[anupmathur]

Originally Posted by Arch-Angel

....
1. Firstly, the higher backpressure will ensure a slightly higher volume of gas to be sent to the turbo which will bring it up to its operational rpm faster, which would mean slightly improved low end torque. However, the same low end torque can be brought about by a smaller turbo.
......
I might not be spot on with my analogies and would like the experts to comment on this because i feel as though my mind is clouded with soot

Indeed, there is a bit of soot around!
The back pressure is created because of the turbo being in the exhaust path! If not for this restrictive element, there would be far less back pressure.

Turbocharger rpm depends on the quantity of exhaust gas and the temperature of the exhaust gas.
Larger quantity of exhaust gas is the result of more fuel being burnt (which needs more air for proper/full combustion), which also raises the temperature of the exhaust gas. Any back pressure created, as from the turbo resistance, further increases the exhaust temperature due to adiabatic compression of the exhaust gases.

Greater quantity and temperature of exhaust gas translates to higher velocity (kinetic energy) after passing through the nozzle ring which is just upstream of the turbine blades. This helps to increase the rpm of the turbo and thereby supply more air from the blower wheel to the inter cooler and thence to the combustion chambers.

[Arch-Angel]

Originally Posted by anupmathur

Indeed, there is a bit of soot around!
The back pressure is created because of the turbo being in the exhaust path! If not for this restrictive element, there would be far less back pressure.
........

Arent restrictions in the exhaust system design also a part of the consideration for an engine which is going to be turbocharged? Agreed that the obstruction in our case namely the turbo is what is causing the back pressure (Major contributor) but then we have the catcon and the expansion chamber and isnt the turbo plumbing coming from one of the valves in between the catcon and the expansion chamber? Just a question since i am still learning on how things go about. Also, arent headers also responsible for creating this back pressure?

[ramzsys]

What's with these Indica(b)'s CR4 engines? The smoke when accelerating, agreeable, but then some of them smoke even when cruising. Is the engine faulty or the cab driver to blame?

[s_pphilip]

I read somewhere earlier in this thread that a VGT should give a better A/F ratio thereby minimizing or negating the black smoke effect, when I occasionally accelerate I do notice clouds of black smoke, I checked with the Hyundai service guys, they state it is normal,
however thought its better to cross check on T-BHP as they may not be technically correct apart from the service experience they have,
so is it normal for an Embera crdi with a VGT to emit clouds black smoke intermittently under acceleration?
Does this necessitate a proactive check?

Originally Posted by rubbermeetsroad

But it is possible that if it just a laggy turbo you will probably see black smoke only while accelerating. This would mean a lagging Turbo.

So as asked earlier does a VGT qualify for a lagging Turbo as VGT is variable.

This thread also corrected my perception that Modern Diesels are cleaner, Petrols still have the upper hand.

[anupmathur]

Originally Posted by s_pphilip

....
This thread also corrected my perception that Modern Diesels are cleaner, Petrols still have the upper hand.

Not quite as simple as you imagine!
The pollutants emitted from each are different and there is a difference in the visibility of the pollutants. Just because petrol engine emissions are not very visible do not assume there are none or that they are insignificant.

[akshay4587]

I have a Scorpio Mhawk,and a Linea MJD at home.
Linea belches out black smoke every time she hits turbo zone,not much,but enough to be noticed in the rear view mirror,however i never even get a hint of smoke in the Scorpio even under hard acceleration??

PS:Linea is the pampered baby here,the air filter is cleaned every 2K kms,and replaced at 7.5K kms mark along with one of the best diesel engine oil.

[anupmathur]

Originally Posted by akshay4587

...
Linea belches out black smoke every time she hits turbo zone,not much,but enough to be noticed in the rear view mirror,however i never even get a hint of smoke in the Scorpio even under hard acceleration??
....

Doesn't take a genius to say which is the technically superior engine as far as emissions go!

[FarPatel]

Hi All,
My first post, mainly since so far anything I wanted to say was already discussed threadbare before I could get to it.
Anyway, about the issue of black exhaust smoke during hard acceleration, I have been driving a Qualis for 13 years, with absolutely no trouble of this kind, until I noticed it in my rear view mirror a few weeks ago. So off I went to my usual authorised service centre (Madhuban Toyota in Kurla, Mumbai), where they checked the fuel quality, compression etc., with no indication of any apparent problem. Finally they told me that they would try the last option in their list of solutions, that is, clean out the exhaust with a high pressure jet.
Well, whatever they did, I was floored. When I took her out for a test drive, I swear, if she had wings she would have taken off. I suppose the engine performance had deteriorated, due to carbon buildup, so slowly over the years that I couldn't detect it, since I have driven only this car and no other all these years. Needless to say, along with this boost in performance, the visible smoke I noticed on acceleration has also disappeared.
I have also noticed that my FE has reduced from an almost constant 10-10.5 kpl since she was new, to about 9.5 after the cleanup. Maybe it will slowly improve, as discussed in "Engine Decarbonising - Demystified" in the Technical Stuff section.
This is off topic, but please allow me to say it: At the end of the day I am becoming more and more impressed by the quality and longevity of the Qualis. She may be a simple vehicle compared to today's wheels, with no bells or whistles but boy, is she a great drive or what?
Cheers.

[Vkrm_Rghvn]

Originally Posted by akshay4587

I have a Scorpio Mhawk,and a Linea MJD at home.
Linea belches out black smoke every time she hits turbo zone,not much,but enough to be noticed in the rear view mirror,however i never even get a hint of smoke in the Scorpio even under hard acceleration??

PS:Linea is the pampered baby here,the air filter is cleaned every 2K kms,and replaced at 7.5K kms mark along with one of the best diesel engine oil.

Hello,
My two cents, please check your EGR valve whether its stuck or not. If its pneumatic remove the vacuum pipe and check for air suction power in idling and full throttle (vehicle stand still condition). Usually in these engines the valve is closed in idling and opened in full throttle. So the suction force is less and idling and more in full throttle. If you do not feel the difference check the valve(in German it's called the EPW valve).
If that's okay on the EGR valve there are vents provided from which once can notice the valve movement . Perform the same idling and full throttle test (I.e. just depress the accelerator) and check for valve movement.
I hope this helps.
P.S. EGR valve failure is one of the causes. Sometimes it can also be oil in turbo (check for oil in the turbine side), or injector coking( I.e. injector holes are blocked) also.
For the turbo or injector issue please take it to the nearest mechanic. These fitting have a specific tightening or loosening torque for mounting or disassembly.
EGR valve check is a DIY. It requires only a torch light.
I shall click some pics and share with the community as to how to clean a blocked or clogged EGR valve in the near future.

Chao,

Vikram Raghavan

[rubbermeetsroad]

Hi phillip , I think its fair to say that you are on the right track with your question. An Ideal variable geometry turbine SHOULD not have any smoke cloud during acceleration bursts as well. But that is not what happens right. Well let me assure you that if your power plant did not have the VG turbine, the smoke would have been a lot more than it is now. I know thtat's not a very satisfying answer but let me put it like this. The Turbo lag that we feel in standard turbocharged engines is significant, the one that we feel in VGT charged engines is lot less. But It IS there nonetheless. So with all else same the more is the lag you m ore feel, you can be sure that more would be the black smoke. Less lag less black smoke and more lag more smoke. Because when you are lagging 5he Turbo is trying to spool up to generate the desired boost.this catching up take more time in STD Turbo engines because there turbine has been designed for efficience at certain RPM band.Not so for the VGT which have a way to change the geometry of the air path using moveable fins. Which means that they can work up a boost effectively over a wide band of rpm.if the air speed through the turbine core is low it changes the effective cross section of the air path meaning that the same air goes through a smaller tunnel and naturally its speed increases to those levels that the turbine core is designed for. Voila!! You have yor wind speed even though youy are whirring at 2000rpm.

[a4anurag]

Originally Posted by akshay4587

PS:Linea is the pampered baby here,the air filter is cleaned every 2K kms,and replaced at 7.5K kms mark along with one of the best diesel engine oil.

Why don't you try changing the filter at 5K kms rather than 7.5K kms?!

I drive the Ritz VDi and initially used to clean the filter every 5K and change at 10K kms. The smoking issue was too high and noticeable so I change the filter at 5K and clean it every 2-2.5K kms. The smoke that used to plummet earlier has decreased to a large extent.

Just an observation.

Anurag.

[thecoolsundar]

Originally Posted by unni.ak

One of those things I've noticed is that deisel engines emit black smoke when under hard acceleration or being revved. It doesnt matter if its a beat-up old Fiat or a E Class Benz. While Petrols are cleaner. Even under hard acceleration they dont emit any "visible" smoke.

Any technical reason behind this? Is it that Petrol engines emit smoke, but then of the invisible type?

Diesel has a stoichiometric ratio (the amount of air required to completely burn the diesel) of approx 14.5:1 by mass.

Most of the time, especially when idling, diesel engines run very lean, upto 60:1 ratio, which is just enough to keep the engine turning over without load.

Diesel engines deliver their maximum torque at slightly richer than Stoichiometric ratio, so when you are accelerating hard, the actual air-fuel ratio can be as low as 10:1. This leaves a lot of unburnt fuel, which comes out as particulate matter.

Also, diesel injection systems, have an arrangement for advancing the injection timing, when the engine rpm goes up. This provides more time for the fuel to burn. However, most of these systems rely on feedback from multiple revolutions of the engine. (mechanical systems rely on the increased pressure of fuel delivered by the feed pump and electronic systems rely on input from various sensors.) Therefore, there is a lag between the engine speeding up and the advancement of injection timing. During this lag phase, the fuel injected does not have time to burn completely and produces particulate matter.

[thecoolsundar]

Originally Posted by unni.ak

One of those things I've noticed is that deisel engines emit black smoke when under hard acceleration or being revved. It doesnt matter if its a beat-up old Fiat or a E Class Benz. While Petrols are cleaner. Even under hard acceleration they dont emit any "visible" smoke.

Any technical reason behind this? Is it that Petrol engines emit smoke, but then of the invisible type?

Also, turbocharged mechanical injection diesel engines, suffer from something called turbo-lag, since the injection pump is mechanically coupled to the engine, it starts pumping more fuel as soon as you press down on the accelerator pedal, the turbocharger being a fluid coupling only revs up once the exhaust pressure becomes higher. during this lag, there is insufficient air to burn the increased fuel, leading to partially burnt gases coming out of the exhaust

[DerAlte]

Originally Posted by thecoolsundar

..., the turbocharger being a fluid coupling only revs up once the exhaust pressure becomes higher. ...

Err... Turbocharger is / has fluid coupling? Perhaps you could expand on this? Otherwise it is a rather strange abstraction.

[thecoolsundar]

Sorry that was badly phrased. What I meant was that the turbocharger is driven by the exhaust gases and so can be thought of as being fluid-coupled to the engine