Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 8th August 2009, 16:48   #31
BHPian
 
Join Date: Jan 2009
Location: Chennai
Posts: 41
Thanked: 15 Times
Default

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
VeeTee is offline   Reply With Quote
Old 8th August 2009, 18:12   #32
BANNED
 
Join Date: Jul 2009
Location: back in gods own country :)
Posts: 118
Thanked: 0 Times
Default

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!!
Thomas8700 is offline   Reply With Quote
Old 8th August 2009, 20:37   #33
Senior - BHPian
 
Join Date: Sep 2007
Location: New Delhi
Posts: 3,083
Thanked: 252 Times
Default

Quote:
Originally Posted by VeeTee View Post
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.
anupmathur is offline   Reply With Quote
Old 9th August 2009, 13:27   #34
Senior - BHPian
 
kuttapan's Avatar
 
Join Date: May 2007
Location: Melbourne
Posts: 1,155
Thanked: 12 Times
Default

Quote:
Originally Posted by Thomas8700 View Post
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?
kuttapan is offline   Reply With Quote
Old 9th August 2009, 16:44   #35
Senior - BHPian
 
ImmortalZ's Avatar
 
Join Date: Jan 2008
Location: Trivandrum
Posts: 2,133
Thanked: 139 Times
Default

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.

Last edited by ImmortalZ : 9th August 2009 at 16:46.
ImmortalZ is offline   Reply With Quote
Old 10th August 2009, 10:22   #36
Senior - BHPian
 
Join Date: Jul 2008
Location: Bangalore
Posts: 2,035
Thanked: 384 Times
Default

Quote:
Originally Posted by DerAlte View Post

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
amitk26 is offline   Reply With Quote
Old 10th August 2009, 13:51   #37
Senior - BHPian
 
Join Date: Sep 2007
Location: New Delhi
Posts: 3,083
Thanked: 252 Times
Default

Quote:
Originally Posted by dadu View Post
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!

Last edited by anupmathur : 10th August 2009 at 13:52.
anupmathur is offline   Reply With Quote
Old 10th August 2009, 14:04   #38
Senior - BHPian
 
Join Date: May 2007
Location: Bangalore
Posts: 3,652
Thanked: 244 Times
Default

Quote:
Originally Posted by anupmathur View Post
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.

Last edited by dadu : 10th August 2009 at 14:06.
dadu is offline   Reply With Quote
Old 10th August 2009, 14:06   #39
Senior - BHPian
 
Join Date: Jul 2008
Location: Bangalore
Posts: 2,035
Thanked: 384 Times
Default

Quote:
Originally Posted by anupmathur View Post
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

Last edited by amitk26 : 10th August 2009 at 14:08.
amitk26 is offline   Reply With Quote
Old 10th August 2009, 14:56   #40
SUV
BHPian
 
SUV's Avatar
 
Join Date: Apr 2005
Location: BLR
Posts: 256
Thanked: 2 Times
Default

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
SUV is offline   Reply With Quote
Old 10th August 2009, 18:31   #41
Senior - BHPian
 
Join Date: Sep 2007
Location: New Delhi
Posts: 3,083
Thanked: 252 Times
Default

Quote:
Originally Posted by SUV View Post
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.
anupmathur is offline   Reply With Quote
Old 11th August 2009, 09:28   #42
Senior - BHPian
 
Join Date: Jul 2008
Location: Bangalore
Posts: 2,035
Thanked: 384 Times
Default

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
amitk26 is offline   Reply With Quote
Old 11th August 2009, 19:21   #43
Senior - BHPian
 
DerAlte's Avatar
 
Join Date: Mar 2007
Location: Bangalore
Posts: 8,076
Thanked: 2,876 Times
Default

Quote:
Originally Posted by dadu View Post
... 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?
DerAlte is offline   Reply With Quote
Old 11th August 2009, 20:18   #44
Senior - BHPian
 
Join Date: Sep 2007
Location: New Delhi
Posts: 3,083
Thanked: 252 Times
Default

Quote:
Originally Posted by DerAlte View Post
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.
anupmathur is offline   Reply With Quote
Old 11th August 2009, 23:05   #45
Senior - BHPian
 
DerAlte's Avatar
 
Join Date: Mar 2007
Location: Bangalore
Posts: 8,076
Thanked: 2,876 Times
Default

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.
DerAlte is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Do all Turbos require idling before shut-off? GTO Technical Stuff 117 24th October 2012 20:10
Variable Geometry Turbo - VGT NFS_Carbon Technical Stuff 7 1st December 2006 23:12
Twin turbos for Turbo Diesel indian SUVs? neo_trace Technical Stuff 5 4th August 2006 18:55
Intercool and Turbos zulfikar Modifications & Accessories 3 22nd April 2005 13:39
Wanted Used Turbos Domnic Shifting gears 17 15th February 2005 17:05


All times are GMT +5.5. The time now is 05:17.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks