t18a96 turbo jet

[sub22b]

I have a video that i will post. The engine ran away on me and i couldnt stop it. I think it was running on oil vapour. The combustor got to a pressure of around 30psi and oil pressure was 50psi unfortunately i dont have a exhaust gas temp reading.

[sub22b]

youtu.be/IO8TsulM1nA



as you can see the oil temp increased very very quickly. And i just cant believe what happend i never had a chance to stop it.

[Johansson]

Bugger! If you had a piece of plywood or any other flat and hard material you could have plugged the compressor intake and choked the engine, this would have extinguished the combustor effectively stopping the engine.

[sub22b]

Yea i wish i had a piece of wood but i didnt. So now i will have to find a new turbo charger and change my running procedure.

[Johansson]

I am a bit confused about the oil vapor running, it takes plenty of fuel to run a turbine of that size until it grenades so I somehow doubt that some ingested oil smoke would be enough. Was the compressor shaft oil seal leaking so bad that it got oil into the combustor that way?

[sub22b]

Yea well the oil seals only had a hour or 2 on them but there didnt seem to be any oil in the comp housing. But i see what you mean as the smoke from the oil really wouldnt have been enough for it to run. Im going to check my fuel system and see if something there failed.

[racket]

Yeh , can't see the oil being the problem , once past the bearings its open to atmosphere with nil pressure to feed into the airflow .

The sudden extra smoky fumes could have indicated a turbine wheel very out of balance from possibly losing a blade , but that wouldn't cause a run away .

Do you have a combustor drain ??

If yes, was it open??

Did the turbine wheel detach itself from the shaft ??

Need lotsa pics of the components

Cheers
John

[enginewhisperer]

there are a few puffs of smoke out the exhaust before it blows up - maybe something was moving around and contacting the housing.

Could the turbine housing bolts have come loose?
It almost looks like it just blew the turbo core out of the housing under pressure.

The oil vapour did look a bit excessive, but maybe if the seals were bad and / or it was out of balance / rubbing the turbine housing it could have let hot gas into the bearings.
A loose turbine housing would also mean a loose rear bearing heat shield.

[sub22b]

Hi guys i will take some pics this aftermoom but there isnt much left. Both bearings are still in one piece with a few scratches in them. The unloaded thrust washer has melted and the turbine wheel did break off from the shaft. The core was tight on the exhaust housing but it broke the cast iron and bent the steel tabs that hold it in the housing. The only piece that isnt damaged is the comp wheel and comp housing

[sub22b]

The rear oil seal was found 20metres behind the engine. I measured the oil that was left over and im missing a litre so it must of burnt some. I dont have a drain on the combustor. Im starting to think the fuel control valve is to blame or the motor speed controller.

[racket]

Hi

You mention the "unloaded" thrust washer was "melted" , do you mean the one fitted to the centre housing ??

Maybe a combination of oil pressure/flow being too low combined with an overspeed/temp , without any running data to go by its gunna be hard to determine the cause :-(

Your turb scroll is a 2.0 A/R , this is kinda large and very easy for you to start running into the choke region of the comp map where rpm lines are dropping fast , allowing an overspeed at relatively low comp discharge pressures

Cheers
John

[sub22b]

Hi john yes it will be hard to find out what went wrong but i think its a combination of to much rpm not enough oil and way to much heat. I know i should of waited a few weeks to get all the sensors working but unfortunately couldnt help my self. If i had the bypass valve working i think that may have stopped the complete failure of the turbo or atleast would of had a few more seconds to block the air intake.


what turbo would be the best one to use for the next version as im not going stop because of one failure.

[racket]

LOL..........yep , always a temptation to get them fired up prematurely , but turbines self destruct in seconds , its a fine line between max performance and scrap .

Try and find a more modern turbo , the old one was pretty dated.

I still can't fathom out why the thrust "washer" was damaged , its really only there to keep end float within limits , the thrust bearing on the rear of the comp backplate is the one that takes the air loads , how are its 3 thrust pads looking ??

Cheers
John

[sub22b]

The 3 pads show a bit of wear but nothing major. When it failed many months ago the 3 pads looked much worse than they do now.


ok cool i will find a newer model. What about sizes of turbo's are bigger ones better or what size is good.

[racket]

Big is best ............bigger is even better :-)

But if you wanted go shaft power then the size can be reduced considerably compared to a thrust unit .

For a thrust unit you probably need at least a ~90 mm inducer on the comp , whereas a 50 mm inducer would supply equal/better performance if shaft powered .

So the thrust bearing survived relatively unscathed , very strange :-(

Could the oil pressure have dropped during the run ??

If it did and the rotor started to "gyrate" , it can shake the turb wheel off , a bullet proof oil system is a must , and it must be able to provide >50 psi ( measured at the turbo lube inlet) even with hot oil if we want the oil to control rotor dynamics , for a big turbo like yours I wouldn't consider anything less than a 10 litre/minute supply potential , and to make everything even more foolproof, a Hobbs switch to kill the fuel pump if oil pressure drops below 50 psi..................our engines can survive a lot of things , but lack of lube pressure and flow will kill them very quickly .

With my TV84 turbo based engine I was advised to run oil pressures of ~100 psi using 15W-50 semi synthetic oil as the TV84 , being the largest in the Garrett "4 inch" range , had a fragile thrust bearing when run in the racing truck engines, the largish diameter comp wheel exerted too much air loading onto the thrust bearing at 45 psi of boost.

If you haven't already got a copy , maybe get one of these www.amazon.com/Turbochargers-Hugh-MacInnes/dp/0912656492/ref=sr_1_2?s=books&ie=UTF8&qid=1502163778&sr=1-2&keywords=turbochargers+macinnes or the latter editions www.booktopia.com.au/turbochargers-hp49-hugh-macinnes/prod9780895861351.html my early edition has been invaluable .

Cheers
JOhn