Deleted
Joined: January 1970
Posts: 0
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Post by Deleted on Sept 24, 2023 20:45:39 GMT -5
Wow I'm sorry John, I've been following this amazing build for quite some time. I'm also very curious on your diagnosis. Possible oil leak causing a hot streak scenario?
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Post by racket on Sept 24, 2023 22:14:50 GMT -5
I think it was caused by not getting sufficient air between FT and shaft tunnel , the flametube wall damage indicates flames exiting the flametube and impacting the shaft tunnel with sufficient force to melt the thin steel sheathing around the ceramic blanket protecting the shaft tunnel from radiant heat , I had something similar happen with my 10/98 engine 13 years ago jetandturbineowners.proboards.com/thread/19/10-98-engine?page=4. The solution was to construct deflectors at the diffuser outlets to "force"air towards the shaft tunnel . Lots to think about before any remedial work is started :-) Cheers John
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Post by enginewhisperer on Sept 24, 2023 22:53:32 GMT -5
that's certainly not ideal!
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Post by racket on Sept 25, 2023 1:49:56 GMT -5
Hi Andrew
Nope,......but could have been worse , its fixable , I've already split the NGV , lotsa "spray metal" everywhere .
The compressor wheel is OK :-)
Cheers John
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Post by andym on Sept 25, 2023 1:58:36 GMT -5
Hi John Ouch..... not much more can be said Glad you are ok, well as ok as can be, Yep 10/98 did the same thing.... you sorted that, and sure you will sort this Chat soon All The Best Andy
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ripp
Veteran Member
I'm sorry, I don't speak english, so I torment you (and myself) with a translation program,Sorry
Joined: January 2013
Posts: 236
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Post by ripp on Sept 25, 2023 2:26:37 GMT -5
Hi John, 1, I don't think there is too little air flowing between the FT and the shaft tunnel, as long as the flow area is large enough that all Bk holes can be served. 2, the professional manufacturers certainly do not use stainless steel but rather a heat-resistant material that can withstand hot spots. www.youtube.com/watch?v=yWfWlEUp4MYwww.youtube.com/watch?v=MgL0GW248mE&t=334s3, with such air scoops (you've used it before with your 9/94) you could fight the hot spots. A viewing window would of course be ideal Cheers Ralph
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Post by racket on Sept 25, 2023 4:08:23 GMT -5
Hi Ralph
Unfortunately the air doesn't want to "voluntarily" go towards the shaft tunnel , theres plenty of flow area for it to do so , >1.5 times the hole area its feeding.
The edges of the flametube burn holes are folded "out" towards the shaft tunnel indicating higher pressure within the flametube , the flame then hits the shaft tunnel , you can see the melted patch on the pics I posted .
There something different between engines equiped with radial turb wheels vs axial turbs , the entry to the radial NGV is at the outer diameter of the flametube vs the inner for the axial .
The similar problems I experienced with my 10/98 engine were with an engine whose flametube was constructed from 800 series Inco , which melted the same as this stainless one .
The flametube outer wall is OK .
Some more extreme air deflectors at the diffuser outlets will fix the problem , it did for the 10/98 engine :-)
Cheers John
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Post by racket on Sept 25, 2023 4:22:10 GMT -5
Hi John, This was the turbine wheel I think. It was a contained engine failure. Waiting for your diagnosis😫 Andy Hi Andy The turbine wheel is "odd " , its not like a normal overtemp failure where the tips are thrown off and leave sharp edges , the wheel has nicely smoothed edges like its been cut with a oxy torch . Heres my thoughts ..............the turb tips were hit by molten metal , this increased the temp of the tips well above gas temps whilst removing tip "slowly" , the outer edge is smoothed over , very strange . I've run hotter temps before and never had this result with a wheel , strange one :-( Cheers John
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Post by racket on Sept 25, 2023 4:25:02 GMT -5
Hi John Ouch..... not much more can be said Glad you are ok, well as ok as can be, Yep 10/98 did the same thing.... you sorted that, and sure you will sort this Chat soon All The Best Andy Hi Andy I've started cleaning bits up , they never look as bad once the soot is removed . Yep , she'll rise from the ashes Cheers John
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Post by stoffe64 on Sept 25, 2023 15:22:45 GMT -5
WOW, i am VERY sad to see this,i suffer with you John....rebuild everything basicly!
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Post by stoffe64 on Sept 25, 2023 15:23:17 GMT -5
WOW, i am VERY sad to see this,i suffer with you John....rebuild everything basicly!
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Post by racket on Sept 25, 2023 17:10:01 GMT -5
Hi Stephan
Thankfully I have the spare flametube , it has some wear and heat damage but is useable , so that saves me having to repair this badly damaged one .
Its basically just the NGV that needs reworking and a new turbine wheel which I might not clip quite as much as previously, I'll redo my calculations for a higher pressure ratio of ~5:1 .
I should have it going again in a month or so :-)
Cheers John
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slittlewing
Senior Member
Joined: November 2017
Posts: 493
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Post by slittlewing on Sept 26, 2023 6:52:36 GMT -5
Hi John,
How do the NGV vanes look? Hope there isn’t too much repair needed!
Cheers
Scott
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Post by finiteparts on Sept 26, 2023 7:32:24 GMT -5
Sorry to see the damage, but like was said before, glad you're ok.
Here is my theory. Once the liner burned through, the pressure drop across the liner is drastically reduced. This leads to poor mixing, higher local gas temps and a large streak of oxygen rich cold air. So for the majority of the wheels rotation it is overtemping, but when it go through the cold streak the high O2 burns the tips off.
Think of an oxy-acetylene torch. You heat up the metal then hit it with a blast of oxygen to burn the metal away. Thus the different appearance.
When it is jagged, that is due to the metal getting hot enough to loose tensile strength and then chunks are ripped off due to the centrifugal forces.
Now why the combustor burned through, still needs some thinking.
- Chris
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ripp
Veteran Member
I'm sorry, I don't speak english, so I torment you (and myself) with a translation program,Sorry
Joined: January 2013
Posts: 236
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Post by ripp on Sept 26, 2023 8:30:16 GMT -5
Sorry to see the damage, but like was said before, glad you're ok. Here is my theory. Once the liner burned through, the pressure drop across the liner is drastically reduced. This leads to poor mixing, higher local gas temps and a large streak of oxygen rich cold air. So for the majority of the wheels rotation it is overtemping, but when it go through the cold streak the high O2 burns the tips off. Think of an oxy-acetylene torch. You heat up the metal then hit it with a blast of oxygen to burn the metal away. Thus the different appearance. When it is jagged, that is due to the metal getting hot enough to loose tensile strength and then chunks are ripped off due to the centrifugal forces. Now why the combustor burned through, still needs some thinking. - Chris Hi Chris u John, my theory, the combustion chamber is at its limit at 3.0 par (high temperature due to the short combustion chamber and perhaps a special hole geometry). Due to the almost sudden increase to 3.5 par, the already glowing combustion chamber parts melted (purely a guess). The first approach for me would be to lengthen the combustion chamber. In the picture you can see a distance of approx. 40mm, there would have to be another 15-20mm to extend. I hope you forgive me, I can only give advice. Cheers Ralph
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