CHT again

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astaib
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CHT again

Post by astaib » Sat Jun 29, 2019 8:00 pm

Hello guys,

I’m sorry to bring back this topic on the table but I really need your feedback on an easy question:
Is the Arizona baffle really useful to reduce CHT?

My engine usually runs hotter than what I read from others users on the forum (when I’m LOP, it is difficult to have the hottest cylinder at less than 380).
When i’m ROP the cyl1 is always the hottest and when I’m LOP, they are balanced.

Today was very hot in France and I was forced to fly low at 2500 (30 degrés Celsius OAT) and I was not able to have less than 400 when LOP and the only possibility to have something like 390 was in being almost full rich.

For Information I change lately all the baffle seals and all the gaps has been filed with mastic.
My oil analysis are ok and the engine is only 200 hours after overhaul.

The last thing that I can change to (maybe) help is the Arizona baffle, but I don’t want to waste 500€ if the effect is not real.

Thanks a lot.

Arnaud.
Arnaud
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Rich
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Re: CHT again

Post by Rich » Sat Jun 29, 2019 9:00 pm

I think I've posted this before:

When we picked up our plane new in 2002 and flew it back to the West Coast, #1 was the hottest cylinder, always, and we had to run really rich mixtures to keep it at 400. After getting it home we found this remained the situation. We talked to Diamond about this and a few months afterward they supplied us the AZ baffle parts (under warranty). But we had to pay for installation (not outrageous cost).
After this, cylinders were magically pretty well balanced and it's no real trick keeping temperatures below 400 in cruise. ROP max cruise speed power in summer temps will be ~380. LOP they typically plummet down around 340. By definition you're producing less power LOP and normally I only do this at higher altitudes when I'm trying to cut out a fuel stop.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal.
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Re: CHT again

Post by blsewardjr » Sat Jun 29, 2019 10:00 pm

I've tried everything recommended on this board to get the #1 CHT down -- Arizona baffle, sealing all holes, silicone on the wavy part of the soft top baffles, tightening the lower part of the hard baffle with the wire between the front and back etc. None have produced any dramatic reductions, although making sure the lower parts of the hard baffle are flush on the cylinder fins seemed to help the most. The pattern for my engine is the same regardless of whether ROP or LOP - #1 hottest, followed by #4 (10-15 cooler) followed by #3 and #2 (20-30 cooler). My conclusion is that different individual engines just run differently, so any or all of the possible solutions may or may not work. That said, adding the Arizona baffle wouldn't hurt and by aviation standards 500 euros plus installation is not that bad.
Bernie Seward, IR, AGI
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Re: CHT again

Post by astaib » Sun Jun 30, 2019 7:08 am

Sorry Rich, I didn’t remind this post and in the meantime I was hoping that the seals change will solve this problem, but no.
Thanks Bernie too.
Arnaud
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Re: CHT again

Post by Rich » Sun Jun 30, 2019 3:42 pm

I just reviewed a couple of GAMI tests I ran last year. In virtually all cases in both tests the sequence from highest to lowest CHTs was 3-1-2-4. Which means the starboard side cylinders run warmer than port side. #4 trails #3 by about 20-25 deg. 1 and 2 trail #3 by about 10 deg. There seems to be an EGT component to this, as #4 EGT runs lower than the other 3 and peaks later (lower fuel flow) than the others.However, the relationship between EGT and CHT for 1,2, and 3 is somewhat muddled, however.
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Re: CHT again

Post by blsewardjr » Sun Jun 30, 2019 5:11 pm

Rich inspired me to look at my data again. My memory of the CHT spreads was not entirely accurate. My #1 cylinder is always the hottest and #3 is always the coldest with an average difference of 34 degrees. #2 and #4 are in between. They alternate as to the next hottest cylinder after #1 but in general #2 averages about 4 degrees hotter than #4. The average difference between #1 and the next hottest cylinder is about 10 degrees.

On my left side the temps are nearly the same (4 degree difference) while on my right side the temps are significantly different (34 degree difference). I have GAMI's as well.

I looked at three other DA40's that had posted their data. Each had a different hottest cylinder -- 1, 2 or 4!
Bernie Seward, IR, AGI
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Re: CHT again

Post by Charles K » Sun Jun 30, 2019 6:23 pm

I usually run 350-360 in my 04. What power settings are you guys flying at. I'm usually no more than 65%.

Typical settings 2200/22 and 2300/22 most of the time. Usually run at peak as power below 75%. Fuel burn around 7.8-8.0. 130kts TAS.

Thanks
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Re: CHT again

Post by blsewardjr » Sun Jun 30, 2019 6:38 pm

Almost always run 65% , 2300rpm and 7.8-7.9gph LOP in cruise, with 21.5-23 inches MP, depending on altitude. The 65% is derived from the LOP formula of 14.9 times the fuel flow divided by the horsepower (180). TAS is 133-137kt.
Bernie Seward, IR, AGI
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Re: CHT again

Post by astaib » Sun Jun 30, 2019 6:59 pm

My results indicated in the first post is at 75% around 2500 ft. LOP: 2200/26.5 ff: 7,8. 125 kts.
When i’m at FL 065 and above, i’m 65%, cooler CHT still in LOP: 2400 /21. ff: 7,3.
Arnaud
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Re: CHT again

Post by Rich » Sun Jun 30, 2019 10:40 pm

I do not have GAMIs but have performed the test - twice. I'm still on the fence about pursuing this option. There is this statement on their website:

The GAMI Spread is calculated by determining at what total engine fuel flow each cylinder reaches peak exhaust gas temperature (EGT) and subtracting the lowest flow from the highest flow. Most engines are considered to have good fuel/air ratio balance if the GAMI Spread is less than 0.5 gph.

The tests were somewhat inconclusive, given neither EGT's nor fuel flows never seem to settle down to precise numbers where I believe them as quantitative data. But qualitatively, they do indicate:

In both tests the sequence of reaching peak EGT's is 2-3-1-4. The spread is dictated by 2-4 peaks and was .3 GPH in one test and .4 GPH in the second. Highest peaks were 3-1-2-4 in one test and 3-1-4-2 on the second. The spread of EGT Peaks was 27 degF in one test and 20 degF in the second. Only #3 gave me the same peak reading in both tests.

In all tests the peak CHT in any cylinder was 377 (these were done in the fall, OATs fairly moderate) at 7000-ft. I have no real problem with CHT's (the main topic here) and can go deeper into LOP at higher altitudes than at this test altitude.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal.
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