LOP "quirk"

[231LV]

OK...this question is for those of you who are very well aquainted with the physics of LOP. I have been flying my 231 for 16 years and always run LOP. I am very comfortable with what is happening in the cylinders as I lean past peak EGT and have explained it to a couple of A&P's who were clinging to the old wive's tale of cooking the cylinders, ect, ect......however, I am stumped  with what I am observing when I run deep into LOP. Recently, I upgraded to a Merlyn when I had my engine overhauled. It has an intercooler, Gami's and was a GB rebuilt to a new service limits LB. As I was getting used to the Merlyn, I was pushing deeper and deeper into the LOP realm and noticed that at a point just before the engine starts stumbling the TIT climbs rapidly forcing me to enriched. Now, I normally fly a cruise power configuration when LOP of about 10 gph,  2500 rpm and about 32 inches MP....this yields the hottest jug at around 330 degrees and a TIT of about 1610ish...as I continue to lean...the FF drops as does the MP BUT TIT will start climbing toward 1650 degrees and I can't figure out just what is happening. It should not be seeing hotter turbine temps as I lean and effectively lose power unless I am missing something?

[N201MKTurbo]

The leaner you get the slower the combustion charge burns. This leaves heat in the combustion charge when it leaves the cylinder through the exhaust. The more heat in the exhaust the higher it’s temperature. If you could advance the spark at that point you could put more of that combustion energy to work before it was exhausted.

[231LV]

ahh......so for us turbo drivers, there is a boundary  between too rich and too lean and we have to exist within that boundary.....FADEC would be nice to have at this point!

[ziggysanchez]

I've never experienced the TIT rising as I run deeper into LOP. I've only experienced the TIT rising as a result of running closer to peak EGT. The leaner I run LOP,  the cooler the TIT. I do not have an intercooler but do have a Merlyn. I have found the higher my manifold pressure is, the easier it is for me to manage turbine inlet temps. Mine without the intercooler runs best at between 34 and 35 inches of MP @2500 rpm's with a FF of 10.5 gph, TIT is 1610-1620. My FF will start to drift upward while running LOP so I have to keep an eye on it and seem to always have to keep adjusting while in cruise. My engine has never seemed very happy running LOP.

Edited September 26, 2019 by ziggysanchez

[Bob - S50]

A bit off topic, why do you want to go deeper and deeper LOP?  If you are doing it to limit power, I think there are better ways.  Seems to me the goal should be to get to the most efficient LOP setting.  If I'm not mistaken, that is about 30 - 70 LOP.  Any leaner than that and the burn starts becoming  less efficient.  I would think you would want to aim for about 50 +/-20 LOP and then if that too much power, either reduce MP or RPM or both.

[ArtVandelay]

A bit off topic, why do you want to go deeper and deeper LOP?  If you are doing it to limit power, I think there are better ways.  Seems to me the goal should be to get to the most efficient LOP setting.  If I'm not mistaken, that is about 30 - 70 LOP.  Any leaner than that and the burn starts becoming  less efficient.  I would think you would want to aim for about 50 +/-20 LOP and then if that too much power, either reduce MP or RPM or both.

Testing your engine (fuel balance, plugs, etc), if you can run 70°, your engine is good. I thought the target was closer to 20°?


Tom

[gsxrpilot]

1 hour ago, 231LV said:

ahh......so for us turbo drivers, there is a boundary  between too rich and too lean and we have to exist within that boundary.....FADEC would be nice to have at this point!

I don't think this is the case. I've run my M20K everywhere from 20° to 80° LOP and the TIT is never a factor. It's always below 1600. I think the challenge here is that with the 231 and a manual waste gate, moving one lever such as the throttle, affects the others. So you're constantly needing to rebalance the Black, Blue, Red knobs. It can be done, but it's not a trivial effort. FADEC would be nice.

With the 252 and the automatic waste gate, it's much simpler. I can set throttle and RPM, and then go play with the mixture to get to my target LOP setting.

One thing that is unique about flying the Turbo's LOP is that we don't run max throttle. So there is that additional adjustment point.

With my 252... 80° LOP requires more MP and a bit more fuel than 20° LOP. Which might seem counterintuitive. 26" 2500, 9.5 is about 20° to 30° LOP or 30" 2500 10 is about 80° LOP.

I generally run 26" 2500 9.5.

[PT20J]

Probably the best engine for even mixture distribution is a single row radial. The fuel mixture enters at the eye of a fast spinning supercharger impeller and is forced out to the cylinders through equal length intake tubes. I once tried to see how lean I could run an R-985 on a Beaver. As I pulled the mixture slowly back, it ran pretty smoothly until it just stopped. But just before it stopped, the weak mixture was burning so slowly that there was still fire in the hole when an intake valve opened and it backfired.

There is no operational advantage to running too deeply LOP.  LOP efficiency comes from running at lowest BSFC which is minimum and nearly constant over a fairly broad range. That's why power is a function of mixture strength LOP -- up to a point. But if you keep going leaner, the BSFC starts to increase. Looking at the BSFC curve for your engine will tell you the most efficient place to operate -- it's generally in the range of 25-50 degrees LOP.

Skip

[jaylw314]

You could also be having intermittent ignition failures as the mixture gets leaner if your ignition system is weak anywhere.  Since it is not happening on every cycle, you may not notice roughness or loss of power, but the addition of unburnt fuel into the exhaust even 10% of the time would be enough to raise the TIT or EGT a few degrees.

Are you watching your individual EGT's too while this is happening?  

[kmyfm20s]

I don’t have a turbo but if your going so far lean of peak that your significantly dropping you MP you are also slightly changing you fuel/air ratio and inadvertently slightly enriching the mixture, possibly. Just thinking out loud.

[231LV]

to answer a couple of posters....I do this to simply experiment and try to learn the limits of my engine....no reason to run deep LOP during cruise

for me....running 35MP is not possible as I would have to lean so far that my TIT climbs....again....the problem I was referenceing in my OP

I'm still liking the initial explanation that leaner means slower burn means heat escaping into the turbine but that doesn't explain why all turbo drivers are not experiencing this...

finally, iginition system was overhauled with the engine.....less than 50 hours on it so I don't believe that is the culprit...

I will pull a Savvy record and see what lurks there...

 

[kortopates]

So no-one has answered the question of what is happening to describe the rise in TIT as the mixture is leaned well past peak.

Hint, every engine will display this behaviour, it has nothing to do with being turbo, having a Merlyn or intercooler. To get to the answer, don't focus on TIT. I bet if look at your 6 different "engines" or cylinders individually with EGTs you'll recognize what's happening pretty quickly. Down load your data and take a closer look. 

Comments on running too deeply LOP are spot on. Power drops off very rapidly on the LOP side, you only want to be a LOP as the amount required to safely stay out of the Red box for good detonation margin and avoiding high ICP's. And Skip is right on, in that maximum BSFC is also on the LOP side around 25-50, but you'll find the curve is very flat in that range and hence isn't giving you a significant appreciable gain in BSFC by going any deeper LOP than the red box is already demanding but it does start to drop off more quickly past 50F LOP.

Edit - Jay is on the right track! But I wouldn't use the word intermittent - again all our engines do this.

Edited September 26, 2019 by kortopates

[N201MKTurbo]

If one plug starts to misfire it will exasperate this effect a lot. As one of the posters mentioned.

[jaylw314]

24 minutes ago, kortopates said:

So no-one has answered the question of what is happening to describe the rise in TIT as the mixture is leaned well past peak.

Hint, every engine will display this behaviour, it has nothing to do with being turbo, having a Merlyn or intercooler. To get to the answer, don't focus on TIT. I bet if look at your 6 different "engines" or cylinders individually with EGTs you'll recognize what's happening pretty quickly. Down load your data and take a closer look. 

Comments on running too deeply LOP are spot on. Power drops off very rapidly on the LOP side, you only want to be a LOP as the amount required to safely stay out of the Red box for good detonation margin and avoiding high ICP's. And Skip is right on, in that maximum BSFC is also on the LOP side around 25-50, but you'll find the curve is very flat in that range and hence isn't giving you a significant appreciable gain in BSFC by going any deeper LOP than the red box is already demanding but it does start to drop off more quickly past 50F LOP.

Edit - Jay is on the right track! But I wouldn't use the word intermittent - again all our engines do this.

I figure slow or failed ignition probably does not happen 100% of cycles initially, since you'd see an EGT rise of 75-100 degF, similar to shutting off one mag.  As you continue to lean, and the mixture gets harder to ignite, it looks more and more like shutting off one mag, and every cylinder will behave differently.

When I had a weak left mag, the richest cylinder would never go LOP reliably--as I leaned further, its EGT would climb to peak, slow down, then gradually start climbing again until it started feeling rough.  This flummoxed me for months as to why it was happening.  After getting the left mag fixed, it'll still happen but only after getting about 50 degF LOP

[kortopates]

38 minutes ago, jaylw314 said:

I figure slow or failed ignition probably does not happen 100% of cycles initially, since you'd see an EGT rise of 75-100 degF, similar to shutting off one mag.  As you continue to lean, and the mixture gets harder to ignite, it looks more and more like shutting off one mag, and every cylinder will behave differently.

When I had a weak left mag, the richest cylinder would never go LOP reliably--as I leaned further, its EGT would climb to peak, slow down, then gradually start climbing again until it started feeling rough.  This flummoxed me for months as to why it was happening.  After getting the left mag fixed, it'll still happen but only after getting about 50 degF LOP

Many have referred to this phenomenon as the second Peak and asked why do we see this second peak? We've discussed a few times on Mooneyspace, I think it was our Mooney Bravo owner that has been the most successful Bravo guy at operating LOP and wrote quite a bit of good stuff here. But i digress.

Jay, your describing it to a T with the first bolded quoted text above, what your describing is exactly what we see, as you say, when we shut off one mag. We're down to a single plug in that cylinder and now the EGT has spiked up typically 75-80F or more from what it was when you had both plugs operating. Depending on the health of your ignition system, you'll also see a slowly increasing but widely fluctuating EGT as Rich @N201MKTurbo was referring to above. But we don't always see that, sometimes the plug just goes from minimal missing to flame out when the mixture is too lean for the plug to fire.

99% of the time, its always the same plug that flames out first - assuming both are otherwise healthy. Which one is more stressed? 

But a healthy ignition system should not be seeing these symptoms at 50F LOP. I personally refer to any misfire at or below 50F LOP as premature meaning maintenance is recommended to correct. But since there is no need for the majority of us to operate at a mixture above 50F LOP I would consider anything higher acceptable - i.e. no sense at throwing $ at it. But a "healthy" ignition system will typically easily handle 100F LOP without any missing, let alone flameout. But not all ignition systems are as strong or resilient as the better ones. The Dual mag ignition system used on the J is one example (partially IMO because so hard to keep their timing in synch without opening them), the turbo systems on some are weaker - the Rocket's mags are even pressurized (jeez)!, the Bravo is another challenged one, but not the Acclaim's ignition system as well as any of the IO-550's & TSIO-550's used on the longbody's, Cirrus, Cessna are amongst the very best. But given we don't have a real choice, every ignition systems  resilience can be improved with fine wire plugs. And then we do have more electronic ignition options....

Sorry, but the college instructor in me wanted to encourage some critical thinking before going to the answer - not meaning to play with anyone. For a few of you, the answer was clearly on the tip of your tongues

[jaylw314]

42 minutes ago, kortopates said:

Many have referred to this phenomenon as the second Peak and asked why do we see this second peak? We've discussed a few times on Mooneyspace, I think it was our Mooney Bravo owner that has been the most successful Bravo guy at operating LOP and wrote quite a bit of good stuff here. But i digress.

Jay, your describing it to a T with the first bolded quoted text above, what your describing is exactly what we see, as you say, when we shut off one mag. We're down to a single plug in that cylinder and now the EGT has spiked up typically 75-80F or more from what it was when you had both plugs operating. Depending on the health of your ignition system, you'll also see a slowly increasing but widely fluctuating EGT as Rich @N201MKTurbo was referring to above. But we don't always see that, sometimes the plug just goes from minimal missing to flame out when the mixture is too lean for the plug to fire.

99% of the time, its always the same plug that flames out first - assuming both are otherwise healthy. Which one is more stressed? 

But a healthy ignition system should not be seeing these symptoms at 50F LOP. I personally refer to any misfire at or below 50F LOP as premature meaning maintenance is recommended to correct. But since there is no need for the majority of us to operate at a mixture above 50F LOP I would consider anything higher acceptable - i.e. no sense at throwing $ at it. But a "healthy" ignition system will typically easily handle 100F LOP without any missing, let alone flameout. But not all ignition systems are as strong or resilient as the better ones. The Dual mag ignition system used on the J is one example (partially IMO because so hard to keep their timing in synch without opening them), the turbo systems on some are weaker - the Rocket's mags are even pressurized (jeez)!, the Bravo is another challenged one, but not the Acclaim's ignition system as well as any of the IO-550's & TSIO-550's used on the longbody's, Cirrus, Cessna are amongst the very best. But given we don't have a real choice, every ignition systems  resilience can be improved with fine wire plugs. And then we do have more electronic ignition options....

Sorry, but the college instructor in me wanted to encourage some critical thinking before going to the answer - not meaning to play with anyone. For a few of you, the answer was clearly on the tip of your tongues

Egads, If you think the dual mag is problematic, I have an A3B6 with two Slick mags.  I suspect the best I can do with mine is "somewhat shitty"  

[kortopates]

1 hour ago, jaylw314 said:

Egads, If you think the dual mag is problematic, I have an A3B6 with two Slick mags.  I suspect the best I can do with mine is "somewhat shitty"  

Nah, they're not that bad, just not as good as the best  

[231LV]

4 hours ago, kortopates said:

Many have referred to this phenomenon as the second Peak and asked why do we see this second peak? We've discussed a few times on Mooneyspace, I think it was our Mooney Bravo owner that has been the most successful Bravo guy at operating LOP and wrote quite a bit of good stuff here. But i digress.

Jay, your describing it to a T with the first bolded quoted text above, what your describing is exactly what we see, as you say, when we shut off one mag. We're down to a single plug in that cylinder and now the EGT has spiked up typically 75-80F or more from what it was when you had both plugs operating. Depending on the health of your ignition system, you'll also see a slowly increasing but widely fluctuating EGT as Rich @N201MKTurbo was referring to above. But we don't always see that, sometimes the plug just goes from minimal missing to flame out when the mixture is too lean for the plug to fire.

99% of the time, its always the same plug that flames out first - assuming both are otherwise healthy. Which one is more stressed? 

But a healthy ignition system should not be seeing these symptoms at 50F LOP. I personally refer to any misfire at or below 50F LOP as premature meaning maintenance is recommended to correct. But since there is no need for the majority of us to operate at a mixture above 50F LOP I would consider anything higher acceptable - i.e. no sense at throwing $ at it. But a "healthy" ignition system will typically easily handle 100F LOP without any missing, let alone flameout. But not all ignition systems are as strong or resilient as the better ones. The Dual mag ignition system used on the J is one example (partially IMO because so hard to keep their timing in synch without opening them), the turbo systems on some are weaker - the Rocket's mags are even pressurized (jeez)!, the Bravo is another challenged one, but not the Acclaim's ignition system as well as any of the IO-550's & TSIO-550's used on the longbody's, Cirrus, Cessna are amongst the very best. But given we don't have a real choice, every ignition systems  resilience can be improved with fine wire plugs. And then we do have more electronic ignition options....

Sorry, but the college instructor in me wanted to encourage some critical thinking before going to the answer - not meaning to play with anyone. For a few of you, the answer was clearly on the tip of your tongues

Duh-oh! OK, now I'm seeing it......been a "few" years since I was sitting in a college classroom, Professor! Makes perfect sense...essentially I am synthetically dropping a mag by running leaner and leaner which triggers higher EGT's which runs into the TIT.....got it! Thanks

[kortopates]

Duh-oh! OK, now I'm seeing it......been a "few" years since I was sitting in a college classroom, Professor! Makes perfect sense...essentially I am synthetically dropping a mag by running leaner and leaner which triggers higher EGT's which runs into the TIT.....got it! Thanks

Exactly, but to be a little more precise, we're leaning more and more till the bottom plug flames out first causing the same effect as switching to a single mag. All things being equal one of the leanest cylinders should be the first to start flaming out first. How far LOP you need to go to see this will depend on how healthy your ignition is.

 

 

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[kortopates]

@231LV Since you just overhauled your GB to an LB would you mind sharing how you got all the new LB induction system parts and othet different parts for the LB? I.e. did you get an overhaul exchange from Continental or someone else or did you find an engine builder that could rebuild your LB economically without buying all the new parts? You are welcome to PM me if you prefer. Thanks

 

 

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[Shadrach]

My anecdotal experience with my Lycoming at high MP, deep LOP is that the combustion event continues to propagate from both plugs even at the lean limit. I get an EGT rise of ~30-50° before the cylinder goes offline. Perhaps I am misunderstanding what I am seeing.

[Shadrach]

My anecdotal experience with my Lycoming at high MP, deep LOP is that the combustion event continues to propagate from both plugs even at the lean limit. I get an EGT rise of ~30-50° before the cylinder goes offline. Perhaps I am misunderstanding what I am seeing.

[231LV]

9 hours ago, kortopates said:

@231LV Since you just overhauled your GB to an LB would you mind sharing how you got all the new LB induction system parts and othet different parts for the LB? I.e. did you get an overhaul exchange from Continental or someone else or did you find an engine builder that could rebuild your LB economically without buying all the new parts? You are welcome to PM me if you prefer. Thanks

 

 

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Ly-Con....as to economically....the cost for the rebuild by Ly-Con considerably exceeded the estimate (as did the time to do it) but comparing the reman quote from Continental against the final bill from Ly-Con....they were essentially equal.....Only reason I went with Ly-Con (other than the hope that my engine wouldn't need too many replacement parts) was I wanted to keep my crank and lower end....didnt really trust a reman crank.....time wise, I would have been 4 months ahead with a reman. All said, Ly-Con did a great job and corrected a couple of issues and reimbursed me my costs incurred to deal with them.

[kortopates]

32 minutes ago, 231LV said:

Ly-Con....as to economically....the cost for the rebuild by Ly-Con considerably exceeded the estimate (as did the time to do it) but comparing the reman quote from Continental against the final bill from Ly-Con....they were essentially equal.....Only reason I went with Ly-Con (other than the hope that my engine wouldn't need too many replacement parts) was I wanted to keep my crank and lower end....didnt really trust a reman crank.....time wise, I would have been 4 months ahead with a reman. All said, Ly-Con did a great job and corrected a couple of issues and reimbursed me my costs incurred to deal with them.

Oh, did Ly-Con's estimate go up to Continentals because of the all the parts that changed? That would include a larger throttle body, different induction system, relocated overboost valve, pressurized mags and different exhaust. Those can really add up, and I imagine especially the induction system and throttle body. Or did there original quote account for all those changes? Glad to hear they did a great job on it though. 

[kortopates]

3 hours ago, Shadrach said:

My anecdotal experience with my Lycoming at high MP, deep LOP is that the combustion event continues to propagate from both plugs even at the lean limit. I get an EGT rise of ~30-50° before the cylinder goes offline. Perhaps I am misunderstanding what I am seeing.

The rise will be misfire, but I am sure your downloaded data (with a 1 sec sampling rate) will show one plug flames out before the other when leaned slowly and all things being equal, it'll be your bottom plug that goes first because of the harsher environment.