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Post by racket on May 22, 2021 5:15:57 GMT -5
Hi Cullen If you bleed off P2 air , then your turbine stage will need full expansion through it with the remaining hot gases just to power the compressor , leaving exhaust gases at ambient pressure which can't be used in a freepower as we need a pressure drop across a freepower to produce high gas speeds and deflection for power production . The high pressure P2 bleed air could be fed to a much smaller freepower stage though , in the example I gave of a bleed of 70 lbs/min at 4:1 PR , the gas producer turbine has put some 130 horsepower into compressing it , if that was fed through a gas turbine starter , often available on ebay , www.ebay.com/itm/353431387573?hash=item524a26fdb5:g:xW0AAOSwhcdgW4Pm ..... www.ebay.com/itm/143211354409?hash=item21580fd929:g:JxsAAOSwuvVbfMg2 you'd produce some serious horsepower Cheers John Cheers John
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Post by turbojet atv on May 22, 2021 19:35:59 GMT -5
Hey John, the sound of the turbine starter sounds like a interesting concept. It looks like the routed bleed air would power the starter and the starter would then go to a sprocket? Does that sound correct?
Would the exhaust gasses from the turbine housing just go to the atmosphere like a regular exhaust?
Or just a small thought since I like incorporating ideas that sound far out. Could both bleed off air from P2 & exhaust gasses from P4 merge into a turbine starter and power the starter. The starter would then be attached to a sprocket and chain to the rear wheels.
I thank you for helping me a lot on this project. I’m learning a ton of information from you.
-Cullen ✌️
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Post by racket on May 22, 2021 20:10:24 GMT -5
Hi Cullen
The idea of using a large "performance " turbo with an undersized turb stage and bleeding off air has been floated around on here for some time , so it looks like you're the one thats going to do it , LOL.. we'll hold your hand all the way :-)
Yep , the starter generally has a pretty large gear ratio inside to reduce the high freepowers rpm down to modest levels suitable for a sprocket .
The exhaust gases from the turbo will just go to atmosphere , though you could "burn" them for a flame show as long as that didn't put backpressure on the turbo , we want max pressure drop across the turbo turbine .
Nope , we can't blend the hot exhaust gases and P2 air, things wouldn't work , the starter is designed for P2 air , lowishish temperature and high pressure .............P4 is generally only 5 or 6 psi static pressure with a normal setup feeding an afterburner or full sized freepower taking all of the comps flow .
Being able to use a turbine starter makes your job a lot easier as gearboxes for freepowers are a pain to source/make, a "cold" freepower can't produce as much power as a "hot" freepower , but I don't think you'll be disappointed with the results .
Cheers John
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Post by turbojet atv on May 23, 2021 3:04:18 GMT -5
Hey John,
Man sounds like I’m making a new road in the diy turbine world. I never noticed until I joined here that most people used old diesel turbos but I like making new challenges with a high performance turbo. I’m ready for this fun journey!
That makes since after you mentioned the exhaust gas pressure. P2 air going to the starter will be better for it. Makes since after I looked at a diagram of how one works.
Now bleeding air out to the starter, the best way I can think of working that is a wastegate. I understand how they work but how it would affect the engine running I’m not sure. A wastegate is a easy way to work it.
-Cullen
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Post by racket on May 23, 2021 4:02:36 GMT -5
Hi Cullen Yep , you'll be breaking new ground :-) A 2 inch exhaust cutout butterfly valve in a branch off the air delivery tube between comp stage and combustor should be adequate , you probably need it adjustable so that you can control the amount of bleed air so that your maximum turbine temperatures aren't allowed to be exceeded .................the more air you bleed , the higher your turb temps as the turb wheel struggles to power the comp with less and less mass flow through it, the higher temps compensate for the lower flow, its a balancing act .............maybe something like this www.holley.com/products/exhaust/cut_outs_and_multi_mode_kits/parts/5424 Cheers John
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Post by wannabebuilderuk on May 23, 2021 6:09:56 GMT -5
Cullen, you could always put the bleed air straight into a standard engine and basically have a turbocharged engine at all rpm ranges like this - youtu.be/6EMleegZQLw
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slittlewing
Senior Member
Joined: November 2017
Posts: 458
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Post by slittlewing on May 23, 2021 6:12:23 GMT -5
Hi Cullen
Following your thread with interest, nice to see something a bit different and your turbo is absolutely huge!!!
Good luck, shaft power via air starter could be a nice way of extracting some power with an “off the shelf” type unit (compared to home brew freepower)
Look forward to more pictures, use the “bbcode full size” on imgbb and they will appear inline.
Cheers
Scott
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Post by turbojet atv on May 24, 2021 1:06:03 GMT -5
Hey John. The info about a exhaust cutout sounds like a better way to fine tune an exhaust bleed to the turbine starter. It definitely sounds like a fine tuning battle to get a perfect ratio of air to the engine & starter. Lol, I like a good challenge like this. I found on eBay a very good turbine starter that was a complete setup with what looks like a butterfly valve on the turbine side. It’s made by Honeywell. www.ebay.com/itm/384107403682?hash=item596e95d9a2:g:XAUAAOSwsWRgf5CdI’m looking into this as a primary option to go with as it looks like it will work best...but that’s to be determined. And thanks for that info Scott! Thanks Cullen
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Post by britishrocket on May 26, 2021 3:10:03 GMT -5
I was just wondering if it would be possible, in theory at least, to divert your 70lb/min of excess air from the compressor into a combustion chamber with a convergent/divergent nozzle. This could generate thrust as in a rocket engine, so you'd have a sort of "turbo rocket"? The rocket engine could be brought in to augment thrust as needed.
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Post by racket on May 26, 2021 4:36:47 GMT -5
It is possible to "bleed and burn" , but the thrust produced isn't as great as expected due to the fact we need to expend greater amounts of pressure drop to get less and less increase in jet nozzle velocity , unfortunately thrust is simply mass times velocity , whereas the kinetic energy has a "velocity squared" component , kinetic energy in the exhaust goes up faster than the velocity increase. This is what you invisage www.youtube.com/watch?v=4EZJkwWHQ8MCheers John
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Post by britishrocket on May 26, 2021 7:43:41 GMT -5
Thats not really what I envisaged. If the nozzle is a convergent - divergent one, not a convergent one as in the clip, then assuming it is sized correctly, the gases generated will go supersonic in the throat which will give even more velocity increase in the divergence.
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Post by madpatty on May 26, 2021 9:25:46 GMT -5
It is possible to "bleed and burn" , but the thrust produced isn't as great as expected due to the fact we need to expend greater amounts of pressure drop to get less and less increase in jet nozzle velocity , unfortunately thrust is simply mass times velocity , whereas the kinetic energy has a "velocity squared" component , kinetic energy in the exhaust goes up faster than the velocity increase. This is what you invisage www.youtube.com/watch?v=4EZJkwWHQ8MCheers John Or this- youtu.be/hCwz7mnymr4Cheers.
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Post by wannabebuilderuk on May 26, 2021 12:59:47 GMT -5
It is possible to "bleed and burn" , but the thrust produced isn't as great as expected due to the fact we need to expend greater amounts of pressure drop to get less and less increase in jet nozzle velocity , unfortunately thrust is simply mass times velocity , whereas the kinetic energy has a "velocity squared" component , kinetic energy in the exhaust goes up faster than the velocity increase. This is what you invisage www.youtube.com/watch?v=4EZJkwWHQ8MCheers John Or this- youtu.be/hCwz7mnymr4Cheers. Ahh another one who watches that great channel!
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Post by racket on May 26, 2021 17:18:44 GMT -5
A C/D nozzle will allow full expansion and velocity if correctly configured ( area ratios) for the available pressure ratio, but you lose the pressure thrust component of total thrust when only a convergent nozzle is used .
Often the extra losses from the CD nozzle don't make up for any increased thrust , we'd be using a 4:1 PR at most, unlike 20:1 PR of a rocket engine , so things don't "work" quite the same .
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Post by turbojet atv on May 26, 2021 21:53:48 GMT -5
Good evening/morning/afternoon everyone
Looks like some interesting stuff walking around here lately. Turbo rockets? Interesting haha.
So it’s about time I get to working on mine. I’ve got all my material to build my engine (minus some charge piping). I’ll try to send some pictures as I make it all. I’m cutting the end cap & ring for the spark plug and injector side of the engine soon. The exhaust side looks fun. Is there any particular way you make it? Do I channel the whole 10” chambers into the turbo or do I just channel the 8” flame tube into the turbo? Or is there a better way to do that?
Either one, I’ll be in for some welding to get it all fabricated together.
I also have a air turbine starter coming in Friday & that will be mocked up in the frame this weekend.
✌️ Cullen
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