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Post by racket on Feb 2, 2020 22:10:24 GMT -5
Hi Chris Good explanation of the perils associated with tangential delivery tubes , theres been some horrible outcomes with a number of our DIY engines over the years because of them
LOL ,......... I suppose I should put my diffuser advice as "diffuser" , not an aerodynamic diffuser but more of a distribution diffuser to spread flow over a greater area at the junction of the delivery tube and outer can even at the cost of some turbulence from the large angles used , but any cone "diffuser" is going to be better than a constant cross section delivery tube stuck to the outer can with air attempting to turn through a restricted space ..........considering that airflows in delivery tubes are generally less than a few hundred feet per second theres not much aerodynamic diffusion to be had, but plenty of scope for laymens distribution "diffusion" .
Cheers John
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Post by tinkerer1999 on Feb 3, 2020 13:38:55 GMT -5
Thank you very much for your suggestions. I think I will try to put some baffles on the inside of the liner to redirect the flow and extend the flame tube so that there is no gap at the end.
Also the holes in the hex plug are I think about 1/16" or 1.5mm. They might be a little larger, I don't really remember. I'd have to take it apart to be sure.
This has definitely been a very educational research project
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Post by turboron on Feb 3, 2020 14:58:27 GMT -5
All, this an interesting discussion since some very successful gas turbines from the 1950's have "distribution" diffusers. Consider the Allison 501 (military T-56 with 1000s in C130s around the would it has a wide angle (approximately 45 degrees?) "diffuser" after its 14 stage axial compressor and before its 6 can combustion system. The Allison Model 250 (military T-63) has unique air distribution before it enters the combustor. Modern engines seem to primarily use a dump diffuser after a short 7 degree diffuser. The problem in design of a gas turbine is that there is no room in the bearing span for a long diffuser.
Thanks, Ron
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Post by tinkerer1999 on Feb 10, 2020 15:28:19 GMT -5
Its going to be a few weeks until I can make the changes to my combustion chamber, so I decided to learn how to use solidworks flow simulation and run a simulation on a few different variations. I ran one for a combustor with baffles installed, with a longer flame tube, and with both. I plan on running one with my current setup just out of curiosity. Here are some pictures of the results: This is the version with both a longer flame tube and baffles installed: This is just a longer flame tube: This is just baffles Red is high pressure and blue is lower pressure
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Post by finiteparts on Feb 10, 2020 21:54:14 GMT -5
CFD is always fun...just be careful of believing the results. Low resolution models can be very misleading and getting good results from CFD involves good meshes, proper set-up, well selected and defined boundary conditions, etc. But using low resolution CFD as a means to point you in a direction for your design is a VERY good tool. Here is a shot of a Airesearch combustor with some flow damns on to help recover some of the dynamic pressure at the dilution holes because of a swirled flow from the compressor. With this swirl, there is a potential that the dilution jets might suffer low penetration and thus insufficient mixing. Definitely something we can use as homebuilders. Good luck! - Chris
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Post by tinkerer1999 on Feb 12, 2020 21:26:00 GMT -5
I think welding the baffles to the flame tube is better than welding them to the outer liner but since my flame tube slides in with only about a 1/16" of clearance around it I'm not sure how to do it. What I could to is make them the same height as the entire gap and drill holes in them. then I could weld them to the outer liner. Or I could make them with tabs that would be welded to the outer liner and hold them against the flame tube. Here are some pictures of what I mean
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Post by racket on Feb 12, 2020 23:44:48 GMT -5
Easier to simply fix how the delivery tube meets the outer can , adding baffles is a case of "two wrongs trying to make a right" .
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Post by finiteparts on Feb 15, 2020 12:41:14 GMT -5
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Post by tinkerer1999 on Mar 4, 2020 8:51:25 GMT -5
Hello again, I was able to go home and weld in the baffles and extend the flame tube. We had three successful lightings of the combustion chamber in a row so now today we will try to start the whole engine. I unfortunately don't have the tachometer fully set up yet so we will be monitoring it with the exhaust temperature. The next project will be to get the tachometer sensor mounted assuming the engine runs. Thank you all for all your suggestions
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Post by tinkerer1999 on Mar 4, 2020 14:27:58 GMT -5
Well tested it and it started right up and ran at about 900degF or 482degC. I didn't open the throttle up too much since I don't have a tachometer set up yet
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Post by racket on Mar 4, 2020 15:23:13 GMT -5
Without a tach use your P2 pressure gauge as an indicator of "speed" , keep P2 to below 20 psi
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Post by tinkerer1999 on Mar 5, 2020 10:22:51 GMT -5
Would that be the combustor Pressure?
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Post by racket on Mar 5, 2020 17:09:50 GMT -5
Yes
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Post by tinkerer1999 on Mar 9, 2020 16:52:07 GMT -5
I am now trying to think of a way to spin a shaft with this engine. I have seen some turbines on ebay but unfortunately they are way out of my price range. I need something around $100. Is there any surplus place any one knows about that I could get one cheap?
I found a 1st stage compressor wheel from a Lycoming LTS-101 pretty cheap cause it had a bunch of nicks in the blades. Would it be possible to use it for a turbine? I think it is made of steel.
I'm not really comfortable with making my own. That's I need is a piece flying off.
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Post by racket on Mar 9, 2020 18:23:28 GMT -5
Hi
You need to have a suitably sized wheel so that gas velocities are high enough otherwise your power output will be disappointing .
Considering the size of your gas producer , a large truck turbo core would probably be large enough , checkout a turbo overhaul shop for a scrap turbo , as long as the turbine wheel exducer has an area twice your gas producer turbines exducer area you should be OK
Cheers John
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