Absolute EGT value

For sure all this has been done to death but I still think an EGT this high is not right. Especially as Timothy wrote “ROP”. But he didn’t say how far ROP, etc. Something is missing…

Something doesn’t hang together here.

• You may need to get GAMI injectors. You can collect the data for ordering them on one flight, logging the data via the EDM. There is little point in fiddling with temperatures unless you have this sorted.

• The high EGT suggests you are flying peak EGT at a high power; perhaps 80-90%. A lot of turbo owners do that, saying “I paid for the turbo and I am going to use it”. Then they wonder why they have to throw away their cylinders before 1000hrs. I have never heard of a turbo engine (of the flat variety) which provably (usually that means under the one ownership) made TBO. There was an “I know somebody who did; let me ask” attempt to challenge this on the Socata owner group (TB21=TIO-540 too) but nobody came up with evidence.

• CHTs have not been posted.

• The sensor type config may be wrong, or the EGT probes may be in the wrong place. All this has been done. One pressurised twin owner, well known in the UK scene, reported that for years he flew ROP to keep CHTs below the limit on one specific cylinder, and then it was discovered the CHT probe on that cylinder was in the wrong place! IIRC, the usual cockup, where the factory CHT probe is wrongly used to feed the EDM CHT on that cylinder, but that probe is in a different place to the other five. As a result he burnt some absolutely vast amount of extra avgas – probably literally tons – over the years.

• With balanced injectors, LOP should work fine because it is cooler than peak (obviously).

• LOP delivers less power than peak EGT, obviously, because while both are stochiometric, less power is being burnt when LOP, so you will be going slower.

• LOP doesn’t deliver more MPG than peak EGT because power comes only from burning fuel – unless you get into second order factors e.g. flying with a low RPM.

• You might get through a lot of EGT probes.

Timothy wrote:

Hence my keeping TIT in limits. I am asking whether I should worry about EGT as well.

What exactly is the difference between the temp at EGT and TIT position? I mean, when running outside BEP (ROP for instance), fuel may still burn when exiting the cylinders, it is burning inside the exhaust pipes. Wouldn’t excessive EGT temps simply mean you are rather way off with the mixture on those cylinders? It can’t be good for the turbo either way. (Even though TIT is below limit, it is still much higher than what it should be).

I think the difference is that a particular EGT is just an average of the hot gas pulses, which on a 4-stroke come out on every 2nd revolution of the crank, while the TIT is a combination of the gas pulses from all 6 cylinders (if single turbo) or a combination of 3 cylinders (if twin turbo). So the temperature of a large component (not an EGT probe but e.g. a turbine disk) is going to be higher when subjected to TIT than EGT.

Peter wrote:

• With balanced injectors, LOP should work fine because it is cooler than peak (obviously).
• LOP delivers less power than peak EGT, obviously, because while both are stochiometric, less power is being burnt when LOP, so you will be going slower.
  

LOP your cylinder temperatures will be quite a bit cooler than the equivalent power setting ROP.

LOP operation does not need to deliver less power than ROP. You can achieve for example 70% on both sides of peak. Of course if you set 70% ROP and just pull back the mixture to LOP, you will loose 5-10% power. If your targeted power setting is 65%, you can set MAP and RPM for 75% (or a little less) and lean to LOP.

Here is a graph that illustrates the values of EGT and TIT for a Continental TSIO550-C engine.

In 1 is the initial climb, then I pull the power back to 30"/2400 RPM for cruise climb and in 2, reaching cruise, I pull back the mixture to somewhere in between between 1620 and 1650°F TIT, or between 16 and 16,5 GPH. The CHTs are around 310°F. Power output is about 70% BHP

The engine runs just as smoothly ROP as LOP – in other words the cylingers are well balanced. It is a “Platinum Ed” engine, and as such was delivered with tuned injectors from Continental AFAIU. When you pull the mixture back you can absolutely not feel any difference, except for the loss of power.