High EGT vs normal CHT and TIT

[Fly Boomer]

16 minutes ago, A64Pilot said:

Here you go. But yes since the beginning I guess ignition “busting up” under high loads has been an issue. I wouldn’t expect to see it in aircraft though, but ICE while a mature technology, hasn’t reached a dead end, there are still advances. I personally see Mazda’s spark ignition, gasoline Diesel as a big achievement.

https://www.researchgate.net/publication/256463297_Estimation_of_In-Cylinder_Pressure_Using_Spark_Plug_Discharge_Current_Measurements

The Internet is a wonderful thing.

[Shadrach]

13 hours ago, A64Pilot said:

Internal cylinder pressures have been monitored since well before WWII.

Horsepower and CHT closely follow pressures.

It’s very simple and more accurate to move the pressure peak around with timing, but it’s not usually done as it reduces power.

I was wrong, cylinder pressures have been measured since 1796

https://www.fs.isy.liu.se/en/Publications/Articles/IFACWC_17_LE_AT.pdf

Spark plugs have been used to measure internal cylinder pressure at least since Henry Ford did it with the Model-T, they didn’t use piezo crystals to measure pressure, they were direct to the cylinder, thise same plugs could be used to prime early engines to help with hand starting by putting fuel directly in the cylinder. 

https://www.mtfca.com/discus/messages/179374/231606.html?1314245899

 

Not to pick nits, but Horsepower follows MEAN ICP. Peak pressure is obviously moveable with timing. It is also movable with mixture. At a given horsepower, both lean and rich mixture settings will have the same mean cylinder pressure, however the ROP setting will have higher and lower peaks while the LOP setting will have a lower peak but more constant pressure throughout the power stroke.

[Stetson20]

Update:  Waiting on getting my plane in to get the injectors and fuel distributor (spider) cleaned. Savvy recommends taking the plane up for the SavvyAnalysis Flight Test Profile.

Thanks to @kortopates for the guidance. I'll add to the thread once my injectors are cleaned and I'm able to gather some more engine monitor data.

[jlunseth]

To the OPs question, I would think instrument error, not an issue with an actual higher EGT. Especially since this is a new installation. The CHT is unremarkable as is the TIT, so why suspect you have one soaring EGT? There are a number of possible sources of instrument error. Bad probe. Probe was placed differently than the other probes. Probe installed incorrectly. I am not an A&P nor have I installed probes, but understand from the installation in my own engine that there is a specific sequence and orientation for the probe and the washers, and if a washer is left out or reversed you will get a wrong reading. Mine was JPI so might or might not apply, but worth looking at.

HP does not go down LOP. LOP gets that reputation because those who fly NA engines cannot raise their MP, and in fact it goes down as you go up in the air column, so fuel flow has to be reduced or you have to go ROP to make more power. Also, many pilots have gotten it into their heads that 65% is the limit for LOP OPS. It is not. I fly at 71% HP while LOP pretty much all the time. I have a turbo and can add air to keep the air/fuel ratio lean while keeping the HP up. Engine with a TBO of 1800 is currently at 2380. The HP produced is just as Shad says. The power is the area under the combustion curve. You can have a curve with a short high peak ICP or a curve with a longer lower peak ICP and the area under the two curves, and thus the HP produced, is exactly the same. The “longer lower” is going to be easier on your engine and will produce lower CHTs because CHT is directly related to max ICP during the combustion cycle. Lower CHTs is one benefit of LOP. In fact, we are in the time of the year here in MN where it becomes a little bit of a problem because with the cold weather we are having CHT’s will run close to the lower operating limit (240) while LOP and operating in cold dense air. Something you almost never hear about. So I have to “heat up” the mixture a little just to get some heat in the cabin.

[Pinecone]

On 10/15/2022 at 2:00 PM, Shadrach said:

Dead plug would be my first guess. Nothing wrong with doing it in cruise mag check to verify everything is firing provided you don’t have squeamish passengers on board.  It may not show up in a mag check on the ground. I’ve had plugs that fire fine at run up power but drop out on takeoff, or in cruise

This was my thought.

Dead plug, single flame front, so still burning when the exhaust valve opens.   Low CHT as a good bit of the energy in the fuel is going out the exhaust vavle.