Team-BHP - Black smoke from diesel engines

Quote:

Originally Posted by anupmathur (Post 3531689)

Hmm, persuasively presented but I'm afraid there are factual errors here.
Excess fuel will always result in black smoke only, never white.
White smoke is the result of an engine being a tad starved of fuel and having surplus air.
The reason why black smoke can be seen from perfectly healthy vehicles is that during acceleration, before the turbo has spooled up, there is a lack of air in the cylinder, which is the same as too much fuel.
Faulty fuel metering or timing will result in white smoke only if the amount of fuel injected is less than optimal for the amount of air present in the cylinder.
If the fuel injected errs to surplus injection the car will emit black smoke.

And sir, my learning is not from Google, as you are well aware. :)

Anup sir; can you explain this?

This year in June;At Chitkul 11400Ft above sea level.
Two Thar's both 6 months old with under 10K kms on odo started spewing out bluish white smoke at cold start up.There was another Brand new Bolero DI turbo doing the same; was this due to excess fuel being burnt and lack of air?

This happened with 3 vehicles with under 10K on odo,so engine oil being burnt can be ruled out.

Quote:

Originally Posted by akshay4587 (Post 3534752)

Anup sir; can you explain this?

This year in June;At Chitkul 11400Ft above sea level.

Two Thar's both 6 months old with under 10K kms on odo started spewing out bluish white smoke at cold start up.There was another Brand new Bolero DI turbo doing the same; was this due to excess fuel being burnt and lack of air?

May be due to lack of oxygen I guess and he engine fuelling a rich mixture.

Anurag.

Quote:

Originally Posted by akshay4587 (Post 3534752)

Anup sir; can you explain this?

This year in June;At Chitkul 11400Ft above sea level.
Two Thar's both 6 months old with under 10K kms on odo started spewing out bluish white smoke at cold start up....
This happened with 3 vehicles with under 10K on odo,so engine oil being burnt can be ruled out.

Hmm, you mention bluish white smoke.
Yes, both are possible simultaneously.
A cold engine will burn some oil depending on how cold the ambient is. The piston rings, and specifically the oil scraper ring, take some time to reach steady state temperature at which they provide the best sealing action. A wee bit of lubricating oil can find its way into the combustion chamber and low temperatures also cause some fuel to be expelled unburnt. Hence bluish white. However, this will never last for more than a few seconds after a cold start.

Quote:

Originally Posted by anupmathur (Post 3534931)

A cold engine will burn some oil depending on how cold the ambient is. The piston rings, and specifically the oil scraper ring, take some time to reach steady state temperature at which they provide the best sealing action.

However, this will never last for more than a few seconds after a cold start.

By this all vehicle should release this type of smoke in every cold start. Right?!

I haven't seen any smoke in my Swift ZDi during regular cold starts. Just a doubt buddy.

Anurag.

Quote:

Originally Posted by a4anurag (Post 3534948)

By this all vehicle should release this type of smoke in every cold start. Right?!

I haven't seen any smoke in my Swift ZDi during regular cold starts. Just a doubt buddy.

Anurag.

Maybe you should take your vehicle to Chitkul(11400 feet) and check!?

Well, I have taken my Swift Diesel to Ladakh and those heights, so I can share a little bit of my experience.

Yes, at those altitudes, the Swift did blench out a little bit of black smoke on acceleration but that is understandable considering the air was thinner, turbo was spooling at much higher rpms and to climb the slopes the car had to keep its momentum and hence higher rpms in lower gears were a common feature.

About the Bluesmoke/white smoke, I think its more of a condensate which is leaving the exhaust during a cold start up than anything else. During cold climate, even in Mumbai my Swift does it for a minute on a cold start up and it did the same in Ladakh too. A little bit of this white/blue smoke can be seen during very cold starts in the morning. And no, neither is the engine oil getting depleted, neither is there coolant in oil or oil in coolant and neither is there any power decreased or anything like that.

Quote:

Originally Posted by a4anurag (Post 3534948)

I haven't seen any smoke in my Swift ZDi during regular cold starts. Just a doubt buddy.

When going to office today morning saw an Audi diesel belching black smoke but I doubt the driver would've noticed the smoke on the ORVMs though. The place I am in is hardly 150 m above MSL. So I doubt it has anything to do with altitude as such.

Quote:

Originally Posted by narayans80 (Post 3535061)

When going to office today morning saw an Audi diesel belching black smoke ...
....The place I am in is hardly 150 m above MSL. So I doubt it has anything to do with altitude as such.

It isn't altitude alone that deprives an engine of adequate oxygen; there are other factors that can deprive an engine of adequate air: choked air filter, fouled turbocharger, clogged intercooler, etc...
Incorrect injection metering and bad fuel can also cause black smoke.

Quote:

Originally Posted by a4anurag (Post 3534948)

By this all vehicle should release this type of smoke in every cold start. Right?!

I haven't seen any smoke in my Swift ZDi during regular cold starts. Just a doubt buddy.

Anurag.

It has to do something with altitude.
Since in extreme winters here when temperature was like 1-2 degrees; it did not spew out any smoke.
I guess it's just the excessive fuel being burnt due to lack of air and it doesn't last long as probably ecu regulates the fuel supply in sometime.

Sent from my iPhone using Team-BHP

Quote:

Originally Posted by akshay4587 (Post 3535112)

....
I guess it's just the excessive fuel being burnt due to lack of air and it doesn't last long as probably ecu regulates the fuel supply in sometime.
....

Indeed, ECU controlled engines can be made to behave pretty much as desired. A plethora of sensors, oxygen sensor, mass flow sensor, air and fuel temperature sensors etc enable 'control' to a large extent. However, this applies in large part to steady state running. In some cases sensors are bypassed at start up, for a few seconds, to enable a successful start. Sensors can get in the way of a quick, or successful, start, particularly if emission control sensors are also enabled at start up.

Quote:

Originally Posted by Sankar (Post 3534552)

I don't want to butt into this discussion but just want to clarify that the quantity of air getting into the cylinder in an NA engine is not the same at every induction stroke across different RPM. Cylinder filling varies depending upon RPM and intake tracts which are designed to aid better cylinder filing at certain RPMs to increase efficiency. So volume of air in the cylinder per induction stroke will not be the same at different RPM.

Hi Shankar,
No issues with the volumetric efficiency varying with rpm. (Incidentally I think it is better to think in terms of mass of air, rather than volume). But couldn't figure out your stand on

Quote:

Originally Posted by SS-Traveller (Post 3533835)

And therefore normally aspirated diesels should not emit black smoke during acceleration - is that correct?

Quote:

Originally Posted by anupmathur (Post 3534005)

No, that is not correct.
Naturally aspirated engines will also emit black smoke during acceleration till the air stream being inducted attains the pressure (velocity and mass) to match the fuel being injected. There is always a small lag due to inertia of physical masses. Fuel can be increased much more rapidly than air induction. Air through the intake scoop, filter and manifold takes a little longer to get distributed to each cylinder. Once the air intake stream exactly fills the partial vacuum created by the downstroke of the pistons there will be no black smoke.

Regards
Sutripta

Just a wild thought after reading these posts on lag in feeding O2 to cylinder in required quantity

Why cant we have a cylinder to store compressed air in engine bay , Similar to air stored for brake system in trucks and buses. This cylinder can be filled by running a pump from engine at steady state and at all times this compressed air can be used to provide required fuel - air mixture as per the condition giving full fuel burn.

In other words turbo will be replaced by air compressor.

Quote:

Originally Posted by amitk26 (Post 3572070)

Just a wild thought ....
... This cylinder can be filled by running a pump from engine at steady state and at all times this compressed air can be used to provide required fuel - air mixture as per the condition giving full fuel burn.
....

You've just re-invented the supercharger! :)

Quote:

Originally Posted by ashis89 (Post 3110647)

I agree with you Sagar. But what I was trying to tell is that it is much more prominent in some car models, to the point of looking ugly. Where as in other models, one rarely gets to see soot deposit unless its a very badly maintained example.

Guys, please share your thoughts on this.

The white logan diesel taxi looks grey from behind. But well maintained dzire diesels always look good from behind. I can show you a Dzire that is golden yellow but looks greyish from behind. It is a diesel dzire. I have never come across such a punto diesel. Basically it depends on the driver. If you rev the diesel car hard, you will get black smoke only.NO POWER BOOST. This is perhaps what blockhead drivers do not know. And the case of adulterated fuels is surely the most important criterion. All cars have different EGR valve settings that are predefined. Maybe the EGR valve reflow gas volume for the multijet is more when compared to the Renault. Even the Beat Diesel looks a bit greyish from behind. You will rarely come across a Ford Diesel with a clean rear. The exhaust valve design of Dzire is different from the Ritz. My Ritz's rear goes a bit black after driving 500 kms. But it is less black for the Dzire.