[RedMM340]

Black smoke from a diesel is unburnt fuel. The richer the fuel to air mix, the more black smoke. But you also get more power with a rich mixture. Conversely if you make the mixture leaner, the smoke goes away. Typically the factory settings for a diesel is to have it burn as lean as possible to minimize emissions and maximize fuel economy.

Diesel is delivered and metered by a mechanical pump that has a calibrated flow curve that increases fuel as a function of engine rpm.

When you stomp on the throttle, there is a chuff of black smoke because the fuel flow increases just a bit faster than the air flow. Excess smoke will stop at a steady throttle regardless of rpm.

An EGR system will help reduce smoke since it recirculate some of the unburnt fuel out of the exhaust and back into the intake manifold where it will subsequently be fully burnt.

Vehicles that continuously emit black smoke are just plainly in a poor state of repair. It is easy to blame fuel suppliers for low quality diesel, but my guess is that if you examine the cars that chuff black smoke, they have not been maintained per the manufacturer's specification.

Regards,

Gaurav

[dadu]

No they allow for an equivalent and achievable levels as the chemical properties of these fuel are different and therefore you cannot eat apple and oranges and expect them to taste the same .

I have taken the below from India's Auto fuel policy.

Originally Posted by newcoolgadgets

So does this mean that Euro III Diesel engines are allowed higher emissions levels than Euro III Petrols because diesel is a less refined fuel than petrol? If this is so how are their emission levels on par? Can someone throw light on this?

Also to add to what gaurav said, if the mfg's make the fuel:air ratio too lean it affects the engine directly and leads to more wear & tear (forgetting the ratio's now) but generally its balanced. This is also defined in the ECU map unless you keep an open-ended ECU map which adjusts dynamically.

Originally Posted by RedMM340

Black smoke from a diesel is unburnt fuel. The richer the fuel to air mix, the more black smoke. But you also get more power with a rich mixture. Conversely if you make the mixture leaner, the smoke goes away. Typically the factory settings for a diesel is to have it burn as lean as possible to minimize emissions and maximize fuel economy.

Diesel is delivered and metered by a mechanical pump that has a calibrated flow curve that increases fuel as a function of engine rpm.

[vijit.gangwar]

Please read the below.....looks interesting-

Forget about all those smoky old buses and trucks, the truth is that the modern diesel car is as clean, and probably cleaner than an equivalent petrol car. Don't believe me? Read on.
The five main emissions for petrol and diesel cars are:
Carbon Dioxide (CO2)
Carbon Monoxide (CO)
Nitrogen Oxides (NOx)
Hydrocarbons
Particulates
Of these five, a diesel car is better than a petrol car with three of them, about the same with one, and worse with one. Only one of these classes of emissions is visible (particulates, or soot), and rather unfortunately for diesel cars, that is the one which is worse for them. The three emissions for which petrol cars are worse are invisible, so you won't realise that they are there; however they still cause harm to health and the environment.
What problems do these emissions cause, and how does diesel stack up:
Carbon Dioxide
Carbon dioxide is the main cause for concern at the moment, and is the subject of international agreements to try to reduce its output. Carbon dioxide is causing global warming; this is a known fact. Carbon dioxide is produced by any burning of fossil fuels, and is caused by production of electricity by most current powerstations; this means that electric cars cause carbon dioxide emissions too. Carbon dioxide does not cause any health issues.
Carbon dioxide emissions are directly proportional to fuel consumption, and as diesel cars use 30 to 40% less fuel, they emit 30 to 40% less carbon dioxide than petrol cars. Natural gas and LPG cars are actually quite fuel inefficient, if otherwise cleaner burning, and so produce more CO2 than a diesel.
Although CO2 emissions are not directly harmful to us, they are changing our climate. The legacy these emissions will leave will be felt by every generation after us.
Carbon Monoxide
Carbon monoxide is a poison. It has no smell, but can kill you without you realising what is happening. Carbon monoxide is the reason why you should not run you car engine (petrol) in a confined space. Diesel engines produce virtually no carbon monoxide, a petrol engine produces enough to kill you. The main remedy to carbon monoxide emissions of petrol engines has been the introduction of catalytic converters, however there are problems with cats:
They don't work until they are hot, maybe 10 or 15 minutes of driving. As most car journeys only last 10 or 15 minutes, the cat is not terribly effective.
They increase fuel consumption.
They are easily poisoned and stop working.
They are easily mechanically damaged.
Nitrogen Oxides
Nitrogen is the main constituent of the air that we breathe. When it is exposed to high pressures and temperatures it combines with oxygen in the air to form nitrous oxides. The nitrous oxides then combine with low level ozone to form smog. Because of the way a diesel engine works, with an excess of air inside the engine (rather than "just enough" as in a petrol engine, which is what causes CO emissions), nitrous oxides are more likely to be formed. However tests of actual cars reveal that whilst emissions of NOx are higher in a new diesel than a new petrol car, that by 50,000 miles or so they are the same, and after that the petrol engine produces more than the diesel. Therefore over the life cycle of the car, petrol and diesel engine emissions of nitrous oxides are similar. Emissions of nitrous oxides can be effectively reduced in both petrol and diesel cars by use of exhaust gas recirculation (EGR). EGR reduces the combustion temperature to below the point where nitrogen effectively burns.
Hydrocarbons
Hydrocarbons include chemicals such as benzene. Benzene is an extremely carcinogen chemical, and has been declared unsafe by the World Health Organisation in any concentration. Hydrocarbon emissions are contained in petrol engine emissions much more than in diesel engine emissions. Benzene is also present in the fumes which can be smelt when filling up with petrol at a service station, this is not a problem with diesel.
Particulates
Particulates or smoke are really the only problem for diesels (compared with petrol engines). Most of the controversies and newspaper scare stories center around particulates. Various groups have been trying for years to prove a link between diesel smoke and cancer, and so far have failed to actually prove anything. Friends of the Earth may come up with statements such as "Small particles are believed to lead to 8,100 premature urban deaths every year (1.9% of all deaths in urban areas)" and then apply them to diesel emissions, but this is flawed because:
The studies were carried out in American cities where the penetration of diesel in the market is lower. Any increase in deaths due to particulates, if it exists, may be caused be particulates from some other source; the particulates in question have not been indisputably linked with diesel emissions.
Even in Europe, particulates from diesel cars are a very small percentage of the particulate emissions which we breathe; most are from industry.
Diesel engines emit more PM10 particles, that is particles which have a diameter up to 10 microns, but petrol cars actually emit more PM1 particles than diesel ones. These particles are smaller than 1 micron and are invisible. They are also more likely to penetrate deeply into human lungs (as they are smaller) and look less like a natural dust particle, which human lungs have evolved to cope with.
Even if particulates are a factor in the deaths of 8,100 people every year in the UK, then these are the most seriously unwell people in the country. The fact is that we are talking about 8,100 people who are about to die, with or without particulates around.
The original research which led to the link between deaths and particulates is being questioned. See Merlise Clyde's paper, Model Uncertainty and Health Effect Studies for Particulate Matter, which can be downloaded from THE NATIONAL RESEARCH CENTER FOR STATISTICS AND THE ENVIRONMENT in Washington.
Summary
Diesel cars are better than petrol cars with reference to carbon dioxide, the global warming gas.
Diesel cars are better than petrol cars with reference to carbon monoxide, a poison.
Diesel cars are better than petrol cars with reference to hydrocarbons which cause cancer.
Diesel cars are similar to petrol cars with reference to nitrous oxides, which cause smog.
Diesel cars are worse than petrol cars with reference to particulates, which have unproved health impacts.

[unni.ak]

Totally agree to the fact that at a steady RPM there is no smoke, but happens more with the sudden flooring you do to overtake etc. But with drive-by-wire technology (cable-less accelerator) and ECU shouldn't this problem of more fuel going in before the turbo can spool (more air can get in) be nulled. I mean for carb-type engines, I agree that when you stomp on the pedal, more fuel goes in and such. But, with all this technology should it not "look" more cleaner!!!

Its great to know that diesels hurt the environ less

[gd1418]

What is a diesel if it doesn't smoke or leave oil stains..

[srishiva]

Originally Posted by vijit.gangwar

Please read the below.....looks interesting-

Summary
Diesel cars are better than petrol cars with reference to carbon dioxide, the global warming gas.
Diesel cars are better than petrol cars with reference to carbon monoxide, a poison.
Diesel cars are better than petrol cars with reference to hydrocarbons which cause cancer.
Diesel cars are similar to petrol cars with reference to nitrous oxides, which cause smog.
Diesel cars are worse than petrol cars with reference to particulates, which have unproved health impacts.

Only modern diesels are better in CO2 than petrol
There are about 40 different hydrocarbons emitted from diesel engine which I think is more than in petrol
Nitric oxides are more in diesel (forget the lifecycle part, I dont know who did the research)
Particular emission is more in diesels.

A recent study indicates more respiratory problems in areas which are located around truck routes in the U.S.

Why would California and New York ban the registration of diesel cars if the only bad thing to come out of Diesels was soot ?

You can find a lot of information similar to the one you have posted telling diesel is better than petrol in emissions. If that was the case, automakers would not be scratching their heads to clean up the exhaust to make it look as good as petrol emission.

[jat]

As mentioned by few guys, the diesel car smokes when floored because in diesel, the fuel is directly controlled (NA or TC) while in petrol the air is directly controlled. Therefore, in diesel, you can inject maximum fuel when engine at bottom of the rpm curve (when air flow is low) and the air fuel ratio is going to be extremely rich. Which means, that unburnt fuel is going to go out as carbon (black smoke)

Another factor is that in diesels, the flame speed is much less than petrol engines. So time required for combustion is more. This gets worse when air temp is low.

In modern engines, if this is happening the air flow monitoring or oxygen monitoring system is not working or engine tune up is off the mark.

[jat]

Regarding the pollution by diesel engines, present problem is due to sulphur content of the fuel rather than the others. Because others have means of controlling it, but sulphur is a big problem and worst damaging.

On the specific passenger traffic, diesels do have advantages due higher thermal efficiency but a badly maintained diesel is 1000 times more polluting (on particulate matter - unburnt carbon, carbon monoxide etc - funny NOx production goes down)

[veyron-w16]

all the modern diesel cars are first customized as per Indian standards (fuel quality, road conditions and temperature), so we cant say that smoke is basically due to adulterated diesel.

[TaurusAl]

Dear All,

If I floor the accelerator and the RPM reaches turbo range (2k in DDiS engines) and if i happen to look in my rear view mirror, I see a black smoke coming out from the exhaust pipe.

I know DDiS engines are fun to drive in turbo mode and simply love the power. At the same time i feel little guilty of polluting the environment thrill sake. So most of the time when the tacho needle is about to reach 2K rpm, my concern for environment urges me to ease the accelerator and drive sedately. I know this is the least i can do for the environment but its gives some feeling of satisfaction. Also, goes without saying it must be surely saving a lot of fuel improving overall economy.

Similarly, I have seen Tata engines and emitting smoke on a low rpm if higher torque is at work.

Considering the increasing sale of Diesel Cars, I urge fellow bhpians to contribute their knowledge of peculiarities of their car's diesel engines, so we can all drive optimally when possible and do our bit for the environment.

Cheers!

PS : Any other tips to control smoke welcome.

[fine69]

Isn't the black smoke due to unburnt fuel? Not certain how much more polluting black smoke is than the regular emission of a diesel car.

By the way if you don't floor it and accelerate gradually you wouldn't see black smoke, at least that's how it is with most modern car diesel engines if I'm not wrong.

[mayankjha1806]

Similar thread exists here

http://www.team-bhp.com/forum/techni...l-engines.html

I believe this is also related to Air filter being clean, and when its cleaned the amount of Black smoke that gets released is very less.

[srishiva]

That black smoke with unburnt fuel should also be lost efficiency. Its because of how diesel engines work where more fuel is dumped with not much air to match.

[revintup]

Ok now am seriosly confused. Doesnt turbo forcefeed air into the combustion chamber(?) so that the fuel burns more efficiently? So doesnt this mean very less wastage of fuel when the turbo is on song? Or am i missing something here?

[anupmathur]

Originally Posted by revintup

Ok now am seriosly confused. Doesnt turbo forcefeed air into the combustion chamber(?) so that the fuel burns more efficiently? ....

When you floor the gas pedal, the amount of fuel being sent in to the combustion chamber is much more than the turbocharger can cope with (in terms of supplying the required quantity of air) at its current rpm. It takes a while for the turbo to attain suitable speed to supply the required quantity of air to burn the 'extra' fuel being injected. Remember the turbocharger is driven by the exhaust gases and will spin faster as the load on the engine increases, but it does take a wee bit of time to attain the required speed.
For a second or two there will be black smoke emitted, till equilibrium is reached.