonic all have their own characteristics, control wise as well as flow.
Nothing about it is emissions reducing! Flys (pun) in the face of the efforts to reduce.
I think one reason at least must be efficiency.
The EKPO NM12 stack (a version of which is being tested in ZEROe through the Aerostack GmbH company) gets efficiency from tank to output of 50%. The current bleeding-edge of turbine cores would do extremely well to get above 35%. Whilst the conversion losses on the back end of that system are usually cited as killing any benefits, I think Airbus’ recent excited press releases about super-conducting motors and power conditioning likely suggests they feel that is less of an issue.
Besides, fuel cells have a theoretical limit of like 80%, which leaves plenty of room for development whilst gas turbines are now butting up against thermodynamic limits. In a world where the size of your tank determines the saleability of the design, more efficiency = more range = more payload.