Compound turbo setup re-design

[ShadowTrooper]

So I was studying the design and operation of gas turbine (read: jet) engines yesterday and I noticed that they are remarkably similar in design to a turbocharger. A typical gas turbine has multiple compression stages utilizing either axial compression or centrifugal compression. Centrifugal compression is what your typical turbo has. Air comes in and is flung outward while undergoing compression. Axial compression is when air is brought in, compressed, and discharged parallel to the shaft.

What if a turbo could be designed that utilizes both axial and centrifugal compression? By putting the air through one or two stages of axial compression before delivery to the centrifugal compressor wheel this would effectively work the same way as a compound turbocharger setup inside a single (albeit slightly longer) turbo!

The benefits are more pronounced than just form factor. Consider that the smaller volume between an axial compressor and the centrifugal compressor is much smaller than the volume of a coldpipe. This means that there could be less lag because there is not as much volume to compress.

Keep in mind that if an additional axial turbine wheel was added after the regular centripetal turbine that you would extract more heat from the exhaust as well. The same principle as above would apply here too, there would be much less in heat losses and less volume between the turbine stages as well vs a hotpipe.

Anybody have any feedback?

 

[Hurley]

have you googled this... pretty sure it's been done before [first to post]


(good discussion, but.... practicality?)

 

[oldestof11]

Are you suggesting additional fuel be burned in the exhaust?

 

[nwpadmax]

The axial-centrifugal compressor concept was published long ago.

 

[Hurley]

Are you suggesting additional fuel be burned in the exhaust?

no (can't tell if you're being facetious)


he's suggesting that multiple stages be achieved by a single unit

 

[ShadowTrooper]

Well, the first question I ask myself when it comes to ideas is has somebody done it/thought of it, and the second, if so, what were the results and why is idea x not more commonplace.

 

[ShadowTrooper]

Multiple compression stages in one unit, yes. That's exactly what I'm talking about.

 

[apocalypse1812]

why is idea x not more commonplace.

$$$

 

[oldestof11]

no (can't tell if you're being facetious)


he's suggesting that multiple stages be achieved by a single unit

I got lost somewhere...

 

[Hurley]

???

turbo = centrifugal
ceiling fan = axial

jet engines use axial fan design to compress air over many stages, combust, then use the exhaust to drive a set of turbines all on the same shaft, extracting as much energy as possible.

 

[BramanteCummins]

Look at the really big turbos found on container ships and such. The turbine is alot like a jet engine turbine.

 

[GorillaDave]

Excessive temps and money would be my thoughts as to why this is not commonplace.

 

[Cummins2000]

My guess would be that in such a small scale it is not worth it in a cost/practicality sense.

 

[dvst8r]

Efficient operation window is another.

 

[chevota84]

I would think part throttle would be an issue, you'd still have to drive all of the compressor mass with very little drive energy.

Sent from my DROID RAZR HD using Xparent BlueTapatalk 2

 

[crackerman]

A setup similar to a new powerstroke, vnt turbine side, mirrored compressor wheels, except have a large and a small comp wheel, large as atmosphere, compressing into smaller backside wheel. May also need an external gate to help with drive pressure.

Other than that, i am lost.
Check out mobacken racing's build over on land racing forums, he built his own turbine using a large turbo, approx 150 shaft hp... Impressive to say the least.

 

[ShadowTrooper]

The new powerstroke turbo has a large and small wheel but they are *not* compounded internally. Both centrifugal compressors share a common discharge.

As far as rotating mass I think it may be required to run concentric shafts so that the primary/secondary stages would be able to rotate independently of each other. Vnt for the secondary (centripetal) turbine would be a plus.

As for heat, it shouldn't be as big an issue as it is on aircraft, those see higher temps than what is safe internally for our trucks.

 

[nwpadmax]

The Garrett LST has a twin wheel compressor that is compounded internally, but it hasn't made it into production yet. My guess is long term reliability isn't where it needs to be for OEM use, and cost versus two off the shelf units.

I don't believe that hanging extra mass off both ends of the main shaft is as simple as you're implying. When I read that something "shouldn't be a problem," I kinda LOL

 

[ShadowTrooper]

As far as stabilization and balance, it would absolutely require additional bearings. Placement is the question as is composition of said bearing, it will obviously have to be able to withstand high rotational speed and high heat for the turbine side as well as having a provision for lubrication.

 

[nwpadmax]

As far as stabilization and balance, it would absolutely require additional bearings. Placement is the question as is composition of said bearing, it will obviously have to be able to withstand high rotational speed and high heat for the turbine side as well as having a provision for lubrication.

I could be wrong, but I don't see that being done on the hot end.

All of the designs I have seen have the axial turbine being quite large, much larger than the normal turbine housing. The packaging alone could kill the usefulness of it, unless everyone is going to put one in the bed of their pickup.

This kind of theoretical thing is fun to kick around but I doubt it ever happens. There are much larger thermal losses in the ICE that one would go after way before one would likely build a really complicated turbo.

Remember too if it's built for joe schmoe street car, it has to be capable of being abused and shut off hot and run with crappy oil for 200k miles. Heck, VNTs still have issues, and they've had those out on the streets for 10 years or so already.