[VeeTee]

VGT need not be described as turbos in which the vanes are controlled. Certain VGTs have fixed vanes, but the complete turbo can be moved back and forth thus creating variable volume.

VGTs have closed operation i.e., lowest volume at lower speeds to develop higher boost and have open operation i.e., maximum volume at higher speeds so as to reduce the boost developed. The tunable charcter is usually the position of the VGT based on the engine speed and throttle position.

Satish

[Thomas8700]

wow what all is going on in this thread .

have any of you guys worked on a VGT unit??

lot of wrong notions going around!!

[anupmathur]

Originally Posted by VeeTee

VGT need not be described as turbos in which the vanes are controlled. Certain VGTs have fixed vanes, but the complete turbo can be moved back and forth thus creating variable volume.

More precisely, it is a nozzle ring that controls the apertures and the angle of incidence of exh gases on to the vanes.

[kuttapan]

Originally Posted by Thomas8700

wow what all is going on in this thread .

have any of you guys worked on a VGT unit??

lot of wrong notions going around!!

Thomas Sir, I have said this before, I will say it again. Please enlighten us when you think wrong notions are being passed around. Or do you think it not worth your while?

It is very evident that you work in the automotive line(or study), so you must have knowledge in these areas. However, let that not put you on a higher pedestal, everyone here has some or the other specialization. Instead of wasting your time saying - wrong notions going around, you could have used your time to say what is the right notion, then. I admit that some Fiat guys took offense at your turbochargers post, but then this is a public forum, you should expect all types here and not be riled by posts which do not match your thinking/expectations.

So will you oblige?

[ImmortalZ]

With a normal turbo, you have to strike a balance between turbo lag and top end boost. A small turbo will spool up very fast, but will choke the engine at high RPM. However, a massive turbo needs high exhaust pressure to spool up, so it'll make no boost at low RPMs and is pretty much a big restriction in the intake and exhaust as far as the engine is concerned.

A way to imagine this is with a garden hose. Imagine that the rate of flow of water is constant. If you reduce the aperture of the hose with your thumb, the water will fall farther. However, when open the taps a bit and now, either your finger will have to be forced off to let the water through, or the hose pops off the tap.

A VGT is different in the sense that the finger in our example is ECU controlled and moveable. So at low RPM, with the exhaust pressure low, the vanes are moved so that the mouth is constricted (to be crude). As exhaust pressure builds up with RPM, the vanes are continually adjusted so you're always on boost and yet the turbo isn't limiting the flow of air.

However, it is still a turbocharger. It cannot make full pressure while at zero RPM, like an electric motor can. A VGT just widens the usable power band of a turbo charged engine.

Oh and Thomas is better served if he keeps quiet. We all know what happened to sameel.

[amitk26]

Originally Posted by DerAlte

VGT really does not make a racing car out a plodding Safari, instead it actually makes a 2.2l Safari far more cleaner burning than the old TCIC. Had Tata's not used a VGT and stuck to TCIC, we wouldn't have had a BS3 compliant Safari. 2.2l is just an incremental boon, it is not a revolutionary improvement as far as diesel engines are concerned.

VGT is not plonked on to TCIC engine.

To be Euro 3 Compliant they introduced Common Rail Diesel engine badged as Dicor with 3 L Block , After one year they reduced the block size and increased power by fitting in VGT, IMHO They could not have increased the peak power while reducing the block size otherwise

[anupmathur]

Originally Posted by dadu

Why is it so difficult to understand that this technology is present and works, thats the key selling point for VNT, no doubt some may be overhyped but then this technology wouldn't have survived for long and no auto manufacturer is a fool.

So where do we stand now, with respect to the above statement?
Is there or is there not the cure-all VGT?
Are there trade-offs that need to be made? Or is the ECU capable of deriving complete satisfaction from a VGT?

I'll never forgive M&M for the compromise they have sold to me, if such technology actually exists! Seems like only a re-programming of the ECU is required!

[dadu]

Originally Posted by anupmathur

So where do we stand now, with respect to the above statement?
Is there or is there not the cure-all VGT?
Are there trade-offs that need to be made? Or is the ECU capable of deriving complete satisfaction from a VGT?

I'll never forgive M&M for the compromise they have sold to me, if such technology actually exists! Seems like only a re-programming of the ECU is required!

VGT's provide for a wider band of service from low to higher RPM's, depending on the engine and its configuration. There is nothing called a cure all, but a better managed Turbo compared to Fixed Geometry ones.

It depends on the manufacturer, since 2.2l was a new engine with a VNT turbo, TM came up with a better handling of the VGT through the ECU upgrade.

My statement stands as is.

[amitk26]

Originally Posted by anupmathur

I'll never forgive M&M for the compromise they have sold to me, if such technology actually exists! Seems like only a re-programming of the ECU is required!

Did M&M CRDe sell VGT ? Or did they ever claim they have variable geometry turbo ?
I think they introduced it in mHawck engine.

IMHO various posts on this thread means a VGT + ECU program to control the same , The change in geometry either by closing and opening of vanes of by expansion of chamber has to be microprocessor controlled.
So why is it so hard to belive that ECU is the Processor controlling it and a change in ECU programm can change the pattern on when exactly the geometry should be changed ?

M&M must be controlling VGT using ECU as well and if required they can change the map as well

[SUV]

Not sure if this link was posted on this thread earlier .... It should provide enough insight on "VGT ECU Tunable or NOT" ...

VGT Turbo Discussion: Function, Specifications and Stock vs. Upgraded - TheDieselGarage.com

[anupmathur]

Originally Posted by SUV

Not sure if this link was posted on this thread earlier ....

SUV, the debate here is not whether VGTs are ECU tunable - they are.
The issue is slightly different - that there is only a limited range which even a VGT can address. The requirements for minimizing turbo lag and for full power boost are contradictory. Any turbo is therefore a 'compromise' and is ECU tuned to provide the best optimized solution, not the complete solution.

A more cpmplete solution could come from a combination of supercharger for low loads handing over to a turbo for high loads. But the cost of such a setup would be significantly higher.

[amitk26]

OK I got the ECU reflash done yesterday and the torque curve is smoother then before no pronounced turbo-kicks and feel the surge couple of hundred RPMs then before without a kick .

So probably the ECU Reflash has some effect on VGT operation

[DerAlte]

Originally Posted by dadu

... Closing the vanes also increases the back pressure in the exhaust manifold which is used to drive the exhaust gas through the EGR cooler and EGR valve into the intake manifold. This is also the position for cold ambient warm up.
... as well as providing the necessary back pressure for EGR operation.

During engine operation at high engine speeds and load, there is a great deal of energy available in the exhaust.

... Hope this clarifies ...

Honestly, @dadu, it didn't - it created more questions in my mind than it clarified!

1. EGR system does not need anything to help it drive gases through the cooler and valve. It was, and is, available on naturally-aspirated diesels. We are not talking of massive amounts - usually the feedback is low %v-v, and that doesn't need pressure help since the engine is anyhow operating against back-pressure, and inlet pressure < outlet pressure

2. Why should there be a great deal of energy available in the exhaust during engine operation at high engine speeds and load? That would imply the engine efficiency is much lower at high speeds/loads than at low?

[anupmathur]

Originally Posted by DerAlte

2. Why should there be a great deal of energy available in the exhaust during engine operation at high engine speeds and load? That would imply the engine efficiency is much lower at high speeds/loads than at low?

Not quite.
The engine might be operating at its best efficiency at higher loads but it will still produce far greater amounts (in absolute terms) of 'waste' heat because a much larger quantity of fuel is being burnt.
There is always much more heat wasted at high bhp than at low bhp. Efficiency cannot be deduced from this fact alone. It needs to be related to the calorific value of the fuel burnt.

[DerAlte]

What is 'efficiency' here (of the engine as a unit)? Ratio, isn't it? Ratio of which parameters? Maths unclear, please help!

Intuitively (I can only do that) the effect of absolute values like calorific value etc. will be the same, when we are comparing efficiency at low load/rpm v/s high.