Hydrogen Jet Engine

[Forest Green]

View: https://www.youtube.com/watch?v=qmrWFX5b9ts

 

[FighterJock]

I am all for Hydrogen powered aircraft engines especially when they have just discovered green hydrogen in the north of France under ground and there seems to be enough to last for a good number of years, it would be better than trying to manufacure hydrogen with all the problems that it currently has.

 

[Justo Miranda]

The eternal temptation of hydrogen returns again with the monotony of a season. They will never learn.

 

[FighterJock]

With modern technology that they never had back in the past I am certain that Hydrogen engines that we have now will be much safer.

 

[Byeman]

With modern technology that they never had back in the past I am certain that Hydrogen engines that we have now will be much safer.

Safety with the engines was never the issue. It is the logistics involved with H2

I am all for Hydrogen powered aircraft engines especially when they have just discovered green hydrogen in the north of France under ground and there seems to be enough to last for a good number of years, it would be better than trying to manufacure hydrogen with all the problems that it currently has.

There is no "reserve" of hydrogen that was found. It is just a plan to produce H2 using electrical power generated by green sources.

 

[sferrin]

View: https://www.youtube.com/watch?v=qmrWFX5b9ts

Welcome to 1957.

ch8-9

https://www.secretprojects.co.uk/threads/lockheed-cl400-suntan.7228/

 

[Zoo Tycoon]

If LH2 becomes the predominant aviation fuel commercial air travel will only be affordable by a tiny minority of the wealthy people. The laws of physics mean that simple frequent/routine maintenance operations, normally taking minutes or hours will take days…… who pays for that?

H2 is only an energy store, the energy contained still has to be fabricated….. from what I can tell most costing models ignore this inconvenience. The U.K. is building a massive 40 billion $ nuclear station. If London Heathrow used LH2 produced from nuke it would need three to four of these say 150 billion spent before operating cost and the first 1Kg of LH2 has been dispatched. Who pays for this?

And the sad reality is H2 inherently leaked from even this operation will cause as much global warming today’s Carbon fuelled civil aviation operations;- its nearly impossible to stop it leaking.

 

[Archibald]

Hell yes. CL-400 Suntan... That old weird paradox of hydrogen: far more energy for jet engines and on paper a far better fuel, BUT - a colossal PITA to store, at every level: density, temperature, explosivity... it has everything against it.

 

[Archibald]

If LH2 becomes the predominant aviation fuel commercial air travel will only be affordable by a tiny minority of the wealthy people. The laws of physics mean that simple frequent/routine maintenance operations, normally taking minutes or hours will take days…… who pays for that?

H2 is only an energy store, the energy contained still has to be fabricated….. from what I can tell most costing models ignore this inconvenience. The U.K. is building a massive 40 billion $ nuclear station. If London Heathrow used LH2 produced from nuke it would need three to four of these say 150 billion before operating cost and the first 1Kg of LH2 has been dispatched. Who pays for this?

And the sad reality is H2 inherently leaked from even this operation will cause as much global warming today’s civil aviation operations;- its nearly impossible to stop it leaking.

I knew storage and handling of LH2 sucked immensely, but its production seems to suck as well...

 

[Scott Kenny]

*gasp, wheeze*

No, hydrogen is NOT going to be the aviation fuel of the future. Density sucks, 1kg of liquid hydrogen is still 14.8 liters volume. And then you get to deal with all the other fun that comes with handling deep cryogenic materials.

Synthetic kerosene is the likely winner, AKA Sustainable Aviation Fuel. Maybe butanol, the contest really comes down to costs of production and storage (and documentation, since this is aviation related). It took something like 14 years to get unleaded avgas approved with full STCs and any mix % between 100LL and 100UL allowed, so that the flight ops people can just top off their avgas tank with 100UL and not worry about it. 100UL STCs are something like $10/hp from the STC holder, you put your aircraft info into a website and print off the STC as soon as the credit card info goes through. $2000 for most single engines, obviously lots more for warbirds with 1500+hp.

 

[Forest Green]

Well, it's not like the first EV wasn't invented over 140 years ago.

A brief history of the electric car

While many consider electric cars to be a relatively new invention, the first vehicles were produced and used in the early 19th century.

energysavingtrust.org.uk

 

[FighterJock]

And we all know what happened to the EVs after they were invented 140 years ago the rival combustion engine took over and sadly replaced them, things could have been very different if the EV had been properly marketed as an alternative then things would have been very different today.

 

[Byeman]

And we all know what happened to the EVs after they were invented 140 years ago the rival combustion engine took over and sadly replaced them, things could have been very different if the EV had been properly marketed as an alternative then things would have been very different today.

Not really. It had nothing to do with "marketing". It was technology - batteries. They didn't have the storage capacity. Plus the micro electronics to monitor them.

 

[green.nova343]

Reminds me of a recent news story about supposedly non-petroleum-based synthetic jet fuels, where some company was advertising it as the "future" for their airline...but the costs involved were going to cause ticket prices to go up by a factor of 10 (minimum) compared to regular airline tickets for the same destinations, because the fuel is so expensive to manufacture.

 

[Justo Miranda]

https://en.as.com/latest_news/why-did-nasa-cancel-the-artemis-i-mission-for-the-second-time-n/

 

[Scott Kenny]

Reminds me of a recent news story about supposedly non-petroleum-based synthetic jet fuels, where some company was advertising it as the "future" for their airline...but the costs involved were going to cause ticket prices to go up by a factor of 10 (minimum) compared to regular airline tickets for the same destinations, because the fuel is so expensive to manufacture.

Currently, yes, SAF is (expletives deleted) expensive. Get more people making it to increase production volumes means you can get economies of scale involved. Process flow chemistry instead of step by step.

Again, biobutanol or a similar fuel is another option that is relatively simple to make (e.Coli bacteria, for example), and can be manufactured from yard waste and all the other stuff that normally is just burned off the fields.

 

[green.nova343]

Economies of scale can run into issues, however, if there are a lack of materials to use.

I see that SAF can be made with used cooking oil. Great, sure, we make a lot of fried food in the world...but how much of the oil used in cooking -- not just in restaurants, but in homes -- is actually recycled? How much will it cost to collect the cooking oil that is currently not recycled, which then will be incorporated into the cost of SAF?

As for making SAF from plants...I'm not sure about the long-term effectiveness of turning plants (which turn CO2 into O2) into jet fuel to lessen the amount of CO2 in the atmosphere. I suspect that you'll reduce more CO2 in the atmosphere by planting more plants & trees than by substituting plant-based jet fuel for petroleum-based jet fuel...

 

[Byeman]

Economies of scale can run into issues, however, if there are a lack of materials to use.

I see that SAF can be made with used cooking oil. Great, sure, we make a lot of fried food in the world...but how much of the oil used in cooking -- not just in restaurants, but in homes -- is actually recycled? How much will it cost to collect the cooking oil that is currently not recycled, which then will be incorporated into the cost of SAF?

Very little deep frying actually happens in the home, and even less now with air frying

 

[green.nova343]

That would depend on the household, as the current per-household usage of air fryers is still extremely low (apparently 0.03 worldwide)...& I would imagine that would probably vary regionally (for example, in countries with less efficient or less reliable electrical grids, the market penetration of air fryers is going to remain extremely low, but frying over gas or wood flames would still be available). You're also assuming a binary of "everything is deep-fried" vs. "everything is air-fried without oil". There's also the pan-fried option -- which is how you prepare, say, bell peppers & onions for use with fajitas, pan-fried chicken, etc.

Then there's also the other biofuels that will be fighting for that used cooking oil. Every biofuel wants used cooking oil, & I doubt the biodiesel makers are going to give it up to help make SAF costs go down.

 

[Byeman]

That would depend on the household, as the current per-household usage of air fryers is still extremely low (apparently 0.03 worldwide)...& I would imagine that would probably vary regionally (for example, in countries with less efficient or less reliable electrical grids, the market penetration of air fryers is going to remain extremely low, but frying over gas or wood flames would still be available). You're also assuming a binary of "everything is deep-fried" vs. "everything is air-fried without oil". There's also the pan-fried option -- which is how you prepare, say, bell peppers & onions for use with fajitas, pan-fried chicken, etc.

Then there's also the other biofuels that will be fighting for that used cooking oil. Every biofuel wants used cooking oil, & I doubt the biodiesel makers are going to give it up to help make SAF costs go down.

We are talking US households, ones that can participate in recycling.
Panfried does not produce quality nor the quality of oil worth saving. Sautéing foods like peppers and onions is usually with olive oil or butter and leaves no remaining oil to reclaim.

 

[Scott Kenny]

Economies of scale can run into issues, however, if there are a lack of materials to use.

I see that SAF can be made with used cooking oil. Great, sure, we make a lot of fried food in the world...but how much of the oil used in cooking -- not just in restaurants, but in homes -- is actually recycled? How much will it cost to collect the cooking oil that is currently not recycled, which then will be incorporated into the cost of SAF?

As for making SAF from plants...I'm not sure about the long-term effectiveness of turning plants (which turn CO2 into O2) into jet fuel to lessen the amount of CO2 in the atmosphere. I suspect that you'll reduce more CO2 in the atmosphere by planting more plants & trees than by substituting plant-based jet fuel for petroleum-based jet fuel...

You do not have to use biodiesel processes to make SAF. In fact, I'm pretty sure you DON'T WANT to use biodiesel processes, due to the high gel temperatures that biodiesel has. Let the ground transportation folks use biodiesel.

 

[green.nova343]

SAF isn't being produced exclusively in the US...or did you not realize that? The US is also not the only country that has people flying on airliners, nor are they the only destinations that people fly to. Of the top 5 companies currently producing SAF, #3 through 5 are not located in the US -- Oriental Energy Co. (Singapore & Indonesia), Alfanar Group (Teesside, UK), & UPM Biofuels (Finland). I seriously doubt any of those companies is importing their used cooking oil from US sources. Nor is the US the only nation that engages in recycling of used cooking oil -- a simple Google search found this company that has offices in multiple European nations as well as Egypt, for exampel.

Nor is olive oil the only oil used -- some people don't like the taste (and yes, there is a difference in canola oil vs. vegetable oil vs. olive oil vs. butter) -- & the amount of oil used will vary from person to person, so a blanket statement of "no oil will remain" is disingenous. And again, just because oil usage is low in US households doesn't mean that oil usage is also low in other countries. Some countries treat cooking oil as its own food group.

And I see you also completely ignored the part where I pointed out that SAF isn't happening in a vacuum, with other biofuels competing for the same limited resource. When demand exceeds supply, you don't get "economies of scale", you get higher prices for the oil...which means higher prices for SAF. Airline fuel usage is at most maybe one percent of that used by the trucking industry, so the demand from non-airlines is going to be much higher than that of the airlines...which either means a) their supplies of SAF will be limited (probably keeping prices high), or b) they'll have to pay a premium to outbid the other users demanding used cooking oil for their biofuels (which, again, will keep SAF prices higher).

 

[Byeman]

Nor is olive oil the only oil used -- some people don't like the taste (and yes, there is a difference in canola oil vs. vegetable oil vs. olive oil vs. butter) -- & the amount of oil used will vary from person to person, so a blanket statement of "no oil will remain" is disingenous. And again, just because oil usage is low in US households doesn't mean that oil usage is also low in other countries. Some countries treat cooking oil as its own food group

Wrong. Pan frying doesn't require large amounts of oil (more than a cup)
And the amount for sautéing is in the tablespoons.
The blanket statement that "no oil will remain" is spot on because any remaining will not be of quantity (daily or weekly) to merit the infrastructure required to gather it for recycling. Only deep frying generates those amounts. Few home buys oils in those amounts (More than a liter per week). I had work in both fast food and grocery store stocking.

The point is that there isn't enough to gain from domestic recycling.

Again, talking from a US POV. And it doesn't matter about the rest of the world, home collection wouldn't significantly affect the recycling amounts.

 

[Scott Kenny]

SAF isn't being produced exclusively in the US...or did you not realize that? The US is also not the only country that has people flying on airliners, nor are they the only destinations that people fly to. Of the top 5 companies currently producing SAF, #3 through 5 are not located in the US -- Oriental Energy Co. (Singapore & Indonesia), Alfanar Group (Teesside, UK), & UPM Biofuels (Finland). I seriously doubt any of those companies is importing their used cooking oil from US sources. Nor is the US the only nation that engages in recycling of used cooking oil -- a simple Google search found this company that has offices in multiple European nations as well as Egypt, for exampel.

Nor is olive oil the only oil used -- some people don't like the taste (and yes, there is a difference in canola oil vs. vegetable oil vs. olive oil vs. butter) -- & the amount of oil used will vary from person to person, so a blanket statement of "no oil will remain" is disingenous. And again, just because oil usage is low in US households doesn't mean that oil usage is also low in other countries. Some countries treat cooking oil as its own food group.

And I see you also completely ignored the part where I pointed out that SAF isn't happening in a vacuum, with other biofuels competing for the same limited resource. When demand exceeds supply, you don't get "economies of scale", you get higher prices for the oil...which means higher prices for SAF. Airline fuel usage is at most maybe one percent of that used by the trucking industry, so the demand from non-airlines is going to be much higher than that of the airlines...which either means a) their supplies of SAF will be limited (probably keeping prices high), or b) they'll have to pay a premium to outbid the other users demanding used cooking oil for their biofuels (which, again, will keep SAF prices higher).

Again.

You do NOT WANT to use biodiesel processes for SAF, biodiesel gels at flight temperatures!

Good SAF is made from other processes.

 

[green.nova343]

I never said they were using the same process. I said they use the same raw material. Just like you can't fill your tractor-trailer's tank with jet fuel, but both diesel & jet fuel are currently both produced from petroleum: same raw material source, different products after refining.

 

[Scott Kenny]

I never said they were using the same process. I said they use the same raw material. Just like you can't fill your tractor-trailer's tank with jet fuel, but both diesel & jet fuel are currently both produced from petroleum: same raw material source, different products after refining.

Different processes use different raw materials. I'm talking about Fischer-Tropsch process, Bergius process, and others. Not, say again NOT BIODIESEL!

Biodiesel is not jet fuel! Any fuel made from plant oils gels at too high a temperature to be usable in aviation.

 

[green.nova343]

Again, I never said "put biodiesel in jet engines". What I said was that both fuels use the same raw materials.

If you have two companies that both use a specific kind of timber, with one making furniture out of it & the other making homes, they're making two separate products but from the same raw material....& if the supply of the resource is limited and isn't enough to meet the demands from both manufacturers, then the price for the supply will go up, as will the products, & neither manufacturer will be able to make as many items as they want...unless one of them is willing to pay even more money for exclusive access to the limited supply of that critical resource.

That's basic business, economics, & accounting, all rolled into one. Biofuels -- whether SAF, biodiesel, or other types -- all need the same raw materials, regardless of what process is used.

And FYI...Fischer-Tropsch process may have been invented for coal gassification, but that's not what they're using for SAF...they're using the saw "biowaste" that is used to make biodiesel. And there are zero plants using the Bergius process (the last one, which only produced 200 tons a day, was closed by Germany in 1993) -- which only used coal (& not the "good" coal either). And coal-to-liquid isn't any cleaner than petroleum-based gasoline...again, it requires "biomass" to provide any significant drop in CO2 emissions. That same biomass raw material, though, is also sought by the other "biofuels" like biodiesel. Again, though, I am NOT SAYING THAT BIODIESEL IS SAF & CAN BE PUT INTO AIRCRAFT ENGINES. I'm saying that all biofuels -- SAF, biodiesel, & others -- need the same raw materials. Again, supply & demand: limited supply of a specific resource & higher demand for said resource means higher prices for the finished product, not lower prices, & also puts an upper limit on how much "economies of scale" you'll ever get from it.

Even if you intensified recycling efforts, setting up drop stations for "biowaste", scouring landfills & trash sites, etc., that will still require more money being spent to collect the materials. Because no one is going to take the job of crawling through garbage dumps looking for materials to toss into a F-T reactor without getting paid...& since no one is doing that right now (or at least not on the scale needed), that means the expenses for the raw materials go up (since procurement & transportation are part of those costs). And if you scale up procurement before you scale up production capacity, then you have to spend money to store the rotting garbage...which will be even more expensive since you'll have to store it safely so that it doesn't contaminate the environment & water supply.

So it's not as simple as you think it is.

 

[Archibald]

To me SAF cannot be the definitive answer. Only ammonia, or - more pointedly - ammonia cracked into hydrogen, in flight: to get more energy (since ammonia is only 0.5 the energy of kerosene, but hydrogen is 2.5 or even 2.7 so maybe there is a right "in between" to be find)

 

[Byeman]

Just like you can't fill your tractor-trailer's tank with jet fuel,

JP-8 - Wikipedia

en.wikipedia.org

 

[Scott Kenny]

Again, I never said "put biodiesel in jet engines". What I said was that both fuels use the same raw materials.

If you have two companies that both use a specific kind of timber, with one making furniture out of it & the other making homes, they're making two separate products but from the same raw material....& if the supply of the resource is limited and isn't enough to meet the demands from both manufacturers, then the price for the supply will go up, as will the products, & neither manufacturer will be able to make as many items as they want...unless one of them is willing to pay even more money for exclusive access to the limited supply of that critical resource.

That's basic business, economics, & accounting, all rolled into one. Biofuels -- whether SAF, biodiesel, or other types -- all need the same raw materials, regardless of what process is used.

WRONG! They all use different raw materials!

The Fischer-Tropsch Process uses Carbon Monoxide and Hydrogen from whatever source. Could be wood gas, coal, whatever. DOES NOT REQUIRE waste vegetable oil. https://en.wikipedia.org/wiki/Fischer–Tropsch_process

The Bergius Process was designed around coal, but can just as easily use charcoal from renewable sources, with the addition of some extra catalysts that are naturally present in coal. DOES NOT REQUIRE waste vegetable oil.

Bergius process - Wikipedia

en.wikipedia.org

Biobutanol uses yard waste, corn stalks, wheat chaff, sawdust, etc if produced by E.Coli, or needs sugars from whatever plants if produced by Clostridia (not my preference, but has higher yields without extensive selective breeding or genetic engineering of E.Coli). DOES NOT REQUIRE waste vegetable oil.

Butanol fuel - Wikipedia

en.wikipedia.org

 

[green.nova343]

If the F-T process doesn't use biomass, the resulting fuel emits MORE CO2 than petroleum-based fuels...which would go completely against the whole purpose of producing SAF. It's ONLY when the F-T process incorporates biomass that the resulting SAF emits lower CO2 levels when burned.

It's also why non-biomass feedstocks are NOT the primary sources for SAF.

IATA (International Air Travel Authority) statement regarding SAF

 

[Scott Kenny]

If the F-T process doesn't use biomass, the resulting fuel emits MORE CO2 than petroleum-based fuels...which would go completely against the whole purpose of producing SAF. It's ONLY when the F-T process incorporates biomass that the resulting SAF emits lower CO2 levels when burned.

It's also why non-biomass feedstocks are NOT the primary sources for SAF.

IATA (International Air Travel Authority) statement regarding SAF

Right. But look at WHAT BIOMASS is being used. "Biomass" is not only vegetable oil.

All three can use sawdust, corn stalks, wheat chaff, etc as their sources. All waste products from either lumber or food production. Or you can start growing things like bamboo for turning into fuel. Grows quickly and can be harvested often.

 

[green.nova343]

The crop from bamboo, just like any agricultural product, is going to vary depending on the climate & region. And as with any kind of replacement of the existing ecosystem to focus on cultivating a particular crop, you'll run into that if you start slashing forests to plant bamboo. Not to mention the 2-3 year leadtime to get your new bamboo grove established before you can start harvesting it -- & it looks like once per year (not multiple crops) is what you'll get.

As with everything when it comes to agriculture, there is no "miracle cure", no "this solution will fix everything". There's give & take in everything, & bamboo isn't just something that you can slap into the ground & let grow. It needs deep, neutral-to-slightly-acidic soil, lots of oxygen, plenty of water without overwatering (unless you pick the right subspecies), & apparently at least 3 sets of fertilizer per year. So saying "we can just use bamboo" is like a solar power enthusiast saying "we can just build batteries for when the Sun isn't shining enough"...

 

[Scott Kenny]

So? Harvesting 10k acres of bamboo annually is better than harvesting 10k acres of lodgepole pine every 20-30 years.

Plus it's not a food crop, so no driving up the price of lots of different foods because gooberment just created a huge new demand for feed corn and sugar beets.

Again.

SAF is not using waste vegetable oil. Save that for the buses.
SAF can use organic waste like sawdust.

Hydrogen keeps getting proposed for aviation fuel, which gets some research dollars and flying prototypes, which never get translated into money-making commercial aircraft. Because the fuel storage takes up the entire aircraft!

 

[green.nova343]

Neste Oyj (Finland): uses vegetable oil to make SAF
UN Climate Change (self-proclaimed) "Champions": story of an Airbus A380 that used SAF made from cooking oil to power one of its engines for a 3.5-hour flight
Japan Times: Japanese manufacturers of SAF running low on the used cooking oil they need
Honeywell press release: partnering with Oriental Energy to build a plant that refines used cooking oil into SAF

So far, there weren't that many companies I found that specifically says they DON'T use cooking oil. DG Fuels (plants in Louisiana & Maine), for example, says they use wood products such as sawdust. However, their current annual production (75,000 gallons) is much, much less than the 120 million gallons that they claim they'll eventually get to, which led Air France-KLM to partner with them...the only problem being that in 2022 AirFrance-KLM used 2.34 BILLION gallons of jet fuel for its flights (1 gallon = 6.7lbs). 120 million gallons would literally be a drop in the bucket (~5% of their annual fuel usage). Note that same source says that was the "pure" jet fuel; SAF only contributed another 42,000 metric tons, or ~13.8 million gallons (~0.6% of their current usage). And...while they aren't cutting the trees down, even though they're using the wood waste that might not otherwise be used, they are still depending on trees being cut down for their supply of raw materials.

As for UPM Biofuels, they're using "crude tall oil" -- which is a byproduct of wood fiber separation for pulp production, & therefore also relying on trees being cut down for production. Even worse, their biorefinery won't just be making SAF, it's already tasked with making other products from their "bio naptha"...such as beauty products, biodiesel (ooh, look at that...another biofuel using the same raw material as SAF), plastics, packaging materials, etc.

Again...your claims are refuted by the actual companies & agencies making & proclaiming the use of SAF.

 

[Scott Kenny]

You seem to fail to understand that plants are going to continue to be harvested for paper and lumber until humans cease to exist. Whatever replaces humans as the dominant species will also likely harvest plants for paper and lumber, but there may be a gap between the end of humans and whatever builds cities after us.

Your outrage is literally a "so what" to anyone working around forests.

Do you have a garden? Do you thin your plants? What about weeding? All that also happens in managed forests, just on larger scales.

Bamboo has advantages, not least because it's as aggressive a grower as mint. Is it perfect? No. Nothing is.

But using waste vegetable oil for SAF is just (every expletive deleted) stupid.

 

[green.nova343]

First, "thinning out" of plants & trees will never provide anywhere near as much as full logging operations would be...& at least in the US, the current standard is "plant 2.5 trees for every tree cut down". The problem is, it doesn't take one year to regrow those trees to the point that they can be harvested...it takes 20-25 years for Southern yellow pine, 40+ years for Douglas firs & Western hemlocks. Nor is the 2.5:1 ratio sustainable without expanding the amount of land used to grow timber...& land is always at a premium, unless you plan on simply taking privately owned land (technically called stealing) or insisting that the trees are only planted on government-owned land (which tends to p1$$ off environmentalist groups when you start logging on Federal or state lands, even -- & especially -- if the government gives it permission). And since the current lumber industry already has the primary product (wood) spoken for, this is why they focus on the waste products from the processing...but I also suspect that said environmentalists would probably push for improvements in efficiency in the primary users of the wood (i.e. actual wood products)...which will reduce the amount of waste available for SAF.

Yes, plants continue to be & will continue to be harvested...but there's only so much land available. The world's population is increasing, people need food to eat first, then shelter second, & only then can they focus on luxuries such as growing plants that will only be used for jet fuel.

Using used cooking oil for SAF production is stupid or not does not negate the fact that multiple companies are currently doing so because it's available to them. Where are the current bamboo groves & timber areas that are dedicated strictly towards SAF production...& you still didn't even address the bottleneck of the actual refinery production levels (like how AirFrance-KLM's new partner is only able to provide 0.05% of their current fuel usage).

Then there's also the actual effectiveness in terms of reducing CO2 levels.

C = Ax + By

• A = rate of CO2 emission from current jet fuel, a constant (unitless constant of 1.0c)
• B = rate of CO2 emission from SAF, a constant (unitless constant, we'll assume the generous assumption of 50%, so 0.5c)
• x = total amount of jet fuel used per year (millions of gallons)
• y = total amount of SAF used per year (millions of gallons)
• C = total CO2 emitted

In 2022, AirFrance-KLM used a total of 2.354 billion gallons of fuel: 2.34 billion gallons of jet fuel, ~14 million gallons of SAF. That puts their carbon emissions as C1 = 2,340(1.0c) + 14(0.5c) = 2,340c + 7c = 2,347c. Had they only used jet fuel it would have been C2 = 2,354(1.0c) + 0(0.5c), or 2,354c. Reduction in CO2 emissions was 7.0c...a reduction of only 0.300%. C3 (when their new partner finally reaches 120 million gallons per year) = 2,234(1.0c) + 120(0.5c) = 2,234c + 60c = 2,294c; reduction is still only 60c, or 2.549% (despite having replaced 5% of their jet fuel with SAF). To reach even a 25% reduction in CO2, that airline would have to replace 50% of its jet fuel with SAF...a production rate 10 times what the supplier estimates they will eventually be able reach with their facilities. That's just 1 airline company; total usage of jet fuel is estimated to reach nearly 90 billion gallons this year. FYI...Biden's goal is for SAF production to reach only 3 billion gallons by 2030, a paltry amount compared to the actual need.

Am I saying it's a useless pipe dream? No, never said that. Am I saying don't plan on "economies of scale" in the production of SAF, due to bottlenecks at every step of the process -- raw materials acquisition, refining of the raw materials, actual production of SAF, & building enough refineries on the scale necessary? Not by 2030, probably not by 2035 or even 2040. Not without massive spending on a scale that would dwarf the actual petroleum industry...& almost certainly result in insanely high taxes that will hit the lower- and middle-classes (the ones who can least afford it) the most.

 

[Scott Kenny]

Whatever replaces petroleum fuels in aviation, it ain't gonna be hydrogen. Density alone says that.

• SAF is an option, and requires the least fancy work on the engines themselves, since it's chemically Jet A. But as we've just hashed around, production troubles abound.
• Biobutanol might be an option. Or a heavier version closer to kerosene, produced via some genetically engineered yeasts. Cyberpunk 2020 suggested that, though they called it something else (CHOOH2 to replace gasoline, CHOOH4 to replace diesel and jet fuel, CHOOH6 to replace lube oil. Refers to how many CHOOH groups are hanging off the core molecule). Should require no work to the engines, but there may be some tuning advantages since there's some extra oxygen in the fuel.
• Anhydrous Ammonia is the longer shot. It's less energy-intensive to produce than SAF and we make it out of thin air, but it requires dedicated engines with catalytic crackers to turn at least some ammonia into hydrogen and nitrogen gas. Then you burn that hydrogen in the engine to have hot enough flames to burn Ammonia directly, which requires longer combustion chambers. I think it works fairly well in low to medium RPM diesels, but struggles a bit at 3000+rpm. Major plus is that Ammonia has ZERO carbon in it, the only way you generate carbon in the production is by coal or oil electrical production to power the conversion processes.

Those are the options I know about.

 

[Archibald]

100% agree about Ammonia. With in-flight cracking of a few hydrogen to energize the fuel mix. Ammonia is relatively easy to store but only has half the energy of kerosene. And hydrogen is the exact opposite. 2.7 times more energy than kerosene, but awful to store - temperature sucks, density sucks, explosivity sucks, leakage sucks... it sucks at every storage level !
How about methanol ? same major issue as ammonia, that is only half the enrgy of kerosene. Plus it has carbon, unlike ammonia. Then again, ammonia's nitrogen leds to NOx, which can be a major health issue if no handled the right way.

 

[Scott Kenny]

100% agree about Ammonia. With in-flight cracking of a few hydrogen to energize the fuel mix. Ammonia is relatively easy to store but only has half the energy of kerosene. And hydrogen is the exact opposite. 2.7 times more energy than kerosene, but awful to store - temperature sucks, density sucks, explosivity sucks, leakage sucks... it sucks at every storage level !
How about methanol ? same major issue as ammonia, that is only half the enrgy of kerosene. Plus it has carbon, unlike ammonia. Then again, ammonia's nitrogen leds to NOx, which can be a major health issue if no handled the right way.

Funny enough, the "Diesel Exhaust Fluid" used to help control NOx emissions is urea, which breaks down to ammonia under heat to do the actual work.

So it looks like the way to do Ammonia-as-fuel is to run it a bit rich, so there's some unburned ammonia to deal with NOx.