Drop-in 100LL Replacement "Impossible"?

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100LL Drop-In Replacement 'Impossible' Says PAFI Candidate - AVweb

The company behind the only candidate left in the FAA-driven Piston Aviation Fuel Initiative process to create a high-octane unleaded replacement for 100LL says it’s impossible, according to Aviation Week. “There is no such thing as a drop-in unleaded fuel to replace 100 [LL],” Dan Pourreau...
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Excerpt:

Pourreau told Aviation Week the issue is achieving the 104 Motor Octane Number (MON) of 100LL. His team hasn’t been able to do that without adding octane boosters that leave unacceptable deposits in the engines. “If you take lead out or you don’t use manganese or other octane boosters, the best you can probably do is roughly 100 MON or above,” he told Aviation Week. “It is just virtually impossible to do that without changing other properties [of the fuel] so much, it’s no longer practical and effective.”​
 
If I understand it correctly, G100UL doesn't quite fall within all the ASTM specifications of 100LL - I think it's slightly too dense or something like that - which is one of the reasons they aren't part of the PAFI/EAGLE program. So the guy quoted in this article may be correct - it may be that you can't make an unleaded 100LL replacement while still staying within the ASTM standards.

And it may well be that the ASTM standards are unnecessarily restrictive.
 
CaptainXap said:
If I understand it correctly, G100UL doesn't quite fall within all the ASTM specifications of 100LL - I think it's slightly too dense or something like that - which is one of the reasons they aren't part of the PAFI/EAGLE program. So the guy quoted in this article may be correct - it may be that you can't make an unleaded 100LL replacement while still staying within the ASTM standards.

And it may well be that the ASTM standards are unnecessarily restrictive.
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My understanding is that the ASTM standard for 100LL requires there to be lead in it.

I found an ASTM standard for unleaded avgas, but apparently it only applies to fuels for testing.

www.astm.org

Standard Specification for Unleaded Aviation Gasoline Test Fuel Containing Non-hydrocarbon Components

AbstractThis specification covers formulating requirements for purchases of a UL100 unleaded aviation gasoline test fuel under contract and is intended solely for use by purchasing agencies for testing purposes. It prescribes the required properties of un
www.astm.org www.astm.org
 
It would have been easier and less costly (except for the piston owner) than this 50 year fuel fiasco for someone to have come up with an STC that involves a knock sensor that modifies anything (timing, fuel, rpm) if a ham fisted pilot or bad fueled engine begins to detonate. Buick figured it out for their turboed production vehicles in the 1980’s. Then the need for lead would go away. Lead fouls O2 sensors, so there’s that chicken & egg thing.
 
StraightnLevel said:
The challenge with this approach is that unlike a straight direct magneto pair, it requires power. Is that acceptable from a reliability standpoint?
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There are dual electronic ignitions that are now approved, which negates that concern. The bigger issue I have with a knock sensor is that you’re likely going to be limiting power on at least some engines in the fleet which are already knock limited. That is not an approach that I would find acceptable. Further, the amount of research that would be necessary to have a reliable implementation in all airframe and engine combinations would be far greater than most would assume. While I would be in favor of some electronic timing control, it would probably be best implemented as a complimentary item rather than as a band aid for inadequate fuel.

Water/methanol injection and perhaps full power time limitations would be a far better approach to using low octane fuel in my opinion.
 
mondtster said:
Water/methanol injection and perhaps full power time limitations would be a far better approach to using low octane fuel in my opinion.
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Thing is, unless you want to recertify every airplane in the fleet, you can't do any of that.
 
I thought it was pretty fascinating they would just come right out and say it. The whole thing is just amazing to watch unfold. Why is EAGLE pretending GAMI's fuel doesn't exist? Why isn't G100UL for sale anywhere? Why did Cirrus knock it? Are they really going to stretch this thing out to 2030?
 
On the Turbo V6 Buicks, those knock sensors were a protective measure, allowing for cheap fuel or premium. It saved the engine in a wide operational envelope. It was a safety net. We started to throw more boost at it (in many cases from the stock 13psi to a crazy 20+, sometimes 25psi, with stock heads and gaskets). Just use better fuel to keep the knock sensor from pulling timing. Then timing maps were tweaked aftermarket, and the sensors used as a safety tool (to save $$, lol).

All I’m saying is that if the FAA certification process were easier, one STC would lead to another, and then the aftermarket would have solved the problem between 1974-2024…including the manufacturers. Would the lessons be paid in blood? No telling. But the political cluster and millions of $ spent over the last 50 years might have been more successful and for those who care about lead in envir and health would have been resolved.

What we have is 100% focus on fuel technology to rid lead vs engine technology to eliminate the need for lead. The only thing standing in the way of either is regulatory restrictions. And now that there might be fuel options, supposedly there are unresolved technical and thus safety concerns. The engine tech is one way to eat the lead elephant step by step over a half century, because that lead elephant couldn’t be eaten in one fell swoop (sweeping acceptable fuel) in that same 50 year period.

One is reality, the other is hypothetical, I know that. Just sayin.
 
kyleb said:
Thing is, unless you want to recertify every airplane in the fleet, you can't do any of that.
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You couldn’t do it with knock sensors either, which is what I was mainly responding to. They’re taking the most practical approach, which is changing the fuel.
 
Jim K said:
Why is EAGLE pretending GAMI's fuel doesn't exist? Why isn't G100UL for sale anywhere?
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Because they weren't part of the EAGLE program?

Jim K said:
Are they really going to stretch this thing out to 2030?
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Perhaps. Is there an incentive to reach a conclusion before then? Or a penalty if they take longer?
 
StraightnLevel said:
It can be done with lambda sensors, closed-loop mixture control and unleaded fuel.

Assuming you're willing to accept a requirement for electrical power and the possibility of reduced power in certain conditions, that is the appropriate technology for the application.
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That's not a practical approach for existing TCd aircraft. Perhaps new design and construction units could implement that but even then, the market has generally spoken and isn't in favor of adding electronic controls. Lycoming has had an EFI engine around for years and there has been little interest in it.

But again, if you're going to fixate on hanging a ton of electronics on something and accept a reduced power in certain conditions, why on earth wouldn't you use water injection instead and have no power limitations and a cooler, cleaner engine?
 
We would add a 7th injector to the intake and spray isopropyl + water based on a driver adjustable boost (pressure) sensor for the on-signal and adjustable flow rate knob for the pump speed (spray pressure and thus flow rate). Those knobs would be manually adjusted until the knock sensor was calmed down or just barely tickled. That was 30 years ago. Today they could be electronically adjusted, but I haven’t followed the tech for a couple decades since.

But I’ll liken this to BRS. Just because it’s certified in Cirrus or able to be STCed for a few models doesn’t mean it’ll permeate the market. It’s been 23 years since Cirrus and few airplanes come from the factory with BRS and few have modified their personal planes because of cost or “religion”.
 
This whole thing is reminiscent of the autogas STC hand-wringing back in the 80s. Autogas was going to rot out your fuel system, destroy your valves/valve guides, or otherwise cause some sort of nefarious issue of one sort or another. Didn't happen. STC'ed low compression engines ran on autogas just fine, and very clean and cheaper to boot. Then they started adding ethanol to most gasoline spoiling the party for many STC owners, making conforming autogas harder to find, and many airports quit providing it.

G100UL is chemically very similar to unleaded autogas, with a higher xylenes content to achieve the required octane/detonation margin. Why not get it out there and see how it goes, and make any minor adjustments from there. TEL probably won't be manufactured in bulk forever. Time to move on. At some point there won't be a choice about it. Big oil has been a dismal failure in developing an alternative to 100LL. The whole ASTM thing is just a paper exercise/red herring impeding progress.
 
StraightnLevel said:
The challenge with this approach is that unlike a straight direct magneto pair, it requires power. Is that acceptable from a reliability standpoint?
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the fact that you have to rebuild a magneto every 500 or so hours tells me that reliability was not an option. if you can rebuild a farm tractor mag you can replace a battery.
 
Capt. Geoffrey Thorpe said:
It's not like no one can come up with a 100 octane fuel that actually works in airplanes.

It's a paperwork problem, not a technical problem.
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i think it's more of a liability problem. the FAA doesn't want to grant a universal stc or change the regs and lawyers don't want to see a cash cow taken from them.
 
From my understanding an ATSM standard is just something agreed to by a committee.

The only reason there isn't an ATSM standard for 100 octane unleaded avgas is because the big oil companies that make up those committees haven't come up with one yet.

GAMI doesn't have the money to bribe fund those committees to make G100UL the standard so they went the STC route.
 
One more Buick anecdote. When we were turning the boost up and running high timing in one of my street cars, I would grab three 1 gallon cans of xylene and toluene from the local Sherwin Williams store Friday before they closed, go to the gas station, dump all 3 gallons in, then fill up with premium 93. That would result in an R+M octane rating of 99.5.

Then grab dinner with my fellow car buds and then go to the local cruise parking spot. Invariably, smack talk would ensue around 11p to midnight, and then the county back roads would determine truth.

Same fuel mix at the track, but with slicks and open dump.

Just reiterating the comment about xylenes from @chemgeek because it brought back fun memories.
 
Somewhere in Oklahoma George Braly has a grin on his face.
 
Here's a link to a YouTube video of George Braly's presentation about G100UL at 2024 Osh. It's a bit long, but it is pretty interesting...in an unleaded kind of way. Thanks Martin Pauly!

 
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Pinecone said:
Hmm, G100UL
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StraightnLevel said:
Sounds like a possibly terminal case of sour grapes. Take two tankfuls of G100UL and call me in the morning.
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www.avweb.com

Stains On AOPA Baron Wing To Be Checked By Mechanic

AOPA says it left its dual-fuel Beech Baron behind in Oshkosh so mechanics can trace the source of some stains that were discovered under the left wing while it was...
www.avweb.com www.avweb.com

Have a look at the goo coming from AOPA's G100UL test Baron. This left wing is the G100UL fueled wing. Curious to learn the cause after AOPA team investigates. Perhaps the materials compatibility testing part of ATSM might be helpful?

Screenshot 2024-07-30 at 9.24.05 PM.png
 
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455 Bravo Uniform said:
It would have been easier and less costly (except for the piston owner) than this 50 year fuel fiasco for someone to have come up with an STC that involves a knock sensor that modifies anything (timing, fuel, rpm) if a ham fisted pilot or bad fueled engine begins to detonate. Buick figured it out for their turboed production vehicles in the 1980’s. Then the need for lead would go away. Lead fouls O2 sensors, so there’s that chicken & egg thing.
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Knock sensors won't work in piston GA aircraft due to overall noise level. If knock could be heard, a full FADEC with other sensors would be needed to process knock sensor data to retard spark or adjust fuel mixture. Also retarding spark in reaction to knock degrades horsepower possibly putting the plane in flight performance jeopardy, like reducing power on a high density altitude climb out.
 
NordicDave said:
Knock sensors won't work in piston GA aircraft due to overall noise level. A full FADEC with other sensors would be needed to process knock sensor data to retard spark or adjust fuel mixture. Also retarding spark in reaction to knock degrades horsepower possibly putting the plane in flight performance jeopardy, like reducing power on a high density altitude climb out.
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your 80 year old tractor motor is always experiencing intermittent detonation.... just not severe enough to cause damage... but like you said, you simply cannot hear it.

a knock sensor is tuned to a specific frequency... so it doesn't hear anything other than the pings.. but who is going to spend the $$$ to tune the sensor and ECU?
 
pfarber said:
your 80 year old tractor motor is always experiencing intermittent detonation.... just not severe enough to cause damage... but like you said, you simply cannot hear it.

a knock sensor is tuned to a specific frequency... so it doesn't hear anything other than the pings.. but who is going to spend the $$$ to tune the sensor and ECU?
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Yes, the knock sensor has a narrow frequency range of vibration which is masked by other vibrations or "noise" in the system.
 
NordicDave said:
Have a look at the goo coming from AOPA's G100UL test Baron.
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Never happens with real avgas...

www.pilotsofamerica.com

Thick black sticky residue under my wing.

When I was pre-flighting my plane I noticed I had overfilled my fuel tanks and had some blue dye on my landing gear which is typical when I put too much fuel in however when I was looking down there I noticed significant streaks of black mixed in with the blue. The only way to describe it is...
www.pilotsofamerica.com www.pilotsofamerica.com
20240501_112311-jpg.128358
 
clear_prop said:
From my understanding an ATSM standard is just something agreed to by a committee.

The only reason there isn't an ATSM standard for 100 octane unleaded avgas is because the big oil companies that make up those committees haven't come up with one yet.

GAMI doesn't have the money to bribe fund those committees to make G100UL the standard so they went the STC route.
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THIS ^^^^^^
 
pfarber said:
i think it's more of a liability problem. the FAA doesn't want to grant a universal stc or change the regs and lawyers don't want to see a cash cow taken from them.
Click to expand...

Whatever minimal liability the FAA might have was already incurred when the FAA granted the STC for G100UL.
 
This saga gets more interesting every day. Now I really wish Swift's comments during Braly's Oshkosh forum were available in Martin's video.

From the comments in https://www.avweb.com/aviation-news/100ll-drop-in-replacement-impossible-says-pafi-candidate/

lee3607 July 30, 2024 At 2:24 pm
"Y’all should’ve seen the folks at Swift at AirVenture this year. Their booth was across from the AOPA booth and they had the Baron on display that’s running both GAMI G100UL and 100LL in separate engines. Our booth was near there too. The Swift guys beat a path over to the Baron all day long, anytime anyone stopped to look at the banner showing the data so far. Then they started telling folks that G100UL was eating the bladders and causing fuel leaks. They crawled all under that airplane. They badmouthed G100UL the whole week. And AOPA didn’t do anything to stop them. We took pictures of this. It was pathetic. How do we know what they were saying? We sent a friend over to look at the Baron and see what was up and sure enough within a minute of him walking up they headed out of their booth over to him and started telling him this. It’s just typical Swift and their arrogant team badmouthing their competitor because of the true data that GAMI has."
 
baboss said:
This saga gets more interesting every day. Now I really wish Swift's comments during Braly's Oshkosh forum were available in Martin's video.

From the comments in https://www.avweb.com/aviation-news/100ll-drop-in-replacement-impossible-says-pafi-candidate/

lee3607 July 30, 2024 At 2:24 pm
"Y’all should’ve seen the folks at Swift at AirVenture this year. Their booth was across from the AOPA booth and they had the Baron on display that’s running both GAMI G100UL and 100LL in separate engines. Our booth was near there too. The Swift guys beat a path over to the Baron all day long, anytime anyone stopped to look at the banner showing the data so far. Then they started telling folks that G100UL was eating the bladders and causing fuel leaks. They crawled all under that airplane. They badmouthed G100UL the whole week. And AOPA didn’t do anything to stop them. We took pictures of this. It was pathetic. How do we know what they were saying? We sent a friend over to look at the Baron and see what was up and sure enough within a minute of him walking up they headed out of their booth over to him and started telling him this. It’s just typical Swift and their arrogant team badmouthing their competitor because of the true data that GAMI has."
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I'm sure the Swift people are being completely objective and data-driven about the competitor's product. ;)
 
And greed and self-serving behavior on one, both, or many sides of the investments in aviation fuel keep the rest of us and the environment in limbo one more day while the truth is buried in there somewhere, whatever it is.
 
And this kind of an attitude is one of the reasons why we don't have a modern, cost-effective engine to replace the ones we currently fly behind, which would completely negate the need for 100LL.
 
Meh....all the flub-hub over the leakage. Like a AvWeb commenter said....it's probably some kids chocolate ice cream cone rubbed on the bottom of that wing. Nothing to see here folks.....;)
 
pfarber said:
the fact that you have to rebuild a magneto every 500 or so hours tells me that reliability was not an option. if you can rebuild a farm tractor mag you can replace a battery.
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Magnetos can be reliable. We don't actually have to rebuild them every 500 hours, only inspect them. And those flying part 91 don't even have to inspect them (it's not an AD), though it is a good idea to do so. If it passes inspection, as it often does, put it back into service.
 
455 Bravo Uniform said:
And greed and self-serving behavior on one, both, or many sides of the investments in aviation fuel keep the rest of us and the environment in limbo one more day while the truth is buried in there somewhere, whatever it is.
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It’s not the greed, etc. that’s the problem. It would work out just fine if the gov would allow the best solution to enter the market and let the chips fall where they may. The guy who came up with GAMI was probably “greedy” when wanting to make a profit with his formula. He should be allowed to do so.
 
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