Using a water-cooled turbo on an air-cooled engine

[Gustafson]

I recently read about someone attempting to adapt a water-cooled turbo for an air-cooled motorcycle engine. His plan was to run oil through the water jacket to provide cooling for the turbo.

Is this a realistic possibility? Would it be better to just use a normal "oil-cooled" turbo?

 

[MikeHalloran]

It's certainly possible, but the oil will need to get rid of a _lot_ of extra waste heat, so he'll need an extra oil cooler and probably a fan.

I'd be inclined to use glycol/water, a radiator, a fan, and a circ pump, if I were to contemplate such a thing. On a motorcycle, that could be a serious packaging challenge.

On balance, at least a liquid cooled turbo housing isn't _glowing_ in normal operation, so that eases the packaging constraints a little.





Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Do you mean water cooled exhaust housing or just water cooled bearing.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[Lou Scannon]

I suspect the OP means just a typical water cooled center housing. In any case, it shouldn't be beyond the wit of man to engineer a thermosiphon system, with a bit of R&D. As the steady state heat loading will have stong correlation with vehicle speed, I think a passive radiator in the airstream would be adequate.
During the development phase, if I were doing it, I would bench test the thermosiphon systen using a bare center housing and a propane torch.

I forgot what I was going to say

 

[rmw]

Well..... this thread is all about heat transfer and fluid flow. I would have expected to find it in the Thermo and HT forum. It just happens to be about an automotive gadget so it landed in this forum.

First, the oil doesn't have the heat capacity (Cp) that water does, so it will take a higher rate of oil flow than the normal water flow to remove the same amount of heat.

Second, the oil is more viscous than water and a so it has higher resistance to flow (friction factor) so it will have to have a higher pressure to drive it to get enough through the turbo to take away the required heat.

So now you are needing to stuff more oil flow through passages that are designed for water flow so.....

Will it work - yes. Is it doable, probably if the guy/gal knows what he/she is up against and does it right.

Me - I'd just go find an oil cooled turbo, one designed day one to do the job rather than trying to stretch the limits of a water cooled model.

rmw

 

[MikeHalloran]

The water-cooled turbos used on marine engines are _fully_ jacketed, not just the bearing housing, to reduce the fire hazard in an engineroom.

Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Mike.

I know your marine background and guessed you may have presumed that. That's why I asked. On a bike I would expect a water cooled bearing only.

Personally I would find a simple water cooling system with a very small electric pump and a very small heat exchanger, maybe something like a small transmission cooler and a fish or bait tank pump or even a 12 volt tap water supply pump for caravans.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[Lou Scannon]

From anecdotal information I have read, particular to the Ford 2.3 turbo application which initially used a non-water cooled turbo, the biggest issue was post shutdown heat soak, not steady state operation. In steady state, the oil flow through the turbo removes a great deal of heat. However, Ford saw fit to update the application to a water-cooled center section turbo after a couple of years, due, it is said, to excessive replacements under warranty due to oil coking. The upshot is, the period where the water is doing the most good is after shutdown, when any coolant circulation is due to free convection only. The moral of the story is, a little water goes a long way, due to it's Cp as Mike points out, as well as to the fact that it will boil, if necessary, placing somewhat of a ceiling on the local temperature.

I forgot what I was going to say

 

[70btdc]

Exactly as Hemi said. The water cooling on the turbo provides a thermo-siphon when the engine is shut off and prevents coking in the centre housing as the oil boils on the shaft. Some systems even use a small electric pump to assist the water flow after engine shut-off. However, if the person in question should be happy to allow the engine to idle for a few minutes after a hard run, then the water cooling is not necessary. Peak sustained turbine in temps will not be affected by the water cooling, only bearing teperatures in normal operation which are rarely the limiting factor.

 

[Gustafson]

I stumbled across a great article by Garrett on water-cooling turbos that addreses this issue specifically on page 7.

http://www.turbobygarrett.com/turbo...nter/Garrett_White_Paper_01_Water_Cooling.pdf