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Post by racket on May 13, 2024 21:00:35 GMT -5
Hi Richard
They're nice bellmouths , too expensive though when I take in exchange rates and postage..........half a weeks income :-(
They're in alloy , I've used alloy ones before, they're a tad thin to hang my heavy/powerful starter off, I found my mountings suffered after a time , nice for leafblower starting though :-) .
Cheers John
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Post by racket on May 13, 2024 17:06:16 GMT -5
Hi Richard
The problem is the comp inducer angle , its too high at ~34 degrees , it wants to bite off more air than the engine can process due to limited flow through the turb stage , when you do the inlet velocity triangles theres too much incidence at the inducer , the wheel is actually doing a very good job of not going into full blown surge, it needs a much higher flowing turb stage to allow the comp to work properly , by adding my IGVs I'm simply reducing its performance potential.
The current bell mouth is a compromise , but there are other considerations influencing its use .............LOL, the main one is theres no off the shelf bell mouths for 5" inducers , then there's the matter of its strength to cope with the starter motor .
There are some pretty good Papers on bell mouths , I've read quite a few over the years whilst trying to optimise things ............ideally my engine needs a new test stand where the inlet isn't anywhere near structures , the extra flow from this engine has probably unearthed some shortcomings :-(
I'll have a read through those Papers today , theres always a "gem" to be found in every Paper :-)
Cheers John
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Post by racket on May 13, 2024 4:22:34 GMT -5
Hi Ralph
I opened up the jet nozzle by a few millimeters from the previous test .
Compressor efficiencies are good , but theres a lot of shaking of the test stand and chuffing from the comp , I'm refitting the IGV stator into the bellmouth with a 25 degree angle on the vanes .
I've pulled the engine outer can off and things look OK inside , I'll have a better look once its all disassembled .
Afterburner will be refitted for the next test
Cheers John
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Post by racket on May 12, 2024 20:34:08 GMT -5
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Post by racket on May 12, 2024 4:20:35 GMT -5
Hi Andy
LOL :-)
Great power to weight ratio , good for ~130 kph top speed , pump those tyres up .
This afternoon I was looking at your last video of the engine run and its turning out some serious power with the afterburner performing nicely , you'll have some summer fun for sure :-)
Cheers John
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Post by racket on May 12, 2024 1:02:02 GMT -5
Hi Guys
The new battery arrived , then the rain started :-(
Hopefully in the next few days
Cheers John
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Post by racket on May 10, 2024 23:56:20 GMT -5
LOL.... Such a pretty baby :-)
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Post by racket on May 10, 2024 23:46:50 GMT -5
Hi Eric
A short pipe is handy to fit a thermocouple into for measuring your turb gas temps ...............and firing her up pointing into the wind is a good idea whether a little DIY gas turbine or a huge aircraft jet engine as Richard said ;-)
Cheers John
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Post by racket on May 9, 2024 23:57:08 GMT -5
Hi Eric If you checkout the closet Garrett turbo www.garrettmotion.com/wp-content/uploads/2022/06/Turbine-Flow-Maps-GT30-scaled.jpg you'll notice the 0.63 turb scroll only flows ~19 lbs/min Corrected Flow at a 2:1 PR and at only 69% effic , even with full expansion across the turb stage using your 2.36 PR it only goes up to ~20 lbs/min Corrected Flow . Assuming a TIT of 1061K and a 2.36 Pr that equates to a Actual Flow of ~25 lbs/min or 0.4 lbs/sec which on the small GT28 comp map www.garrettmotion.com/wp-content/uploads/2018/05/Comp-Map-GT-2871R.jpg is OK Now with a lot less mass flow due to the tight turb scroll , your potential jet nozzle sizing will be smaller ............I'd suggest NO jet nozzle to begin with as the very low efficiency of the turb stage will require a larger pressure drop so less energy left over for making thrust The engine should run :-) Cheers John
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Post by racket on May 9, 2024 20:12:45 GMT -5
Hi Eric
If your turb wheel exducer diameter is less than 2.25" and your comp inducer is 2" you might not be able to flow your 0.7 lbs/sec as it'll depend on your turb scroll A/R.
Could you please provide a Link to the turbo specs
Cheers John
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Post by racket on May 9, 2024 16:38:18 GMT -5
OK , please let us know how the testing goes .
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Post by racket on May 8, 2024 17:00:30 GMT -5
I just had another look at the pic of your drawing that you posted imgbb.com/k0P9Jft , you'll notice it has a long axial section of diffuser , this is critical to maximise comp efficiency as the outer can is only ~50% greater than wheel diameter , the design has traded off radial diffusion distance for extra axial diffusion distance
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Post by racket on May 8, 2024 16:53:09 GMT -5
48mm wheel in a 61 mm can , thats only a 27% increase ...............it ain't gunna work :-(
I don't know where you got the plans but without a much more complex diffuser design that wraps around the "corner" you're not getting any efficient diffusion, this will require the turbine stage to work much harder, with very high temperatures.
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Post by racket on May 8, 2024 4:21:52 GMT -5
Scaling off your pics , the outer can is only ~33% greater than the comp exducer diameter , this is not a good number , for a homebuilt engine it pays to be a tad more generous at >60% greater
The KJ66 has a 66mm comp wheel in a 107mm outer can ID.
Is this engine your own design or is it built from an available design ??
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Post by racket on May 8, 2024 4:12:57 GMT -5
LOL...........don't be embarrassed , you're not alone , we've all been there at one time or another , thankfully it seems you've escaped any damage :-)
A ball valve can be used , but they can be a bit "crude" for throttling vs a needle valve, you might simply need a larger flow needle valve that only requires a couple of rotations .
Might I suggest you have your start air bottle over besides the propane to minimise time loss between starting the spoolup and opening the propane.
Also your propane usage , is it simply for a pilot light to ignite the liquid fuel , if it is then a smaller supply might be safer to prevent any damage in the event you have a similar problem.
In the past when using propane I get the propane ignited before starting the spoolup and immediately start feeding in the liquid fuel as the rpm increase on the starter , the propane isn't used as "fuel" .
Yep , make sure your starter has maximum power available to minimise spoolup time
All the best on the weekend :-)
Cheers John
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