Turbo heat

[Jerry/MT]

There should NOT be issues associated with tolerances with the case and the turbine under normal operating conditions. If this is a concern then they're not engineered correctly. Yes, housing contact IS the path to utter failure. These things nearly always occur due to tolerance problems with the turbine shaft and bearing, and these problems can occur for several different reasons:

Failure-Diagnosis

Garrett has a nice chart showing all the reasons for problems (and nowhere does it mention concerns with turbine wheels rubbing casing due to not allowing turbine to cool; none of their "solutions" mentions needing to allow the turbine time to cool down):

https://turbobygarrett.com/turbobygarrett/sites/default/files/Garrett_Troubleshooting_Guide.pdf

I've got cars running more complex turbos -VNTs- and these have no such issues as a first failure point (rubbing ONLY occurs as a secondary issue, after the turbo is basically needing to be replaced [at a minimum the CHRA]).

All said, when going to stop an engine it's still a good idea to allow the turbo to cool a bit after running hard. If you note above, however, the origins of a lot of the problems lie elsewhere (even a bigger issue with proper management/care when cold).

Look, I don't want to et into a peeing contest with you, but having worked on turbo machinery in my professional career (aircraft propulsion), respectfully,neither of the cited references are the type of resource on which to base these types of discussions. First of all, "Failure-Diagnosis" appears to be automotive turbo charger information and the duty cycles for cars are significantly different from off road machinery.

As I stated before, my New Holland owners manual makes reference to cooling periods before shutdown from high power operations to prevent "...deformation of ...components.." Contrary to your statement, case rubs are not always "utter failure". Rubs can increase tip clearance which leads to inefficiency but not destruction. In extreme cases they can cause failure. As to the Garrett info, look at their answers for and "Damaged Turbine Wheel". They say" Remove turbine housing inspect for cracks and wear, replace if necessary". How would the turbine housing be damaged by cracks and wear? They don't say. Certainly excessive bearing wear can lead to rubs but so can thermal effects. Your experience with cars apparently sees a lot of bearing failures that lead to fatal rubs.

You live in Arlington. Go take the Boeing tour and look at the turbine cases on the engines. You'll see a lattice work of tubes that spray cooling air on the turbine case to control clearances and prevent rubs. There may also be some on the high compressor case because they need to control clearance on the hot end of the compressor. There are sophisticated control systems to meter this cooling air. This is done for performance reasons as less tip clearance means better TSFC

New Holland would not go to the trouble to placard the cooling period on a "B" pillar in the cab and in the manuals if it were not for a good reason. This is done because it potentially prevents damage. It sounds like you work with automobile turbos and you don't see these type of problems, but remember the duty cycle is much different. Ag machinery, in many cases, operates at maximum power for hours at a time in dirty conditions so EGT's are high and engines and the turbine are really hot before shutdown. So cool them down before you shut them off.

So maybe we can agree to disagree.

 

[DieselBound]

While the equipment may differ, the mechanical properties are the same and it's about the response of materials to heating and cooling cycles, along with the various thrust and torsional stresses that they may encounter. The mechanics are the same. Yes, tractors have different duty cycles, but tractor trailer rigs loaded and going up the mountain passes here in the PNW can be running for quite some time with heavy boost. It ALL comes down to the same thing: EGTs, lubrication and clean air.

I don't have access to the document that you are referring to. Best I can do was to track down what I could off the Internet and I came up with a document covering the New Holland 8000 series tractors circa early 2000s: 24615692 FORD New Holland 867 877 887 897 WSM And in this document it does mention shutdown procedures, stating that allowing the engine to cool down helps, in regards to the turbo, helps reduce component distortion. From Section 10 Page 7:

Before stopping the engine, allow the turbocharger and exhaust manifold to cool down by idling the engine for approximately one minute. This will prevent the distortion of any components.

I don't think that we see differently on this, that there's a need to allow temperatures to come down (it might even be more important for heads and cylinders than the turbos).

The point of difference is in WHY. In this document, Section 10 Page 10 and Page 11:


Turbocharger failures are usually a result of dirt ingress into the intake manifold, which damages the fins,or through lack of lubrication which destroys the bearing surfaces, and the turbocharger seize

On Page 11 they note problems associated with the rotating assembly binding or dragging. If it was known that fins were distorting due to high temp shutdowns then I think that somewhere they'd mention it. As it is is a general statement of "distortion of components." Fins have a lot of surface area so heat dissipation is likely to happen more quickly when one drops off boost than does the housing.

Oh, and there ARE Garrett turbos available for New Hollands. Not sure if they're an OEM or not.

I'll leave you as the resident expert on the airplane stuff

 

[Jerry/MT]

While the equipment may differ, the mechanical properties are the same and it's about the response of materials to heating and cooling cycles, along with the various thrust and torsional stresses that they may encounter. The mechanics are the same. Yes, tractors have different duty cycles, but tractor trailer rigs loaded and going up the mountain passes here in the PNW can be running for quite some time with heavy boost. It ALL comes down to the same thing: EGTs, lubrication and clean air.

I don't have access to the document that you are referring to. Best I can do was to track down what I could off the Internet and I came up with a document covering the New Holland 8000 series tractors circa early 2000s: 24615692 FORD New Holland 867 877 887 897 WSM And in this document it does mention shutdown procedures, stating that allowing the engine to cool down helps, in regards to the turbo, helps reduce component distortion. From Section 10 Page 7:

Before stopping the engine, allow the turbocharger and exhaust manifold to cool down by idling the engine for approximately one minute. This will prevent the distortion of any components.

I don't think that we see differently on this, that there's a need to allow temperatures to come down (it might even be more important for heads and cylinders than the turbos).

The point of difference is in WHY. In this document, Section 10 Page 10 and Page 11:


Turbocharger failures are usually a result of dirt ingress into the intake manifold, which damages the fins,or through lack of lubrication which destroys the bearing surfaces, and the turbocharger seize

On Page 11 they note problems associated with the rotating assembly binding or dragging. If it was known that fins were distorting due to high temp shutdowns then I think that somewhere they'd mention it. As it is is a general statement of "distortion of components." Fins have a lot of surface area so heat dissipation is likely to happen more quickly when one drops off boost than does the housing.

Oh, and there ARE Garrett turbos available for New Hollands. Not sure if they're an OEM or not.

I'll leave you as the resident expert on the airplane stuff

Hey guys, new to the forum and have a quick question. My kubota has a turbo. Do I need to let the tractor sit there and idle for a while before I shut it off to cool down the turbo? And do I always have to do this ( if I have to ) even if I am just putting around the yard? Thanx


This quote above is the initial post. It basically asks "why do I have to do that?" (i.e. allow for a cool down). And that's what I responded to.

Respectfully, it doesn't ask about the common failure modes. Dirt ingress, as mentioned above, generally affects the compression system which adversely affects flow capacity, pressure rise, and efficiency. If the intake air is used to pressurize seals than I suppose it could also contaminate the oil and lead to failure also. There is no argument from this quarter about the results from lack of lubrication. Been there, done that and got the Tee shirt to prove it. Turbo's generally use cast wheels in the turbine they have a pretty big thermal mass that does not use any auxiliary cooling and takes time to cool from ~ 90% of the EGT at max power to ~90% idle EGT so the question becomes does the resultant change in wheel diameter occur faster than the casing. Obviously it is a concern for the manufacturer.

I respect your experience with turbos as you obviously have hands on experience with them and I have enjoyed this discussion.