Message-ID: <39FCB39F.CAB0A268@progress.com>
Date: Sun, 29 Oct 2000 18:32:47 -0500
From: Marcelo Pacheco <pacheco@progress.com>
Organization: PROGRESS Software Professional Services
To: lancair.list@olsusa.com
Subject: Lean of peak operations
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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Had an interesting conversation this last friday.
Was on a long flight side by side with a long time A&P, that performs
all maintenance on piston engines and PT-6 turbines for over 10 years.
I approached him about lean of peak operations, asking his opinion on
the matter.
He told me he performed testing that showed lean of peak operations to
cause holes on piston heads and to burn valves. I asked if he had any
data on the quality of fuel distribution between cylinders on those
engines. He wasn't aware of that concept. They just started doing
testing on Gamijectors recently and he doesn't have firm data yet. He
agreed that their lean of peak operations never involved leaning beyond
50 degrees lean of peak, nor that they had all cylinder engine
monitoring packages to see what was happening on the other cylinders
except for the one that has the EGT/CHT probe.

Umm, this reinforces the fact that people (understandably) keep bad
situations in mind. It's normal for people to be scared of damaging very
expensive engines. However, as those people aren't scientists, they
don't qualify all details around the issue, they just mentally label it
a no-no zone... And that's all they normally pass ahead, namely their
impressions on the subject.

If I understand the stuff behind CHT/EGT probes, they're installed on
the hottest cylinder for rich of peak operations. This means that other
cylinders are likely to be running richer (on the rich of peak side,
richer=cooler). Now when you go lean of peak (where richer=hotter,
leaner=cooler), and you got one cylinder lean of peak, and the others
are richer, hence HOTTER. Humm, wouldn't that explain why people get
burned valves when operating only 50 degrees lean of peak without good
fuel distribution ??? If they only went 100 or more degrees lean of peak
(if the engine doesn't go rough before that), now they should have all
cylinders lean of peak. Of course there are other variables like the
uneven cooling airflow through the engine, which makes those conclusions
questionable I grant.

I showed him the articles on lean of peak on engines with gamijectors,
he was definitely shaken by the stuff in those articles. He said he'll
look those up to get a better opinion on the subject.

Another very interesting finding from the articles is that the leaner
the mixture, the longer it takes to burn. Visualize the fact that the
pistons are cyclical movement. If you had combustion pressures at it's
max right when the piston are at its top position, you wouldn't have any
useful power being generated, while the best position to capture the
mechanical force of combustion is at 90 degrees past TDC (top dead
center). Because today we're stuck with a fixed combustion point
(usually 18 degrees before TDC), the leaner the engine runs, the more
mechanical power of the combustion is going towards generated power.
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