Turbo "Wastegate" Surprise

[diverpat]

Finally opened up my ebay turbo to have a look and what I thought would be a simple wastegate was more of a regulator using actuated fins. Can I discard this assembly or do I need to fab a way to keep it open and fixed?

ibb.co/6HGZ6kK

[racket]

You've got a nice variable vane turbo which will allow you to "tune" your engine .

Initially you probably want to fix the vanes in a midway position between fully open and fully closed so that the outlet gap ( throat) between vanes is mid width , the pic sorta indicates somewhere around fully open with the vanes pointing more towards the wheel than at a tangent which would be the fully closed position .

Depending on how the engine eventually operates you can vary the position of the vanes to optimise output , generally fully open will increase temperatures and fully closed will cool them , but only up to a point where the compressor starts to complain , so any adjustments need to be very minor between test runs

[diverpat]

Interesting, but the part of me doesn't like the extra variable for a first time build. Would a turbo like this work in a jet turbine if the assembly was removed? The rest of the exhaust side of the turbo is a simple swirl.

[finiteparts]

It would probably not work, as the turbine is sized for the set of nozzle guide vanes (NGVs) that are installed. You are better off gettting a different turbo or as John stated, just lock the NGVs to a middle setting and run your engine. In a sense, the VNT (variable nozzle turbo) arrangement may be better for a first turbine engine because it at least gives you some ability to "tune" your engine's operation if your compressor/turbine matching is not optimal. With a standard turbine housing you are stuck with what you have and if the compressor to turbine matching is not very good, there is little you can do about it.

I actually have a nice little VNT set-up from a GTi that I have been meaning to make into a cool little engine. Maybe I'll get around to that this summer...maybe...

Good luck,

Chris

[racket]

The simple answer is NO , the scroll will be too open , just fix it mid range for initial testing

[diverpat]

Appreciate the information! It's amazing how quickly you can get helpful responses for such a niche hobby.

[noshell]

Hi, i am an automotive engineer and have a differing opinion.

If the turbo you have came with an actuator I would disagree with setting the vanes "mid way". I think you would be best off having them shut as far as the actuator allows, this is the setting for maximum spool up and this would be most comparable to an internally gated turbo with the gate shut which is generally how most of our jets operate.

I also think that a variable vane turbo (what you have) offers some advantages, i would try running it with the actuator plumbed in, it could prevent over spooling and increase thrust as when the vanes open it allows extra gas past the turbine.
My next engine is based on a VVT Although its delayed because of my newborn haha.

Disclaimer, im far from the most experienced on here regarding jets, but i do know a fair bit about turbochargers. Take this with a pinch of salt. Im here for discussion, not to tread on toes

[racket]

LOL............I've got tough toes :-)

With the vanes fully closed theres a good chance that the compressor will go into surge , our engines don't have the luxury of pistons to force the gases through the turbine stage at a higher pressure than that coming from the compressor , which is often the case on an IC engine .

Set it mid position , get it fired up , then adjust the position to regulate turbine temperatures ..............if you'd like to know more , please ask away :-)

Cheers
John

[noshell]

Build it and let us know whos right haha.
I rekon the actuator would do all the work for you.

Werent there a few turbine racing cars that had variable geometry or something?

[racket]

For our simple low pressure ratio engines fitted with a fixed area jet nozzle theres no need for variable bits unless the engine is being forced to operate with a miss match of components .

The turbine cars had variable geometry on the freepower wheel where opening up the vanes reduced backpressure during idling conditions to reduce temperatures , similar to the bypass valve I fitted to my 12/118 engines interstage ducting .

[finiteparts]

Mar 21, 2023 12:18:58 GMT -5 noshell said:

Hi, i am an automotive engineer and have a differing opinion.

If the turbo you have came with an actuator I would disagree with setting the vanes "mid way". I think you would be best off having them shut as far as the actuator allows, this is the setting for maximum spool up and this would be most comparable to an internally gated turbo with the gate shut which is generally how most of our jets operate.

I also think that a variable vane turbo (what you have) offers some advantages, i would try running it with the actuator plumbed in, it could prevent over spooling and increase thrust as when the vanes open it allows extra gas past the turbine.
My next engine is based on a VVT Although its delayed because of my newborn haha.

Disclaimer, im far from the most experienced on here regarding jets, but i do know a fair bit about turbochargers. Take this with a pinch of salt. Im here for discussion, not to tread on toes

FYI, most VNTs use vacuum to close the vanes.  They default to the NGVs being opened up so that if the vacuum line got damaged and loose vacuum signal, you wouldn't overspeed and damage the turbo or the engine.  Additionally, the vacuum signal is usually modulated through a PWM controlled valve so that the ECM can control the VNT over the entire engine operating range.   It is controlled to not only control the boost for performance but also to set the EGR pressure ratio, so the set-up of most VNT control is likely very different than what we are asking them to do here. 

So the first concern that I have is how exactly would the actuator be "plumbed up" as there is no real good source of vacuum to close the vanes down at low flow demand.  As the flow demand increases the vanes would open up which would be relatively easy by just bleeding off the vacuum.

Since I don't think the actuator is an option, I would say that starting with the NGV fully closed is probably not a good way to go.  This would be like setting up a turbo with a tiny A/R, which we all know doesn't work.  I stick with my agreement with John, start with the NGVs half way open and see how things go.  I think it would be way better to build a manually operated control for the NGVs that will allow you to quickly get a "feel" for how the turbo responds to vane movement.

Good luck,

Chris