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Post by z28guysteve on Oct 8, 2021 0:22:31 GMT -5
I used acoustics from the video to isolate the audio frequency and divide it by compressor blades to estimate the rpm.
The P2 reading was being taken off what's normally the propane line. The propane was hooked to the fuel ring. I wanted to try a propane run just out of desperation.
I'm almost certain now the complete shit diffuser is causing a total lack of pressure.
Oil comes from the fuel ring, prior to a short propane only run I'll lube the bearing with oil and limit run time to 30 seconds.
I designed my own diffuser I'm going to have CNC machined on xometry.com in China, I feel it's my only hope to get pressure from this thing.
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Post by racket on Oct 8, 2021 3:08:52 GMT -5
RPM is very suspect in that case :-(
Propane line will be measuring pressure "inside" the flametube , not compressor discharge pressure .
Designing a very small turbine engine is difficult , manufacturing the parts to the required precision is even harder ,there could be a number of reasons why your engine is having "problems" .
We don't really know if the engine is at fault without accurate and reliable data about its build and running paramaters .
Currently you are only guessing whats wrong , hard data will change that .
How did you design your diffuser ??
Cheers John
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dieselguy86
Veteran Member
Joined: September 2014
Posts: 186
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Post by dieselguy86 on Oct 8, 2021 5:20:32 GMT -5
It's also worth noting that your diffuser has 12 wedges, which matches up with the compressors 12 blades. I've always been told this is a no-no.
-Joe
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Post by z28guysteve on Oct 8, 2021 8:40:52 GMT -5
Fusion 360 and taking all the design recommendations from the Thomas Kamps book. Using recommended expansion angles, wheel clearances, and a correct number of wedges.
As for blade count in the current diffuser matching the compressor wheel. I've been informed this can create unnecessary resonance and noise, and potentially unstable combustion. But it's what came with the engine and there are some videos out there of this turd running and making some thrust. Although it has a small amount of external combustion in said video, and I've never seen one running correctly with nozzle.
I'm going to obtain an accurate p2 reading shortly by referencing immediately behind the diffuser here shortly and will post results.
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Post by z28guysteve on Oct 8, 2021 8:41:40 GMT -5
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Post by z28guysteve on Oct 8, 2021 9:49:54 GMT -5
2psi measured immediately behind the diffuser
No leaks evident
This diffuser is awful
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Post by z28guysteve on Oct 8, 2021 9:58:33 GMT -5
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Post by racket on Oct 8, 2021 15:54:10 GMT -5
Hi
You might still be below self sustain.
2 psi P2 will mean poor comp efficiency and high turb temps .
Suggestion..............keep your starter power being applied until you have 5 psi of P2, this will mean you're well above selfsustain speed and will negate some of the inefficiencies as the comp will entering a higher efficiency area of its map .
Cheers John
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Post by z28guysteve on Oct 8, 2021 18:56:52 GMT -5
I cannot get anything above 2 psi no matter how much air I deliver to it.
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Post by racket on Oct 8, 2021 19:34:53 GMT -5
What are you using for a starter ??
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Post by z28guysteve on Oct 8, 2021 20:56:43 GMT -5
150 psi from 4 different airguns
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Post by racket on Oct 8, 2021 21:38:59 GMT -5
Do you have a large workshop vac that blows air ??
If you do, then use it to spoolup the engine , its only a very small engine , your airguns should be able to do the job if directed correctly .
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Post by z28guysteve on Oct 8, 2021 23:31:48 GMT -5
I have tried every air source you can imagine, including a 50cc two stroke commercial leaf blower, sealed completely to the intake of the engine. The blower itself even produces 1.5 psi when you stick the reference hose to the gauge inside the duct. Even this powerful leaf blower will not get a significant amount of boost from this engine.
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Post by jetjeff on Oct 9, 2021 3:07:55 GMT -5
Hi Steve,
What kind of clearance do you have between the turbine wheel to turbine shroud and compressor to front cover plate?
A piece of paper is .004", a 3" x 5" index card is around .009".
Excessive clearance will cause the engine to run very hot (if at all).
Regards
Jeff
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Post by racket on Oct 9, 2021 3:57:20 GMT -5
Hi Jeff
I think you're on the right track , theres something fundementally wrong , especially when it won't even work with propane
WE need detailed pics of the components and a lot more info about the construction .
Cheers John
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