OMG, LOP and GAMIs again...

[Nemesis]

Machine. 1980 231, LB engine with 1275 SMOH, Merlyn wategate, no intercooler, ROP always good CHTs <360dF and oil temp <185dF, overall an excellent running engine. This thread is definately not to restart the debate. I finally was able to have GAMIs installed a couple of months ago. Even with the initial installation the engine is pretty smooth LOP. I may still adjust one injector but I want even more data before I talk with the people at GAMI.

The problem that I have is that I seem severely limited by TIT. When LOP and as I go above 60% power at around 9 GPH, I reach 1650 dF on the TIT. Trying to get any more power than that only results in even higher TIT and it makes no sense to me to run the turbo at 1650 for any length of time. I know it is certified to 1650 but certified and good practice are rarely the same thing. Heck, at 60% I can run at peak egt and low MP but 60% is not where I want to run. What have other turbo operators found, and in particular 231 owners? Are other turbo operators able to get 70% or 75% LOP?

[testwest]

Actually, this thread may turn into a thread on intercoolers......which, if you want to gain any economy of operation with your low compression ratio engine, may be the only alternative. Also, check your spark plugs for high resistance on the center electrode. There is an encyclopedia's worth of information on that subject here, and on Beechtalk.

BTW, I would suggest lurking on Beechtalk for anyone who has any interest in this subject. The APS guys (Deakin, Braly, Atkinson) hang out there and post all the time.

[Parker_Woodruff]

Hi Dave,

I just responded to your PM and I was asking if you were intercooled or not.

Testwest - I went with yours and a couple others' good reviews and am putting the Tempest Fine Wires on my M20K.  Really excited to fly it on Sunday.

I like to sit right around 74-78% power LOP.

[testwest]

Some very good information on intercoolers here:

http://www.cirruspilots.org/blogs/braly/archive/2009/02/13/intercoolers-are-wonderful-devices.aspx

[jlunseth]

Your engine is not certified to operate continuously above 1650 TIT. It is certified to operate above 1650 and up to 1725 for up to 30 seconds, for the purpose of allowing you to lean out the engine, but continuous operation about 1650 is not allowed.

The intercooler article by George Braley is good information, and I will get to that in a minute, but the intercooler does not affect TIT.  The intercooler is installed in the induction air system downstream of the compressor section of the turbo, and TIT occurs in the inlet side of the section of the turbo that accepts exhaust gases - they are two different gas streams and one is upstream of the turbo while the other is downstream.

I am a little surprised at your numbers, and would suggest that if you are indeed LOP, you are not very far LOP.  TIT should fall when you get into the "operating range" of LOP, which depending on who you talk to, is somewhere between 25 and 60 dF after the last cylinder EGT peaks on the LOP side.  (The recommendation given at the APS seminar I attended for operating turbo engines LOP was 60 dF, but that is pretty far LOP and your engine may not be able to get there.)  In the process of leaning you may see TIT go over 1650 for a brief period depending on how fast you pull the mixture, but I would expect it to fall back below 1650 once you are sufficiently far on the lean side.

As for the intercooler, the biggest issue I have seen that would impact a non-intercooled engine, is a Compressor Discharge Temperature in excess of the 280 dF redline.  My engine is the same as yours, but intercooled.  In my experience, you will begin to see CDT's over redline whenever you climb above FL200 or 210.  You will not be able to stop the redlining except by reducing power, which will reduce a climb rate that is already anemic at that altitude.  The purpose of the redline is to prevent detonation caused by high induction air temps., and the intercooler steps in to provide that protection by cooling the hot compressor discharge gases by as much as 100 dF and sometimes a little more.  The CDT redline becomes irrelevant in an intercooled 231, the Induction Air Temp. is never close to that number; it is a concern in your non-intercooled engine.

[Nemesis]

Do you have an intercooler?  I think that might help you a bit.  The 231s sometimes do run hotter, so I'm not terribly surprised. Also, is yours a GB or LB engine?

Also, at what altitudes are you seeing these high TITs?  How do your TITs compare to your EGTs at those altitudes?  What engine monitoring system do you have?

You never know - you may just have a bad probe.  I know my factory TIT probe has started to be a bit sketchy on the low end.  However, once I start leaning, it indicates like it always has.

I typically sit around 1570 - 1620 dF when LOP when burning 12 GPH.  The highest I've taken my plane so far is FL190 and it has never wanted to exceed 1650 dF when leaning.

Parker

------------------------------------

I am sure that Parker will not mind that I also posted above his private response to me.

My temperature device is a JPI-830. I also have seen my factory guages fluctuate at times, but for the most part, they agree with each other - ie. if I see a rise measured in degrees on the JPI, then I also see a rise on the factory guage although can only guess at the real temp on the factory guage. The engine is LB and it does not run hot at all; in fact it is quite cool compared to other 231 temps that I have read about here and elsewhere. At 75-78% ROP, my hottest cylinder is about 355dF and my oil temp is 180-185dF. The hottest temps that I have ever seen on this engine during climb and over a 117dF desert were 368dF cyl and 192dF oil.

I also have been to APS and undertand and agree with the theory and practice. I kind of doubt that an intercooler will have much to do with EGT and TIT beyond a handfull of degrees. If the intake air is cooled 100dF or so but then combustion takes the hot gasses as read on the EGT a few split seconds after combustion up to 1450dF, I am pretty sure that the difference between intercooled air and non-intercooled will be very small. I am not really counting lack of an intercooler as an issue.

All of my testing thus far has been at 17,500. I did a little testing at 65% all the way from 150 ROP to more than 100 LOP right over the top of peak. Lately, I just leave the MP at 30" or so and do a BMP to a fuel flow of about 8 GPH and well more than 100dF LOP and then I enrich from there searching for first to peak from the lean side (I also tried up to 32" as suggested by Braly and Atkinson as a pseudo WOT position for a turbo engine). As I approach 9 GPH from the lean side, the TIT is up near the 1650dF mark and I have to stop. That leaves me in the low 60s as percent HP.

I have not really compared EGT and TIT while trying to run LOP. I know when I am 125 ROP EGT (leanest), I am 95 or 100 ROP on the TIT. While LOP I have only watched for prohibitive temps. In other words, I am only looking for anything that redlines as I try to find the richest cylinder, and of course I always find the TIT going through the roof. Then I notice that I am at such a low power state, I try to evaluate for a bit, and then I return to ROP so that I can get to where I am going. As far as probes go, the placement of the JPI and factory probes for TIT are as close as humanly possible on near opposite sides of the exhaust. However, I also have to add that when the JPI reads 1650, the factory guage is well below that, maybe 50 or 75 degrees. I have more faith in the JPI and use that as my limiting factor.

I have done a LOP mag check and the ignition system feels strong with little change from 2 mags except EGT rise as normal. The plugs are Champion massives and are about 16 months old and a bit less than 200 hours and cleaned and gapped about 40 hours ago. I can do some resistance checking when I next have the cowl off.

While climbing the CDT reads a little above mid scale and then lower when I reduce power. I have never seen the CDT anywhere close to redline but I have also never been above FL190.

[jlunseth]

I doubt that an intercooler makes a significant difference in EGT, and probably no difference at all in TIT which is mainly exhaust gases still burning.  No matter what temp. the induction air starts out at, the temp. of combustion is governed by, well, the combustion temp. of gas + air and that does not change within a range, so the exhaust gas temp. is not likely to change because of induction air temp.  It is more a matter of how much unburned fuel is left to burn in the collector and turbine.

I have not tried LOP in my 231 for awhile because the cylinders were too far out of sync, but had the engine rebuilt this winter and it is now broken in, so will be trying some LOP next week.  The issue I had in my 231 was engine roughness, that would not let me get past about 60% HP.  I will let you know if I see your TIT issue.

[testwest]

D'oh, got my TITs and my CDTs mixed up!

At any rate, those low-compression boosted engines just have a little more challenge when it comes to operating LOP, however....the fine wire Tempests may help. Check your spark plug center electrode resistances and replace any that are trending high. Good luck!

Also, your mag timing may be a little on the late side, equally on both mags, so your combustion event is slightly delayed. This would explain both the lower CHTs and the higher TITs. Let us know what you find!

[xftrplt]

I doubt that an intercooler makes a significant difference in EGT, and probably no difference at all in TIT which is mainly exhaust gases still burning.

FWIW, I agree completely.  I remember seeing an analysis that showed that the KCals removed by the IC are but a minuscule fraction of the KCals generated by the combustion events.  Science confirming intuition.

[FBCK]

Nemesis, I have a 231 with Mrylyn Wastgate and its intercooled and I have the same issue if I try to turn the mixture down, the TIT will just pop up to 1650 and the alarms go off.  I just do the big pull now and the situation is much better and govern my activity by adding more fuel to increase and decrease power with an eye on the TIT and cylinders. I use some numbers that Parker posted back a while ago and they worked amazing well. I used to fly at 28 inches, but now I push it to 31 inches and a fuel flow of 11.5 to 12gph and everything stays cool (10000-17000 feet).  As I come down again I find I have to either lean again and go rich or the TIT become an issue again, the MP also will increase as I decend.  I have to whach my cylinders in climb, number 2 will hit 380 even when its cool oAT.

[Nemesis]

Quote: FBCK

Nemesis, I have a 231 with Mrylyn Wastgate and its intercooled and I have the same issue if I try to turn the mixture down, the TIT will just pop up to 1650 and the alarms go off.  I just do the big pull now and the situation is much better and govern my activity by adding more fuel to increase and decrease power with an eye on the TIT and cylinders. I use some numbers that Parker posted back a while ago and they worked amazing well. I used to fly at 28 inches, but now I push it to 31 inches and a fuel flow of 11.5 to 12gph and everything stays cool (10000-17000 feet).  As I come down again I find I have to either lean again and go rich or the TIT become an issue again, the MP also will increase as I decend.  I have to whach my cylinders in climb, number 2 will hit 380 even when its cool oAT.

[FAST FLIGHT OPTIONS LLC]

I dont have an intercooler or automatic wastegate and run cool T.I.T.'s even up high:

http://youtu.be/Yn9ZHkRwf2U