Glowing turbo / high TIT?

[Johansson]

Last weekend I found a picture that made me wonder quite a lot.

Some of you might have seen a brightly glowing turbocharger in a street/race car that threatens to melt the hood paint and thought for yourselfs that it cannot last for long. The strange part is that with water cooling to keep the bearings chilled the turbo seems to survive this kind of torture really well.

If I remember it right the EGT in a race engine can reach and possibly exceed 1000C, so the turbo lives a much harder life than it would ever do in a DIY-turbine. The extra exhaust back-pressure from the turbo makes even more heat even if the A/R ratio is high.

How can it be that we are "restricted" to a 780C TIT with the example above in mind? Is it because the gas turbine version normally revs higher than a turbocharger fitted to an engine and therefore needs lower temperatures in order to keep the blades from excessive stress?

Please enlighten me...

//Anders

[Fricke]

How can it be that we are "restricted" to a 780C TIT with the example above in mind?

Normally the big (and old) diesel turbochargers are not designed to run with EGT over 750°C.

And the 780°C (~1450°F) "rule" is based on the commonly accepted 'standard' set on the DIYGT mail-list on Yahoo, because the maximum 'safe' speed of a turbo is 1450 f/s.

And the turbine wheel on that turbo in the picture is actually black... It´s the turbine housing that is glowing. There is a picture somewhere on the net showing this...

[racketmotorman]

Hi Anders

The max figures on DIY cover all turbos irrespective of age or condition .

Modern high performance turbos have much higher capabilities.
Compressor maps for "high pressure" turbos regularly go beyond a 4:1 PR which will require more than 1450 ft/sec .
On my bike I regularly run TOTs of 1450F at 4:1 PRs, TITs would be some 300 deg F higher .
I've measured TOTs of 900C at PR of >3.5 for short periods (several seconds) during the bikes development without anything coming out thru the housings :-))

Be careful though when you start adding more fuel and increasing your temps and pressures .

Cheers
John

[Johansson]

Aha. Is it perhaps so that most turbine melt-downs are caused by bad combustor design with local hot spots (or flames spewing out of the turbine) rather than high TIT on a well-designed engine?

Anyway, I will be quite conservative with temps on the bike since the future shaft power will be more than enough anyway. The cart reaches a TOT of perhaps 720-730C with the afterburner lit, but since I need every little bit of thrust to get that heavy bastard up to speed I will keep the temps high and my eyes away from the EGT-gauge... *LOL*

Thanks for the explanatons!

//Anders

[Ash Powers]

I drive a Nissan TwinTurbo Z car and used to do a lot of street racing in Gainesville, FL where I am from. Highway 441 across the prarie is pretty much desolate after 2AM where a group of us used to go out and street race, and there are no street lights in that ~2 mile stretch of 4-lane road.

In one race between a friend in his single-turbo Supra and myself, we wound them up to around 130MPH, (close run between the two of us), turned them around and ran WOT back to where everyone was on the side of the road. We stopped and my friend popped his hood and the Supra's have the turbo mounted high in the engine bay and the turbine housing was glowing red hot. I was amazed to see this so I popped my hood and my two smaller twins were still glowing a deep amber color. Pretty exciting to see, but scary at the same time. To say the least, I started the car back up to keep the oil and coolant flowing (cartridges are water cooled in the Z). It took a couple of minutes for them to cool enough that they weren't giving off visible light.

We dont exceed 850C EGTs in the cars.