My "Low Tech" Gas Turbine

[dennis]

Hi to all, since I'm new here I guess a short introduction is in order.
My Name is Dennis, I'm 23 and student (Bachelor, Automotive Engineering).
Around 5 years ago I started a turbine build when I was still in high school but it didn't really go anywhere because I lacked the skills, understanding and somewhat the funds too... (There is a topic on the "other forum")
Anyway the fascination for turbines never really let me go and I still dreamed of buying or preferably building my own one day, so some months ago I decided to have another go
At first I hesitated to join up and make a topic here because everyone seems to own a commercial engine or have a homebuild of incredible quality and mine is/will be... well.... not so incredible. I do it mostly for the relaxation I get from being in the workshop but of course it would be nice to have a running engine in the end haha
And because the "other site" seems dead and I quite certainly will need help rather sooner than later I'm here now.
And, as you might have noticed, English is not my first language so please excuse any errors or misuse of words.


The subject says "Low Tech" turbine, but of course the turbine will be at the same tech level as any turbine
It's just that my workshop is rather short on machinery... I have lathe (very old), bench drill and some dremel, angle grinders and other basic stuff also a lot of hand tools but no mill, press and so on
So there will be a lot of auxiliary tools and workarounds. At least I hope there will be...

Enough of the text, time for pics I promise

This is how my diffusor plate should look like, and looks in my CAD:



For an easier build I decided to use as many parts from the turbo as possible. Including the shaft tunnel, bearings and compressor backplate.
To give it a bigger diameter the compressor backplate got a nice sleeve and this is what it looked like fresh off the lathe:




Drilling some holes...




Pieces that don't look like a diffusor plate have to go




Much better




Time to make the wedges. To get 14 exactly equal wegdes with holes at the exact same position every time I made this:




Starting to look a bit like it should




My version of Schreckling's alignment tool




Almost there...




The finished part from the back




And from the front. The finish looks rough and flimsy, but it's actually very very smooth there are no burs felt by touch. The look is because I sprayed it with some wonder-aluminium-paint that is heat-resistant up to 800° C but unfortunately has a very rough surface texture that had to go again... Maybe the texture can be seen in the photo of the backside.




Random view




Comparison between the new diffusor plate and the one of my old project.
The compressor wheels are almost the same in size




Thanks for reading this long post, if you have any questions, suggestions or want to point out a problem with my build please don't hold back
And if someone should even want drawings I would be glad to share them.
Don't expect any progress too soon though, this will be a very slow build since I'm rather busy the next months and everything has to be done literally by hand

[Johansson]

Hi Dennis and welcome to the forum!

The work so far looks great, your engine will fill the DIY gap between the pure turbocharger turbines and the engines John, Ash and myself is building so it will be very insteresting to follow the progress even if it will take some time between the updates.

If you would like to post some numbers and a drawing of the engine it would be appreciated, the inducer diameter of the compressor etc.

What about your old project, did you finish it? Pics?

Cheers!
/Anders

[racket]

Hi Dennis

Welcome :-) ......................yep, theres a bit more life on this Group :-)

Diffuser is looking good , ......with it being so large in diameter I'd have perhaps started the wedges a little further away from the comp wheel to gain a bit of "operational flexibility" from a larger vaneless space.

Looking forward to the builds progress :-)

Chers
John

[dennis]

Hi Anders and John,
here is some data

comp wheel:
- inducer diameter: 50,5 mm
- exducer diameter: 76 mm
- blade height 4 mm
- blade angle at exducer (roughly) 63°

turbine wheel (roughly):
- inducer diameter: 74 mm
- exducer diameter: 64 mm
- blade height: 11 mm

diffusor plate:
- outer diameter: 180 mm
- vaneless space diameter: 86 mm
- cutouts begin at 159 mm diameter
- angle from tangent of comp-wheel to middle plain of guide vane: 25°
- guide vane angle: 12° (14 vanes)
- angle between guide vanes: 13,7°

Anders, my old "turbine" was basically born dead I didn't really have the skill nor the understanding necessary to build such a device. Also I had almost no sources for materials, so I made everything out of stainless steel because that was basically the only thing I could get haha
The diffusor was crooked, the shaft tunnel was a catastrophy , the bearings would have been a special size (at least here) and so very expensive and so on and so forth...
I don't really have photos of this catastrophy, but I still have the parts lying around so I could take some if you want

Now here is a quick render of how I imagine my engine until now and what I already modelled in CAD...

[Johansson]

Ok, I have one of those "early" unfinished projects as well that probably would have served best as a paper weight... =)

What kind of combustor type will this engine have? It looks like the lube lines will steal a lot of space for an annular combustor, perhaps some arrangement of can-annular combustors would work?

[dennis]

Haha that would be an ugly as hell paperweight in my case
Better for it to stay hidden in the shelf hehe

Yes, the oil lines are in the way, but I can't really think of a better way to get them out. And like this I can use the other big holes for fuel lines, measuring pressure and so on...
Can-annular combustors would be interesting, but I thought of a reverse flow CC since length isn't really an issue for me. The CC will actually get a little longer than needed go give her enough time to burn the fuel and maybe get a little more efficiency.

[Johansson]

Ok, a reverse flow combustor like the one Ash is building is probably a good choice. Plenty of room for a decent sized combustor that way.

Just out of curiosity, are you from Sweden? I sort of recognise my own way of putting foreign words together in your writing. ;D

[dennis]

Haha yeah there is a slight similarity ;D
But I'm not from Sweden, I'm from Germany. Our languages might be not too different though...

[Johansson]

I was not entirely riding a bicycle then (swedish saying), our language is quite similar to german in how to build a sentence.

Back to topic, have you seen the lathe mounted DIY mills? I´ve seen some pics of compressor diffusors being milled in a lathe but never understood exactly how they lock the lathe head and manage to indexate it to get the right number of wedges.

Might be someone here with more info about it, perhaps worth a try if you only have a lathe in your workshop.

[ashpowers]

Hi Dennis,

After looking through your build for the ~6th time I really like your approach to the diffuser vanes. That is so much simpler to build compared to machining from a billet or casting! I would imagine the NGV could be done the same way and allow for rather easy changes in throat area and vane angle. =) If I had seen your approach to this a few years back that is how my parts would have been built. ;-)

Ironically, the turbocharger you are using is identical to the rotating group I used in my T04 project. P-trim T4 turbine and 76mm 60-1 comp wheel. Should be good for around 25-30lbs thrust.
www.pulse-jets.com/phpbb3/viewtopic.php?f=6&t=3659&st=0&sk=t&sd=a

[dennis]

Hi Johansson,
I know what you mean, my old company had a lathe that could use a similar setup. Basically a big disc with a whole lot of holes that could be mounted in the back and then locked by sticking a pin through the hole that gives the right angle. We normally used the powered tool to drill holes and make flanges, but a little milling would have been possible
My lathe on the other hand didn't come with many accessories, actually it was rescued from being scrapped over a decade ago. And it's missing the original motor and gearbox because it was coupled to a diesel engine powering many machines to allow them to operate during air-raids when electricity was cut
(Yes, my lathe was built around 1938-1940 lol, but it's still working incredibly well for its age and the abuse it got )
Congratulations on your engine btw, nice to see she runs

Ash,
yeah JetSpec says I can expect 27lbf, let's see how it will turn out
Unfortunately I couldn't find much info about my charger so I just used the flow map of the roughly similar T04E 46 trim...
I really enjoyed reading along on your T04 project even back when you were still building it. If I had your workshop, I would have taken the same route by casting and then milling for sure! My diffusor is just a product of necessity, but necessity makes for good ideas as we say here
Since my vanes are glued on there is unfortunately no real space for adjustment once the glue has settled...

I thought about making the NGV pretty much like the way it's done in VTG-Chargers from the start, since it will only add minor difficulties to the design I would have to choose anyway while having the advantage of easy adjustments and optimization. Especially since I want to add a freepower stage sometime in the (hopefully not too) far future... And if it doesn't work as intended I can still weld it shut haha ;D
Until now it's only an idea and a rough sketch in CAD, but as soon as I have more free time I will give it a more serious thought and do the math. What NGV angles will I be looking at? I was thinking roughly between 25° and 50° from turbine wheel tangent to middle plane of the vanes?...

cheers,
Dennis

[dennis]

I'm back and luckily with a lot more free time in the future, so this should make a lot faster progress, a lot faster for my pace that is haha
I used my free time to make some more parts, at least start to make them.
Compressor cover, NGV base, turbine cover. I even found a radius tool with the exactly perfect radius for my turbine cover, talk about lucky haha.
Unfortunately I have made nothing really worth photographing so far, but of course I will share pics if someone wants to

I crunched some numbers for my NGV. Looks like I will go with a 20° vane angle and a throat area of 0,000726m² for my 74mm radial turbine. Has any of you had similar numbers in the past? Does any of you have any rules of thumb for things like this? I'm kinda worried that my calcs are a bit faulty.

What NGV angle have you used on your builds?

[racket]

Hi Dennis

The NGV angle is tied in with throat area and number of vanes , but ~20 degrees is close to whats required

As a guide to throat area , I use a total NGV throat area of ~40% of the compressor wheel inducer area .................for my 98mm inducer of ~7540 sq mms I use 18 throats of ~20mm X 9mm or a total of ~3240 sq mms

Cheers
John

[dennis]

Hi John,
thanks for the tip looks like my throat area was a little bit on the small side...

My comp inducer area is around 2003 mm²
My new NGV throat area will be 780mm²
And I will use 17 throats at 3,8mm x 12,2mm, NGV angle 20°

Since I want to make my NGV somewhat adjustable I will aim for a possible angle between 15° and 25° that should cover the sweet spot lol

Cheers,
Dennis

[racket]

Hi Dennis

15-25 degrees will certainly cover it :-)

Cheers
John