Leeham News and Analysis
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Leeham News and Analysis
- Bjorn’s Corner: New engine development. Part 4. Propulsive efficiency April 19, 2024
- Boeing unlikely to meet FAA’s 90-day deadline for new safety program April 18, 2024
- Focus on quality not slowing innovation, says GKN April 18, 2024
- Boeing defends 787, 777 against whistleblower charges April 17, 2024
- Dissecting Boeing CEO’s statement next new airplane will cost $50bn April 15, 2024
Bjorn’s Corner: The challenges of hydrogen. Part 32. Wrap-up: Going forward
By Bjorn Fehrm
April 9, 2021, ©. Leeham News: Last week we made a summary of the history of initiatives for sustainable aviation, now we look at the likely developments over the next 10 years.
What is the likely development for different classes of airliners and what technologies will be popular?
Sustainable aviation over the next 10 years
In the week, another project, the Britten-Norman Islander Fresson project, abandoned trying to make a retrofit hybrid-electric propulsion system work and changed the project to a hydrogen-based aircraft. When working through an operational system, including safety precautions and redundancy, the project found the plane consumed the same or more carbon fuel than the engines it should replace.
I’ve been writing about this reality for over three years, and it’s now catching up with more and more projects. So what is the path ahead? The Fresson project, which is for a 10 seater, will go for gaseous hydrogen.
It’s noteworthy, ZeroAvia which started with a gaseous hydrogen fuel cell system and has flown a Piper Malibu demonstrator, converts to liquid hydrogen for the fuel cell system it’s developing for 50 seater turboprops. The gaseous hydrogen demands too much space once the range requirements grow.
Universal Hydrogen addresses the same market with its retrofit fuel cell project but stays with gaseous hydrogen. Airbus, looking at a range of airplanes from 80 seats and larger, is firmly in the liquid hydrogen camp.
Developments until 2030
We shall first realize Sustainable Aviation Fuel, SAF, will be an essential part of de-carbonized air transport. The number of aircraft that will be qualified for SAF will grow, and we can foresee that no new airliners will be developed that will not be certified for running on SAF.
SAF is also the only viable alternative for long-range aircraft. The problem is how to produce sufficient SAF for the worlds’ 20,000 to 30,000 commercial aircraft?
The feed-stock, be it bio-mass, fat waste, or syngas production with different processes starting with CO2 and H2O, is not sufficient to deliver SAF to all these aircraft. We need a complement, and the only viable alternative at present is hydrogen.
Do we need UAMs?
For extreme short-haul, like UAMs, batteries work. But these vehicles are not the most environmentally friendly solution for short-haul transport. There are other, better alternatives like trains and road transport where green energy solutions are already available.
The main segment
The bulk of all air transports today are made with 100-200 seat aircraft flying routes between one to two hours. This will extend to 220 to 230 seats over the next 10 years, but the travel time will not change.
About two-thirds of the airliners that fly every day is of this type. This is where a hydrogen solution fits, liberating the available SAF for the segments where hydrogen does not work.
What to expect
So what will be the steps we can expect until 2030? We can expect the first prototypes flying with fuel cells and liquid hydrogen before 2025. The first demonstrator with gaseous hydrogen feeding a fuel cell has already flown, ZeroAvia’s Malibu last year.
We shall understand this was a short demonstration flight with one person onboard a test aircraft filled with gas tanks and fuel cell gear, driving an electric motor, far from something operationally viable. This experience has enabled ZeroAvia to go forward with a 1.6MW system for a 50 seat turboprop, with market entry by 2026.
Airbus is already active with component tests for a fuel cell propulsion system, as are others. We can expect an ATR 72 size demonstrator to fly mid-decade, latest, at the Paris Air Show 2027.
Based on the results of the ground tests over the following years and the flying demonstrators, we will know if the first commercial aircraft larger than 50 seats will be turboprops or jets, and if these jets will address the sub 150 seat market or the heart of the market, the 180 seaters.
One area that must go forward for all the hydrogen projects to be viable is the hydrogen-producing ecosystem. Without it, the airliner projects will fail. How the ecosystem develops or not, we look at next week.
“”SAF is also the only viable alternative for long-range aircraft””
Depends on the weight of the LH2 tank. If the LH2 system has an weight advantage, it will benefit long range even more.
LH2 engines should also be much cheaper.
The industry should get away from the monsters, big planes and long range. Instead it’s much easier to design smaller planes for long range and use them point to point.
Easy to increase MTOW on the A319, A320, MAX7 which will result in over 5000nm range.
“Instead it’s much easier to design smaller planes for long range and use them point to point.”
Thats what 1960s planes were like and airfares were 5x what they are today.
Twin aisles with large fan engines mean cheaper airfares.
The issue is not weight, it is space.
H2 is lighter that jet fuel, but it has lower volumetric density.
The size of the tanks needed for such a long flight will require something like a A380 where all the upper deck is a gigantic LH2 tank.
In this series the LH2 tank is supposed to be very heavy, but since LH2 is less dangerous the tank must not be so heavy.
If the fuselage diameter is big the LH2 tank can be short and the space is less of a problem.
Weight can cause a CG problem which is lower if the tank is shorter and lighter. Less weight will make it more economical.
There is some serious errors involved.
Original Travel Fares: this was a limited travel era. It also was regulated. Costs were very low in those days (labor, fuel) – between the various aspects, fares were high but that is an apples to pineapples comparison. Freddy Laker proved that.
I had one trip that I flew from AK to Puerto Rico on under $400 due to a rare route sales opening in those days.
Hydrogen Fuel Tanks: They have to be heavy enough to contain the Hydrogen and they are not amenable a wet wing which means fuselage and space taken up.
If Bjrons written has been read at all, or the EU program on this, a single aisle A320 type is the immediate goal and its RANGE limited.
So, even if the route worked, you are not going to fly from Atalanta to Rome with this bird unless you have an aircraft carrier mid Atlantic (more like two of them)
There is a reason Single Aisle have displaced some VLCA and there is a reason the 757 is no longer needed as the LCA have range and capacity and more so in the A321.
A Hydrogen A320 as I recall would have at best half the range of a kerosene A320.
But equally, JAL opened a Narita (or Tokyo) to San Jose/Boston with the 787. Call it quasi hybrid point in that it was a large hub to a no hub vs Okinawa to those two destinations.
Leon, that is discussed in parts 5 and 6
https://leehamnews.com/2020/08/21/bjorns-corner-the-challenges-of-hydrogen-part-5-the-hydrogen-tank/
https://leehamnews.com/2020/08/28/bjorns-corner-the-challenges-of-hydrogen-part-6-tank-placement/
And a nice quote from part one:
“It has some very attractive features like three times higher energy density than jet fuel (batteries have 70 times worse) but also challenges like four times worse volume density and a non-existent production ecosystem for air transport.”
https://leehamnews.com/2020/07/24/bjorns-corner-the-challenges-of-hydrogen-part-1-background/
Airbus’s spokesman espoused Liquid hydrogen for medium haul jets but noted that SAF “Sustainable Aviation Fuel” was the only option for long haul.
Airbuses thinking is to put the liquid hydrogen in the tail in a spherical or cylindrical tank. Bjorn has done to the calculations in past corners that show that the Centre of Gravity shift is too small to destabilise the aircraft in medium haul flights since although liquid hydrogen is bulky it is also about 1/3rd the weight of jet fuel. Putting the hydrogen above the fuselage may be acceptable from a safety or engineering point of view but I feel it presents impenetrable psychological problems for customer acceptance. Integrated LH tank engine pods was another option.
I suspect the thinking at Airbus is that SAF hydrocarbon fuels when made from agricultural waste biogas or through Power to Liquids from capture of unavoidable carbon dioxide emissions will be affordable but there won’t be enough resources for it without turning to Direct Air Capture of CO2 for PtL Power to Liquids synfuel. As this is possibly more expensive cryogenic hydrogen can be used to operate medium haul while leaving enough SAF hydrocarbon fuel at low enough prices for long haul.
Price wil be key. These fuels will be expensive so the airline industry must compete. I can easily see a system where a business traveller checks in bags on an eVTOL urban port like Volocopter or Lilium jet in their pleasant suburb to fly to a landing port on the secure side at a Very Fast Train station all checked in. If aviation becomes expensive, trains look cheaper and if they are 300km/h trains that take one to the heart of the city or where there is another eVTOL port then they are not too slow for a 1000km journey.
” Instead it’s much easier to design smaller planes for long range and use them point to point.”
Ha,Ha.
You are definitely not an engineer.
The smaller the plane the higher the penalty for structure.
Contrary to Boeing’s PR P2P over long distance is about the most inefficient way to go.
Sure, the smaller plane has a penalty per seat, but you will not get to many points with a widebody.
The advantage of a long range widebody is the nonstop flight. Small planes are not designed for long range, they need one stop.
But if your destination is a small city you need a stop too and change the plane because the widebody will not fly to that small city. If your starting point is a small city either you will have two stops and need to change the plane twice to fly with the widebody, while the small plane still only needs one stop and only for refueling.
Long range widebodies burn much fuel only to carry more fuel for the nonstop flight. Small planes don’t have this fuel penalty because they take one stop.
Two A320neo burn less fuel than one 787-8.
P2P has advantages if not flying between big cities.
“Two A320neo burn less fuel than one 787-8”
The 320neo burns 2.8 kg/km, while the 787-8 burns 5.2kg/km; but the 320neo has a 20t max payload, while the 787-8 can carry 43.3t – so the 320neo burns 140g/t/km, while the 787-8 burns 120g/t/km (and the -8 is the shrink, not the more efficient 787-9/10).
A widebody is more efficient per t of payload, we often forgot the cargo payload and focus on the pax efficiency. A short-range widebody would be even better, but the range is needed for transoceanic networks. The concurrence in air transport is humbling, if there was a magic trick to be 5% more efficient than the competition, it would be used. The current situation (outside pandemic times) is certainly close to the optimum.
The weight issues is entirely dependent on the range.
There is a break point where the heavier weight of a twin aisle pays back in no fueling stops.
That in turn also is related to route allowed as fuel stops require compromised routes adding costs of distance as well as the fuel stop.
They are chipping at the edges but a wide body still works and no single aisle can carry the passenger numbers the distance a wide body can.
There is a trade off at the extremes where Singapore carries all of 170 some passengers to New York in an A350 which puts it into Single Aisle territory.
Equally Single Aisles when they add aux tanks for range have to give up passengers to do so.
Marc,
your fuel burn assumptions are wrong.
The 787-8 can’t carry so much payload on long range.
You forgot something else, OEW:
787-8 120t with some help from the marketing fools
A320neo 45t x 2 = 90t
On short range, how can the 787-8 compensate for a 30t OEW penalty.
If a widebody would be so good on shorter range, nobody would buy the XLR.
If the XLR had 110t MTOW and with it more range, nobody would buy the 787-8.
Leon:
While not common that is wrong.
Japan has a history of long range wide body in domestic short range service.
China has done some of that with the A330 Regional setup.
Its due to slot availability and China has airspace limited as the military owns it all.
United I believe uses 787 coast to coast US.
A 787 can carry a full pax load 6000+ miles and an A321 cannot even in the XLR setup.
TW,
slot restrictions are a point, but that’s poor management of the country. Countries should get away with big airports and instead use more smaller airports. Much time could be saved and then nobody would use widebodies on short range anyway.
Also the turn around time of widebodies is longer. Instead of one 72m E gate, two 36m C gates could be used, it seems it is poor management of the airport, Of course enough runways are needed, but that shouldn’t be a problem with more smaller airports.
I don’t think there is a structural disadvantage to a small airframe. Just perusing some numbers suggests that one factor is that the larger aircraft are operating at higher wing loadings, using that to carry more fuel but pay a penalty in runway length. There seems to be a minor advantage in wetted area and certain overheads like cockpit space. The A321XLR with a range of 4700NM and the proposed Irkut/Sukhoi MC21X with a range of 5300NM suggests twin engine narrow bodies might start challenging twin aisle aircaft. The MC21 uses an aisle wide enough for a passenger to pass a luggage trolley thus nulling one supposed advantage of big aircraft: getting to the toilet during meal service,
It is interesting that some folks and Governments seem to have determined (prematurely in my view) that hydrogen will be cheaper than carbon neutral PtL Power to Liquids synfuel or SAF fuels made from biogas obtained from agricultural waste and the vast amount of industrial and as yet partially collected domestic food waste. A Dutch study found that Holland’s agricultural waste could make enough biogas that if converted to jet fuel would be sufficient for Hollands entire aviation needs. Furthermore the CO2 from the fermentation itself can be a feed stock for PtL.
At present we would be lucky to produce hydrogen at 90% efficiency using unproven solid oxide technology and to convert it to a cryogenic liquid at 80% efficiency (using theoretical te4hnology) to achieve 72% efficiency.
The coelectrolysis of CO2 and water to produce syngas combined with Fischer-Tropsch synthesis produces jet/diesel fuel at 65% efficiency according to Sunfire. This is not the only company looking at coelectrolysis. Others have found Fischer-Tropsch catalysts that directly produce fuel from CO2 & H2. These of course require a concentrated source of CO2 but this can be obtained from unavoidable emissions such as fermentation, biogas production, cement and aluminium plants etc. Finally DAC direct air capture is moving along as well though it drops efficiency from 65% to 45% in the case of amine absorbers. There are many other kinds of absorbers under development both wet(alkaline) and dry (amine) as well as units that absrobe on to novel alloys and are very efficient and ion exchange from water (where CO2 is concentrated 134 times atmospheric levels)
So how do we know cryogenic hydrogen is the solution? It seems even Airbus is hedging both ways. It will be an extremely expensive route and Governments often get it wrong. Synfuel through the PtL Direct Air Capture route may be less efficient but it has other cost advantages and in addition can work through capture of unavoidable emissions.
Of course they may have determined that both will be needed.
My feeling is that Direct Air Capture of CO2 will prove itself in the next few years and greatly impact the need for cryogenic hydrogen fuel for flight. In addition use of concentrated CO2 will also evolve.
William:
All good points and partly this all gets mixed into existing structure so that we really do not know what the real costs are (and that is ture with Fossil Fuel when tax structure and lack of cost adder in what its environmental impact is)
You can have very short term great prices at a massive impact (which we are seeing now, its 5 Deg F here this AM and that is record setting for this time of the year and worse up North)
EU: Keep in mind this is an EU creation, not Airbus. Airbus is taking the money because its there and part of the politics in Europe.
What they acualy believe they won’t say.
And yes, Boeing would do the same.
I certainly agree that the general public don’t know what the real costs are in many cases. Renewable electricity costs are certainly faked down for public consumption by producers and a willing politicised media quoting the load levelized cost of production and not the cost of connecting them to a network (transmission loses due to distances and stabilization measures , which are extremely high for renewables approximately doubles/trebles costs, something not the case with conventional generation.
Nevertheless I expect when Renewable Energy is used to generate Hydrogen or PtL synfuel rather than transmit electricity these costs will no longer be such a factor since production of the fuel will be near the RE source and the electrolysers can simply be turned down.
But as Bjorn points out a hydrogen-producing ecosystem must exist. Without it, the airliner projects will fail.
The below studies given some costs for SAF PtL synfuel obtained from direct air capture The first reference gives prices in US$ barrel equivalent ($85 to $135/barrel) and the other gives prices in centrs per KWHr of product. (A Litre of jet fuel contains 8.5kW.Hr/Litre).
Basically Production costs will be around $0.50-$0.75 per litre for the first study to about $0.80-$1.20/L for the second. I’ll let you do the conversions as I know you are good at maths. Since existing fossile fuel has a cost that has sometimes exceeded $85/barrel the differential is not too great.
Liquid hydrogen would seem to require only 60% of the energy to produce as PtL carbon neutral synfuel. It will of course be a lot more expensive to handle but I’m sure the technology can be made to work. It would be perfect for say Dublin to London, Stockholm Munich, LA Seattle.
https://www.sciencedirect.com/science/article/pii/S1876610216310761
https://www.lbst.de/news/2016_docs/161005_uba_hintergrund_ptl_barrierrefrei.pdf
“The first demonstrator with gaseous hydrogen feeding a fuel cell has already flown, ZeroAvia’s Malibu last year.”
Before that, Boeing converted a 2-seat Diamond DA20 to run on a fuel cell, first flown on April 3, 2008.
And even Before that, the Tu-155 flew without a fuel cell on 15 April 1988, and there was an inflight experiment of a Martin B-57B in February 1957.
Thankyou Marc, you always make a succinct & positive contribution, I’ve learned much. Compressed hydrogen based flight with fuel cell electric propulsion is interesting way forward for general and light aviation. The infrastructure and technology being developed for Toyota’s MIRAI (now with BMW) would be completely applicable and also work with ground handling vehicles. A small airport used to maintain a daily connection to an island or a remote mine site might even generate its own hydrogen with an electrolyser powered by roof top solar.
OT. BAC quality issues. Boeing grounds some Maxes for an electrical issue.
“The affected airlines should verify “that a sufficient ground path exists for a component of the electrical power system” on certain Max planes, Boeing said. ”
https://www.nytimes.com/2021/04/09/business/boeing-737-max.html
The good news is they are not being given 5 years to fix this.
One of the ugly secrets of aviation is they often find issues, some are critical as MCAS 1.0 where the pilots have to adjust from training to alternatives to deal with and they are given 5 and 10 years to correct.
Both the Norwegian 787 out of Rome were bad engines. The one that failed time wise was the “better” bad engine. If the one close to the line had failed we would have had a crash.
We should not even allow ONE bad engine on an aircraft.
India dealt with that with the P&W GTF when they tried to go with a known failure prone engine. They ruled that it aircraft had to have two good engines to fly, period. Hurah!
Some better detail here.
https://www.chicagobusiness.com/manufacturing/boeing-grounds-dozens-737-max-jets-electrical-flaw
Post build grounding and quality control strikes again.
Someone will need to design a plane where the LH2 tanks are long tubular structural members. As long sa people look at the tanks as added dead load it will be no-go.
I could imagine a large single aisle/small twin being built like this because of the trade offs in range, passenger capacity, fuel load, and efficiency.
Now we just need to make the H2 using electrolyzers and renewable power …..
Yes one way is to start the aircraft structure with a long LH2 tube as a keel beam and build it from there. Another is finish the structure with a long tube on top of the fuselage a bit like the small ones on Mirage 2000 or on the F-100. You have conformal fuel tanks on some fighters not all good locking (F-16)
A sphere minimises surface area to volume ratio. This minimises boil of, the amount of tank material, plumbing and insulation required. It’s all a trade of.
Tip for next column: Look at Plug Power and DOE’s Airport Ground Handling Equipment project. A lot of the H2 for Plug’s business is distributed as LH2. So applicable for part of the supply chain for LH2 aircrafts too.
Link?
UAM’s might be popular with busninessmen once they are autonomus flying to meetings at factories, banks, politicians, suppliers, logistic hubs, customers each having a small italian designed helipad with charging on the lot or the roof. Their size can be 1/2 of the once found on luxury yachts. Most likley with a skybar where the top dog can entertain while wainting for ATC clearance to jump in, buckle up and press the OK button to autofly a few miles to the next meeting..
Your ‘way forward’ is backward to a world lit only by fire.
https://www.amazon.ca/False-Alarm-Climate-Change-Trillions/dp/1541647467/ref=sr_1_1?crid=30DNAFRS08O26&dchild=1&keywords=false+alarm+bjorn+lomborg&qid=1618069790&s=books&sprefix=False+Alarm%2Caps%2C236&sr=1-1
https://www.amazon.ca/Fake-Invisible-Catastrophes-Threats-Doom/dp/B08TFYJFMR/ref=sr_1_1?dchild=1&keywords=Fake+invisible+catastrophes&qid=1618069995&s=books&sr=1-1
https://www.amazon.ca/Toxicity-Environmentalism-George-Reisman-ebook/dp/B00RZUJ5OU/ref=sr_1_9?dchild=1&keywords=george+reisman&qid=1618070008&s=books&sr=1-9
Dear Bjorn, has a canard configuration similar to Boeings “Sonic Cruiser” or SAAB Viggen been considered? The LH2 tanks could be placed over the rear main spar area.
Sorry Bjorn, I just can’t resist the last comment in https://www.avweb.com/features/reader-mail/top-letters-and-comments-april-9-2020/.
“Sounds like a lot of methane to me.”
(Think about it.)
Second to last is one good perspective: “Fuel is fuel. As long as it is available, high energy:mass ratio, cheap, safe, who cares?”
(Many of the comments show ignorance. Hey! its pilots, some of who need to go back to ground school. 😉
The solution will come from where the greatest investments are made. Taking H2, and building facilities for chilling, compressing, transporting, storing and using H2 may be more expensive that chemically reacting H2 to liquid fuel and then using existing fuel infrastructure.
Investment into Power to Gas (P2G) is at much larger scale than developing H2 aircraft and may produce an easily transported fuel because it is part of a much larger issue than aviation.
Electricity production costs are falling (solar/wind) and smaller nuclear plants with high burn-up, or waste re-processing are also receiving significant investment.
In time, the capital costs of designing and certifying a new fuel solution for aviation will be greater than the “losses” involved in producing SAF. Re: Climate, best bang for buck right now is replace the most carbon intensive producing elements and while aviation has an image issue, there isn’t a cost effective solution that will not involve leveraging existing investment into sustainable fuels.
Slightly off topic, but an interesting article that shows the dangerous scapegoating that’s starting to arise in the climate discussion:
“The world’s wealthy must radically change their lifestyles to tackle climate change, a report says.
It says the world’s wealthiest 1% produce double the combined carbon emissions of the poorest 50%, according to the UN.
The wealthiest 5% alone – the so-called “polluter elite” – contributed 37% of emissions growth between 1990 and 2015.”
https://www.bbc.com/news/science-environment-56723560
An interesting comparison that you’ll never see in reports like this is that a motorcycle used for 4 hours per day produces as much CO2 as a large car used for 2 hours per day. Seeing as motorcycles are the predominant mode of transport in developing countries, the authors of this report need to rethink their headline conclusions.
Also interesting: a “non-elite” who lives 75km from work and who commutes on weekdays to work in a mid-sized single-occupancy car produces the same annual CO2 emission as someone who flies from Europe to Australia and back 2.5 times in a modern jetliner with a high load factor. Again, you won’t find this type of comparison in this report.
Aviation has a public relations problem in terms of emissions and so the issues you raise are relevant.
Unfortunately most of of us in the hard technical fields are not educated in the science and art of public opinion forming (call it manipulation). Unless the industry becomes savvy and reacts appropriately it will suffer. Humans are hierarchical social primates and will use any means including moral manipulation to gain resources. Virtue signalling, establishing moral superiority, blaming, scapegoating, claiming victim status are all part of this.
The down side of this blame/victim culture is that the focus becomes not about up lifting the “have nots” but bringing down the supposedly guilty “have too muchs” to take from them. You can see that the ‘wealthy” are so often hapless western middle classes struggling under a mortgage. Meanwhile some of the wealthiest people that ever lived wrap themselves in the tokens and symbols of social justice and equality to protect themselves while throwing the middle class under the bus as it were.
The focus needs to be on solutions and uplifting everyone, not blaming or bringing down others which is often about taking from one group to give to ones own without actually changing the cause of unequal living standards.
The zero emission solutions are EV, FCEV, hydrogen, SAF/PtL fuels, renewables, nuclear and on the other side an elimination of corrupt dysfunctional systems in some countries that are the true cause of have nots.
The true issue there is that nations with retarded economic development naturally cause less emissions and hence they must transition directly to low emissions technologies while developed nations transition over to those same technologies.
In the meantime a good understanding of public opinion forming is needed. I suggest a reading of UVA psychology professor Johnathen Haidts “The righteous mind” and Saul Alinsky’s “Rules for Radicals” to see how the world works.
The industry must not cave in. No one must cave in to manipulation.
The answer is to produce sustainable wealth for all not blame and take and bring down.
In case anyone is still reading these comments at this late juncture:
The Port of Amsterdam is investing in a SAF production facility that will produce 50,000 tons of SAF per year (using green electricity) and transport it to AMS airport by pipeline. A key reasoning behind this move:
“The current generation aircraft engines require liquid fuels. These aircraft engines cannot switch to alternative energy sources such as hydrogen or electricity in the short term. SAF is, therefore, the solution to drastically reduce CO2 emissions in aviation. This aviation fuel is known as a ‘drop-in’ fuel, meaning that pure SAF can be mixed with fossil kerosene. No further modifications to infrastructure or equipment are required. It is a clean, liquid alternative to fossil kerosene.”
https://news.schiphol.com/synkero-builds-facility-in-the-port-of-amsterdam-producing-sustainable-aviation-fuel-from-co2/
I have a question: Why is not the Syngas to “JetA1” path more attractive than Hydrogen. What I understand is the energy required to make Syngas from Water / CO2 less than making hydrogen from H2O. And the current infrastructure and equipment can be used to the end of its economical life.
I suspect that the syngas route is not popular because it does not involve huge subsidies to industry like with the Hydrogen path. Also the idea that the fossil JetA1 still can be used is a red curtain.
With Power to Liquids Synfuel the technology we have least experience with is Direct Air Capture of CO2. It obviously can be done and has been done but need to go through bigger scale pilot plants. Electrolysis is mature from the 1920’s when Norsk Hydro and Canadian hydro electric producers used it to make hydrogen for fixation into ammonia. The rest of the chain (syngas production, fischer-tropsch, etc) is understood. Climworks has been operating DAC via amines coated on to ceramics. Other techs involving absorption of CO2 onto aqueous hydroxides and their liberation via electrodialysis etc are less understood. Issues exist around water use. I suspect cryogenic hydrogen will be made via expensive Baltic Sea wind power locally and some from SAF from capture from industrial processes but SAF will come from for instance cheap renewables from Wind Farms and Solar on the Australian coast (there is a 50 billion project to do this) because its so much easier to transport. The shipping industry looks like it may use Ammonia with MAN diesel promising to have duel fuel 2 stroke ammonia and diesel engines. Energy will be exported via ammonia, Power to Liquids and Hydrogen.
But how much energy to take the further step of ‘syngas’ to aviation kerosene?
Need to include all the steps from H2 to the output energy provided at the point of use
At the moment compression and liquifaction seems to be about 70% efficient but there are approaches in the pipeline to reduce this to around 3.2 kWh / Kg or 90%. Methanation of H2+CO2 to Methane is 70% efficient (so similar), and new approaches can reach nearly 90%. https://www.frontiersin.org/articles/10.3389/fenrg.2020.570112/full
There is an additional step required after methanation, one process known as STG+, this has losses of ~40% (so 60% efficient). However, aircraft are sensitive to volumetric efficiency as well as mass efficiency. Liquid fuels have other benefits that offset the lower efficiency in producing them.
Looking at the whole path from H2 to end-use, there are more losses with H2 as the molecule is small. The idea of using natural gas infrastructure for H2 could result in high losses; H2 losses are recognised with dedicated H2 pipeline and storage facilities.
The jury is out whether producing chemically similar fuels, vs adapting to a new H2 fuel is going to be the best option. There is a lot of research in this area for obvious reasons. Fuel cells are not as far advanced as batteries … not redesigning the entire aircraft base is an obvious benefit of a chemically similar fuel…
And over the hills, at least from Scott, someone may use wasted water energy to make hydrogen: https://www.seattletimes.com/seattle-news/it-was-an-old-apple-orchard-now-it-could-be-the-future-of-clean-hydrogen-energy-in-washington-state/
(‘well water’ sounds like an editing botch, plenty of water in the river at the Wells Dam that will produce the electricity.)
And Warren Buffet may be happy about the prospect of making hydrogen from coal, as he is big into it as well as into transporting it: https://www.powermag.com/doe-backs-projects-to-produce-hydrogen-from-coal-biomass/
(BTW, the relatively small Wells Dam may be unusual in that it often has to spill water in the spring, and there are complications with that. Production of hydrogen might be variable with time of year, snow pack, and melting rate.
The maker of its trial hydrogen production unit, Cummins, is well known for diesel truck engines. It has natural gas conversion models of its heavy truck engines.))