Diesel Smoke Problem in India | Read the Full Article. 

Gasoline engines in the automobile and other sectors make the environment pollute for a long period. Diesel fuel is also the part of a gasoline engine that makes the environment uneasy. In this article, I will discuss the diesel smoke problem in India.


Diesel Smoke Problem in India

The rapid growth of population and Industries in India during the last two decades has resulted in the need for adequate mass transport facilities for quick movement of men and materials. The diesel engine has always been a preferred prime mover for haulage of heavy loads due to its superior fuel economy.

In the last 15 years, there has been a rapid increase in the number of diesel vehicles. A majority of automotive diesel engines are rated at about 100 BP and are almost exclusively used in city buses and trucks.

A normally rated and well-maintained diesel engine emits a negligible amount of carbon monoxide and hydrocarbons, through a considerable amount of nitrogen oxides are emitted. The diesel exhaust is objected to by the public due to the following reasons :

  1. It causes a reduction in visibility. It may thus constitute a traffic hazard also.
  2. It has a disagreeable odor due to the presence of certain aldehydes, ketones, and oxygenated compounds.
  3. The soot particles in the exhaust gases settle down on buildings and trees, in the vicinity of the source. It may thus spoil the appearance of buildings in the long run.
  4. Diesel smoke is dangerous for health and causes trouble breathing.

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Diesel Engine Combustion and Smoke


In a diesel engine, the air is compressed inside the cylinder and fuel is injected into it. As the mixing of air and fuel has to take place entirely inside the combustion chamber, complete mixing is virtually impossible, and infinite variations in air-fuel mixture richness exist within the same cylinder. Therefore, the complete combustion of the fuel hardly takes place.

Also as the load requirements are met through variations in the quantity of the injected fuel the, overall air-fuel mixture ratio varies within wide limits, about 20:1 to 60:1. Local over-rich zones thus exist within the cylinder and the high pressure and temperature generated due to combustion make the condition favorable for some fuel molecules to undergo thermal decomposition and de-hydrogenation resulting in soot formation due to the lack of oxygen in these over rich zones.

J.F. Alcock and W.M Scott carried out photographic investigations into diesel engine combustion and have shown that soot formation during the early part of the combustion process is common to all diesel engines. The soot is consumed in the later part of the combustion process under favorable conditions. But the burning rate of the soot particles is low; and if the amount of soot generated is large, the exhaust smoke density is high.

Although diesel smoke has been extensively studied, the mechanism of soot formation is not yet completely understood. It is, however, observed that soot formation is an almost essential feature of conventional diesel engines.

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Types of Diesel Smoke

According to P.H. Schweitzer, the diesel smoke is of two types :

  1. White or cold smoke.
  2. Black or hot

The third accepted type is, however, the blue smoke. It is the black smoke that causes maximum concern from the point of view of air pollution.

#1. White smoke

The white smoke normally arises due to the following two reasons :

  1. Two low operating
  2. Too long a delay between the start of fuel injection and the beginning of combustion.

In both cases, the droplets of unburned or partially burned fuel appear as white fog in the exhaust. The white smoke appears during starting and warming up. The warm-up period is short if the ambient temperatures are high. Except for a few regions in the northern parts, the average ambient temperatures are fairly high in India.

The white smoke thus lasts only for a short while and need not cause much concern from the air pollution point of view. One of the chief characteristics of white smoke is its strong odor and lachrymatory nature attributed to the presence of aldehydes.

If you notice persistent white smoke, it is advisable to have the vehicle inspected by a qualified mechanic. They can perform diagnostic tests to identify the specific cause of the issue and recommend the necessary repairs. Ignoring white smoke could lead to further engine damage and decreased performance.

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#2. Black smoke

The black smoke is a suspension of soot particles in the exhaust gases and results from the incomplete combustion of fuel. It appears after the engine has fully warmed up and accelerating or pulling under load.

The most common cause of black smoke is over-fueling, where more fuel is injected into the combustion chamber than can be efficiently burned. This can be due to a malfunctioning fuel injector, incorrect injection timing, or a faulty injection pump.

A malfunctioning EGR system can cause excessive exhaust gas to be recirculated into the combustion chamber, leading to incomplete combustion and the production of black smoke. If the injector nozzles are not the right size or are clogged, they may deliver an incorrect amount of fuel, leading to black smoke.

#3. Blue smoke

The blue smoke is usually due to excessive lubricating oil consumption and its emission indicates a very poor condition of the engine, such as worn-out piston rings or valve guides, etc. Besides, as it is possible to completely prevent the emission of blue smoke, it is not considered a serious problem from the point of view of air pollution.

If the PCV system is not functioning correctly, it can cause increased pressure in the crankcase, leading to oil being pushed into the combustion chamber and resulting in blue smoke. A malfunctioning fuel injector may cause improper combustion, leading to increased oil consumption and blue smoke.

Factors Affecting Diesel Smoke

Diesel engines or the mechanism of combustion of diesel fuel depends on some factors. Diesel fuel is a type of gasoline fuel that has some factors that affect the diesel smoke. These factors are-

1. Fuel Factors

The important properties of the diesel which affect the diesel smoke are-

  1. Cetane number. Diesel engines, especially in cold weather, benefit from fuels with higher cetane numbers as they promote easier starting and more reliable combustion. In cold conditions, low cetane fuel can lead to increased smoke due to poor ignition and incomplete combustion.
  2. Volatility. The volatility of diesel fuel plays a role in achieving optimal combustion conditions in a diesel engine. Proper volatility contributes to complete and stable combustion, reducing the likelihood of smoke formation. Fuel quality, additives, and environmental conditions (especially temperature) are factors that can affect the volatility of diesel fuel and, consequently, its impact on smoke emissions.
  3. Viscosity. It’s important to note that diesel fuel viscosity is typically regulated within certain standards, and modern diesel engines are designed to work with fuels within these specifications. However, variations in fuel quality or the use of additives can still impact viscosity. Regular maintenance, using fuel within recommended specifications, and ensuring proper engine conditions can help mitigate issues related to fuel viscosity and minimize smoke emissions.
  4. Chemical Composition. High sulfur content in diesel fuel can contribute to the formation of sulfur dioxide (SO2) during combustion. Sulfur dioxide is a major component of diesel smoke and is also a precursor to particulate matter. Regulations in many regions mandate low sulfur content in diesel fuel to reduce emissions and improve air quality.

It is generally found that the black smoke emission increases with the increase in cetane number and decreases with the increase of volatility. It is, however, extremely difficult to generalize such facts because the effects are different at different operating conditions and for different designs of combustion systems.

Also, a change in one fuel property is invariably associated with changes in others, which influence exhaust smoke density. The benefits obtainable in diesel smoke characteristics by changes in fuel quality are so marginal, compared to the cost incurred in obtaining a charge in fuel quality. Therefore, it is accepted that the diesel smoke problem cannot be viewed from the fuel point of view.

Considerable success has been achieved in recent years on diesel smoke problems by fuel additives. Certain additives containing barium effectively reduce the exhaust smoke density.

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2. Engine Design and Rating

The type of combustion system is the most important engine design feature that affects exhaust smoke density. An indirect injection engine gives less smoke than a direct injection engine for a large part of the operating range of loads, due to the high rate of air swirl resulting in better air utilization.

The indirect injection engines thus have a low air-fuel ratio under maximum load conditions and, therefore, are more sensitive to over-fueling than direct injection engines. Direct injection engines, however, are preferred due to their superior fuel economy characteristics. At present, most of the automotive diesel engines manufactured in India are direct injection type.

A diesel engine is normally given a maximum power rating based on the acceptability of the exhaust smoke density. Because excess air is available in the engine even at the minimum air-fuel ratio used, it is possible to get still more power from the engine by pumping in more fuel but at the cost of increased exhaust smoke density.

From the experimental investigation, it is found that the engine over­ rating, though attractive from the point of view of batter hauling capacity and pulling power is objectionable from the point of view of smoke emission.

3. The effect of Engine Life and Maintainance.

High smoke density from a properly rated diesel engine can often be attributed to poor engine condition or bad maintenance. Deterioration in the quality of smoke during the service life of a diesel engine is brought about by many factors, such as :

  1. Loss of compression due to worn-out piston rings or badly seating valves.
  2. Restricted air-breathing due to choked air cleaner or intake manifold.
  3. The faulty injection is caused by sticking injector needle, blocked injector hole or worn-out fuel pump plunger, insufficient injection pressure, etc.

J B. Durent and L. Ellinger, who simulated several different conditions of maintenance of diesel engines have found that poor engine breathing may result in an increase in smoke density by 25% to 30%. The maximum effect is near the mid-load. They have also reported a considerable increase in smoke density with defective components of the fuel injection system.

From the engine maintenance point of view, the condition of the fuel injection system has the greatest influence on exhaust smoke density. The fuel injection equipment of a diesel engine is required to deliver fuel to the engine in the right quantity, at the right time, and in the right state, failing which the engine performance deteriorates and smoke appears in the exhaust.

To perform these functions satisfactorily throughout the engine service life, all the components of the fuel system must be in good mechanical condition and must be correctly assembled and adjusted. As the wear of these components with increasing use is inevitable and as deposit build-up takes place on some of the critical components, periodic maintenance is essential to keep the smoke level low.

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Diesel Smoke and Legislation

Legislation has come into force in several countries to limit diesel smoke. Except in the USA where the regulations require full-scale dynamometer testing and continuous recording of smoke, the methods prescribed in most other countries yield readily to roadside application and can be used by trained police personnel.

The test methods include the free acceleration test, used in France, Belgium, and Italy, and full-scale road testing used in Germany and Sweden. The formation of diesel smoke standards in India also is in progress. Closely associated with smoke regulations is the need for a reliable smoke meter and an accepted test procedure that will give results most representative of the engine operating condition.

There is also a need for effective machinery for the implementation of the smoke regulations. The other important aspect is the need to train and educate the servicing personnel in proper engine maintenance. It must be remembered that good engine maintenance not only reduces smoke pollution but also results in better engine performance and longer life.

Conclusion on Diesel Smoke Problem In India

With the increasing number of diesel vehicles, diesel smoke has come under severe criticism in India, especially in large cities. Black smoke emission from automtive diesel engines increases in smoke emission from overhauled engines which kilometerage builds up faster as compared to that from the original engines.

The over-rating of the engine causes a considerable increase in black smoke emissions. The solution to the diesel smoke problem lies within the engine itself. If the engine isn’t over-rated and proper preventive maintenance is carried out, the diesel smoke problem can be considerably solved. Legislative steps to prevent engine over-rating and to ensure scientific engine maintenance at proper intervals should help to control the diesel smoke nuisance to a considerable extent.

Frequently Asked Questions(FAQ’S)

How does fuel quality contribute to diesel smoke issues?

Low-quality diesel fuel, with high sulfur content and inadequate additives, can lead to incomplete combustion, increased particulate matter emissions, and visible black smoke in the exhaust.

How does inadequate maintenance impact diesel smoke levels?

Poorly maintained diesel engines, with issues such as clogged air filters, malfunctioning injectors, and worn-out components, are more likely to produce excessive smoke due to inefficient combustion.

Are there any government policies addressing diesel smoke in India?

Governments are increasingly focusing on policies promoting cleaner fuels, stricter emissions standards, and incentivizing the replacement of older vehicles with newer, more environmentally friendly models.


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