Aviation Fuel

[bwalker]

Frank, I cant remember for certain, but its some oxide of lead. Thats what the white stuff you see coating the exhaust of airplanes is.
I dont know about elevated levels found on road sides, but that seems plausible.
BTW the lead ban didnt have to do with lead a problem per say. It had to do with the addition of catalyst to cars because of the clean air act. Lead poisons cat cons in short order.

 

[jimbo1490]

The big problem with TEL in fuels is not inhalation of the exhaust fumes, per se. Instead, imagine if all gasoline engines burned leaded fuel (as they once did). What you get after a period of years is a very fine dust of lead oxides coating EVERYTHING, the ground, all the leaves on all the trees, the road surface, roofs of buildings and etc. When this dust blows around, this then becomes the dominant way you are exposed to lead. Then when it rains the dust turns into a silt and gets into a whole bunch more stuff. A couple of years after completion of the US lead phase-out, environmental lead levels receded back to background (natural) levels.

Jimbo

 

[SFO]

I have a friend who is a fuel guru.
I asked him about this thread.
This were his thoughts...

A high output chain saw is one of the few places where AvGas could prove to
be an advantage.

There is a high temperature hook in the end of the distillation curve that
tends to leave fuel in a liquid state in the combustion chamber at high rpm
. While this would be a problem on a CRF250 it could be an advantage on a
high strung two-stroke.
The closer you get to the thermal limits of a particular engine design the
more useful fuels with high end points become. Properly chain saw engines
tend to flirt with the thermal limits quite regularly. The end point
distillation temperature of AvGas is high enough that some of the fuel can
make its way into the combustion chamber in liquid form. While this would
normally prove to be a liability in most engines it could be useful when you
are tuning to the ragged edge. The liquid fuel droplets entering the
combustion chamber will leech some heat and help to cool the piston crown.
In an engine that is pushing the thermal limits this can be the difference
between a win and a holed piston. Some specialty fuels like Philips P45 are
designed with a large jump at the end of the distillation curve to
specifically provide this cooling effect. It’s not uncommon for a fuel with
higher octane (like B37) but lower end point temperatures to experience
preignition problems long before fuels with high end points. It's the tuning
equivalent of making lemonade out of lemons. For engine combinations that
aren't near their thermal limitsthis high end temperature just ends up as
oil spooge dripping out of the silencer even when the jetting is lean. Due
to it's high end point temp saw engines is one of the few applications where
AvGas can prove to be useful.

 

[BostonBull]

Well lets get some saws out there with temp readings with both fuels in them. I know if what he is saying is true then I would use AV in the summer.

 

[jimbo1490]

Even this bit of fuel esoterica was mentioned, albeit briefly, in the previous thread on 100LL. A downside of the high end point distillates is going to be unburned HC, since some species are not getting vaporized until the very moment of combustion. Though these can act as a sort of 'persistent' power enrichment as you mentioned ievitably, some will ultimaley go unburned.

Jimbo

 

[BostonBull]

SFO did he really mean the CRF250?? Thats a 4 stroke engine...kind of apples and oranges!

 

[bwalker]

SFO, you wouldnt happen to be quoting Rich Rohrich are you?
In general the gist of what you say is spot on. The problem with a saw is the conditions in which it is ran, intermitten load with brief periods of time at full load. If you where in big wood where you can stay on the gas for 3o seconds or more av gas would be of use, but for the average woodtick blocking up firewood its not of much use and actually mat hurt performance.

 

[SFO]

SFO, you wouldnt happen to be quoting Rich Rohrich are you?
In general the gist of what you say is spot on. The problem with a saw is the conditions in which it is ran, intermitten load with brief periods of time at full load. If you where in big wood where you can stay on the gas for 3o seconds or more av gas would be of use, but for the average woodtick blocking up firewood its not of much use and actually mat hurt performance.

The crf reference I believe was a datum, not an abstact.
BWALKER, I thought you might be you...
How could RR be anything but RR?
Your points BTW, are relevant.
Just very twitchy around fuel threads.
I don't believe my first post was a thread highjack.
Sorry...

 

[weimedog]

I have no scientific background to draw from....but I have used AV gas in my two strokes for a while. My old vintage bike (Husky 430) runs cooler and smoother. Especially at low RPM's under load. My old saws run cooler as well. After milling with my McCulloch I can actually put my hand on the fins where with regular pump gas I can't. That a tangible (no pun indended) difference. With the old motorcycles the difference is pronounced enough that its worth the extra expence. The Saws?? With the Milling situation and the BIG old saws..maybe the rest maybe not. I can't see any real difference in my 365 but I certainly can in my older Homelites in particular the 925 I run.

I have some 4-Stroke motorcycle experience as well....(As some here may know) My four strokes don't thrive on AV-Gas. They run fine and all but they like pump gas the best. (NOT 87 regular!! But 93 Octane "Hi-Test") Snappier with the cheap stuff. One actually likes the "mid-Grade 89 octane the best. (A mild tuned 450 fourstroke) Data? I spend the better part of a year field testing jetting, timing, and fuel combinations at several altitudes for a small company a while back.

 

[bvaught]

One thing I forgot to mention 100LL is rated at 100 octane during "lean setting" operations and 130 octane during "rich setting" operations.

 

[spencerhenry]

at the off-road races we go throught several drums of 110 octane leaded each race, but we almost always have some left over in a dump can. dump cans are plastic. the guy who supply race fuel say not to store it in plastic. if you are not going to use it for more than a couple of days, put it back in a drum.
i ran about 35 gallons of 110 throught the splitter, everyday when i started the splitter it reminded me of race morning, starts and runs just fine, but honestly noticed very little difference in starting or performance. maybe i need to bump up the compression on the splitter's honda. 11.5 :1 ought to do it.