Too Lean?

[alextstone]

Please help me settle this question for once and for all:  Is it possible to run an engine (turbocharged or NA) too lean (from the perspective of damaging something)?  My current understanding is "no" although poor performance is the limiting factor.  I know that's probably too simplistic...what do the experts on the forum have to say?

For the sake of context, I fly a Bravo with GAMI's and I run about 20 degrees LOP in cruise (30 in MP, 2400 RPM, 14.3 GPH).  I have yet to "tune the GAMI's" because I do not have FF recording.  That's coming soon with a swap of the JPI 700 for either an 830 or 900.  

Thanks.  

[Hank]

I thought the danger in running LOP without an all-cylinders engine monitor was in not having all cylinders lean enough rather than being too lean. Keep leaning it out, power and speed will decrease significantly, and at some point the engine will begin running rough due to uneven distribution of what fuel there is. Then it will shut off . . . .

But don't take me too seriously, my C doesn't have fuel injection oor an engine monitor. But I do read a lot!

[LANCECASPER]

21 minutes ago, alextstone said:

Please help me settle this question for once and for all:  Is it possible to run an engine (turbocharged or NA) too lean (from the perspective of damaging something)?  My current understanding is "no" although poor performance is the limiting factor.  I know that's probably too simplistic...what do the experts on the forum have to say?

For the sake of context, I fly a Bravo with GAMI's and I run about 20 degrees LOP in cruise (30 in MP, 2400 RPM, 14.3 GPH).  I have yet to "tune the GAMI's" because I do not have FF recording.  That's coming soon with a swap of the JPI 700 for either an 830 or 900.  

Thanks.  

What's the Turbine Inlet Temperature at those setiings?

[alextstone]

1 minute ago, LANCECASPER said:

What's the Turbine Inlet Temperature at those setiings?

I monitor it and keep it at 1600.  If it goes higher, I reduce the MP slightly to get it back at or below 1600

[gsxrpilot]

I don't believe there is any way to damage the engine from running too lean. I've had my 252 to almost 80 degrees LOP. It didn't run very well, but it was smooth and quite cool. At some point, the engine will just shut down the same way it shuts down when we pull the mixture all the way out. But it can't damage anything.

[alextstone]

9 minutes ago, gsxrpilot said:

I don't believe there is any way to damage the engine from running too lean. I've had my 252 to almost 80 degrees LOP. It didn't run very well, but it was smooth and quite cool. At some point, the engine will just shut down the same way it shuts down when we pull the mixture all the way out. But it can't damage anything.

Paul, that's my understanding also...BTW, I watched your Burning Man Arrival video yesterday...WOW!

[FloridaMan]

21 minutes ago, alextstone said:

I monitor it and keep it at 1600.  If it goes higher, I reduce the MP slightly to get it back at or below 1600

Is there a procedure for the Bravo for calibrating the TIT gauge? The Rocket manual spells out that TIT gauges are notoriously inaccurate and has a specific calibration procedure to ensure you’re not overtemping the turbocharger. 

[takair]

I don’t fly an M, but I would say, it depends on the power setting.  At above 75% power (many will say 65%), leaning can cause detonation and serious damage.  Now, if you go lean enough, the power goes below 75% and detonation is less likely.  Are you simply asking about leaning at below 65%?  

Edit:  I see you have power settings listed.....I assume those are less than 75%...but don’t have the charts....

[FloridaMan]

From the Rocket manual, but relevant to TIT gauges I believe on any turbocharged piston aircraft and possibly a cause of early mortality and the failures associated with LOP operations. 

[LANCECASPER]

You might want to read through this:

https://mooneyspace.com/topic/18213-bravo-power-settings/

[Ragsf15e]

2 minutes ago, takair said:

I don’t fly an M, but I would say, it depends on the power setting.  At above 75% power (many will say 65%), leaning can cause detonation and serious damage.  Now, if you go lean enough, the power goes below 75% and detonation is less likely.  Are you simply asking about leaning at below 65%?  

“Leaning” isn’t causing detonation.   Setting a fuel flow that leaves you too close to peak egt depending on your power setting can cause detonation, sure.  However, continue to lean past peak egt, outside the “red box” approximately 20 lop or less than 65% power, and you are again in a good place.  Continue to lean past that and performance will deteriorate but you won’t hurt anything, it’ll just run cooler and cooler. Eventually it will just shut down.

[takair]

24 minutes ago, Ragsf15e said:

“Leaning” isn’t causing detonation.   Setting a fuel flow that leaves you too close to peak egt depending on your power setting can cause detonation, sure.  However, continue to lean past peak egt, outside the “red box” approximately 20 lop or less than 65% power, and you are again in a good place.  Continue to lean past that and performance will deteriorate but you won’t hurt anything, it’ll just run cooler and cooler. Eventually it will just shut down.

Isn’t that saying the same thing?  At high power settings, you need to either stay on the rich side or the lean side of detonation.  My point is that you could lean right into detonation if you linger long enough near peak at high power settings.  With a turbo, these settings are easier to stumble into, especially if one doesn’t know where peak is.  I don’t disagree with what you said, I think we both agree there is a zone in “leaning” (maybe a better term is “adjusting the mixture” that can damage the engine, and you either need to stay above or below that.

Edit again...I gotta go to bed...I reread my original post and understand your point.....

[carusoam]

This is a goofy thread’s way of discussing the ‘RED BOX’ 

1) you can go too lean.... if you stop in the red box, you are too lean...

2) you can get out of the red box by leaning more... or enrichening some...

3) there are other ways to leave the red box... use %bhp...

4) Using the throttle or prop or altitude to control %bhp you can leave the red box...

5) Transitioning through the redbox may be required to get to where you want to operate...

6) this Transition is aptly named the big pull....

7) the big pull requires some knowledge regarding where your red box is, so you can get through it quickly...

8) a well balance intake and fuel system can go too lean, and just shut-off... that would be too lean...

9) too lean for an IO550 would be when the kias are getting too small...the more you lean the smaller the kias grow...

10) for more info about the red box and how it applies to you and your engine.... ask the makers of the Gami fuel injectors....

PP thoughts only not a mechanic...

Best regards,

-a- 

[N231BN]

3 hours ago, carusoam said:

This is a goofy thread’s way of discussing the ‘RED BOX’ 

1) you can go too lean.... if you stop in the red box, you are too lean...

2) you can get out of the red box by leaning more... or enrichening some...

3) there are other ways to leave the red box... use %bhp...

4) Using the throttle or prop or altitude to control %bhp you can leave the red box...

5) Transitioning through the redbox may be required to get to where you want to operate...

6) this Transition is aptly named the big pull....

7) the big pull requires some knowledge regarding where your red box is, so you can get through it quickly...

8) a well balance intake and fuel system can go too lean, and just shut-off... that would be too lean...

9) too lean for an IO550 would be when the kias are getting too small...the more you lean the smaller the kias grow...

10) for more info about the red box and how it applies to you and your engine.... ask the makers of the Gami fuel injectors....

PP thoughts only not a mechanic...

Best regards,

-a- 

To correct #1 above...You can go not lean enough, if you stop in the red box you are too rich.

The key to understanding LOP ops lies in the original question. You cannot hurt your engine by running it too lean. You CAN hurt your engine by not running it lean enough.

[midlifeflyer]

I know the guys who do the big courses on this, but for my money ($0 :D) , the best simple explanation is Martin Pauly's video on YouTube

 

Edited March 31, 2019 by midlifeflyer

[201er]

12 hours ago, Ragsf15e said:

“Leaning” isn’t causing detonation.   Setting a fuel flow that leaves you too close to peak egt depending on your power setting can cause detonation, sure.

No. What causes detonation is pressure (and temperature). Detonation occurs at/around peak ICP and not peak EGT! Peak EGT is usually on the back side of the ICP curve and often a safe place to operate. Peak ICP typically happens at around 25-50 ROP. Excessively high CHTs (especially when combined with high ICP) can also cause detonation. They tend to go hand in hand.

[Austintatious]

15 hours ago, alextstone said:

Please help me settle this question for once and for all:  Is it possible to run an engine (turbocharged or NA) too lean (from the perspective of damaging something)?  My current understanding is "no" although poor performance is the limiting factor.  I know that's probably too simplistic...what do the experts on the forum have to say?

For the sake of context, I fly a Bravo with GAMI's and I run about 20 degrees LOP in cruise (30 in MP, 2400 RPM, 14.3 GPH).  I have yet to "tune the GAMI's" because I do not have FF recording.  That's coming soon with a swap of the JPI 700 for either an 830 or 900.  

Thanks.  

out of curiosity, what sort of cruise speed do you get at that power setting at various altitudes?

[alextstone]

6 minutes ago, Austintatious said:

out of curiosity, what sort of cruise speed do you get at that power setting at various altitudes?

Below 10,000, 165kts TAS (+-)

15,000, 175kts TAS (+-)

18,000, 180 kts TAS (+-)

I have not been higher yet.

Mid weight, with TKS.  

[Austintatious]

thanks.... I have a deal in the works for a Rocket, but if it falls through there is a nice Bravo I have been looking at.  The cruise numbers are vastly different on those 2.

[Ragsf15e]

10 hours ago, 201er said:

No. What causes detonation is pressure (and temperature). Detonation occurs at/around peak ICP and not peak EGT! Peak EGT is usually on the back side of the ICP curve and often a safe place to operate. Peak ICP typically happens at around 25-50 ROP. Excessively high CHTs (especially when combined with high ICP) can also cause detonation. They tend to go hand in hand.

Yep I’d buy that.  I guess the point is, leaning doesn’t cause damage.  Leaning to the wrong place on your icp curve could given the right circumstances.  It’s just that we have to use cht and egt and some educated guesswork to know where we are on the curve.  If jpi could give us an icp measurement in the air that would be awesome!

[gsxrpilot]

43 minutes ago, Ragsf15e said:

Yep I’d buy that.  I guess the point is, leaning doesn’t cause damage.  Leaning to the wrong place on your icp curve could given the right circumstances.  It’s just that we have to use cht and egt and some educated guesswork to know where we are on the curve.  If jpi could give us an icp measurement in the air that would be awesome!

We do know that peak ICP is on the rich side of peak EGT. So therefore the safe place to be is on the lean side of peak EGT. And peak EGT is easy to find with any engine monitor.

[ArtVandelay]

Yep I’d buy that.  I guess the point is, leaning doesn’t cause damage.  Leaning to the wrong place on your icp curve could given the right circumstances.  It’s just that we have to use cht and egt and some educated guesswork to know where we are on the curve.  If jpi could give us an icp measurement in the air that would be awesome!

It’s not that the absolute value of icp is bad, it’s the timing. After all, no ICP, no HP. They could add a knock sensor easily (it’s just a microphone).


Tom

[Shadrach]

On 3/30/2019 at 11:12 PM, takair said:

I don’t fly an M, but I would say, it depends on the power setting.  At above 75% power (many will say 65%), leaning can cause detonation and serious damage.  Now, if you go lean enough, the power goes below 75% and detonation is less likely.  Are you simply asking about leaning at below 65%?  

Edit:  I see you have power settings listed.....I assume those are less than 75%...but don’t have the charts....

If the engine has an adequate supply of surplus air (mp) it can be run just as safely at high power LOP as it can ROP. In either case you’re slowing the combustion event to prevent detonation. When ROP you're using air, LOP you’re using fuel. TIT is a limiting factor in many cases because air (LOP) is a much more efficient method of slowing the combustion event. If you look at it in a graph, 75 LOP offers the same margin of detonation resistance as 225 ROP. Unfortunately, it puts you closer to TIT limit. A well balanced engine will run smoothly way past 100LOP. My Lycoming with stock injectors will run smoothly passed 125LOP, though I have no operational use for it. The APS guys can go even further in their TNd Bonanzas.

As a naturally aspirated data point, I run my engine at very high power LOP (>82%) in the winter at low altitude. I run between 50-70 LOP at that setting depending on what it takes to keep CHTs around 300 as they tend to drop into the 200s if I lean further.

Edited April 1, 2019 by Shadrach

[Shadrach]

9 hours ago, Austintatious said:

thanks.... I have a deal in the works for a Rocket, but if it falls through there is a nice Bravo I have been looking at.  The cruise numbers are vastly different on those 2.

Are they really “vastly” different other than maybe in climb?

[Shadrach]

2 hours ago, ArtVandelay said:

It’s not that the absolute value of icp is bad, it’s the timing. After all, no ICP, no HP. They could add a knock sensor easily (it’s just a microphone).


Tom

Knock sensors have proven to be very unreliable in aircooled aviation engines because of the noise inherant to the application.