Today's Message Index:
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1. 10:04 PM - Re: Lycoming EGT, IO 540 (Mike)
2. 10:07 PM - Re: Lycoming EGT, IO 540 (Gary Casey)
3. 10:11 PM - temps (Bob & Toodie Marshall)
4. 10:47 PM - Re: Lycoming EGT, IO 540 (Bob Buckthal)
Message 1
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| Subject: | Lycoming EGT, IO 540 |
Bob,
100 deg? EGT or CHT? What you are trying to do is to get each cylinder
to peak at the same time. What you=92re looking for is the delta
between
when each cylinder peaks. In a perfect world all the cylinders should
peak at the same time at the same temperature. That never happens
because of many factors; cooling effect, induction difference, valve
opening, ect. It is very common to see on a well setup engine peak
deltas around 30~60 deg. between each other. The CHT by itself is for
limit purposes and the EGT is to help find when each cylinder peaks. I
hope this helps.
Mike Larkin
-----Original Message-----
From: owner-engines-list-server@matronics.com
[mailto:owner-engines-list-server@matronics.com] On Behalf Of jrc
Sent: Friday, November 09, 2007 5:09 PM
Subject: Re: Engines-List: Lycoming EGT, IO 540
Have you moved the thermocouples around too, to assure that your 100
degree difference isn't due to a thermocouple difference?
JimC
----- Original Message -----
From: HYPERLINK "mailto:rtmarshall@osbtown.com"Bob & Toodie Marshall
Digest Server
Sent: Friday, November 09, 2007 12:22 PM
Subject: Engines-List: Lycoming EGT, IO 540
My question? Is 100 degrees a significant number when compared to the
other five cylinders?
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10/2/2007 11:10 AM
10/2/2007 11:10 AM
Message 2
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| Subject: | Re: Lycoming EGT, IO 540 |
Bob,
First, it would be good to know which version of the IO-540 you have
since the angle-valve and parallel-valve engines have quite different
intake systems. The angle-valve engines have an intake system that
is quite good in that the tubes are well matched, have a reasonable
tuning benefit and don't absorb too much heat from the oil. The
parallel-valve engine, on the other hand, were designed for
carburetion and have much of the intake system buried in the oil
sump, transferring more heat and limiting the freedom of design.
Generally, though, the air distribution of these engines is pretty
good. The first thing to do when sorting out air/fuel distribution
questions is to measure it using the "lean sweep" method. Starting
well rich, record all exhaust temperatures and fuel flow (it's handy
to record CHT's and flight data as well, but it is not necessary for
good results). Lean the engine a step at a time - the finer the
steps the better, although it will start to take too long if done to
the extreme. After all cylinders have peaked continue to go lean
until you get at least 2 or 3 data points on the lean side of the
leanest cylinder. The biggest problem I've had is not waiting long
enough for all the variables to stabilize before recording the data.
It is good to do the exercise a few times to make detection of bogus
data points easier. Plot the temperature of each cylinder against
fuel flow all on the same chart. Pick what appears to be the "best
fit" straight line on the rich side and another on the lean side,
extending them until they cross. That is the fuel flow at which that
cylinder peaks. Do not just pick the highest temperature and call
that the peak as the temperatures have a tendency to round off near
the peak, making the true peak hard to find. Do that for all
cylinders and measure the spread of fuel flow between the leanest and
richest cylinders. Ideally, it should be less than 2%, but 3 or 4%
is probably okay. If the spread is more you should do something
about it. An easier way is to ship all the data off to GAMI and they
will give you an expert opinion.
Back to your questions:
1 - 100 degrees is significant, but there may not be much you can do
about it. The thermocouple readings can be affected by cooling air
flow on the outside of the pipe as well as orientation of the probe
itself. Exhaust flow inside the tube is not uniform around the
diameter - all probes should be the same distance down from the
cylinder and inserted from the same angle. The temperature of the
cylinder itself will affect the measurement. My hottest cylinder
also has the highest EGT reading - does one cause the other, or is it
coincidence? Hard to say. Why, then would one be different that the
other? There are three fundamental factors on EGT - mixture (you're
going to take that out of the equation), Compression ratio (all
cylinders are the same, right?), and spark timing (hard to imagine
the timing for one cylinder being different than the others). That
pretty much brings it back to measurement errors unless the exhaust
valve is leaking a lot.
2 - The temperature of the inlet air won't have much effect on air/
fuel distribution. It's possible that ram air will have a
deleterious effect on smoothness, however. If the manifold pressure
at the intake port becomes higher than the upper plenum pressure it's
possible that some fuel could come out the air bleed vents, although
this usually leaves a tell-tale stain around the injector. I could
also make the atomization of the injector suffer and that in turn
could create a cycle-to-cycle variation in fuel flow, making the
engine feel rough. A good injected engine should be able to be
leaned so much that the power is way down and still be running
smoothly. Not all are that way.
3. - Intake turbulence itself is probably beneficial to mixing the
air and fuel unless one intake runner is different than another.
Lycoming engines are typically pretty good in this regard, but again,
I have no idea which type you have.
Just as an aside, I've messed around trying to figure out the best
air/fuel ratio to run. It all depends on the ratio of your desire
for speed to the size of your wallet. Speed is good, but fuel flow
is bad. As a first shot I used the same equation some people (CAFE,
I think) use - multiply mph by mpg. The peak is the optimum place to
run if speed is just as important as fuel economy (how do you
decide? It's your own choice). This turns out to be TAS^2/GPH. I
found the optimum was just lean of peak. Going as far lean as
possible didn't help, although usually it didn't make it much worse
either. Going rich was like falling off a cliff. Fuel flow goes way
up, but air speed doesn't. What you really want to put into the
equation is ground speed, so that will change the shape of the curve
for every flight. The optimum with a headwind is on the rich side
and with a tailwind it is more on the lean side.
FWIW,
Gary Casey
>
> Time: 03:20:57 PM PST US
> From: "Bob & Toodie Marshall" <rtmarshall@osbtown.com>
> Subject: Engines-List: Lycoming EGT, IO 540
>
> Hi all, At overhaul I had the cylinders flow balanced, the engine runs
> very well, very smooth. Considering the rising fuel costs, I have been
> considering attempting to run the engine LOP, I have been unsuccessful
> as the richest cylinder peaks last and by then the other cylinders are
> running rough. I use the AFP fuel injection system which performs
> flawlessly and have moved nozzles around to effect egt changes which
> have been effective to a point, where cyl #6 runs 100 degrees cooler
> than the others. My question? Is 100 degrees a significant number when
> compared to the other five cylinders?The engine builders out there who
> are making real HP see the different relationships on cooling effects
> and cylinder balancing and the induction system. Question #2 does
> cold
> air induction help to make the lycoming run more evenly balanced in
> respect to temps. #3 Is it possible that the stock lycoming intake
> system generates to much internal turbulence which effects the
> individual cylinder performance? Thanks for any info and taking the
> time
> to answer. Bob
Message 3
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Hi, all the probes are same distance from flange and close to same
clocking. As I see this each cylinder is an engine in itself and the
difference in temp is probably from air induction/fuel differences.
Maybe Barrett (BPE) Or someone else who does a lot of Dyno work has
seen this?thanks for the input. Bob
Message 4
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| Subject: | Re: Lycoming EGT, IO 540 |
First read John Deakins series of articles on engine operation on the
Avweb.com site. Differences in EGT are likely more to do with temp
probe instalation. Your goal is to get all the EGT's to peak(regardless
of the temp) at the same throttle position. It one cyl has not peaked
and the others are in lean missfire, Your FI may not be flawless. The
induction system is well designed. Unless your engine builder left a
tool or a rag in there, that is not your problem. Go back and redo the
nozzles. DO NOT try to achieve an even temp. Once they all achieve
their peak temp at the same throttle position you should be able to get
as much as 150 degrees lean of peak before missfire.
Bob
----- Original Message -----
From: Bob & Toodie Marshall
To: Engines-List Digest Server
Sent: Friday, November 09, 2007 10:22 AM
Subject: Engines-List: Lycoming EGT, IO 540
Hi all, At overhaul I had the cylinders flow balanced, the engine runs
very well, very smooth. Considering the rising fuel costs, I have been
considering attempting to run the engine LOP, I have been unsuccessful
as the richest cylinder peaks last and by then the other cylinders are
running rough. I use the AFP fuel injection system which performs
flawlessly and have moved nozzles around to effect egt changes which
have been effective to a point, where cyl #6 runs 100 degrees cooler
than the others. My question? Is 100 degrees a significant number when
compared to the other five cylinders?The engine builders out there who
are making real HP see the different relationships on cooling effects
and cylinder balancing and the induction system. Question #2 does cold
air induction help to make the lycoming run more evenly balanced in
respect to temps. #3 Is it possible that the stock lycoming intake
system generates to much internal turbulence which effects the
individual cylinder performance? Thanks for any info and taking the time
to answer. Bob
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