|
Re: [LML] Re: cylinder wear-to lean or not too lean
Here is what I was taught by Braly et
al
- Max power is at approximately 80 to 100 degrees
rich of peak
- Max CHT and Intra Cylinder Pressure is
approximately 50 degrees rich of peak
- In a situation in which you are at or above 70%
power (takeoff and climb), you want to be well more than 100 ROP or conversely
very lean. However since the power curve is broader on the rich side, it
is easier to manage the engine rich.
- You have no reason to be at 50 ROP (max
CHT) - it is neither peak power nor peak efficiency. It is also the
most stressful/damaging place to operate the engine.
- Flying lean of peak costs you about 3 knots and
saves you about 3 gallons/hr - a very good deal in my opinion.
D. Brunner
(I have drunk the GAMI Koolaid)
----- Original Message -----
Sent: Tuesday, February 10, 2009 12:50
AM
Subject: [LML] Re: cylinder wear-to lean
or not too lean
Here’s the quote:
“So as the mixture is
leaned, power peaks first, with CHT peaking at very close to the same point.
In practical terms, if we lean to max CHT, we'll have max power for that
MP/RPM setting. Doesn't that make sense, intuitively? Max power, max CHT? It's
not precisely true, but it's close
enough.”
John
On 2/8/09 11:23 AM, "Colyn Case at earthlink"
<colyncase@earthlink.net>
wrote:
John,
Did they really print that about
CHT?
I don't remember that max CHT equates to
anything useful although it may correlate very well to max internal cylinder
pressure (ICP), which is a bad thing. ...but it's also affected by
cylinder cooling, while EGT is (mostly) not. Max EGT would be stoichiometric
which is most efficient if your engine can take it. Usually
slightly rich of that (e.g. 50 dF ROP) is better power but also involves
more pressure before top dead center and is close to max
ICP.
There's a really scary picture you get early
in the APS course which shows how the internal cylinder pressure varies in
relation to crank position when you are running at "best power". A
measurable amount of the combustion expansion is actually pushing backwards
on the crank until it comes over the top. Great for torsional
stress.
Colyn
|