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  #11  
Old 10-05-2010, 08:49 AM
gereed75 gereed75 is offline
 
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Default 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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Last edited by gereed75 : 10-05-2010 at 09:03 AM.
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  #12  
Old 10-05-2010, 11:05 AM
erich weaver's Avatar
erich weaver erich weaver is offline
 
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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
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  #13  
Old 10-05-2010, 01:28 PM
gereed75 gereed75 is offline
 
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Default 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.
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  #14  
Old 10-05-2010, 04:21 PM
Bill Dicus Bill Dicus is offline
 
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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!
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  #15  
Old 10-05-2010, 06:29 PM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by David-aviator View Post
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.
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).

Quote:
Originally Posted by gereed75 View Post
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.)
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.

Quote:
Originally Posted by erich weaver View Post
"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
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.

Quote:
Originally Posted by gereed75 View Post
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.
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.
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  #16  
Old 10-05-2010, 08:52 PM
Moura Moura is offline
 
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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
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  #17  
Old 10-06-2010, 03:32 AM
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Andy Hill Andy Hill is offline
 
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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
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  #18  
Old 10-06-2010, 10:32 AM
gereed75 gereed75 is offline
 
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Default 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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Last edited by gereed75 : 10-06-2010 at 10:40 AM.
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  #19  
Old 10-06-2010, 11:40 AM
erich weaver's Avatar
erich weaver erich weaver is offline
 
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Quote:
Originally Posted by AlexPeterson View Post
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.
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
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  #20  
Old 10-06-2010, 11:44 AM
Moura Moura is offline
 
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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"
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