maxime
New Member
Joined: November 2016
Posts: 5
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Post by maxime on Nov 3, 2016 13:21:50 GMT -5
Hi all, First post, lots of great projects here !! wow Few years ago I built a turbojet based on a T3 turbo, went good, no pic to prove it, sorry... The unit eventually got dismantled to scavange parts for other projects, but recently I got 2 rather large turbos for free and the idea of making a turboshaft is itching me badly. Those turbos are from a 875 hp V12 380kw generator used for emergency during powerloss in a school. Schwitzer 4MD-755 Compressor inducer 75mm Compressor exducer 110mm Turbine Indicer 100mm Turbine exducer 80mm Dated 1974 All I could find about those turbos is that the type of compressor they use is good for high pressure but in a limited range (fullfills the bill of a generator) In my basement next to it lays a rebuilt Garrett TV7701 Compressor inducer 65mm Compressor exducer 94mm Turbine inducer 88mm Turbine exducer 70mm Would the newer style compressor of the garret outperform the larger Schwitzer ? Both models use a twinscroll turbine housing, wich I understand isn't ideal for turbojets. Making a reverse flow combustion chamber around the turbine but keeping the compressor housing would be the plan. On the Schwitzer there's a nice NGV that would get usefull for the reverseflow combustor, the Garrett doesn't have any. Any tought on witch would be the best candidate ?
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Post by racket on Nov 3, 2016 16:16:57 GMT -5
Hi
Welcome :-)
I'd be using the smaller unit for your gas producer as it would probably produce a better outcome , maybe not as much mass flow as the bigger unit but the comp efficiency would mean more pressure downstream for making power, either thrust or shaft horsepower.
Unless the NGV throat area was the right size for the mass flow , temperature and pressure coming from your flametube you'd have to make something anyway , also as the turbo was on a heavy duty diesel engine its turbine wheel was probably constructed from a material suited to the lower temperatures than the smaller more modern unit.
The bigger unit could be used for your freepower stage to produce some shaft horsepower.
Cheers John
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maxime
New Member
Joined: November 2016
Posts: 5
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Post by maxime on Nov 4, 2016 7:33:03 GMT -5
Thanks John ! One more thing, (ok, big fat lie) I looked at projects using turbo turbines for the freepower but some had to do a bypass to reduce the flow. Since i have 2 4MD-755, would splitting the jetpipe into 2 separate turbine (both having a sprocket driving the same chain let say) be good or i still would be more efficient making a single axial freepower wheel? Ps, freepower wheel would be milled, can't afford allison parts Im also looking for a lower rpm output, unit is to be fitted under a lawn tractor hood
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Post by racket on Nov 4, 2016 15:42:53 GMT -5
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maxime
New Member
Joined: November 2016
Posts: 5
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Post by maxime on Nov 4, 2016 16:06:34 GMT -5
:/ Wasn't looking for a diesel engine behavior thats for sure... But an 8 inch wheel is what i had in mind of machining. I tought those would be closer to 15k rpm than 40 as a turbo turbine freepower would. Correct me if I'm wrong (plz) Im good at eyeballing and making stuff, but when maths comes in I'm quickly lost Guidelines for the freepower would be great. If I am to mill it, whats wrong about having a large wheel with short blades ? wouldn't it use the correct air speed/pressure while giving a -not so low- rpm ?
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maxime
New Member
Joined: November 2016
Posts: 5
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Post by maxime on Nov 4, 2016 16:25:01 GMT -5
Also, for packaging purpose a reverse flow combustor instead of a tube would be great (and we just got a waterjet cutting machine, would be a nice project to try it out) theres lots of info and guidelines for tube combustor, Johansson did a great job on his bike combustor, but he states you were part of its developpement. Are they more application specific or rules of thumb can also be used for them ?
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Post by racket on Nov 4, 2016 16:36:44 GMT -5
Hi
Large wheels with short blades and full peripheral entry run into problems due to the clearance becoming too great a percentage of the blade length , thats why I suggested partial entry over a segment of the wheel.
Also if you intend to use karting chain and sprockets you could end up with enough power to exceed the chains strength .
You'll need to develop the gas producer first , then once you know the "energy" in your jetpipe you can then design the freepower stage
Cheers John
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Post by racket on Nov 4, 2016 18:45:09 GMT -5
Hi Yep , Anders engine is loosely based on my 10/98 jetandturbineowners.proboards.com/thread/19/10-98-engine, flametubes are pretty similar . The main thing with our "micro" annular flametubes is the cross sectional area is at least 3 times comp inducer area , and that there are sufficient evaporator tubes to provide 6 times inducer area as their OD area , and ~10% of inducer area as the flow area of their bores. Ideally our flametubes could be a tad longer but as the comp to turb distance is fixed we need to make the flametube work despite its short length , this is why its important to have lotsa evaporators so that the flametube cross section is effectively broken up into a multitude of small flametubes with "conventional??" length to diameter ratios. The circumferential evaporator spacing needs to be less than the radial width of the section of annular flametube so that the fuel vapour exiting the evaporator doesn't have to cover too much area. Cheers John
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maxime
New Member
Joined: November 2016
Posts: 5
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Post by maxime on Nov 9, 2016 13:00:31 GMT -5
Thanks John, just trying to have an idea of the finish product for packaging purpose, like roughly the size of the freepower stage since the combustor will partly surround it (reverse flow, keeping the turbo bearing body). I will get back to you after some drawings/thinking
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