REFLECTOR: Running LOP

[John Dibble]

I think lead will tend to deposit at any cylinder temp.  The ethyl
groups in TEL will burn off during combustion leaving lead oxide which
does not boil or burn off at all.  Chlorinated hydrocarbon additives
were used to reduce the lead deposits and make them manageable.  As I
understand it 100LL contains very little TEL, enough to provide some
coating protection to the valve seats (without the use of chlorinated
additives), but too little to be an octane booster.  In summary, I would
expect results with 100LL to be different from the WWII era, because
much less TEL is used.

John

davedent at comcast.net wrote:

> Mack, this question has come up so many times over the years and to
> some it is old and to some the why is new.  But it all comes back to
> the military fuels developed during the war.  The pb (T.E.L.) with a
> boiling point of 360F degrees in the fuels were added to prevent
> detonation.  And it is still there today.  The GA engines were
> designed around this and hasn't changed since.  It's far easier to
> conform then to change. The big thing that has come out of most of
> this, is the fouling of low compression engines plugs.  The cooler the
> engine runs the worse it is.
>
> Lead can be a problem when starting if the engine is cold and at idle
> richness.  Pb deposits can't burn off as fast as carbon deposits.
> You will find that plugs have a problem of fouling out more on those
> engines that have a tendancy of running cool.  I use to race my plane
> and ran the engines at 3000 rpm and I never had the problem of plug
> foiling.  Also on the Lycoming engines I like to run the cylinders at
> the 400 degree range and even a little higher and this gives the best
> volumetric efficiency.  Some people get nervous if the temperature
> even gets close to 400 and want to keep them around 350.  The barrels
> hardly even straighten out at that temperature.
>
> On my old Long EZ the cooling was so efficient that I had a hard time
> getting 400 and I worked hard to get it there in the winter months. On
> most of the Lycoming engines the intakes run through the oil tank, so
> doing brings the temperature of the fuel up and this distributes the
> pb a little better into the cylinders but it also drops the efficiency
> of the engine as much as 20%.
>
> That's why the newer type engines don't run the intakes through the
> oil.  The design of the intake makes a big difference on were the
> deposit form and what cylinders have problems.  That is why you can
> find on some engines that one cylinder will foul out more plugs the
> others, partly, with some reservations.
>
> On the high altitude engines we would have all the intakes the same
> lengths and the exhaust were all insulated and the intake temperature
> was kept at 100 degrees.  This made a big difference, we couldn't
> afford plug fouling.  We also only used electronic ignitions also.
>
> The cooling on the Continental engines are so critical because of the
> valves that baffling is one of the most critical items to watch.  The
> temperature on these engines for cylinder runs a little cooler but not
> much.  But in all this, what I am trying to get across is, if you run
> it cold, you will get lead fouling.  More so in winter long idels and
> alike.
>
> If people think the answer is putting mogas in their engines, they are
> mistaking.  The engines are not designed for it if you have any
> compression much over 7:1 ratio.  And if you live in CA and use the
> alcohol added fuels you add other problems to the plane other then
> just the engine.  Seals, composite tanks and floats, etc.
>
> You find the question of lead fouling come up more in the winter
> months then you do in the summer months.  This has been the trend ever
> since WWII.
> Dave
>
>
>  -------------- Original message ----------------------
> From: MMurp16900 at aol.com
> > subject LOP
> > Hi Scott
> > I did read that one reason some operators run EGT 25/50 rich side
> is so the
> > leaded fuel helps to lubricate  the valve seats.
> > What is your opinion
> > Mack
> > .
>
>
>
>    ----------------------------------------------------------------
>
> Subject: Re: REFLECTOR: Running LOP
> Date: Sun, 31 Dec 2006 16:18:26 +0000
> From: MMurp16900 at aol.com
> To: reflector at tvbf.orgsubject LOPHi ScottI did read that one reason
> some operators run EGT 25/50 rich side is so the leaded fuel helps to
> lubricate  the valve seats.What is your opinionMack.
>
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