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Post by finiteparts on Apr 2, 2023 21:25:08 GMT -5
John,
That is a bummer. Sorry to hear that it got damaged. There are so many things that need to be just right to get these engines running and surviving and the smallest thing can lead to unintended consequences. Glad to see that you getting back up, dusting off and getting back up on that horse.
Good luck!
Chris
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Post by racket on Apr 2, 2023 23:17:25 GMT -5
Hi Chris
Yep , I'm back into it , LOL.....just a minor developmental issue :-)
Cheers John
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Post by racket on Apr 5, 2023 0:46:08 GMT -5
Hi Guys Front wall of flametube "removed", time to make up a new one with a different air entry . Pic of dead turb wheel Just another wall mounted object to remind me about my follies Cheers John
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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 Apr 5, 2023 1:02:38 GMT -5
Hi John,
according to which design will you model the new combustion chamber?
Cheers Ralph
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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 Apr 5, 2023 1:57:06 GMT -5
Hi John
my thoughts!
With such an extreme design of the engine (extra short combustion chamber between the wheels of a turbocharger) you should install as many variables as possible in order to be able to - readjust - after each test run and evaluation. a.) extend the inlet funnel b.) adjustable diffuser wedges (screwable) c.) large diffuser outlet - combustion chamber serves as an air baffle and achieves an extension of the combustion chamber d.) adjustable ngv blades (screwable) e.) first an arrangement of the combustion chamber behind the turbine wheel, so you can quickly make changes without having to disassemble the running rotor
every small change can be made relatively quickly and can bring about an advantage
Cheers Ralph
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Post by racket on Apr 5, 2023 4:28:01 GMT -5
Hi Ralph
Initially I drew up and considered having a rear mounted flametube so that the standard turbo shaft tunnel could be used , but due to the 128 mm turb exducer , the outer can diameter was going to become too large once allowances were made for flametube cross sectional area and flow space around it , so I resorted to my usual practice of making my own shaft tunnel and having the flametube between the wheels
Variables would be nice to have , but the work involved at this size becomes prohibitive for me and my limited workshop abilities and equipment .
The new flametube design will only have differences with the front wall air entry , the rest of the flametube will be the same bits as before , I need to move the flame off the front wall to prevent damage to it.
Cheers John
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Post by stoffe64 on Apr 5, 2023 6:50:27 GMT -5
Hi Guys Front wall of flametube "removed", time to make up a new one with a different air entry . Pic of dead turb wheel Just another wall mounted object to remind me about my follies Cheers John Sorry to hear about AND to see the dead turbine wheel,how did the comp wheel survive?
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Post by racket on Apr 5, 2023 16:28:51 GMT -5
Hi Stephan
Comp wheel is OK , no damage , all the bearings are OK as well , just the turb wheel and NGV damaged
Cheers John
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miuge
Veteran Member
Joined: March 2014
Posts: 200
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Post by miuge on Apr 5, 2023 16:30:42 GMT -5
Initially I drew up and considered having a rear mounted flametube so that the standard turbo shaft tunnel could be used , but due to the 128 mm turb exducer , the outer can diameter was going to become too large once allowances were made for flametube cross sectional area and flow space around it , so I resorted to my usual practice of making my own shaft tunnel and having the flametube between the wheels Since front of the flametube and directing high speed air from comp diffusor seems generally problematic with these micro turbine style engines, would it make sense to route air externally past the flametube to hot end first and then turn it back? I could imagine better and more stable air distribution for the front and inner wall, it would also allow playing with the cross sectional areas to slow down the flow even more at tight turns if needed. Obviously will add complexity and size too.
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Post by racket on Apr 5, 2023 18:21:40 GMT -5
I'd need to build an entirely new engine unfortunately :-(
Gotta get it going with what I have , I'm running out of time, energy and enthusiasm to complete it , one of the less desirable outcomes from trying to push the envelope , theres a lot of things with this engine that aren't "right" compared to the usual RC micro engine with their relatively longer flametubes, ideally mine needs to be at least 50 mm longer to get the length/width ratio into more friendly territory.
Cheers John
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Post by finiteparts on Apr 6, 2023 14:07:04 GMT -5
John, Due to the limited axial length of your combustor, I think it might serve you well to consider using some tangential bulk swirl in your next combustor design. This is a common approach on small APU/helicopter combustors from Honeywell and SAFRAN which gives very uniform bulk gas exit temps with relatively few injectors. The basic logic is that you give longer path length to the fuel droplets, you keep them in the relatively hot forward section longer, to aid in combustor reaction rates (which scale exponentially with temperature), you smear out the hot streaks entering the NGVs and potentially unload the NGVs due to the existence of a bulk swirl component at the NGV entrance. I was hesitant to suggest this since it is a large divergence from what you have built/tested in the past, but if I was making a space limited combustor, I think the success of this in industry would suggest that it is relatively reduced risk design option. Sundstrand's T-100 inplimentation: asmedigitalcollection.asme.org/GT/proceedings/GT1994/78842/V002T04A029/255107?searchresult=1This implementation is a similar design philosophy that was used on their TJ-50 that was shown here: jetandturbineowners.proboards.com/post/9218/threadalso, there are some good cross-sectional images of the TJ-90 here: apps.dtic.mil/sti/pdfs/ADA263727.pdfthis is also the design thinking in this combustor for the T-62... jetandturbineowners.proboards.com/post/9917SAFRANThey have been getting into this with more vigor lately, including working with CERFACS on some beautiful time resolved CFD predicting the combustion performance. Paper: www.semanticscholar.org/paper/The-SAFRAN-helicopter-engine-spinning-flame-concept-Savary-Taliercio/550760edaf04c61e050cbae6cf4dd1fe46f4eeb8Video : www.safran-group.com/videos/revolution-helicopters-engines-combustion-safranGood luck, Chris
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Post by racket on Apr 6, 2023 17:25:43 GMT -5
Hi Chris
Thanks for the Links , looks like I've got a bit of serious reading and contemplation for the Easter holidays :-)
The swirling design has recently been in the back of my mind since Andy from Germany suggested some angled slots to feed air into the Primary Zone instead of my thimbles , the thimbles cured my delayed combustion but the flame was too close to the front wall and distorted it as well as damaged the thinner thimble sections , I'll take a pic and post
Cheers John
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Post by racket on Apr 6, 2023 19:58:48 GMT -5
Hi Chris Pic of the failed/failing thimbles and thermal damage to front wall My thoughts were that the damage happened when I throttled back to idle after the testrun and there was "surge" with pulsing within the flametube with enough force to cause flames to travel back and forth through the thimbles as the molten metal is projected inwards , also the damage to the wheel and NGV vanes isn't like a high power run damage , the vanes were knocked around a bit but not huge chunks out of them as happened with my previous wheel failure , also theres "broken" bits on the turb inducer haven't been thrown off . Cheers John
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Post by racket on Apr 7, 2023 1:08:40 GMT -5
Hi Chris Whilst reading one of your Links I checked out the "back page" and found a reference to this Paper apps.dtic.mil/sti/pdfs/ADA081895.pdf . Some interesting info , especially about losses from straightening the flow going into the A/B , I clipped more off my exducer after my best thrust readings , perhaps there was a tad of swirl previously that improved the A/B combustion performance , I might think about adding some "turning vanes" between exducer and fuel sprayer to see what happens Cheers John
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Post by racket on Apr 11, 2023 1:26:34 GMT -5
Hi Guys Some changes to the flametube I've added 18 short tubes ( evaporator tubing) angled so as to impinge air on the inside of the front wall to keep it cool as well as to produce swirl within the flametube to help promote mixing of fuel and air and aid in keeping combustion within the Primary Zone ...............LOL, that my hopes , lets see what happens The replacement parts for my mills electric motor arrived , the capacitor and overload switch are installed and she's working again , so back to deepening the diffuser channels tomorrow . My workshop is a mess with several jobs on the go and tools everywhere Cheers John
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