https://www.aopa.org/news-and-media/all ... ded-future

Citing the article: "The FAA signed on September 1 supplemental type certificates that allow General Aviation Modifications Inc.’s 100-octane unleaded fuel (G100UL) to be used in every general aviation spark-ignition engine and every airframe powered by those engines."

This is a hugely significant move in finally getting lead out of Avgas. On many airports, you usually have exactly one fuel pump for aviation gasolene, so mostly you only got Avgas 100LL. Now, with a solution that can fit all engines, this will hopefully change and lead will finally disappear.

Wow. What’s next? Dogs and cats living together? 737-7 certification?

This has been in progress for a long time.

This should open the way for regulating lead out of aviation fuel for good.

I expect that leaded avgas will be made illegal as soon as the infrastructure is in place to supply the unleaded fuel. Glad it finally happened...long overdue, but massive progress nonetheless.

How does affect the warbird fleet from WW2, etc??

Exactly, what are the expected effects mechanically (if any?)

LCDFlight wrote:

Exactly, what are the expected effects mechanically (if any?)

Mechanically, it shouldn’t do much.

Lead is added to the fuel to bring stability to it and subsequently allow the high octane to exist. This allows the high compression in the engines that provide the most horsepower for the least amount of weight.

If the 100UL is as stable as promised (and tested and certified), then it should be just as stable in the current engines and there should be no ramifications.

If the 100UL isn’t as stable as promised, then there would be premature ignition “knocking” which over time could damage engine components. That would become apparent pretty quickly though, and if it hasn’t become apparent yet, then I doubt it will.

The issue was a chemistry issue of getting UL up to 100 octane. It wasn’t an issue if lead was or wasn’t good for the engine.

crazyjaydawg wrote:

LCDFlight wrote:

Exactly, what are the expected effects mechanically (if any?)

Mechanically, it shouldn’t do much.

Lead is added to the fuel to bring stability to it and subsequently allow the high octane to exist. This allows the high compression in the engines that provide the most horsepower for the least amount of weight.

If the 100UL is as stable as promised (and tested and certified), then it should be just as stable in the current engines and there should be no ramifications.

If the 100UL isn’t as stable as promised, then there would be premature ignition “knocking” which over time could damage engine components. That would become apparent pretty quickly though, and if it hasn’t become apparent yet, then I doubt it will.

The issue was a chemistry issue of getting UL up to 100 octane. It wasn’t an issue if lead was or wasn’t good for the engine.

Seriously? It was mentioned that 100 octane was quite an achievable thing with standard fuel additives, and quite stable.
The problem -- older engines need additional lubrication, and that additional lubrication is provided with lead, deposited on pistons and cylinders by TEL.
Finding a fuel that meets that requirement, at 100 octane, was a problem.

Phosphorus wrote:

crazyjaydawg wrote:

LCDFlight wrote:

Exactly, what are the expected effects mechanically (if any?)

Mechanically, it shouldn’t do much.

Lead is added to the fuel to bring stability to it and subsequently allow the high octane to exist. This allows the high compression in the engines that provide the most horsepower for the least amount of weight.

If the 100UL is as stable as promised (and tested and certified), then it should be just as stable in the current engines and there should be no ramifications.

If the 100UL isn’t as stable as promised, then there would be premature ignition “knocking” which over time could damage engine components. That would become apparent pretty quickly though, and if it hasn’t become apparent yet, then I doubt it will.

The issue was a chemistry issue of getting UL up to 100 octane. It wasn’t an issue if lead was or wasn’t good for the engine.

Seriously? It was mentioned that 100 octane was quite an achievable thing with standard fuel additives, and quite stable.
The problem -- older engines need additional lubrication, and that additional lubrication is provided with lead, deposited on pistons and cylinders by TEL.
Finding a fuel that meets that requirement, at 100 octane, was a problem.

Seriously.

I provided a short synopsis. Sorry it wasn’t good enough for you.

The lead issue is/was associated with boasting octane. The “lubrication” was a secondary effect, however it was mostly how it helped valve seals and eliminating carbon deposits. I would say that those secondary issues have been solved long ago, it was more the ability to bring a stable high-octane fuel to market that could work in engines that were designed to take advantage of the secondary characteristics of burning lead.

Leaded gasoline was born out of the need for the highest octane concentration in the least amount of gasoline. Everything else is white noise.

https://www.faa.gov/newsroom/leaded-avi ... nvironment

As this is more of a Tech/Ops discussion, I have moved the thread accordingly.

✈️ atcsundevil

crazyjaydawg wrote:

Phosphorus wrote:

crazyjaydawg wrote:

Mechanically, it shouldn’t do much.

Lead is added to the fuel to bring stability to it and subsequently allow the high octane to exist. This allows the high compression in the engines that provide the most horsepower for the least amount of weight.

If the 100UL is as stable as promised (and tested and certified), then it should be just as stable in the current engines and there should be no ramifications.

If the 100UL isn’t as stable as promised, then there would be premature ignition “knocking” which over time could damage engine components. That would become apparent pretty quickly though, and if it hasn’t become apparent yet, then I doubt it will.

The issue was a chemistry issue of getting UL up to 100 octane. It wasn’t an issue if lead was or wasn’t good for the engine.

Seriously? It was mentioned that 100 octane was quite an achievable thing with standard fuel additives, and quite stable.
The problem -- older engines need additional lubrication, and that additional lubrication is provided with lead, deposited on pistons and cylinders by TEL.
Finding a fuel that meets that requirement, at 100 octane, was a problem.

Seriously.

I provided a short synopsis. Sorry it wasn’t good enough for you.

The lead issue is/was associated with boasting octane. The “lubrication” was a secondary effect, however it was mostly how it helped valve seals and eliminating carbon deposits. I would say that those secondary issues have been solved long ago, it was more the ability to bring a stable high-octane fuel to market that could work in engines that were designed to take advantage of the secondary characteristics of burning lead.

Leaded gasoline was born out of the need for the highest octane concentration in the least amount of gasoline. Everything else is white noise.

https://www.faa.gov/newsroom/leaded-avi ... nvironment

Secondary or not, but if engine operation relied on that - new fuel should provide same effect. Any insight on how that is achieved? Burning oil like some motorcycles do may be as bad of an idea....

kalvado wrote:

Secondary or not, but if engine operation relied on that - new fuel should provide same effect. Any insight on how that is achieved? Burning oil like some motorcycles do may be as bad of an idea....

Back when the unleaded fuel was introduced to cars, the best option was to get modern heads, so the unleaded fuel is not a problem for heads and valves. Wherever it was not possible (or too expensive), they used something called MMT - Methylcyclopentadienyl Manganese Tricarbonyl, to make sure coating for valve seat is not gone, and the engine survives. One small dose every tank, if I remember correctly. I guess both solutions will be there for aviation as well.

Cheers,
Adam

gloom wrote:

kalvado wrote:

Secondary or not, but if engine operation relied on that - new fuel should provide same effect. Any insight on how that is achieved? Burning oil like some motorcycles do may be as bad of an idea....

Back when the unleaded fuel was introduced to cars, the best option was to get modern heads, so the unleaded fuel is not a problem for heads and valves. Wherever it was not possible (or too expensive), they used something called MMT - Methylcyclopentadienyl Manganese Tricarbonyl, to make sure coating for valve seat is not gone, and the engine survives. One small dose every tank, if I remember correctly. I guess both solutions will be there for aviation as well.

Cheers,
Adam

Manganeze additive makes sense. Although that dual-cyclapentadien rings are pretty expensive, as far as I understand. They may account for a good part of extra 60 cents per gallon.
And I don't believe mixing things in a tank would be OK with FAA....

gloom wrote:

kalvado wrote:

Secondary or not, but if engine operation relied on that - new fuel should provide same effect. Any insight on how that is achieved? Burning oil like some motorcycles do may be as bad of an idea....

Back when the unleaded fuel was introduced to cars, the best option was to get modern heads, so the unleaded fuel is not a problem for heads and valves. Wherever it was not possible (or too expensive), they used something called MMT - Methylcyclopentadienyl Manganese Tricarbonyl, to make sure coating for valve seat is not gone, and the engine survives. One small dose every tank, if I remember correctly. I guess both solutions will be there for aviation as well.

Cheers,
Adam

MMT is notoriously unstable to light exposure. Many (smaller) fuel companies, who were doing there own blending, outright refused to consider it in their automotive gasoline blends. For them, the whole idea of "light exposure = loss of octane" was outlandish. They'd rather put a lot of MTBE in and call it a day.

There's a reason Avgas has TEL content up to today. There's no straightforward replacement that answers ALL requirements...

hopefully its way cheaper than 100LL. Wondered for a while why aviation even needs leaded gas. Automotive engines have been running unleaded gas for decades at much higher performance levels than any aviation piston. Honda B series has been making 100hp/liter on regular premium since late 80s early 90s reliably for 100s of thousands of miles spinning up to 8000rpms. Something like an IO360 is a big lazy 5.9 liter making a whopping 180hp spinning 2400rpms and needing a rebuild every 2000 hours. flying 10 hours a day at a busy flight school is almost 2 engine rebuilds a year.
Never understood why such a low performance engine needs such high performance fuel thats on par with some race fuels

r6russian wrote:

Wondered for a while why aviation even needs leaded gas.

A big reason is backwards compatibility. The IO360 is a 60s design and still pretty widespread. Some even in airframes from that era.
Automobiles, on the other hand, get a new engine generation every 10 years (or so) and usually get scrapped after 20-30 years. Digital engine control has been a standard feature of automotive engines since the 90s, including anti-knock features. Those developments are only slowly spreading to GA engines, there's just no money in the market.

r6russian wrote:

hopefully its way cheaper than 100LL.

60-80 cents per gallon more at the refinery.

r6russian wrote:

hopefully its way cheaper than 100LL. Wondered for a while why aviation even needs leaded gas. Automotive engines have been running unleaded gas for decades at much higher performance levels than any aviation piston. Honda B series has been making 100hp/liter on regular premium since late 80s early 90s reliably for 100s of thousands of miles spinning up to 8000rpms. Something like an IO360 is a big lazy 5.9 liter making a whopping 180hp spinning 2400rpms and needing a rebuild every 2000 hours. flying 10 hours a day at a busy flight school is almost 2 engine rebuilds a year.
Never understood why such a low performance engine needs such high performance fuel thats on par with some race fuels

How long would a Honda B last continuously putting out 75hp/l.

Looks like their only patent is for methyl benzene additives. Good luck selling that in CA.
Nothing on valve lubricantion so far
https://patents.google.com/patent/US8628594B1/en

The guys at GAMI are pretty amazing. They have said they expect a temporary premium of 50-75 cents per gallon while production ramps up, but then prices to drop once the infrastructure and production are there. They anticipate, probably quite correctly, that this extra cost will be largely absorbed by lower maintenance costs. Lead is actually pretty awful for piston engines and one of the prime causes of fouled plugs and failed cylinders, thanks to the deposits it leaves behind.

sunking737 wrote:

How does affect the warbird fleet from WW2, etc??

It works for them. That's the entire point. It will work in anything from a radial on the front of a Beaver to a brand new Cirrus. G100UL is a drop in replacement for 100LL. It is meant to require zero modifications.

N1120A wrote:

The guys at GAMI are pretty amazing. They have said they expect a temporary premium of 50-75 cents per gallon while production ramps up, but then prices to drop once the infrastructure and production are there. They anticipate, probably quite correctly, that this extra cost will be largely absorbed by lower maintenance costs. Lead is actually pretty awful for piston engines and one of the prime causes of fouled plugs and failed cylinders, thanks to the deposits it leaves behind.

sunking737 wrote:

How does affect the warbird fleet from WW2, etc??

It works for them. That's the entire point. It will work in anything from a radial on the front of a Beaver to a brand new Cirrus. G100UL is a drop in replacement for 100LL. It is meant to require zero modifications.

I thought many planes from late WW2 era actually require 130 octane number?

kalvado wrote:

N1120A wrote:

The guys at GAMI are pretty amazing. They have said they expect a temporary premium of 50-75 cents per gallon while production ramps up, but then prices to drop once the infrastructure and production are there. They anticipate, probably quite correctly, that this extra cost will be largely absorbed by lower maintenance costs. Lead is actually pretty awful for piston engines and one of the prime causes of fouled plugs and failed cylinders, thanks to the deposits it leaves behind.

sunking737 wrote:

How does affect the warbird fleet from WW2, etc??

It works for them. That's the entire point. It will work in anything from a radial on the front of a Beaver to a brand new Cirrus. G100UL is a drop in replacement for 100LL. It is meant to require zero modifications.

I thought many planes from late WW2 era actually require 130 octane number?

If they did, 100LL, 100R or G100UL would be irrelevant to the discussion.

Incidentally, the guys at GAMI found that G100UL outperforms even the old 115/145 Purple Avgas that was used in Constellations and DC-7s.

https://www.google.com/url?sa=t&rct=j&q ... Mag3qrO8Wx

N1120A wrote:

kalvado wrote:

N1120A wrote:

The guys at GAMI are pretty amazing. They have said they expect a temporary premium of 50-75 cents per gallon while production ramps up, but then prices to drop once the infrastructure and production are there. They anticipate, probably quite correctly, that this extra cost will be largely absorbed by lower maintenance costs. Lead is actually pretty awful for piston engines and one of the prime causes of fouled plugs and failed cylinders, thanks to the deposits it leaves behind.



It works for them. That's the entire point. It will work in anything from a radial on the front of a Beaver to a brand new Cirrus. G100UL is a drop in replacement for 100LL. It is meant to require zero modifications.

I thought many planes from late WW2 era actually require 130 octane number?

If they did, 100LL, 100R or G100UL would be irrelevant to the discussion.

Incidentally, the guys at GAMI found that G100UL outperforms even the old 115/145 Purple Avgas that was used in Constellations and DC-7s.

https://www.google.com/url?sa=t&rct=j&q ... Mag3qrO8Wx

I am smelling an oversale. They are using additives, which are not cheap, to increase octane number - and say that they fo past the goalpost?
There may be other issues with the thing; I don't believe "cheaper as production scales up" claim, for example.
But this octane thing breaks me from mildly sceptical to suspicious.

kalvado wrote:

N1120A wrote:

kalvado wrote:

I thought many planes from late WW2 era actually require 130 octane number?

If they did, 100LL, 100R or G100UL would be irrelevant to the discussion.

Incidentally, the guys at GAMI found that G100UL outperforms even the old 115/145 Purple Avgas that was used in Constellations and DC-7s.

https://www.google.com/url?sa=t&rct=j&q ... Mag3qrO8Wx

I am smelling an oversale. They are using additives, which are not cheap, to increase octane number - and say that they fo past the goalpost?
There may be other issues with the thing; I don't believe "cheaper as production scales up" claim, for example.
But this octane thing breaks me from mildly sceptical to suspicious.

Do you understand the ridiculous amount of testing that has gone on?

Lead itself is an additive...to increase octane.

I don't see how you don't believe "cheaper as production scales up." It is all about economies of scale. Indeed, this stuff may well have more applications than aviation, since it can potentially legally be sold for applications outside aviation.

N1120A wrote:

kalvado wrote:

N1120A wrote:

If they did, 100LL, 100R or G100UL would be irrelevant to the discussion.

Incidentally, the guys at GAMI found that G100UL outperforms even the old 115/145 Purple Avgas that was used in Constellations and DC-7s.

https://www.google.com/url?sa=t&rct=j&q ... Mag3qrO8Wx

I am smelling an oversale. They are using additives, which are not cheap, to increase octane number - and say that they fo past the goalpost?
There may be other issues with the thing; I don't believe "cheaper as production scales up" claim, for example.
But this octane thing breaks me from mildly sceptical to suspicious.

Do you understand the ridiculous amount of testing that has gone on?

Lead itself is an additive...to increase octane.

I don't see how you don't believe "cheaper as production scales up." It is all about economies of scale. Indeed, this stuff may well have more applications than aviation, since it can potentially legally be sold for applications outside aviation.

Yeah, 150 hours is a ridiculous amount of testing, I agree. But this is not the point, they will do more as this is introduced.
How much of this stuff was produced so far? 5000 gallons or less?
Aromatics would work as a free radical absorber, no question about that. Used for ages to improve shitty gas. Mesitylene and m-xylene specifically, OK, maybe even separated for the test run.
Mass production would hinge on high volume coal / coke production, and the willingness of coal industry to do (pretty dirty) coke tar distillation, There were supply problems for aromatic compounds in the past decade, as far as I know, as coal goes out of fashion, and health issues become expensive even outside US. Well, lead thing is in the same boat, but it is a dedicated process.
So I suspect prices will grow with mass production, as economy of scale depletes the supply... Availability may also be interesting. And you say they overdo it over the bare minimum of requirement? And their patent is expiring?

kalvado wrote:

N1120A wrote:

kalvado wrote:

I am smelling an oversale. They are using additives, which are not cheap, to increase octane number - and say that they fo past the goalpost?
There may be other issues with the thing; I don't believe "cheaper as production scales up" claim, for example.
But this octane thing breaks me from mildly sceptical to suspicious.

Do you understand the ridiculous amount of testing that has gone on?

Lead itself is an additive...to increase octane.

I don't see how you don't believe "cheaper as production scales up." It is all about economies of scale. Indeed, this stuff may well have more applications than aviation, since it can potentially legally be sold for applications outside aviation.

Yeah, 150 hours is a ridiculous amount of testing, I agree. But this is not the point, they will do more as this is introduced.
How much of this stuff was produced so far? 5000 gallons or less?
Aromatics would work as a free radical absorber, no question about that. Used for ages to improve shitty gas. Mesitylene and m-xylene specifically, OK, maybe even separated for the test run.
Mass production would hinge on high volume coal / coke production, and the willingness of coal industry to do (pretty dirty) coke tar distillation, There were supply problems for aromatic compounds in the past decade, as far as I know, as coal goes out of fashion, and health issues become expensive even outside US. Well, lead thing is in the same boat, but it is a dedicated process.
So I suspect prices will grow with mass production, as economy of scale depletes the supply... Availability may also be interesting. And you say they overdo it over the bare minimum of requirement? And their patent is expiring?

Mixed xylenes are a hugely important, ever growing, petrochemical product at the moment. Asia-Pacific is building dedicated units: crude oil in => paraxylene out. In millions of tons each. China is big on these.
Demand for polyester (bottles and fibres) drives that.
What kind of volumes in Avgas are we talking about, annually?
Chemically pure paraxylene for polyester, alone, is in tens of millions of tons annually.

Phosphorus wrote:

kalvado wrote:

N1120A wrote:

Do you understand the ridiculous amount of testing that has gone on?

Lead itself is an additive...to increase octane.

I don't see how you don't believe "cheaper as production scales up." It is all about economies of scale. Indeed, this stuff may well have more applications than aviation, since it can potentially legally be sold for applications outside aviation.

Yeah, 150 hours is a ridiculous amount of testing, I agree. But this is not the point, they will do more as this is introduced.
How much of this stuff was produced so far? 5000 gallons or less?
Aromatics would work as a free radical absorber, no question about that. Used for ages to improve shitty gas. Mesitylene and m-xylene specifically, OK, maybe even separated for the test run.
Mass production would hinge on high volume coal / coke production, and the willingness of coal industry to do (pretty dirty) coke tar distillation, There were supply problems for aromatic compounds in the past decade, as far as I know, as coal goes out of fashion, and health issues become expensive even outside US. Well, lead thing is in the same boat, but it is a dedicated process.
So I suspect prices will grow with mass production, as economy of scale depletes the supply... Availability may also be interesting. And you say they overdo it over the bare minimum of requirement? And their patent is expiring?

Mixed xylenes are a hugely important, ever growing, petrochemical product at the moment. Asia-Pacific is building dedicated units: crude oil in => paraxylene out. In millions of tons each. China is big on these.
Demand for polyester (bottles and fibres) drives that.
What kind of volumes in Avgas are we talking about, annually?
Chemically pure paraxylene for polyester, alone, is in tens of millions of tons annually.

They need m-xylene, not sure how big the difference is in terms of synthesis.

kalvado wrote:

Phosphorus wrote:

kalvado wrote:

Yeah, 150 hours is a ridiculous amount of testing, I agree. But this is not the point, they will do more as this is introduced.
How much of this stuff was produced so far? 5000 gallons or less?
Aromatics would work as a free radical absorber, no question about that. Used for ages to improve shitty gas. Mesitylene and m-xylene specifically, OK, maybe even separated for the test run.
Mass production would hinge on high volume coal / coke production, and the willingness of coal industry to do (pretty dirty) coke tar distillation, There were supply problems for aromatic compounds in the past decade, as far as I know, as coal goes out of fashion, and health issues become expensive even outside US. Well, lead thing is in the same boat, but it is a dedicated process.
So I suspect prices will grow with mass production, as economy of scale depletes the supply... Availability may also be interesting. And you say they overdo it over the bare minimum of requirement? And their patent is expiring?

Mixed xylenes are a hugely important, ever growing, petrochemical product at the moment. Asia-Pacific is building dedicated units: crude oil in => paraxylene out. In millions of tons each. China is big on these.
Demand for polyester (bottles and fibres) drives that.
What kind of volumes in Avgas are we talking about, annually?
Chemically pure paraxylene for polyester, alone, is in tens of millions of tons annually.

They need m-xylene, not sure how big the difference is in terms of synthesis.

in petrochemistry, mixed xylenes is step 1 (for the purposes of this discussion)
They are then separated into paraxylene (typical target product); orthoxylene (some need it, some don't), metaxylene (some need it, some don't)

Then there's confusion in terms going on.
for some m-xylenes is the mixed xylenes.
for some (most), m-xylene is metaxylene. (I think this is what you have in mind).

If you want metaxylene, it's typically in surplus in petrochemistry. Some finds downstream chemical uses (isophthalic acid comes to mind). Some is thrown back into the pot, to be converted into mixed xylenes again.

Exact preferences, balances and costs are highly regionalized.
Still, I wouldn't be surprised if there's a marginal xylenes unit or two out there, where economics are barely holding together under current supply-demand scenarios. And that would receive a good boost to their viability, if a steady offtake of metaxylene appeared.

Phosphorus wrote:

kalvado wrote:

Phosphorus wrote:

Mixed xylenes are a hugely important, ever growing, petrochemical product at the moment. Asia-Pacific is building dedicated units: crude oil in => paraxylene out. In millions of tons each. China is big on these.
Demand for polyester (bottles and fibres) drives that.
What kind of volumes in Avgas are we talking about, annually?
Chemically pure paraxylene for polyester, alone, is in tens of millions of tons annually.

They need m-xylene, not sure how big the difference is in terms of synthesis.

in petrochemistry, mixed xylenes is step 1 (for the purposes of this discussion)
They are then separated into paraxylene (typical target product); orthoxylene (some need it, some don't), metaxylene (some need it, some don't)

Then there's confusion in terms going on.
for some m-xylenes is the mixed xylenes.
for some (most), m-xylene is metaxylene. (I think this is what you have in mind).

If you want metaxylene, it's typically in surplus in petrochemistry. Some finds downstream chemical uses (isophthalic acid comes to mind). Some is thrown back into the pot, to be converted into mixed xylenes again.

Exact preferences, balances and costs are highly regionalized.
Still, I wouldn't be surprised if there's a marginal xylenes unit or two out there, where economics are barely holding together under current supply-demand scenarios. And that would receive a good boost to their viability, if a steady offtake of metaxylene appeared.

OK, they need 1,3- (meta) or 1,3,5- compounds. Just to avoid further confusion.

gas is said to be anywhere between 1 and 40% mixed xylenes. Looks like they actually try to standardize specific xylene fraction to increase octane number; looks like mixed xylenes is 114 octane.
Avgas consumption is about 0.6 million metric tons, so we may talk quarter million metric tons of 1,3-methyl-benzene a year. Not too much, if production is indeed in millions of tons.

If it only costs 60-80 cents more NOW, hopefully that cost is from availability and once it’s universally produced and available nationwide, it’ll go down.

I would hope.

CarlosSi wrote:

If it only costs 60-80 cents more NOW, hopefully that cost is from availability and once it’s universally produced and available nationwide, it’ll go down.

I would hope.

2 years ago, I had to have significant deposits cleaned out and new valve guides thanks to lead, and I aggressively lean on the ground to prevent such. It got so bad, I was adding TCP to my fuel to clean things up. Given GAMI's history, I'm confident in their estimates about the cost savings.

kalvado wrote:

Phosphorus wrote:

kalvado wrote:

They need m-xylene, not sure how big the difference is in terms of synthesis.

in petrochemistry, mixed xylenes is step 1 (for the purposes of this discussion)
They are then separated into paraxylene (typical target product); orthoxylene (some need it, some don't), metaxylene (some need it, some don't)

Then there's confusion in terms going on.
for some m-xylenes is the mixed xylenes.
for some (most), m-xylene is metaxylene. (I think this is what you have in mind).

If you want metaxylene, it's typically in surplus in petrochemistry. Some finds downstream chemical uses (isophthalic acid comes to mind). Some is thrown back into the pot, to be converted into mixed xylenes again.

Exact preferences, balances and costs are highly regionalized.
Still, I wouldn't be surprised if there's a marginal xylenes unit or two out there, where economics are barely holding together under current supply-demand scenarios. And that would receive a good boost to their viability, if a steady offtake of metaxylene appeared.

OK, they need 1,3- (meta) or 1,3,5- compounds. Just to avoid further confusion.

gas is said to be anywhere between 1 and 40% mixed xylenes. Looks like they actually try to standardize specific xylene fraction to increase octane number; looks like mixed xylenes is 114 octane.
Avgas consumption is about 0.6 million metric tons, so we may talk quarter million metric tons of 1,3-methyl-benzene a year. Not too much, if production is indeed in millions of tons.

I realized I had a brain fart. Yes, you would not want p-xylene (paraxylene) as aircraft fuel. Both for commercial reasons, and also because pure paraxylene has melting point of +13oC or thereabouts. Not something you want in your tanks at altitude.

Metaxylene has mp around -50oC, and if you add some aliphatics -- like isooctane, with m.p. below -100oC, you'll be fine.

And yes, paraxylene production is on scale of tens of millions of tons per year. These days, with trends to on-site integration, plenty of it basically goes from Process A to Process B within the same site, but merchant market is alive and kicking, very much so.

r6russian wrote:

hopefully its way cheaper than 100LL. Wondered for a while why aviation even needs leaded gas. Automotive engines have been running unleaded gas for decades at much higher performance levels than any aviation piston. Honda B series has been making 100hp/liter on regular premium since late 80s early 90s reliably for 100s of thousands of miles spinning up to 8000rpms. Something like an IO360 is a big lazy 5.9 liter making a whopping 180hp spinning 2400rpms and needing a rebuild every 2000 hours. flying 10 hours a day at a busy flight school is almost 2 engine rebuilds a year.
Never understood why such a low performance engine needs such high performance fuel thats on par with some race fuels

Aviation engines run at higher compression ratios and lower RPMs compared to car engines and must do so over a much wider range of atmospheric conditions (hot, cold, high altitude, low altitude, etc.). The high compression/low RPM combination results in higher cylinder pressures which is why high octane fuel is needed; many high performance airplanes use turbocharged engines which only add to this problem. Particularly when turbocharging is involved, the fuel must perfom equally well at sea level and at 25,000+ feet and, because Avgas tends to sit around a lot longer than normal Mogas it must have a longer "shelf stability" as well. Until now, no formula has been found that meets all of the performance and stability requirements of 100LL without some amount of lead to raise the octane rating. 94UL, which is basically 100LL without the lead, was a proposal some years ago but it would not be compatible with all aircraft or engines and the market for Avgas is too small today to support two different fuels, hence the persistence of 100LL. The good news is that, today, many lower performance airplanes/engines can be approved to run on regular unleaded gasoline as long as it doesn't contain ethanol.

Side note: Octane ratings for aviation are calculated differently than for automotive gasoline. 100 octane Avgas is really equivalent to 105-110 octane automotive gas by North American standards and 110-115 octane by European standards.

A lot of the discussion in this thread has focussed on the xylenes, but when I look at https://www.aviationconsumer.com/mainte ... s-the-stc/ for example, an important ingredient also seems to be a nitro amine additive. Are nitro amines commonly used as fuel additives?

Low RPM, I agree with, but Lycoming and Continental compression ratios are nothing to be excited about—7:1 to 9:1 typically. Any car today with electronic controls is much higher—11:1 often. Brake Mean Effective Pressure (BMEP) might be a difference in the two applications. The lack of approved electronic engine controls is a problem.

https://en.wikipedia.org/wiki/Lycoming_O-320

GalaxyFlyer wrote:

Low RPM, I agree with, but Lycoming and Continental compression ratios are nothing to be excited about—7:1 to 9:1 typically. Any car today with electronic controls is much higher—11:1 often. Brake Mean Effective Pressure (BMEP) might be a difference in the two applications. The lack of approved electronic engine controls is a problem.

https://en.wikipedia.org/wiki/Lycoming_O-320

I assume it is also about reliability. Fallback mode for electronic ignition, as far as I know, is to adjust engine condition for lower power. That is no problem for most surface vehicles. May be more of an issue if takeoff roll is slower than expected.

kalvado wrote:

GalaxyFlyer wrote:

Low RPM, I agree with, but Lycoming and Continental compression ratios are nothing to be excited about—7:1 to 9:1 typically. Any car today with electronic controls is much higher—11:1 often. Brake Mean Effective Pressure (BMEP) might be a difference in the two applications. The lack of approved electronic engine controls is a problem.

https://en.wikipedia.org/wiki/Lycoming_O-320

I assume it is also about reliability. Fallback mode for electronic ignition, as far as I know, is to adjust engine condition for lower power. That is no problem for most surface vehicles. May be more of an issue if takeoff roll is slower than expected.

There's some baby steps happening, like the Lycoming IE2: https://www.aviationconsumer.com/uncate ... echnology/

Basically they've automated the three engine controls, injection, and spark timing, but the bore/stroke/cam setup is still the same as in the TIO-540. I think part of the issue with the higher compression ratios is being able to adjust the valve timing, which those pushrod designs don't do well. I wonder what the weight penalty of a DOHC layout looks like on something like this. I suspect that's where the feature snowball gets rolling, then you might start thinking about making it inline, which means liquid cooling, which means a different layout and new failure modes, etc. I do wonder what a new BMW-designed inline 6 for aero applications might look like.

Electronic controls for piston engines would probably also have to be held to the same certification standards that were originally written for FADECs on airliners (because the FAA already has rules for electronic engine controls and they are notorious for "one size fits all"). Divide horrific expense that over a miniscule sales base and you get either absurd prices, or no engine.

There are some electronic ignition/injection systems available for the homebuilt market that can be fitted to traditional aviation engines (I'm putting an SDS EFI system on my airplane) but even those aren't true FADECs and aren't comparable to even a 25 year old car.

GalaxyFlyer wrote:

Low RPM, I agree with, but Lycoming and Continental compression ratios are nothing to be excited about—7:1 to 9:1 typically. Any car today with electronic controls is much higher—11:1 often. Brake Mean Effective Pressure (BMEP) might be a difference in the two applications. The lack of approved electronic engine controls is a problem.

https://en.wikipedia.org/wiki/Lycoming_O-320

True enough, my friend; perhaps I was oversimplifying in my explanation. The main issues as I understand them are that the low RPMs at which these engines operate wide-open (2400-2800 RPM vs. 5000-6000 RPM or more for cars) result in higher cylinder pressures which is ultimately what matters - compression ratio is just a factor that goes into the equation. And, yes, while 7:1 is hardly an impressive compression ratio on paper, when combined with turbocharging (and a low redline RPM) the cylinder pressures can still get quite high in a typical aviation application.

Electronic ignition control with variable timing could help solve this problem but as you point out the FAA is nowhere near approving such technology for the GA piston market, and the fact remains that tens of thousands of engines without such technology remain in service which still require an acceptable fuel.