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Then is that some engines are more sensitive to Indian fuel quality(those with high black smoke) where as others can adapt better to the low fuel quality?

If so then it should adversely impact the engines in the long run. Yet we can see Renault engines running few lakh kms without major overhaul. Even this reason doesnot fit properly and I am even more confused.please:

I guess its something to do with the adulterated fuel.Here in Europe you hardly find any diesel cars emitting smoke even if it is a beat up 300d.Even the trucks run cleaner.I have an Opel astra sports tourer Di and i hardly see any black smoke being emitted on hard acceleration.I was quite amused when the other day i saw a swift diesel happily accelerating from a stop light without any black smoke:D

I don't think this soot development is due to fuel quality.

The soot discharge is seen only under hard acceleration or when the turbocharger kicks in full on. I do hate to see my RVM under acceleration specially at nights when the rear car can see the smoke emitted.

Initially I used to change the air filter every 10K kms and one time for a trial changed it 5K kms and started cleaning it every 2500 kms with pressurized air. I found a remarkable difference in the amount of smoke that is emitted.

I guess this could be of the reason and the air:fuel ratio. Can this be tuned to get the best of the engine and least of the smoke?lol:

Cheers,
Anurag.

Burning oil/diesel always makes carbon/smoke particles. Modern common rail diesel make a much more deadly particle than the old diesel engine, it is so small it can pass straight through your lungs into the blood.

But modern governments prefer it as it appears cleaner, to them. Modern diesels are so complex and expensive to maintain and repair that they are being scrapped well before they are worn - hardly good for the enviroment.

In Europe, the diesel engine is slowly being put to death by its dirty exhaust - soon most new cars will be tiny petrol engines which are made powerful by superchargers, often sequential installtions using exhaust power (the 'turbo') for the secondary turbine.

Black smoke=Excess diesel being injected.

3 reasons i can think of:

Turbo lag: ECU injecting more fuel, because your pedal is as close as to the metal and the cylinders are awaiting for (more) air from the turbo.

Air filter clog: No sufficient air for the fuel quantity injected.

Leaking injector: This is the extreme possibility.

Most diesel engines deliberately overfuel at full load, for various reasons. Many modern ones often put out a pall of smoke when accelerating hard. An injector pump can be adjusted to give even more fuel if the turbo boost is increased, but this is a very specialist thing to do and the risk of damaging the engine is high if you don't know what you're doing.

Oh, is that so? Which ones? How?

Modern CI engines are all controlled via ECU and so far, i haven't heard of any diesel engines overfueling on full load. If so, i only see more black smoke since i am assuming the amount of boost supplied by the turbo to be constant which would mean same amount of air in the cylinders when the fuel is injected before being compressed. This will only lead to more smoke if my analogy is right since more fuel + lesser air compared to fuel = improper combustion with loads of soot. I would be grateful if someone educated me on this :).

Engines which were controlled by mechanical means, certainly often received a larger dose of fuel, ceteris paribus, at full load - it allowed the engine to develop a little more power. There is always a compromise between combustion close to the cylinder walls and in the centre of the chamber - most of the soot particles are from this peripheral combustion zone. At full load, combustion chamber temperatures are higher and so the cylinder can better burn a little more fuel.

This can easily been seen with any traditional diesel engined vehicle in the form of a little grey haze from the exhaust when flat out which isn't present at lower loads. Excess fuelling gradually leads to black smoke under load, a sign of completely wasted fuel.

'Modern' common rail systems are theoretically always perfectly fuelled, with the myriad of sensors and the ECU controlling the fuel very carefully. In the real world this isn't always the case - the number of modern cars which accelerate hard leaving a plume of dark smoke is considerable.

However, the fact remains any diesel engine will produce highly carcinogenic particulates - with the modern CR units producing high amounts of the most dangerous nanoparticulates, sub 100u. Which are invisible to the eye, but most deadly for the human body. Invisible pollution is more threatening, simply because we cannot see it.

As I have mentioned before, even with the over-complexity of the diesel motor car today in attempts to clean the exhaust, it will always be dirty compared with petrol engines - which is why they are the future.

Rakesh, if adulterated fuel is the culprit then heavy black smoke should have been uniform across all diesels, which is not the case. Its very high for some specific engines where as low for others, irrespective of the condition of engine/car. Can you think of any other reason?

I read it somewhere that a petrol engine produces carbonmonoxide(CO, its colourless and hence not visible) and some nitrogen oxides which are much more poisonous than the Carbondioxide produced by diesels which is why the article called petrols to be back-stabbers(you cannot see them coming) and diesels as daring killers(you can see CO2):D.

According to another study, even natural gas run vehicles produce similar poisonous gases which are invisible but the quantity is less. Exhaust fumes of gas run vehicles smell awful, may be due to this reason.


Correct me if I am wrong.
Of the 3 reasons, 1st is valid for all diesels and so smoke shouldn't specific to few of them.

2&3, the cars that I mentioned of were fairly new ones and also it is highly improbable that 'all' cars will have the same problem.

Again unlikely that 'all' cars of a particular make will be going on full-load/pedal-to-metal.


Guys, no offence to anyone but I just wanted to know the root cause why specific cars only.

Also today I noticed that an Amby's exhaust(Isuzu engine) seemed cleaner than a Ritz's. Were the old diesels better off as mentioned above?

Fuel alone does not lead to developing more power. Air+Fuel is the key. Higher combustion temperatures does not mean that more fuel can be burnt effectively. If there is not enough air, the cylinder temperatures will not matter in fuel burn.

As it has been pointed out in this thread before, black smoke is because of there being more fuel than air in the cylinder. Some diesels will have this issue under hard acceleration because of the way they are tuned or because of their mechanical construction.

For e.g. An 1.2 diesel might be using a smaller turbo which is able to spool up quickly to keep the Air Fuel Ratio (AFR) within acceptable terms, where as a larger turbo might take some more time to spool up.
In terms of tuning, Diesels are often tuned to run lean - more air than fuel. There will be some operating regions in the engine, where there will not be enough air to burn off all the fuel requested by the driver, cleanly.
Take one scenario, accelerating hard from standstill. Driver presses the pedal hard, and there is not enough air to burn the fuel requested cleanly. What to do? 2 options, keep the AFR lean (no black smoke), which will lead to sluggish response. The driver will be pressing the pedal and the car will be moving very slowly off the blocks.
2) Make the AFR relatively rich, there will be black smoke, but as the engine starts revving this will even out to the normal AFR.
This will be decided when calibrating the engine, considering a multitude of parameters.

Attributing black smoke to deliberate or designed overfuelling by the manufacturers is naive.

Which is exactly what I didn't say. 'Grey haze' is what I said was the correct fuelling - slightly 'richer' fuel to air mixture than under partial loads and that (constant) black smoke under full load was indiciative of wasted fuel - ie incorrect air/fuel ratio.

Black smoke is not always simple over-fuelling (or lack of air). Poor atomisation of fuel because of worn injectors is as likely a reason for a plume of filthy carcinogenic smoke trailing a diesel vehicle. With the advent of electronically-controlled engines, it may also be a sensor which has failed casuing over-injection of fuel.

When the pedal is pressed suddenly,
Case 1 : Engine under load,RPM less than the turbo spooling RPM.
The mixture becomes too rich,temperature of combustion chamber falls down momentarily resulting in incomplete combustion of fuel.
As soon as the turbo spools up,smoke gets reduced.

Case 2: Engine under load with spooled turbo producing good boost.
The mixture stays optimum due to extra air being pumped-in,temperature does not fall when the fuel is injected. Less soot produced due to proper and complete combustion.

Case 3: Engine under full load,RPM where max torque is produced,pedal to the metal.
Over-fueling takes place much more than what it can burn,mixture get too rich resulting in-complete combustion and soot production.

ECU and mechanical pumps can alter the amount of diesel injected to some extent only. If it keeps decreasing the amount of fuel injected every-time it senses low boost pressure then there is going to be very bad throttle response.
Even a mechanical FIP has a mechanical boost sensor which injects more fuel when turbo kicks-in but when the accelerator is pressed all the way down,it will over-fuel even if the boost produced is low.

Experts can correct me.

I have a Punto 1.3 MJD, and in my most recent highway run, I have observed that black smoke is coming out, when I am exactly around 2K on tacho.
(I have never seen this before..the smoke was visible from the rear view mirror).

As has been suggested, I have cleaned my air-filter (with compressed air), and almost immediately, i could see the difference..with-in a KM or so, the black smoke disappeared clap:

Also the pickup improved slightly. I have to admit that I have not cleaned my air filter since last 6 months or so..in which time, i have covered almost 12K KMs.

Good job Vidyasagar,

Since there was heavy dust on your air filter the amount of air required for combustion was not being possibly sent to the engine causing incomplete combustion. Hence the black smoke.

In my last post here (#48) I had mentioned that changing the air filter every 5000 kms is a good practice to keep the engine breathe happy and better. I have been following this practice since long and more over I pressure clean the air filters every 2500 kms. Not high pressure but the right amount required to blow out the debris.

Cheers,
Anurag.