M

Moura

Well Known Member
Hi folks
I fly a RV-10 with IO540 and dynon skyview and I notice that cylinder number 1 is the first one to peak every time. However, as I continue leaning I notice its temperature continues to fall and suddenlly its trend inverts and it starts to raise as others cylinders are reaching peak or have already reached peak and are getting further down on lean side. Last flight this first cylinder peaked and as I continue leaning and after decreasing about 15 degrees on lean side, the gas temp on the cylinder started to raise, even though other were decreasing on lean side, and even reached yellow line as other cylinder temp were going down. Resuming, this cylinder is the first to peak, temp goes down and then up. What is happening? Any ideas?
Thank you

Moura
 
Bad probes, maybe?

Hi Moura,
My -10's # 1 cylinder recently started intermittently showing 1650, while the others were around 1280-1300. After I started leaning, its temperature went down close to the others, then occasionally jumped to 1650 or so. We decided to change the probe and see if that is the problem. The engine only has 350 hours on it.

Best,
 
Pierre, it does not seem like a bad probe as the temps are all similar and this only happens when I pull the misture. Thanks
 
It is normal to see the rise again, although at only 15 LOP, I'm not sure. I understand it is called lean mis-fire, where the cylinder becomes so lean that it doesn't burn properly. On mine, it takes something like 100 LOP to see it. However, I run dual EI's on mine, if you are running straight mags, it might occur much sooner. I know when I had the Lasar system, and could revert to straight mags in flight, I could not go much lean of peak before roughness. EI really shines LOP.

Run the fuel balance and see where things are - that cylinder may just need a little larger injector.

Here you can see a couple cylinders started to trend upward:

N66AP%20egt%20showing%20lean%20misfire.JPG
 
Alex,

I think the IAS plot is lying to you.

There's no way IAS will increase when LOP, the engine is producing less power.
 
As for the temp goling down and then back up, I don?t see it in the graph. Is it normal to go down and them back up?
 
I see the same thing

And am very curious to hear possible explanations. IO-360, 1 mag, 1 LSE, AFP injection with good injector balance. Typical "Economy Cruise" at WOT at 2200 or 2400 RPM as necessary to get % power to 65% or below.

As I lean, I see an orderly and predictable decrease in EGT past peak to about 25 - 65 degrees LOP (typically in the 1450 degree EGT range). Then I begin to see a fairly abrupt rise (typically just before roughness occurs).

Fearing the worst, I just don't go there (into the increasing EGT range).

The band of confortable LOP EGT temps seems to be dependent on % power. The lower the precent power the more degrees beyond peak I can go before seeing the rise and the less abrupt the rise seems to be.

I have not studied each and every cylinder EGT to see if they are all in concert during this occurrence. When I see one rise, I richen slightly into the comfortable range and go with it. In this comfort range, I see all of the expected benefits of LOP - lower CHT's, lower fuel burns (about 7.5 gph typical) and slightly lower A/S (drops 5 - 7 knots).

Anybody with insights into this??? Thanks
 
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Moura said:
As for the temp goling down and then back up, I don?t see it in the graph. Is it normal to go down and them back up?
Click to expand...

Look at #4, that's what Alex was referring to. EGT levels off, starts to go down and then goes up some more. #1 #2 #3 are smooth curves, #4 is not.

I see it sometimes with #1, it is an aberration of a sort. :)
 
looking at the graph

It appears #2 is the culprit, all others appear to be doing the expected (according to Deakin), and harmless continuous drop off to flame out.

I will have to see if I am also seeing a single temp rise while the others go down as expected.

If so, what is happening in that one cylnder that is not happening in the other three?? If it is "lean misfire", is that a problem beyond rough running??

I still would'nt do it, (run in the one high EGT, rough regime) but I just would like to understand because everything else looks so "text book".

(Oh, the one thing on Alex's graph that looks out of whack is the bottom fuel flow scale. I assume that fuel flow is going down LOP, the graphing software just can't show it. Otherwise, all the data is very much in line with what I see from the standpoint of % power, A/S, alt, MAP, RPM etc.)
 
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"Lean misfire" is a myth, and a term commonly thrown about by non-believers of LOP operations. The roughness that eventually occurs with continued leaning is ultimately due to imperfections in fuel distribution and resulting power pulses. Semantics distinction perhaps, but throught I would throw this out there to aid in understanding.

erich
 
maybe so - not lean misfire

but something is going on in those cylinders whose EGT first fall and then rise LOP. And I don't want to learn the hard way that it is detonation.

So- this is not to say that I don't advocate LOP or that I won't do it. Just hoping to explain this particular (falling then rising EGT) phenomena and eliminate it if possible.

I will still LOP (when in need of long range) and will still avoid the rise region. There is still a useful, beneficial, and predictable power regime available LOP before the un-explained rise occurs.
 
Have you talked to the folks at GAMI? I think they have a wealth of info on this LOP ops and might give you some ideas as to why this is occurring. Worth a try I think, but it might cost you some injectors!
 
David-aviator said:
Look at #4, that's what Alex was referring to. EGT levels off, starts to go down and then goes up some more. #1 #2 #3 are smooth curves, #4 is not.

I see it sometimes with #1, it is an aberration of a sort. :)
Click to expand...

David - both #1 and #3 had egt's that were higher on the leftmost (lowest fuel burn) point. The engine was hardly running. Note that IAS was almost 26 knots slower than at peak! Engine starting to run rough at this point, so no further leaning for the test. I'd never run the engine here other than to gather information, as it is very inefficient (i.e., airspeed drops more than fuel burn).

gereed75 said:
It appears #2 is the culprit, all others appear to be doing the expected (according to Deakin), and harmless continuous drop off to flame out.

I will have to see if I am also seeing a single temp rise while the others go down as expected.

If so, what is happening in that one cylnder that is not happening in the other three?? If it is "lean misfire", is that a problem beyond rough running??

I still would'nt do it, (run in the one high EGT, rough regime) but I just would like to understand because everything else looks so "text book".

(Oh, the one thing on Alex's graph that looks out of whack is the bottom fuel flow scale. I assume that fuel flow is going down LOP, the graphing software just can't show it. Otherwise, all the data is very much in line with what I see from the standpoint of % power, A/S, alt, MAP, RPM etc.)
Click to expand...

Whatever it is called, those cylinders whose egt's have risen at the lowest fuel flow are not performing properly. Harmless, but very inefficient.

I don't understand you comment on the fuel flow scale. LOP is on the left side, peak egt right around 8.1 gph, ROP on right side. This graph does not go through peak power, which would be indicated by a drop in IAS on the right side.

erich weaver said:
"Lean misfire" is a myth, and a term commonly thrown about by non-believers of LOP operations. The roughness that eventually occurs with continued leaning is ultimately due to imperfections in fuel distribution and resulting power pulses. Semantics distinction perhaps, but throught I would throw this out there to aid in understanding.

erich
Click to expand...

Well - if I keep pulling the mixture out, and the engine stops running, what is it called? Deakin defines lean misfire as exactly what is depicted on my chart.

gereed75 said:
but something is going on in those cylinders whose EGT first fall and then rise LOP. And I don't want to learn the hard way that it is detonation.

So- this is not to say that I don't advocate LOP or that I won't do it. Just hoping to explain this particular (falling then rising EGT) phenomena and eliminate it if possible.

I will still LOP (when in need of long range) and will still avoid the rise region. There is still a useful, beneficial, and predictable power regime available LOP before the un-explained rise occurs.
Click to expand...

I believe the explanation for the rise is understood - incomplete combustion before the valve opens. Very lean mixtures are hard to ignite, and burn slowly. At the MAP and RPM settings that I used, it is well below any regime in which the engine can be harmed by any mixture setting, unless it were run rough a long time. The something that is going on in the first two cylinders that get lean misfire is simply that - someone has to go first. As can be seen by the peaks, the injectors are well balanced, so if I'd continued a couple more tenths of a gallon leaner, I may have had all four rise.

The rise region is not really important other than academically, as it is not a place where one would run.
 
I just emailed GAMI describing the issue. As soon as I get a feedback I will post here. In the meantime, if anyone has anything to add, you are very welcome to do so.

Thanks
 
Moura...

The "problem" to me sounds simple...

As you have observed, as you lean, you get increasing EGT towards peak, then falling EGT LOP. However, eventually you get too lean and EGT rises again - we see this... Why I do not know, but as you say, it is getting rough / losing power / don't want to go there.

So the "acceptable" band of operation is after peak, but before too lean that EGT rises again / gets rough. That's fine if all 4 cylinders peak together. In your case, however, #1 is offset too far to get a decent overlap - which needs the injectors balanced (as above). As an aside, this mismatch of mixtures if why Carb engines have difficulty (but some manage) running LOP. We run 2 x Mag, and I believe this does make the "band" smaller i.e. harder to achieve, than EI. I also find running "oversquare" makes the band easier to hit.

See Randy's RV-3 link for more info...

Andy
 
aha!! stupid me

I was reading the graph left to right ROP to LOP. I see my error now.

The other thing that fooled me is that my LOP rise is more dramatic, actually going above peak sometimes, even more than shown by #4 in the graph. Agree that that is a pretty wide spread in which your cylinders reach peak. Mine all peak within .4 gph.

At any rate, I agree with all of the other comments and would really like to hear GAMI or some other expert's oppinion.

Still trying to make better sense of the A/S bar on the right side. Should be highest at 100 F or so ROP (9.5 gph or so). Is there a graphing/scale anomoly happening there?? If A/S was on the top, increasing left to right, it would all make sense, I think. Or am I being stupid again??

Thanks guys. Fly on!!
 
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AlexPeterson said:
Well - if I keep pulling the mixture out, and the engine stops running, what is it called? Deakin defines lean misfire as exactly what is depicted on my chart.
Click to expand...

Forgive me, as perhaps this is detracting from your ultimate question, but the above was not my recollection, so I took a minute to check, and have posted my findings below. In his Pelican's Perch #18 article, "Mixture Magic", available on the Avweb website, he says:

"Now suppose you lean by the classic advice "lean 'till roughness occurs, then enrich just enough to restore smoothness." No one wants to run a rough engine, so this is good advice. A rough engine causes metal fatigue, pilot fatigue, sterility, baldness, imp ?, but, I digress. I think we can all agree that vibration is a bad thing, all around. What's causing that vibration? Aha, I see that hand in back there in the audience. What's that you say? "Lean misfire?"
Sorry Charlie, no tuna. There's essentially no such thing as "lean misfire." It's probably a term some tech rep made up because he didn't know the right answer. A properly set up engine will tolerate leaning and remain smooth right down to that 30% power range (see combustion chart), at which point it just quits cold. There's no reason to shake, at all. Now that said, the real world is not perfect, and even well-set-up engines will show a just a tiny bit of roughness when leaned to the extreme. What does happen to cause that roughness is that the first cylinder to peak and start down on the lean side will produce less power than the others, and unequal power from one cylinder (or more) will cause enough vibration to be obvious. So you enrich until the vibration goes away, restoring that one cylinder (or more) to approximately the same actual power as the others. That gets them all up on the "sort of flat" part of the power curve..."


best regards
erich
 
GAMI?s Response:

"Moura,



That cylinder is very lean, and maybe the injector is partially clogged.

What you are seeing is a ?second peak,? which sometimes happens when a cylinder gets very, very LOP.



It?s normal, but needs to be corrected.



Thanks,



John-Paul"
 
erich weaver said:
Forgive me, as perhaps this is detracting from your ultimate question, but the above was not my recollection, so I took a minute to check, and have posted my findings below. In his Pelican's Perch #18 article, "Mixture Magic", available on the Avweb website, he says:

"Now suppose you lean by the classic advice "lean 'till roughness occurs, then enrich just enough to restore smoothness." No one wants to run a rough engine, so this is good advice. A rough engine causes metal fatigue, pilot fatigue, sterility, baldness, imp ?, but, I digress. I think we can all agree that vibration is a bad thing, all around. What's causing that vibration? Aha, I see that hand in back there in the audience. What's that you say? "Lean misfire?"
Sorry Charlie, no tuna. There's essentially no such thing as "lean misfire." It's probably a term some tech rep made up because he didn't know the right answer. A properly set up engine will tolerate leaning and remain smooth right down to that 30% power range (see combustion chart), at which point it just quits cold. There's no reason to shake, at all. Now that said, the real world is not perfect, and even well-set-up engines will show a just a tiny bit of roughness when leaned to the extreme. What does happen to cause that roughness is that the first cylinder to peak and start down on the lean side will produce less power than the others, and unequal power from one cylinder (or more) will cause enough vibration to be obvious. So you enrich until the vibration goes away, restoring that one cylinder (or more) to approximately the same actual power as the others. That gets them all up on the "sort of flat" part of the power curve..."


best regards
erich
Click to expand...

You are correct. Somewhere I saw (I thought on Deakin's articles), a graph just like the one I put up earlier, with an arrow pointing to the upturn in egt at very lean conditions, using the word "lean misfire". Must not have been Deakin, but I'm not sure who else it would have been.

Automotive error codes use the term, and I'm not sure what they are looking at or referring to either.
 
EGT increase @ extreme LOP?

Well, if that cyl peaks 1st, then it will also 'flame out' 1st. One thing that can increase EGT is burning fuel in the exh pipe, which could be happening due to the slower combustion of the VERY lean mixture in that cylinder.

That being said, I have never heard of a second peak either, but if it happend at extremely lean mixtures, the above explanation is plausible.

Balance your injectors ASAP, tho I doubt you would cause any damage to continue on. Don Rivera at AFP will help you thru the tuning process.

Carry on!
Mark
 
I emailed Don at airflow and below is his response:

"What's happening is that as you lean the mixture the time to burn the mixture in the cylinder takes longer. Since the spark event starts at the same crank angle the leaner mixture is still burning after the exhaust valve starts to open. This is pretty normal for Lycoming engines.

If you richened that cylinder up it would peak closer the other cylinders."
 
Yeah, the guys at AFP are great to deal with..

...and I spoke with Kyle, since Don was preoccupied, for a new set of injector inserts...025" for starters. My airplane is in for annual/condition inspection and totally naked:), so it's a good time to start balancing the cylinders.

Best,
 
You bet Pierre, they sure are... and indeed so are you guys who participate in such a active manner in this forum!!! Thank you all!!!

Moura
 
pierre smith said:
...and I spoke with Kyle, since Don was preoccupied, for a new set of injector inserts...025" for starters. My airplane is in for annual/condition inspection and totally naked:), so it's a good time to start balancing the cylinders.

Best,
Click to expand...

Pierre,
I also switched to .025 from the "std" .028 then tuned from there. Ended up with 2ea .025, an .026, and a .0265, peaks are now within .2 gph
Walt
 
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