Siezed low-time neglected turbocharger

[Brett]

As it happens I flew today and recorded some figures. I too screwed a sensor into the front water jacket on the turbo. Please take these figures with a grain of salt as the sensor looked pretty shabby. I put some new heat shrink around the connections and bolted it on. It is a good guide though. Sensor was a standard spark plug type cht sensor. I had to file it open a little to go around the 14mm plug that screwed into the water jacket.
Outside air temp - 28 - 32 c

Climb out first reading at about 2000 ft when things got less busy in regard to airspace - 280f

in cruise at 2800rpm, 1280 egt, 375 cht, 28" map = 288f

shallow climb 2800rpm 1240 egt 371 cht 27" map = 292F

when holding it at max cruise 35" it stayed about the same 280-290f but I did see 302f somewhere in the flight but was only briefly.

landing temp = 263f

idling back to hangar was at least 3 mins = 252f,,,,,it was starting to rise as I idled it longer stationary so I shut down

1 min= 263f
2 min=274f
3 min= 286f
4 min= 292f
10 min= 315f
12 min= 319f
13 min= 322f
14 min=326f
15 min= 328f

After that is started to cool down ,, also bare in mind I was shut down into wind that was blowing at least 20 kts. I normally park it in the hangar not long after flying usually.

[Onex107]

Good work Brett. Real numbers, not assumptions. Looks like you only have to remove 100 degrees from the shaft housing to get it back down to normal oil temperature. The increase at long idle time is interesting. It must be something to do with air cooling and heat soak time from the hot section. If that is actually happening, the three minute idle time doesn't accomplish anything. Cooling the hot section casting is a different problem. Encasing it in a blanket to reduce cowling temp would only make it worse. Lets add cooling fins to the hot side with a blast tube. Just thinking outside the box.

[lutorm]

This is the rebuild kit I put in: https://www.ebay.com/itm/Turbo-Rebuild- ... lg&vxp=mtr
it is a Garrett gt2554.

The gt2554 is a ball bearing turbo? My understanding is that ball bearing center sections use much less oil than journal bearings which has some advantages (that aren't really that important in our context, like better throttle response.) But the flip side is that, partially because they use less oil, they also have to be water cooled. There's just not enough oil flow through a ball bearing center section to adequately cool it. The water lines are there for a reason. (The exception might be some fancy ceramic ball bearing turbos that use oil cooling only.)

Garrett apparently agrees (https://www.turbobygarrett.com/turbobygarrett/sites/default/files/Garrett_White_Paper_01_Water_Cooling.pdf):

Many customers question the necessity or benefits of plumbing in those extra water
lines to the sides of the turbo’s center housing. Why not just leave them off? The reality is that
a water-cooled turbo can be damaged irreparably without proper water line setup.

Why on Earth would anyone deliberately choose a component designed for water cooling in an air/oil-cooled application when there are plenty of oil-only turbos available?

[NWade]

Thanks for the temp readings, gentlemen! Lots of possible variability in exact readings, but the trend is certainly clear and reinforces our suspicions about what constitutes "public enemy #1" for these turbos (i.e. post-shutdown heat-soak).

I'm reaching out to my auto-racing contacts to see if I can find clever ideas in that world that might be applicable to our air-cooled engines.

--Noel

[lutorm]

Thanks for the temp readings, gentlemen! Lots of possible variability in exact readings, but the trend is certainly clear and reinforces our suspicions about what constitutes "public enemy #1" for these turbos (i.e. post-shutdown heat-soak).

I actually disagree. The post-shutdown situation obviously isn't good, but the number of shutdowns on an aircraft engine is pretty low compared to a car. A steady-state temperature of 300F on a thermocouple at the surface of the center section seems worse to me, given that this almost certainly means the bearings and seals themselves run significantly hotter. The Garrett white paper I linked above says that 300F is where the strength of the bearing races etc start to decline rapidly, and overheating the bearings also shrink the tolerances.

They end with

Vehicles with extremely low exhaust gas temperatures and no water
cooling system (low-output diesels or purpose-built methanol / alcohol fueled dragsters, for
example) may not require a water-cooling system for the turbocharger. In this case the condition
of all turbo components should be closely monitored ...

A gasoline-powered aircraft engine that runs at full power for long periods of time does not seem like a place to try this out. For air-cooled performance engines they suggest setting up a separate water circuit, that might not need a water pump of it's set up to make use of thermal siphoning and the water temperature is monitored. But at that point it certainly seems preferable to switch to a oil-only turbo to me.

[tljones42]

[

I believe in the Aerovee Turbo webinar Jeremy Monnett said the turbo was from a diesel truck. I'm not aware of any trucks that make anywhere around 100hp, so that didn't give me a very good feeling for how well matched the turbo is to the application. Can anyone of you guys that have the turbo find a model number?[/quote]

At some point I heard Jeremy say this turbo was from an Izuzu (sp?) truck application.
Tom Jones

[Sonex1517]

I believe in the Aerovee Turbo webinar Jeremy Monnett said the turbo was from a diesel truck. I'm not aware of any trucks that make anywhere around 100hp, so that didn't give me a very good feeling for how well matched the turbo is to the application. Can anyone of you guys that have the turbo find a model number?

At some point I heard Jeremy say this turbo was from an Izuzu (sp?) truck application.
Tom Jones

I believe it is a Garrett T25

[pfhoeycfi]

Has anyone been able to plot an operating point on the 2554 map for 100hp?

[lutorm]

Has anyone been able to plot an operating point on the 2554 map for 100hp?

It depends on the volumetric efficiency, which we don't know, but at 100hp, 3400rpm and 40" MAP, I'd estimate a corrected airflow of 9.5lb/min and a pressure ratio of 1.35. You can plot that on the compressor graph from Garrett below. It's well below peak efficiency and off towards the surge line. If you tried to run 40" at 10,000 feet, you'd be at 12.5lb/min and 1.9. I don't know if the wastegate setup allows that, but that would be even closer to the surge line. (I don't suppose anyone's equipped their turbo with a wheel speed sensor?)



The GT2052 looks like a better compressor match to me. It's also oil-cooled only... It's possible the turbine is too small though.

[Brett]

I just hope something postive actually comes out of this thread in regard to a genuine solution from the factory. I'll hang in there if I know that's the case. Maybe the new year will bring a fresh look at it.