Building JetOne Gas producer for ultralight turboprop engine

[elmo0104]

Hi everyone. I'm trying to do something new. I bould in past some engines from turbochargers but they were very heavy. Now I need to build something compact in size and light as possible. Have some ideas that I do not know they will work so now I will post some photos of what I have done already. I did  talk with Andreas, bought some literature for more info. I hope that my photos will be interesting for someone Also I hope that someone with more experience will point me on the right way if see or reed something not right in this build thread.


The shaft was grinded for bearings and compressor wheel fit. Bearing are hybryd ceramic bearings.




Compressor wheel is from kkk k31 turbocharger I believe.



The shaft tunel is made from aluminium, has albo slots for bearings. They are no tight and no lose fit(do not know how to tell it in english). Tunel is not finished yet. Will get lubrication system.



Diffuser is cast aluminium. I did the PLA 3d print of it and send to casting company.Next did some milling and press fit the center steel ring for proper seat siling ring on the shaft.

How it looks all together:






Not the exhaust part. Did some water cutings.



Vanes are also cuted but they are in my friends shop, he doing chamfer(some grinding to gas pasing smoth)

I did some fixture for welding vanes:




Now have some question. How to tap turbine shaft for nut? 

The other think is lubrication. My idea is to use comressed air to suck (Venturi effect) oil from reservoir and spray it through the bearings. What do you think, will it work?

[jetjeff]

Hello,

Nice work so far. It's best to cut the threads for the shaft on a lathe, you probably could use a die to cut the threads, but it would be tough to get the threads straight with a die. You have to mill slots (using a ball end-mill, don't go in too deep) in the back of the compressor diffusor to supply air and a small amount of oil via a small tube.

The front cover to the engine has to precisely match the radius of the turbocharger wheel for the engine to work.

Jeff

[racket]

Hi

Your compressor diffuser vanes start to close to the compressor wheel , there needs to be a vaneless space .

Use a positive pump to force oil through bearings

Cheers
John

[ripp]

Hi elmo0104,

Usually one uses a vaneless space. Your compressor diffuser should work. See photo on the GR180.



members.tele2.nl/geraldensuzanne/turbines.htm

Ralph

translate.google.at

[smithy1]

Nice work so far..

Are the bearings "angular contact" ceramic bearings?? If so, they'll need a pre-load spring in the shaft tunnel.

Cheers,
Smithy.

[elmo0104]

Thanks all you guys for replys. I want to minimize electric power involved in engine work so any oil pump is not acceptable(do not know what is "positive pump" but i believe that it need some kind of external energy to work John. Am I right?). Jeff is this milling job good for lower than shaft axle oil canister? Will it suck oil fron that canister? It has to be lower cause oil drain will be lower. I was thinking to connect oil mist and air to center of shaft tunel. The drains then should be on the outside of bearings. The bearings are "angular contact". There will be spring washer to preload them. What kind of preload force is needed. I have the "compressor site" bearing preloaded with spring washer.

[jetjeff]

Hello,

The slots need to be milled on the backside of the compressor diffusor. If you check out my Old + New build thread you'll see what I'm talking about. I lost all my old pictures on my old computer, so I can't show you what I mean.

The milled cooling ducts provide cooling air to the bearings along with oil. The oil is supplied by a small tube, you don't need a very big tube. The lubrication is then supplied by a T fitting coming from your main fuel line, of course you have to mix 5% oil in with the fuel.

The force Thomas Kamps suggests for bearing preload is 15 newtons or about 3.37 pounds.

I concur with John, your diffusor blades are too close to the compressor, the air comping off the compressor is very turbulent and there needs to be a gap between your compressor and compressor diffusor blades.


Hope this helps

Jeff

[racket]

Yep , preload needs to get pretty high for bigger engines , I was using 25 lbs on my FM-1 engine

[smithy1]

Oct 11, 2016 22:08:45 GMT -5 racket said:

Yep , preload needs to get pretty high for bigger engines , I was using 25 lbs on my FM-1 engine

+1....

Even my small turbines use ~4-4.5kg axial pre-load. This helps keep the bearings happy...not enough pre-load will cause the balls to "skid" in their races which will see the bearings fail in a very short time.

Even "too much" lube flow can have detrimental effects. I learned this very early in my turbine fiddling years.

A nice balancing job is also critical to these engines, helps prolong bearing life too.

Cheers,
Smithy. 

[racket]

Hi Smithy

Heh heh , yep , ball skidding with full pressure oil flow to the bearings was a problem I encountered with FM-1 , the balls ended up with flat "equator lines".

I think I read somewhere that the JFS has something like 100 lbs of preload on its bearings to cope with fast spoolup with freezing cold minus 65 F oil

Cheers
John

[elmo0104]

Thanks again for big bucket of informations. Jetjeff and rocket can I simply modify my diffusor blades on the miling machine to make that vaneless space? That preload force- how to calculate? Is it depends on compressor dimentions? I believe that my rotating parts are bit smaller than your FM-1 engine parts John. Will 11kg of preload force will be OK? Jetjeff, want to ask you where goes that cooling air with lubricant in your engine after it pass both bearings? My idea is to provide that mixture  in the area between the bearings. Two drains, one between compressor and compressor bearing ant the other between turbine wheel ant turbine bearings. You ask why that way. The answere is  that my shaft tunel has smaller inner diameter between bearings than  on the ends. If I connect lubrication suply to the outer side of bearing the oil will collect in shaft tunel between bearing and comressor wheel which will cause some leaks through seals. 

Cheers
Peter

[jetjeff]

Hi Peter,

Yes, you should be able to modify your existing disffusor to create a vaneless space ( use a mill with a rotary turntable, make sure you use a dial indicator to center the diffusor) The oil for the bearings, just gets burned out the back. You shouldn't be using bearings with seals, if they have rubber seals, remove them.

Jeff

[elmo0104]

My bearings do not have seals. They are open on both sides. I've rings seal like in turbocharger. Look on the very first photo in this thread. I think that i need to have drains in that case.

[jetjeff]

Hi Peter,

If you mill three cooling channels in the back of the compressor diffusor (using a ball end-mill), you shouldn't need drains. The compressor will force air through these channels, if you add a small oil line, you won't need an oil pump, which I suspect you are trying to avoid to reduce wieght The compressed air will force air and oil to both the front and rear bearings.

Jeff

[racket]

Hi Jeff

I'd be wary of using just P2 air in the way you suggest , I know thats how its "normally" done with RC micro engines , and I tried using the same methods with my FM-1 engine but with disastrous results, I went through a number of rotating assemblies due to failed turbine end bearings.

The radial info turbine stage was part of the problem due to it not having a "balancing" disc to even out axial air/gas loads on the bearings, along with the fact that the airflows static pressure at the entry to those air ports into the bearing cavity was less than the pressure at the turbine end , I had "reflux" , I suspect the high speed gases exiting the NGV ended up behind the turbine wheel where they "recompressed" , the lockwire on my NGV securing screws was burnt. :-(

Eventually I fitted 2 "snorkels" to the supply ports with their "pitot" entry at the diffuser discharge area so as to supply maximum air pressure into the shaft tunnel .

In the end I fitted a couple of time expired #8 bearings from a C20 Allison with a full recirculating pressure lube system , I used the same setup in my 9/94 engine that Andy M is using in his bike .

Cheers
John