Turboshaft?

[elventu]

Hi everyone, I'm Davide, from Italy.
I was in the yahoo group some years ago.
I started my build on a HX60 over ten years ago, meanwhile a lot of changes in my life stopped the project.
Now...I'm wondering to resume.
But...slowly.
At now I'm unable to start building anything, I'm blocked with a broken leg, otherwise I have a lot of time to think about it and doing some drawings.

First of all, I need to start with something little.
I have a Garrett T2, it's small (expecially compared to the HX60!), but...
I prefeer starting with this one.
And I'm wondering to build a turboshaft.

I do not need to carry it on a drag strip, I want to discover if I can build a self-sustaining engine with all his subsystems, for educational purpose.
I'm a skilled 5axis lathe machinist then I'm wondering to machine from solid the power turbines (what material?).
I'm also collecting informations about how to do the gear reduction (it seems that I can do the job sawing a scooter transmission from the motor block ).

Suggestions?

Davide

[monty]

Hi Davide,

Gearbox: I would just make one using commercially available gears rather than trying to chop up a scooter transmission. There should be someone who supplies stock metric gears in Italy. In the USA QTC is the company I use.

You can search their site for sizes. They have some nice hardened, ground, integral shaft pinions that make a good start for the input gear. The hardened ground gears are induction hardened so you can still machine the shaft or hub portion to fit your needs.

Turbine: Most of the materials that work well are pretty nasty to machine. Inconel or stainless. Most of them are cast and the bore is made with an edm. I don't really know what to recommend since I have elected to avoid all of that entirely!

For a demonstration engine maybe you could get away with one of the less difficult to machine stainless steels.

Monty

[elventu]

Thank you!
My starting point is a thing similar to the one that Don G. build (the "gr5").
I find much simple and cost effective to chop off the rest of the engine and use the scooter gearbox.
I find one, used, for 35€.
It's a thing capable of over 15'000rpm from factoy in the input shaft, with a circa 15:1 ratio.
In my opinion it can be a good starting point.
Why do you prefeer to starting from stock gears?
Maybe there are issues that I don't know?

For the milling and turning of stainless steel, there's no problem.
That's my work for years, until last november, I worked since 2002 for operatory table maker, so working Aisi303/304/310/316/420/430 isn't a big problem.
Even now, I moved from the northern Italy, Trento, to Cesena, in the center, changing job I changed even the main business of the factory where I'm employed, from medical to general mechanic, my employers start to take some stainless steel works, thanks to my skills.

I never worked on Inconel or Titanium, however.

I need help on dimensions and design of the power turbine.
There's any source of formulas about them?

Thank you a lot!

Oct 12, 2018 8:07:40 GMT -5 monty said:

Hi Davide,

Gearbox: I would just make one using commercially available gears rather than trying to chop up a scooter transmission. There should be someone who supplies stock metric gears in Italy. In the USA QTC is the company I use.

You can search their site for sizes. They have some nice hardened, ground, integral shaft pinions that make a good start for the input gear. The hardened ground gears are induction hardened so you can still machine the shaft or hub portion to fit your needs.

Turbine: Most of the materials that work well are pretty nasty to machine. Inconel or stainless. Most of them are cast and the bore is made with an edm. I don't really know what to recommend since I have elected to avoid all of that entirely!

For a demonstration engine maybe you could get away with one of the less difficult to machine stainless steels.

Monty

[BFTO]

You need to make your gas producer to work and get some numbers before you can design the power turbine.

What dimensions do you have on your compressor/turbine?

[elventu]

Sure, it's the first step on the stairway to turboshaft 😊

Sincerely, at now I remember only that the outlet of the turbine have a diameter of 45mm.
As I wrote before,at now I'm blocked on the couch with a broken leg (hey...maybe I can use it as a source for surgical grade titanium for the turbine blades!😂), I start to think on what to do, next month maybe I can start working in my garage.

The turbocharger is a Garret T2 from my old Fiat Punto TD.
It's a good unit taken from an engine I tuned with a bigger one.

Oct 12, 2018 10:34:00 GMT -5 BFTO said:

You need to make your gas producer to work and get some numbers before you can design the power turbine.

What dimensions do you have on your compressor/turbine?

[elventu]

Searching with the turbo code, I find that it have 47.19mm inducer and 60.13mm exducer in the compressor side.
Not so big...😊

[racket]

Hi Davide

Welcome back to turbines :-)

You may need to reconsider using that turbo if the turbine wheel exducer is smaller than the compressor wheel inducer , ideally the turb exducer needs to have ~20% more area , so a turb exducer of ~52 mm dia with your comp inducer of 47.19mm .

A stainless steel freepower will survive , though you might find it easier to simply use a ready made turbine wheel rather than manufacture one .

Cheers
John

[elventu]

Thank you!
My "mental illness" comes out after some years in last days, watching some video on YouTube. 😂

I have to take it to do some measurements.
The 47mm measure comes from the web, but the 45mm comes from my memory.
And I take that turbo down from the engine I tuned ten years ago...
Maybe I'm wrong.

I thought to build myself the power turbine because IF the design of the one that I see (the rcdon one) is effective, for me is simple to do with the five axis lathe (only a bit of parametrical programming and a piece of stainless).

I think buying one can be a little too expensive for my pocket...

Oct 12, 2018 15:55:34 GMT -5 racket said:

Hi Davide

Welcome back to turbines :-)

You may need to reconsider using that turbo if the turbine wheel exducer is smaller than the compressor wheel inducer , ideally the turb exducer needs to have ~20% more area , so a turb exducer of ~52 mm dia with your comp inducer of 47.19mm .

A stainless steel freepower will survive , though you might find it easier to simply use a ready made turbine wheel rather than manufacture one .

Cheers
John

[racket]

Hi Davide

A simple turbine will work, its just a case of deflecting the gases , the overall efficiency won't be as high as a commercially produced wheel , but it will work .

As for your freepower gearbox , have you considered using the entire scooter motor , removing the crankshaft and use its bearings to support the freepower shaft/wheel instead ??

Cheers
John

[elventu]

I considered the idea of support the turbine shaft in that manner but the crankshaft is connected to the CVT, and I think the clutch can't work properly.
Probably the power turbine at idle without any load spools up to the speed who engage the clutch, forcing it to drag everytime.
Another possibility is to use a moped gearbox in that manner, but maybe it's only weight on the system.
For now I thought to build something simple for educational purpose.

Maybe I can try to put it on a small trike, but if I need power I must consider the idea of using my HX60, in a next project.

Oct 12, 2018 16:47:36 GMT -5 racket said:

Hi Davide

A simple turbine will work, its just a case of deflecting the gases , the overall efficiency won't be as high as a commercially produced wheel , but it will work .

As for your freepower gearbox , have you considered using the entire scooter motor , removing the crankshaft and use its bearings to support the freepower shaft/wheel instead ??

Cheers
John

[elventu]

I have a question about the freepower turbine.
From what I see, the commercial ones have long "fins", with a small center hub.
For me, if I mill out my wheel from solid, it is more simple to start with a bigger outer diameter and mill out shorter fins.
In my mind this can give me more torque at less rpm...
I'm wrong?

I think I have also to respect some dimensions, there's any advice for what relationship between the area of the turbo outlet and the power turbine?

Thank you!

[racket]

Hi Davide

Short blades on a large diameter hub isn't ideal as the tip clearance represents a larger percentage of flow area than with long blades , so more "losses" with short blades , but the larger diameter will make gearing easier as the pm will be lower , the Allison 250 first stage turbine wheel has relatively short blades and are often available on Ebay , its ~157 mm tip dia with a ~128 mm root dia ,so blades only ~15 mm long, marked flow area 4.41 sq inches - 2845 sq mms, but measured flow area ~10% greater at 3200 sq mms

As for the freepower flow area compared to the turbo exducer area , it will depend on the "energy" level exiting the turbo , but somewhere around twice the area is a starting point , but it really needs to be calculated and designed according to the energy level and mass flow rate .

Cheers
John

[elventu]

Thanks a lot.
I can put some ideas on paper, while my leg heals.
when I will have built the engine, I will ask for more precise information!

[monty]

Oct 12, 2018 9:52:33 GMT -5 elventu said:

Thank you!
My starting point is a thing similar to the one that Don G. build (the "gr5").
I find much simple and cost effective to chop off the rest of the engine and use the scooter gearbox.
I find one, used, for 35€.
It's a thing capable of over 15'000rpm from factoy in the input shaft, with a circa 15:1 ratio.
In my opinion it can be a good starting point.
Why do you prefeer to starting from stock gears?
Maybe there are issues that I don't know?

For the milling and turning of stainless steel, there's no problem.
That's my work for years, until last november, I worked since 2002 for operatory table maker, so working Aisi303/304/310/316/420/430 isn't a big problem.
Even now, I moved from the northern Italy, Trento, to Cesena, in the center, changing job I changed even the main business of the factory where I'm employed, from medical to general mechanic, my employers start to take some stainless steel works, thanks to my skills.

I never worked on Inconel or Titanium, however.

I need help on dimensions and design of the power turbine.
There's any source of formulas about them?

Thank you a lot!

Davide, Sounds like the scooter gearbox will work fine. I just hate dealing with trying to fit whatever I'm doing to existing parts. Always causes problems, but if you aren't particular about the final form use whatever works! Monty

[elventu]

I think that is better to adapt some well enginereed parts instead of building them by myself.
Building precisely a high speed gearbox it's difficult to do, and more costly.
Taking it from the used market allows me to spend a fraction of what can cost me a single gear, having all the thing precisely machined and mounted in a better enginereed box.
I have only to mill out the excess material and to put on the exit shaft some pulleys.
Maybe, if I decide to build a powerful one with the Holset HX60, I mill out a gearbox from solid aluminum for that, because of the different power output.




However, I remembererd I have another turbocharger to use for this project.
It's a KKK K26 unit from a Fiat Ducato engine that I bought some years ago for my ex autocaravan.
Maybe that is better than the smallest Garrett T2!