xcalibur
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Joined: April 2019
Posts: 22
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Post by xcalibur on Apr 16, 2019 3:02:37 GMT -5
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Post by racket on Apr 16, 2019 4:09:16 GMT -5
Hi
With a 70 mm inducer you can probably expect a mass flow of ~1-1.1 lbs/sec , so maybe 50-60 HP from a power turbine wheel without too much trouble..
Cheers
John
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xcalibur
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Joined: April 2019
Posts: 22
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Post by xcalibur on Apr 16, 2019 18:48:13 GMT -5
Hi With a 70 mm inducer you can probably expect a mass flow of ~1-1.1 lbs/sec , so maybe 50-60 HP from a power turbine wheel without too much trouble.. Cheers John Okay that's probably okay for what I want to do does anyone know a rough weight of a flame tube assembly and freewheel assembly? Total engine weight will be deciding factor. Cheers! |
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Post by racket on Apr 16, 2019 19:25:00 GMT -5
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xcalibur
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Joined: April 2019
Posts: 22
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Post by xcalibur on Apr 16, 2019 21:40:10 GMT -5
Okay I've yet to weigh the turbo (will do so tonight) but say it's 40-45 kilos so 80-90 kilos total? (Very roughly) I guess the wet turbine housing would be good too, keeping temps down inside the hull. I'm thinking I might put a small PWC jet unit behind it they take 6-8k rpm at wot and require no gearbox for ahead or astern. I've done this before behind a 45hp outboard engine lying on its side in a 2.6m ridged inflatable and it's a blast to drive. Do you have to gear down from the freewheel to the chosen drivetrain? Or can it be connected direct? (Jet units have no neutral and pump water all the time so decoupling from the rest of the drivetrain is not an issue) |
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Post by racket on Apr 16, 2019 22:17:08 GMT -5
Hi
The freepower shaft will probably prefer to spin ~40,000 rpm for max power , so gearing is essential , though freepower turbine stages can produce 80% power at 50% rpm .
Yep , your weight calcs are OK , plenty of buffer .
Cheers
John
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xcalibur
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Posts: 22
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Post by xcalibur on Apr 16, 2019 23:13:08 GMT -5
Also could you potentially run two engines side by side feeding a shared exhaust and freewheel? Providing of course the turbos are the same and you have a means to balance the two engines when running and throttling. Would be interesting from a marine perspective as may give redundancy if one engine fails?
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Post by racket on Apr 16, 2019 23:45:26 GMT -5
Have them as two seperate engines with seperate ducting to the freepower , you'll need to go to a larger axial wheel to get sufficient flow area , so feed a hemisphere of the axial wheel inlet annulus from each gas producer , similar to how the larger diesel engines feed their turbo to maximise pulse energy
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xcalibur
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Joined: April 2019
Posts: 22
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Post by xcalibur on Apr 17, 2019 1:59:51 GMT -5
Hi The freepower shaft will probably prefer to spin ~40,000 rpm for max power , so gearing is essential , though freepower turbine stages can produce 80% power at 50% rpm . Yep , your weight calcs are OK , plenty of buffer . Cheers John I have weighed the turbo, 43.8kgs, also measured inducer and outlet diameters with calipers and I get 75mm inducer and 105mm outlet. on jet specs program, I'm getting a flame tube length of 450mm, diameter 150mm. It says to add 1-1.5in to get combustion housing diameter, what would you recommend? With regards fo gearing down freepower shaft what's normally the best way ? Cheers   |
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xcalibur
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Posts: 22
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Post by xcalibur on Apr 17, 2019 2:04:45 GMT -5
Have them as two seperate engines with seperate ducting to the freepower , you'll need to go to a larger axial wheel to get sufficient flow area , so feed a hemisphere of the axial wheel inlet annulus from each gas producer , similar to how the larger diesel engines feed their turbo to maximise pulse energy Okay and doing it this way would make decent horsepower? I assume one would use a c20 freewheel? For starters anyway I just want to get the engine running as a straight jet, I'll go from there with options for adding an extra turbo/using a smaller freewheel. I would like to run it off diesel if possible, it's by far the most accessible around my small town in NZ |
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xcalibur
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Post by xcalibur on Apr 17, 2019 2:16:34 GMT -5
With regards to jetspecs flame tube measurements do they reference the diameter as ID or OD? (Or does it not matter) also I have a local supplier near that specializes in stainless tube and pipe 👍 (wine industry so up to large diameters too) so might use stainless if the price is right. What wall thicknesses do you recommend for flame tube and combustor housing?
Cheers,
Sam
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Post by racket on Apr 17, 2019 4:25:18 GMT -5
Hi Sam
That extra 5 mm on the inducer will add some extra mass flow :-)
With regards Jetspecs , it recommends generous proportions to allow for crude construction whilst still producing a working engine.
With more sophistication of the fuel presentation the flametube can be scaled down a bit , an ID of 130 mm will give the minimum 3 inducer areas for its cross sectional area , try and allow for at least 15 mm radial gap ( 30 mm diametric) between flametube OD and outer can ID and give as much flow area as possible where the delivery tube from comp cover joins the outer can.
The flametube needs to at least 1mm stainless sheet to survive the heat , the outer can wall thickness need only be thick enough to contain the pressure , stainless steel fire extinguisher cans in ~7 inch dia are thin , lightweight yet can take many times the pressures we run and are a good unit to use , the two shaft kart used one , and the top half of my turbine bike engine also used one .
With using diesel , put 10-15% petrol in it to get some volatiles
Cheers
John
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xcalibur
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Post by xcalibur on Apr 18, 2019 0:48:00 GMT -5
Hi Sam That extra 5 mm on the inducer will add some extra mass flow :-) With regards Jetspecs , it recommends generous proportions to allow for crude construction whilst still producing a working engine. With more sophistication of the fuel presentation the flametube can be scaled down a bit , an ID of 130 mm will give the minimum 3 inducer areas for its cross sectional area , try and allow for at least 15 mm radial gap ( 30 mm diametric) between flametube OD and outer can ID and give as much flow area as possible where the delivery tube from comp cover joins the outer can. The flametube needs to at least 1mm stainless sheet to survive the heat , the outer can wall thickness need only be thick enough to contain the pressure , stainless steel fire extinguisher cans in ~7 inch dia are thin , lightweight yet can take many times the pressures we run and are a good unit to use , the two shaft kart used one , and the top half of my turbine bike engine also used one . With using diesel , put 10-15% petrol in it to get some volatiles Cheers John Okay that's good news! stainless supplier only has 125mm or 150mm ID tube. 1.5mm wall 🤔 I'm going south in a few days though so might ring around while I'm down in one of the bigger cities and get something 130mm ID. Regarding fuel delivery, what's the best way? High pressure pump with a nozzle to atomize fuel? Cheers, Sam |
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Post by racket on Apr 18, 2019 4:03:03 GMT -5
Hi Sam
Yep , go the spray nozzle , there can be a tad more work getting high fuel pressure but overal I feel its the best system with a "sore thumb" combustor.
Cheers
John
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xcalibur
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Joined: April 2019
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Post by xcalibur on Apr 18, 2019 14:28:34 GMT -5
Hi Sam Yep , go the spray nozzle , there can be a tad more work getting high fuel pressure but overal I feel its the best system with a "sore thumb" combustor. Cheers John Okay sounds good, I've been reading other posts and seems most go for the Bosch 044 pump. I have an option of a twin or single pump setup. I'll control the pump with PWM so would it be best to get the twin pumps then they won't work as hard? Also would you know what spray nozzle I'll need roughly? I'll start getting bits offline now so it'll hopefully all be here when I get back in a week 👍 Cheers, Sam |
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