For the last 25 years, the topic of discussion on aviation fuels has been about an unleaded avgas replacement for 100LL. I have been somewhat negative about these efforts for a number of reasons.
However, at EAA AirVenture Oshkosh 2021, things changed. A 100 octane fuel may be possible, with the announcement from General Aviation Modifications Inc. of Ada, Oklahoma, that it had received an STC for its unleaded G100UL fuel.
The initial approvals are just for Cessna 172s, which allows for extended flight evaluations at some flight schools. In addition, GAMI will run several more engine tests in the next year or so. This should then lead to approval for almost the entire GA fleet, according to company officials.
Pilots are probably wondering how a small company like GAMI, whose main business is engine components, could develop a successful 100 octane unleaded fuel when huge oil companies with all of their experts and background could not.
I have visited the GAMI facility and its engine test stand is probably the best equipped aviation engine test cell that I have seen. This means that they can more accurately measure the knocking profile of a fuel than anyone else. Better tests create more meaningful results.
The other reason is economic. The major oil companies were all trying to develop a fuel using readily available components, plus a miracle additive. While this had some success, these additives all had some negative side effects.
By comparison, GAMI found some very highly refined components to blend as the basis of its fuel. G100UL is based on an alkylate that instead of a 94 to 95 lean rating has about a 98-99 lean rating. In 100LL, the refiners would take the alkylate and add two grams of lead and then add toluene concentrate to bring the octane up to a 100 lean rating.
GAMI takes its high octane alkylate and then adds a super high-octane aromatic to bring the lean rating up to 100. The result is a fuel that is very similar in characteristic to the current 100LL fuel, except without lead. In addition, the rich rating is well above the 130 limit for 100LL. The similar chemistry also means that the new fuel will be compatible with 100LL.
The cost of G100UL should be in the ballpark of the current 100LL or marginally higher, GAMI officials predict. As you might guess, the two main components are going to cost more because of the increased processing and the slight reduction in yield. However, there will be cost savings in transportation and in the elimination of the lead and toluene.
The real savings is going to be from the elimination of the leading facilities for the refineries. So, price will eventually settle out with production, but should be comparable, especially if you take into account reduced spark plug and engine maintenance for aircraft owners.
GAMI is working with Avfuel for the distribution and handling of the product, so that should be done correctly.
I know that I have been critical of the efforts to find an unleaded avgas and the candidates and work that has been done in the past. I also know that there may be some bumps in the road as G100UL is introduced and production ramps up.
But in the roughly 25 years that the GA community has been beating on this, this is the first promising step in the right direction.
This sounds like no one has ever heard of Swift Fuels.
I use swift ul94 whenever I can find it. Finding it is the problem. And I must ask, why do they need 100 octane in a 172?
Some C172s do need 100LL; the T41C [ USAF ] and the C172XP use the 210 HP, Continental IO-360 .
The lower compression Cont. O-300 and Lycoming O-320, don’t need 100LL.
Wondering the same thing…why is Swift 94UL never mentioned? I’ve run 840 gallons of it through my engines the past 3 years and it has been awesome…no fouled plugs, cleaner oil, great storage stability, fully compatible, etc. Even my paramotor and chainsaws are happy with it (after some oil is mixed in, of course…). It is hard to travel x-country and find it, however, and that is a problem.
Ben,
I sincerely hope that GAMI succeed in this venture as I am certainly keen to get lead out of my engine. But many of us remember the high hopes for oxygenates like MTBE and ETBE as octane enhancers. I’d be keen to know more about the toxicity of these super high octane alkylates. There is no point in getting our hopes up unless the replacement will be “known to cause cancer in the State of California”.
Why not use the UL91 AVGAS already widely available in Europe ?
Simply politics, the few that require 100 octane fuel have the dollars to get the attention.
Many Airports also will not handle a fuel not provided by their suppliers as the fuel vendors are often the insurance carrier for the airport as well. Those vendors have no reason to supply a 2nd fuel when we “can” all use 100LL.
Somewhere around 80% of GA needs less than grade 100 fuel but, the 20% uses about 80% of the avgas. These numbers vary depending on what study you look at but they are all close. The “good” news for those looking for other than 100LL is that the 20% of the fleet that burns the most is slowly shrinking as the operators switch to turbine aircraft. That may begin to give the 80% segment more of a voice as to what fuel we need and want.
Many thanks for your reply, good to know !
Why not use 94 octane unleaded car fuel ??? It’s plentiful at gas stations in the east coast !!!
Because a good many GA engines require 100 octane. Plus, most mogas includes ethanol, which is not compatible with many airplane fuel system components. Also, ethanol fuel does not age well, whereas avgas can last a long time in your tank.
Our 1950 era engines no longer have to be polluters. Our engines will be cleaners and will most likely last longer. Thanks GAMI…and thanks to Tim Roehl and George Braly.
“ The major oil companies were all trying to develop a fuel using readily available components, plus a miracle additive. While this had some success, these additives all had some negative side effects.
By comparison, GAMI found some very highly refined components to blend as the basis of its fuel. “
As a certain fictional TV character said more than once, Fascinating. A mere mortal like me would ask, I wonder what the difference is between a miracle additive and some very highly refined components.
Am I correct to understand the corporate guys failed to develop a new effective additive while the Gami guys went to the highly refined component store, mixed batches, ran the mixes in their engines and the mix that didn’t destroy an engine is what we will end up using ?
There was an engineer I worked with at the UAL jet shop in SFO that had a placard on his desk, “ In God We Trust, all else must bring data. “. I hope we get to hear about the hunt for the right mix one of these days.
I wonder what happens if the mix isn’t quite correct, though. How fast do the safety margins erode if a mixing error occurs ? What are the post mixing tests to ensure the fuel is what it is supposed to be, by the way ?
I know there are other considerations as well, operationally and metallurgically. Perhaps others more experienced can ask those questions again. Or perhaps Mr. Visser can list a link to the data that has been submitted to the FAA.
PS I know the tests we not run to engine destruction. Mr. Roehl and Mr. Braly are much more astute Engineers than that. They backed off well before damage occurred since their real time telemetry was closely observed during each run. Fwiw, I do hope this all works very well for the piston engine aviation world.
Well done GAMI. As usual a small business with a few very diligent people have found a practical solution to our problem. I can’t wait for this to become available for my 150 HP Citabria. I am old enough to have worked on cars that ran on leaded fuel and have seen the benefits of getting the lead out of fuel. Now aviation is on the brink of seeing the same benefits.
Does anyone know if this new fuel can be used in MOGAS engines like the Rotax? Lead fuels gum up my engine. And MOGAS is rare to find at most airports.
You betcha. I’m thinking the same for our ULPower 350i. I will be able to travel without searching for Mogas.
Bring it on quickly.
This is indeed a promising solution for the small but vocal part of the fleet that requires 100 octane avgas.
If it does cause the phase out of 100LL it would be fantastic if the producers of 100LL would simply continue to produce the fuel as 94UL. The spec. for 94UL (D-7592) is quite simply 100 LL without the Tet. Lead. It too would have fewer components, not having the TEL in it. It also would not require segregated transport as it would not contaminate pipelines with lead. Avgas is transported in segregated trucks to keep from contaminating the other products with lead, not to keep the Avgas from being contaminated.
In reality it should,but of course not likely, cost less than the current 100LL.
It is impractical to produce more than one grade of avgas because the cost to duplicate the supply channel are exorbitant. Separate fuel trucks, storage tanks, misfueling incidents, all argue for one avgas that can be used by all users. That is why the answer will be to produce a single unleaded 100 octane fuel that is usable by everybody, from the J3 cub to the pressurized twins.
Ben,
Thanks for the article. I’m encouraged that this unleaded fuel will be available soon for our low compression engines.
And, it’s good to hear that the cost premium may not be too high.
Unleaded fuel in autos has made spark plugs last ‘forever’ and oil life is now 2-3x than the previous 3,000 miles recommended.
Besides the indicated health concerns, it was noted that there is only one company, in England, that makes TEL .
Auto Engines are water-cooled
Auto Engines run most of their life at 5% load…..
Auto engines have little space, weight and redundancy constraints
And so on.
Porsche could not build a “good” Aviation engine though they tried very hard.
And the best auto engines are LESS efficient than our aviation engines under high load conditions.
So please, no more comparisons like that.
By the way, I like my lead it does much more than modify the octane rating.
I don’t believe the statement that auto engines are less efficient than aircraft engines. I believe just the opposite is true.Either high or low load conditions GA engines are woefully inefficient.It’s not the engine manufactures fault. Blame that on the FAA. Just look at the Rotax series of engines. They put out more power with much less fuel consumption with a comproable TBO.
you missed the point or lead vs unleaded .!
BTW, Porsche made a fine aircraft engine for the Mooney. It was the pilots that couldn’t adapt to running the engine at 5,000 rpm vs the ‘normal’ 2,600-2,800 rpm.