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Post by z28guysteve on Oct 17, 2021 4:39:26 GMT -5
I'm an airline pilot so I only get to work on this one day a week or so
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Post by jetjeff on Oct 17, 2021 11:11:56 GMT -5
Hi Steve,
I wasn't able to get to the minijetengine.com website from my Mac, but was able to view it from my iPhone. Another issue I'm seeing is with their nozzle guide vane. You can see a parallel gap between the blades, like there is no overlap, there must be overlap, with only a small V (of bladeless space)near the outer shroud.
Not sure where you are located, but I could fix the wedges in your existing comp diffuser on my Bridgeport mill,,,wouldn't take me long nor be that difficult.
Regards
Jeff
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Post by racket on Oct 17, 2021 16:18:10 GMT -5
Yep , blunt leading edges are a no no , especially with smaller engines where the distance between comp exducer is so small and the time frame minute for the air to "adjust" itself before impacting the vane tip , the airspeeds will be the same as a larger engine , I've probably got >10 times the distance/time for air to adjust itself, but still use pointed leading edges.
The divergence angle of the air passageway probably isn't playing such a large part in your diffuser design as theres more "dump diffusion" at the "corner" as the air turns from radial to axial , but this shouldn't be causing your problem ...............the blunt leading edge of the diffuser vane is more likely the culprit .
Have you tried the "piece of string at the inlet" to see if surge is occuring ??
Small comps generally are designed for wide flow ranges as required by the IC engine they're used on , this makes them less prone to severe surge , more like mushy air that can mask problems downstream , ...........a less accomodating comp design would have surge banging away and providing a good indication of problems .
Cheers John
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Post by z28guysteve on Oct 17, 2021 22:37:10 GMT -5
I've never heard of this test but sometimes the engine has a weird pulsing combustion
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Post by racket on Oct 18, 2021 0:02:21 GMT -5
LOL........not uncommon here :-)
just tie off a piece of thin string so that it can't quite touch the comp wheel inducer , the inlet suction should keep it tight , but if it jumps back and forth , its surge , I had one on my last engine
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Post by racket on Oct 18, 2021 0:31:38 GMT -5
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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: 230
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Post by ripp on Oct 18, 2021 2:43:55 GMT -5
Hi Steve, Another issue I'm seeing is with their nozzle guide vane. You can see a parallel gap between the blades, like there is no overlap, there must be overlap, with only a small V (of bladeless space)near the outer shroud. Regards Jeff here you can see a wheel and NGV from Jetmax If the angle is correctly designed, it seems to work even without overlap best regards Ralph www.instagram.com/minijetlabs/can someone ask why he chooses a blunt leading edge? is that perhaps a desired throttle?
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Post by racket on Oct 18, 2021 3:13:22 GMT -5
I can't see any reason why there should be a blunt end on the leading edge , the turbulence created would be enormous considering how close to the wheel it is , that turbulence would be reducing the throat area of the diffuser possibly causing surge .
Theres probably <10mm from wheel to blunt end, the time frame is only 1/10,000 th of a second even at modest exit speeds from the wheel , the air simply won't cope :-(
It needs a sharp leading edge
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Post by z28guysteve on Oct 18, 2021 5:17:13 GMT -5
I should have simply bought a jet Joe kit
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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: 230
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Post by ripp on Oct 18, 2021 14:27:49 GMT -5
until the new diffuser arrives, you could try changing the front edge maybe it will work after all
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Post by jetjeff on Oct 18, 2021 14:50:05 GMT -5
Hi Steve,
If it were me, I'd contact them and ask if you can return it. Tell them what you went through to get this engine to run, see what they say.
The new comp diffuser might work, then maybe not. If nobody said this already, homebuilt turbine builds can be VERY frustrating, with many, many setbacks.
These guys must be relatively new to the micro turbine manufacture.
Regards
Jeff
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Post by smithy1 on Oct 19, 2021 0:16:25 GMT -5
I should have simply bought a jet Joe kit I have a few Jet-Joe kits....whilst they mostly work if built & balanced correctly, they're not the best quality. Their machining and balancing leaves a bit to be desired. I finally settled on Kingtech for my miniature turbines and find them very good and very reliable, not the best available but a good mid-range turbine. The one in my 1/4 scale jet dragster, a K180G is just about bullet proof and I've modified it to take an afterburner system, works brilliantly. I also have a tiny K45G which is equally bullet proof, can do 170,000rpm all day...just normal maintenance is all that is required. Smithy.
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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: 230
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Post by ripp on Oct 19, 2021 2:55:28 GMT -5
xicoy engines would be an alternative as well www.xicoyturbines.com/X45.htmlunfortunately i could not start my x45 yet interesting!!! no free ring space in front of vane tip 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: 230
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Post by ripp on Oct 21, 2021 2:17:29 GMT -5
I would suggest the following three points, firstly, bend the injection tube and make sure that the end of the tube lies under tension on the inside of the sticks, www.youtube.com/watch?v=cvUCuSP6EPs&t=336ssecondly, change the design of the combustion chamber as follows, thirdly, sharpen the diffuse wing at least the first version is shown in red I'm sure that's how you get them to work 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: 230
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Post by ripp on Oct 21, 2021 12:42:48 GMT -5
i posted the wrong picture here the right one
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