Mixing 100LL with gasoline

[Frank Giger]

I've been running straight ethanol free car gas in my VW powered plane, but on a recent trip wound up having to put some AVGAS into the tank to give me a comfortable edge in the amount of fuel I had for the trip home.

I didn't notice any real difference in performance, to be honest - perhaps it's to subtle for the type of flying I do. Fuel burn seemed about the same as well; it might just be my imagination but it looked like I burned more 100LL than I would have gasoline. One fifty mile trip isn't a good gauge at any rate, as I rarely fly consistently on any given leg.

Indeed, I'm not all that interesting in benefits, as in my high drag very slow aircraft there's a diminishing return on performance gains.

The larger question is one of running 100LL causing problems. I'm thinking that I probably won't have any issues with lead gathering on the spark plugs, etc., as it's occasional and in a mix anyhow.

A few facts:

1) I operate at low altitudes - no more than 4,000 feet above sea level (well, with density altitude figured in we can add 2,000 feet to that in summertime. ;) ).
2) I may operate at freezing temperatures once or twice a year...the rest of the time it's temperate or downright hot here in Alabama.
3) It's a bog standard Volkswagen engine with a bog standard Holley carb, with the fuel being pushed through a bog standard Facet electrical fuel pump.

[rwanttaja]

I run a mix of 100LL and auto fuel (no ethanol) in my Fly Baby, and have had no problems with it. I generally try to make every fourth fill 100LL; it has four times the lead of the old 80 octane avgas, so I'm figuring my Continental is getting the right about of lead.

I usually switch to running 100% 100LL in late fall, as I fly less in the winter and avgas is more stable. I've used this system for the ~23 years I've had my airplane, but this spring was the first time I developed apparent lead-fouling. I did some leaning to burn it out, and with the arrival of spring have switched back to car gas. Problem has gone away.

Performance wise, one must remember WHAT the significance of octane is: It is to provide resistance to pre-detonation, or knock. Adding lead is the easiest way to do this, in fact, I believe it's the ONLY economic way to do this above ~93 octane. If one has an engine designed to run on 80 octane fuel, it derives no benefit from a higher-octane gas unless the engine's timing is adjusted to take advantage of it. And if one goes back to 80 octane, one must re-adjust the timing or significant detonation will occur.

Modern car engines have electronic ignition and knock sensors, and can automagically adjust for changing octane levels of the fuel. Don't see that in aircraft engines.

The ironic thing about this is that 100LL fuel actually had LESS energy vs. unit volume than car gas, because of the lead.

Ron "It's a Gas" Wanttaja

[Dana]

100LL occasionally won't do any harm, on a steady diet of it you might see lead fouling of plugs or valves. I ran straight 100LL in the Mosler half VW in my Fisher with no problems for the 100 hours or so I owned the plane. But there won't be any performance gain unless the engine already needs higher octane than the car gas provides.

If, however, you usually run mogas with ethanol (I know you said ethanol free), then switching to agvas can affect jetting... avgas burns richer, in the 2-stroke Cuyuna I had in my Ultrastar I found it to be about a 1/2 jet size increment. I saw that as a safety thing, I jetted for E10 mogas (all I could get), then if I filled up with avgas on a cross country I didn't have to worry about it being too lean.

[FlyingRon]

Both the popular Autofuel STCs allow any mixture of 100LL and (allowable) AutoGas. I've never heard of it being a problem. As Dana and Ron said, the biggest issue is that 100LL will lead choke an engine that was expecting 80.

[cub builder]

I usually run a mix of 80 - 90% 93 octane alcohol free Mogas with 10 - 20% 100LL. I mix the fuels in a 110G tank/fueling rig I have in the bed of my truck. I've got roughly 1000 hours running this type of mix. I do it primarily to keep the lead content down on the O-200 in one of my planes since 100LL has roughly 4 - 5x the amount of lead contained in the 80 octane fuel the O-200 was designed to burn and causes premature valve guide wear, but also for the direct economic reasons of the fuel being less expensive. Both of my engines (O-200 & O-320) are 8.5:1 compression. I have been unable to detect any difference in performance or fuel burn between straight Mogas, 100LL, or a mix. However, since I started running a mix of fuels, I never have to dig lead out of the spark plugs during the annual, and have had no issues with sticky valves or excessive lead build up on the valve stems in the O-200.

[1600vw]

In my vw I use a mix of 100LL and non-ethonal auto fuel. I add a product called TCP to the 100LL to keep lead at bay. When checking for water I like to see my fuel with a blue tint. The reason I use 100LL. First these engines were designed at a time when lead was being used in the fuel. Second 100LL will not vapor lock like auto gas. Now does mixing these two fuels still protect from vapor lock, I would like to think so.

[Mike M]

While in college on the plains of Nebraska I was employed by a large FBO. The boss told me on day 1 that he expected a minimum of one quart be drained from each sump on every fuel truck and every storage tank (80, 91, 100, 115) per day, plus as much as it took to get a clean sample. What I did with it was my business but it did NOT go back into any company tanks and o by the way if I ever took a drop out of a fuel service nozzle I was fired. I bought two 5 gallon fuel cans and for four years never bought gasoline for my 1200cc, later 1500cc Beetles unless I was on a long trip out of town. The tips of the tailpipes turned purple when I burned 115. No other effects noted including average fuel economy. Your mileage may vary. :)

[FlyingRon]

Those old VWs were designed for leaded fuel to begin with (though nowhere near what 100/130 and 100LL have). Unless you've done something to increase the compression on these things, the extra octane isn't going to make any difference.

[Bill Berson]

Softer old valve seats erode faster without a bit of lead for "lubrication". Unleaded engines have harder seats. So put a bit of lead in older engines.

[Frank Giger]

So....add a bit of Marvel Mystery Oil and it'll be okay. Got it.

:)

Seriously, thanks for y'all's input.

[rwanttaja]

So....add a bit of Marvel Mystery Oil and it'll be okay. Got it.
You'll find it keeps the elephants out of the hangar, too.....

Ron "How it got in my pajamas, I'll never know" Wanttaja

[Ron Blum]

I agree with all the previous comments, but will also add a couple more … one for each fuel to be fair :)

1. With autofuel (everyone has mentioned no alcohol), there are two mixes: summer and winter. The RVP (Reid Vapor Pressure) is lower in the winter so that cars start easier under colder conditions. The vapor lock issues arise when you burn winter fuel in the heat of summer.

2. The aromatic content of Avgas is significantly higher than autofuel. One has to be careful of rubber parts reacting to the higher aromatics. It is also blamed for some wet wing fuel tanks to leak when it breaks down older sealants.

My two cents,
Ron "in an earlier life worked the EAA autofuel test program" Blum

[BusyLittleShop]

How lead got into our fuels and how lead was removed or reduced from our fuels are interesting stories...

The story how lead got into our fuels started with high compression
aircraft engines back in 1921... a young engineer fresh out of college
named Charles Kettering started Dayton Engineering Labs Company or
Delco... he invented the first battery ignition systems for aircraft
engines... when protagonists in the field of aviation widely blamed
his battery ignition systems on knock or detonation Kettering
commanded his young assistant Thomas A. Midgley on a investigation of
detonation. motivated as much by a desire to protect Delco's
reputation as by scientific altruism. Midgley worked for months over
his single cylinder engine and famous "bouncing pin" which was devised
to measure differences in detonation pressures. and he soon determined
that detonation depended on both fuel grade and engine compression
ratio. Thinking at first that fuel color influenced knock. Midgley
added iodine to his fuel theorizing a dark-colored fuel would absorb
more heat energy and vaporize more quickly. When the knock diminished
he smelled success, but it did not come in the form . he suspected.
Further experiments forced him to discard the fuel color idea but led
in turn to a long. frustrating line of trial anti-knock additives. GM.
parent company of Delco. encouraged Midgley and his assistant T. A.
Boyd. who in a vigorous program, individually tested more than 30,000
compounds and their discouragement mounted with the list. On December
9, 1921. a chilly Friday. Midgley and Boyd were anticipating the
weekend's respite from their series of relentless, routine tests when
suddenly the engine was not behaving the same at all. Jolted into
disbelief, Midgley had quite literally stumbled onto the remarkable
antiknock properties of an obscure substance called tetraethyl lead.
This proved to be without doubt the greatest single discovery in the
development of aviation fuels; not only did this additive make higher
power possible. it enabled the aeroplane to fly farther on a given
amount of fuel- it gave the aeroplane range- and in turn enabled the
successful engines that dominated aviation until the advent of gas
turbines. In 1967 the remarkable Mr. Midgley was still active as
president of the American Chemical Society.

**************************************************
The story on how lead was legislated out of our fuels started when
Clair Cameron Patterson could not isolate his rock samples from lead
contamination in the lab in an effort to determine the age of the
earth... he was shocked to learn lead was everywhere and developed the
first sealed clean lab to prevent lead from messing up the data...

The University of Chicago developed a new method for counting lead
isotopes in igneous rocks, and assigned it to Clair Cameron Patterson
as a dissertation project in 1948. During this period he operated
under the assumption that meteorites are left-over materials from the
creation of the Solar System, and thus by measuring the age of one of
these rocks the age of the Earth would be revealed. Gathering the
materials required time, and in 1953, Clair Cameron Patterson had his
final specimens from the Canyon Diablo meteorite. He took them to the
Argonne National Laboratory, where he was granted time on a late model
mass spectrometer.

In a meeting in Wisconsin soon afterward, Patterson revealed the
results of his study. The definitive age of the Earth is 4.550 billion
years (give or take 70 million years). This number still stands,
although the margin of error is now down to about 20 million years.

His ability to isolate microgram quantities of lead from ordinary
rocks and determine their isotope composition led him to examining the
lead in ocean sediment samples from the Atlantic and Pacific. Deriving
from the different ages at which the landmasses had drained into the
ocean, he was able to show that the amount of anthropogenic lead
presently dispersed into the environment was about eighty times the
amount being deposited in the ocean sediments: the geochemical cycle
for lead appeared to be badly out of balance.

The limitations of the analytic procedures led to him using other
approaches. He found that deep ocean water contained 3-10 times less
lead than surface water, in contrast to similar metals such as barium.
This led him to doubt the commonly held view that lead concentrations
had only grown by a factor of two over naturally occurring levels.

Patterson returned to the problem of his initial experiment and the
contamination he had found in the blanks used for sampling. He
determined through ice-core samples from Greenland that atmospheric
lead levels had begun to increase steadily and dangerously soon after
tetraethyl lead began to see widespread use in fuel, when it was
discovered to reduce engine knock in internal combustion engines.
Patterson subsequently identified this, along with the various other
uses of lead in manufacturing, as the cause of the contamination of
his samples, and because of the significant public-health implications
of his findings, he devoted the rest of his life to removing as much
introduced lead from the environment as possible.

Beginning in 1965, with the publication of Contaminated and Natural
Lead Environments of Man, Patterson tried to draw public attention to
the problem of increased lead levels in the environment and the food
chain due to lead from industrial sources. Perhaps partly because he
was criticizing the experimental methods of other scientists, he
encountered strong opposition from recognized experts such as Robert
A. Kehoe.

In his effort to ensure that lead was removed from gasoline
(petroleum), Patterson fought against the lobbying power of the Ethyl
Corporation (which employed Kehoe), against the legacy of Thomas
Midgley — which included tetraethyllead and chlorofluorocarbons — and
against the lead additive industry as a whole. Following Patterson's
criticism of the lead industry, he was refused contracts with many
research organizations, including the supposedly neutral United States
Public Health Service. In 1971 he was excluded from a National
Research Council (NRC) panel on atmospheric lead contamination, even
though he was the foremost expert on the subject at that time.

Patterson's efforts ultimately led to the Environmental Protection
Agency announcing in 1973 a reduction of 60-65% in phased steps, and
ultimately the removal of lead from all standard, consumer, automotive
gasoline in the United States by 1986. Lead levels within the blood of
Americans are reported to have dropped by up to 80% by the late
1990s.

He then turned his attention to lead in food where similar
experimental deficiencies had masked the increase. In one study he
showed an increase in lead levels from 0.3 to 1400 nanograms per gram
in certain canned fish compared with fresh, whilst the official
laboratory had reported an increase of 400 to 700. He compared the
lead, barium and calcium levels in 1600 year-old Peruvian skeletons
and showed a 700- to 1200-fold increase in lead levels in modern human
bones with no comparable changes in the barium and calcium levels.

In 1978 he was appointed to a NRC panel which accepted many of the
increases and the need for reductions but argued the need for more
research. His opinions were expressed in a 78-page minority report
which argued that control measures should start immediately, including
gasoline, food containers, paint, glazes and water distribution
systems. Thirty years later, most of these have been accepted and
implemented in the United States and many other parts of the world.

[Ron Blum]

Busy Little Shop: This is a great post!!! ... especially for your second post. I learned a lot. Thanks!

Ron "always learning" Blum

[BusyLittleShop]

You're welcome Ron...

[Ron Blum]

Since we’re proving that we cannot make 100/100LL without the use of TEL, Is there another potential solution?

So ... at Sun-N-Fun ... one of the major petroleum companies said that they are running tests with magnesium as the octane booster. Any thoughts on that?

[Bill Berson]

Pure magnesium, or some compound?
Should be lighter than lead.:eek:

[Ron Blum]

Pure magnesium, or some compound?
Should be lighter than lead.:eek:

I can't image anything but pure magnesium, but weight is probably not a consideration. They also mentioned that they could somewhat control the aromatic content … but lower didn't seem to be part of their objective.