There is an old adage that success has hundreds of parents, but failure is an orphan.
We see that when we look at the history of leaded fuels.
When I started at Shell Oil in 1967, my first project was to optimize the lead and scavenger levels in auto fuels. I started by reading most of the technical reports in the company library.
I was surprised to find that there was a long list of metals that worked as anti-knock additives. Apparently, the metal additives all retarded the pre-flame reaction that occurs just prior to the actual combustion flame in the cylinder.
The reports covered work at Shell and throughout the industry. There was research from many different labs that covered solubility, anti-knock performance, negative side effects, necessary scavengers, and on and on.
The compromised solution was tetraethyl lead (TEL).
TEL was used in almost all auto fuels and avgas because it raises the octane of fuels at a fraction of the cost incurred by increasing the severity of the refining process.
During the 1930s, there was a very large effort by the industry to develop 100/130 avgas. Again, no one person or company was the sole inventor. The formula for 100/130 was set by the government and any oil company could produce it if it had the necessary equipment and facilities.
Then in 1947, ASTM adopted the D-910 specification, which defines the 100/130 formula, as well as 80/87 and 115/145 grades of aviation gasoline. This remains in effect with minor changes, such as the addition of 100/130 low lead in the early 1970s.
That is a brief history of how we got to where we are now. The big question is where do we go from here?
For more than 25 years the industry has been looking for an unleaded 100/130 octane fuel to replace 100LL. But this search is very different from the search in the 1920s and 1930s.
In those searches it was a very large cooperative effort to find an answer — and they were looking for one candidate that could be produced by everyone.
But today in our search for a 100 unleaded avgas, we have two, maybe three candidates, non-standardized specification, and a host of problems and unresolved issues.
So Many Questions
If there are three different standards, would a pilot have to have three STCs or find a fuel qualified against three separate specifications?
Are the fuels compatible with each other?
Do any of the fuels provide protection against exhaust valve recession?
What about seal and fuel system component compatibility with each fuel for every aircraft and fuel system?
Will the fuel cause abnormal and harmful engine deposits?
Will some states not allow the fuel because of ground water contaminates?
The list goes on and on, including a big one: Since no major oil company has a candidate, who will be able to supply an unleaded avgas to all parts of the country — actually all over the world?
I know there are some negative concerns with big oil companies, but they are needed for technical support, adequate supply, and distribution sites to ensure continued and on spec fuel to everyone.
I also know that lead can cause spark plug fouling and some deposits in the cylinders.
But these are problems we know about and, I believe, are better than any of the new problems that may surprise pilots at the most inopportune times — like at 8,000 feet.
My experience of switching from 100LL to UL91 in small Continentals in Europe is that it immediately stopped spark plug fouling and slowly removed deposits on the pistons, cylinder heads and exhaust valves. I guess if you switched between the 2 or mixed them you would see little cleaning benefit.
” Why are the wise so uncertain and the ignorant so sure” comes to mind here.
I completely agree with Ben. The process used to develop a new fuel is cringe worthy at best. I too have some of the research papers of all that was tried in the 30s and 40s in terms of knock resistant fuels.
I drive a 1972 Volvo, sometimes on 100LL, most of the time with unleaded fuel. The amount of deposits does not vary noticeably! “Its the oil consumption stupid”, James Carville would say. So the claim by the new fuel producers that their fuel will produce clean combustion chambers is suspect at best. A reduction in deposits is very important to reduce knock. Unfortunately oil consumption can’t be reduced enough until we go to liquid cooled engines, ask Porsche.
Klaus Savier,
Light Speed Engineering
First… and this drove me nuts… About this post…
Quote “I drive a 1972 Volvo, sometimes on 100LL, most of the time with unleaded fuel. The amount of deposits does not vary noticeably!”
Well, let see where is statement falls apart. OH a 1972 Volvo was on the road when leaded gas was the only fuel available… so when unleaded came to the market and replace all 99.999% of auto fuel… the Volvo would run nicely on both leaded and unleaded. I know… my dad used to feed 80/87 and 90/97 to our 1971 PU truck at the airport ’cause it was cheep enough’… and that old farm truck ran fine on both.
The catalytic converter required for all cars due to soaring dangerous air/water/land pollution was introduce soon after all leaded auto fuel was ‘out of the nations fuel infrastructure…. and gross reduction in dangerous air pollutants followed. The thing to remember… leaded fuel will destroy catalytic converters. YEAH that Volvo never had one.
What bothers me more than anything is the reluctance for Lycoming and Continental and the major GA companies to join forces on the subject of common unleaded aviation version(s)… of existing high grade/quality UL auto-fuels… for GA Acft flying with 95% ‘their engines’. This unwillingness to jointly participate in developing premium unleaded hydrocarbon AvFuels that play nicely with their engines and aircraft [fuel systems]… all environments, all altitudes and all compression ratios…. leaving ‘this tough nut’ for everyone else to crack… is just PATHETIC
OH YEAH… auto racing is the one ‘legal carve-outs’ for high octane leaded fuels… those high horsepower engines simply cannot survive/thunder-along without this traditional fuel… price and limited distribution be dammed.
from their websites;
Nascar uses E15, 98 octane unleaded fuel
Indy cars use E85 , using 15% gasoline to have visible flames i the case of a fire
Formula 1 uses an ethanol mix of unleaded fuels
Drag race cars use mostly nitro-methane , but some do have TEL.
From a book by C Douglas, ‘ The Secret Horsepower Race’, TEL was first added to avgas in about 1931, when RR was participating in the Schneider Trophy races.
The race fuel was 20% aviation gas, 70% benzol, 10% methanol and 4 cc of TEl.
This allowed the engine to run with 60+ inches Hg manifold pressure, getting 2,530 bhp at 3,200 rpm, and the aircraft flying at 407 mph.
So, TEL has been used in fuels for over 90 years.!!!
BTW, they found that higher levels of TEL was highly corrosive to valves.!
Enough already. We have a suitable fuel that is fungible with 100LL. Just because you want to bury your head in the sand and ignore it doesn’t mean it isn’t there.
100LL main component TEL is highly toxic and only one plant makes it and they have decided to stop producing TEL starting in 2030
https://www.avweb.com/air-shows-events/at-some-point-producing-the-lead-in-leaded-avgas-can-become-too-expensive-to-be-worth-it/
So we better make a decision or at least have multiple options in the next 5 years or the decision will be made for us, but 100 LL will not be a choice because no government official or community will sign off on having a TEL plant in there back yard, I live in NJ and the amount of toxic waste site around the states due to the production of agent orange, asbestos tiles and other industries have left many areas toxic dumps in heavily populated area.
https://www.northjersey.com/story/news/environment/2023/12/29/nj-superfund-sites-list-bergen-morris-passaic-essex/71970761007/