What Causes Soot In Diesel Engines?

Fuel and air entering the diesel cylinder ignite spontaneously from the high pressure in the combustion chamber, unlike gasoline engines where the fuel/air mixture is ignited with a spark. When lit, this forms fuel-dense pockets that produce soot.

How do you reduce soot in a diesel engine?

Diesel engines are known for being filthy and producing a lot of black smoke. One of the most common images is of a diesel rig speeding down the highway, black smoke billowing from the stacks. That was pretty much viewed as normal in the 1960s, 1970s, and 1980s. All of this is unfortunate, because a diesel engine is more efficient and reliable than a gasoline engine.

The modern common-rail diesel engines are a significant improvement over older diesel engines, allowing for significant increases in horsepower and performance without producing a lot of black smoke.

The corollary to this is that if your diesel emits black smoke, it means something is wrong and needs to be corrected.

Not only does it make you look ugly, but it’s also bad for the environment, and it’ll cost you more in the long run because black smoke implies lower fuel mileage and more money out of your wallet. So, let’s look at what produces black smoke in diesel engines to see how we might lessen it.

Restricted Air

Fuel that hasn’t completely burned is seen as black smoke. When a diesel engine is working properly, it will totally burn the fuel, producing CO2 and water. As a result, black smoke indicates that something is preventing the fuel from totally burning. The appropriate amount of air is required to completely burn the fuel, which is a vital component of the combustion process. Incomplete fuel combustion results from a lack of air.

What may be the source of this suffocating air? It could be due to a clogged or limited air cleaner system.

Turbocharger Lag = Puffs of Black Smoke

When large diesels with huge loads are about to accelerate from a standstill, they often puff black smoke. This enormous diesel has massive turbochargers that require a long time and a lot of fuel to get up and running “Spool it up.” They’ll do this while they’re waiting for the ball to start rolling “Before the light turns green, they “roll coal,” trying to get the turbocharger up to speed before they move. This consumes a lot of gasoline in an engine that runs at low RPMs.

This problem occurs primarily in older trucks and is a design flaw. There isn’t much that can be done about it besides perhaps adding a combustion catalyst to the fuel to increase the amount of diesel burned at low RPMs.

Incorrect fuel/air ratio or injector problems

Black smoke is produced when a mechanical issue breaks the equilibrium between the proper quantity of fuel and the right amount of air being burned. It could be as simple as tweaking the injector timing or inspecting the EGR system to ensure the EGR valve does not require replacement.

If it’s not like that, you’re dealing with a mechanical issue. It’s possible that the valve clearances are incorrect. Alternatively, the injectors may need to be examined. The most critical component of a well-running diesel engine is the fuel injectors. You won’t receive the finest atomization of the fuel if they’re worn or plugged, which is what the engine relies on for its optimal performance.

Engine Deposits Will Cause Black Smoke

When a car is brand new, it performs at its best. Engine conditions deteriorate over time, resulting in accumulations of combustion product combustion in important regions such as injectors and combustion chambers. And all of this gets in the way of optimal performance.

Diesel engines are particularly susceptible to this since a) they operate for such a long time and b) diesel fuel does not arrive from the refinery with any detergent packets already added.

The solution is to regularly add a detergent component to your diesel fuel. Dee-Zol is a multipurpose treatment that cleans up deposits, reduces the quantity of fuel consumed inefficiently, and can even extend the life of your DPF (because less soot are being produced at any one time).

How do I stop my diesel from sooting?

So far, we’ve determined that a faulty fuel/air combination is the most common source of black smoke from a diesel engine exhaust. It’s critical to address problems as soon as you identify them to avoid further harm to your vehicle. This will save you both money and time.

When you observe black smoke coming from your exhaust, there are a few things you can do:

  • Always seek the advice of a professional. The authorized service of the Motor Company can assist you with any diesel-related issues.
  • Clean the ventilation system. As previously stated, the proper amount of air is required to successfully operate your diesel engine; otherwise, the fuel would only burn partially. If your air filter is dusty or clogged, cleaning it or, better yet, replacing it is a good idea.
  • Check the rings in your engine. When the engine piston rings are destroyed, black smoke can be seen coming from the exhaust when the vehicle accelerates. You should examine them in an auto repair shop to make sure this isn’t the case, and if required, replace them. This will also keep the black smoke at bay.
  • Make sure you have enough fuel. Fuel injection timing is also crucial. Incomplete combustion will occur if there is too much fuel injected. The best course of action is to have a professional mechanic inspect the fuel pump and injection system. A common-rail injection system, which feeds gasoline directly to the solenoid valves, is also an excellent option to update them with. As a result, the car’s exhaust will emit less black smoke.
  • Fuel additives should be used. Using ordinary fuel in a diesel car on a daily basis can lead to debris build-up in the cylinder chamber and fuel injectors. As a result, the engine’s performance will be reduced, and hence the fuel economy will be reduced. Another thing that creates more black smoke from the exhaust when the car is accelerated is this.

As a result, think about combining diesel fuel with a high-quality fuel additive. As a result, the fuel will not create deposits in the engine, resulting in no black smoke.

What can increase soot levels?

As a result of incomplete fuel combustion, all internal combustion engines emit soot. Soot development is more common in diesel engines than in gasoline engines due to the way fuel is fed and ignited.

Growmark is a regional cooperative that sells and services agricultural products and services. FS Energy is a company that makes agricultural and energy-related goods.

They claim that the less air present, the better the conditions for soot buildup. Because the air and fuel have a chance to mix more thoroughly in gasoline engines than in diesel engines, combustion is more efficient.


Soot will accumulate in the oil over time, causing difficulties, he warns. Because the soot in the oil cannot be removed by the oil or totally contained by the oil filter, keeping the soot under control is a difficulty.

Additional soot buildup can be caused by engines with poor fuel combustion or defective fuel injectors, he adds. Additionally, operational conditions such as excessive engine idling or straining the engine can increase the amount of soot produced.

According to Betner, the aggregate outcome of these factors is lower combustion efficiency, which results in more soot particles developing in the engine oil.


They explain that as the piston descends for each power stroke, soot accumulates on the cylinder liners of each bore and is scraped down by the oil control piston rings. Blowby of combustion gases past the piston rings, especially if they are worn, can send soot to the crankcase.

Furthermore, during combustion heat, the thin motor oil film that remains on the bores can partially degrade, resulting in additional soot.


According to Citgo’s Betner, engine oil contains a soot dispersion ingredient that disperses the soot particles. During the engine oil service period, dispersing the soot particles and avoiding the natural tendency for the soot particles to clump together prevents or at least lessens various lubrication-related problems.

According to FE Energy authorities, high quantities of soot in the oil might cause the loss of dispersing chemicals, resulting in the formation of sludge. Soot particles clump together and attach themselves to engine surfaces as the dispersants are depleted. As a result of the obstructed oil flow through the engine, lubrication is diminished. Particle clumps can also develop on oil filters, obstructing oil flow and allowing unclean oil to enter the engine.

According to Lubrizol officials, soot loading also causes an increase in viscosity, which obstructs oil flow and increases engine wear, resulting in premature engine failure. This is especially true in cold weather starts, when a soot-laden engine oil can lengthen the time it takes for the oil to reach crucial engine components like the valvetrain.


Agglomeration is the tendency for soot particles to aggregate or bind together, according to Citgo’s Betner. When the oil can no longer handle or spread the amount of soot in the oil, agglomeration occurs.

Soot particles are incredibly minute and travel through the filter media until they clump together, according to him. The oil condition can pose a number of issues at this point:

  • The viscosity of the oil thickens. Excessive soot causes oil thickening, which can weaken lubrication protection and cause poor oil flow during engine start-up.
  • Plugging of the oil filter. The oil filter will gather more soot as it accumulates and begins to agglomerate, finally reaching filtration capacity. When the oil filter is full, the engine requires either filtered or unfiltered oil.

As a result, Betner claims, the filter is bypassed in order to ensure that the engine receives oil. When this happens, the engine may flash a warning light.

  • Increased engine wear. Soot is carbon, and it grows more abrasive as it agglomerates and collects. Oil analysis by equipment maintainers can reveal the impact of increased soot loading in numerous ways. When the percentage of soot in the oil rises, the viscosity of the oil rises as well. The engine wear metals will also rise if allowed to build to larger amounts.
  • Increase the amount of oil consumed. As the viscosity of the oil increases as a result of increased soot loading, more of the thicker oil tends to deposit on the engine cylinder wall. The greater accumulation of soot-laden oil on the cylinder wall as the engine piston goes upward may result in the surplus oil being released into the combustion process. Increased oil consumption may be a result of this ailment.

According to Betner, several equipment operators have noticed higher oil consumption as the engine oil service interval approaches its end. This is partly due to the higher level of soot as the oil service interval increases in some circumstances. Oils with better soot dispersibility tend to prevent increased oil consumption throughout these periods of the oil service interval.


To assist alleviate the problems related with soot loading in the oil, Betner suggests adopting the following steps:

  • Ascertain that the engine’s fueling system is in good working order and that the fuel injectors are not causing inappropriate fuel injection.
  • Provide operator training in both vehicle operation and engine warning system observation.
  • As needed, make sure the engine’s electronic system is calibrated and/or upgraded.

He also recommends using a reputable oil analysis program. A complete oil analysis program, such as the Citgo LubeAlert HD, will display the amount of soot, the viscosity of the oil, and the extent of engine wear.

According to Betner, knowing these characteristics allows equipment maintainers to acquire a better understanding of the oil state, the influence of oil change intervals, and the engine’s and filtration system’s total impact.

Regular preventative maintenance and the use of high-quality engine oils designed with the newest additive technologies for controlling the soot created in modern engines are two more steps in guaranteeing good engine performance. Be aware that when it comes to handling higher levels of soot, engine oil quality varies.

Citgo’s premium CITGARD heavy duty engine oils, for example, have a “quite aggressive” Soot Arrest Technology, according to Betner. Since the introduction of exhaust gas recirculated engines, this engine oil technology has been engineered to handle the many types of soot produced. These engines produce more difficult-to-disperse soot.

How do you stop black smoke from a diesel engine?

If you want to eliminate black smoke from your diesel engine, the first thing you should do is check the air filter and replace it if it’s unclean.

The presence of black smoke in the combustion chamber indicates that the fuel is only partially burnt. Water and CO2 are produced when a working diesel engine consumes the fuel. Black smoke indicates that something is stopping the fuel from completely burning, which is usually due to an unbalanced air-fuel ratio.

The air mixture entering the combustion chamber is the first place to look. The engine air filter, which may be clogged, is the most straightforward repair. The air-fuel ratio will run rich if there isn’t enough air getting to the engine, leaving unburned diesel fuel behind.

How do you control soot?

“When you look at satellite photographs of very polluted areas like China and India, you can see that there are no clouds.”

Carbon dioxide can linger in the atmosphere for 40 to 50 years, while carbon soot barely lasts a week or ten days before dissipating and has no long-term warming effect.

“Carbon dioxide is primarily a heat absorber, whereas soot is a solar absorber. Black carbon is now nearly a million times more effective than carbon dioxide at warming the air per unit mass. But, because soot, or black carbon in soot, is so potent and warming, and because it is so short-lived, it is crucial for global warming mitigation efforts.”

For example, the Arctic is warming faster than any other part of the globe. The white sea ice, which normally reflects sunlight and heat back into space, is giving way to darker open water, which absorbs heat more quickly and hence accelerates warming. According to current estimates, the Arctic might be ice-free in 30 years.

This tendency, according to Jacobson, can be reversed by reducing the amount of soot in the atmosphere. “You can also slow the melting of Arctic ice. As a result, it may be the only method to avoid or slow the Arctic’s extinction. Of course, this has ramifications not only for climate feedbacks, but also for animals like polar bears who rely on ice floes to exist.”

According to Jacobson, technology exists to solve the problem. Wood-burning cooking and heating systems, which are frequently used in developing countries, can be improved to burn cleaner. We can either stop using diesel altogether or transition to more efficient, low-emission diesel engines.

Other procedures can also aid in reducing the amount of soot discharged into the sky. “Particle traps can be installed on cars, off-road equipment, passenger vehicles, buses, and trucks. However, regulating CO2 and soot, which I believe we really want to achieve, necessitates significant changes to the energy system and transportation infrastructure.”

This would necessitate a switch to electric or hydrogen vehicles that are fueled by renewable energy. Soot levels in the atmosphere might be decreased by 90% in five to ten years, according to Jacobson, with concentrated national and international efforts.

Clean Air System

To properly burn the fuel, the internal combustion process necessitates the proper amount of air intake. If there isn’t enough air in the engine, the gasoline will only be partially burned, resulting in black smoke out the tailpipe. Fuel must be burned completely because it only emits CO2 and water, which do not produce black smoke. That’s why getting the right mix of fuel and air is crucial if you want to avoid black smoke. As a result, inspect your air cleaner system to determine whether it is dusty or blocked, as this could prevent air from entering your home. If your air cleaner system is unclean or clogged, it will need to be cleaned or replaced.

Use Common -Rail Fuel Injection System

The common rail fuel injection system, which is a high-pressure injection system supplying fuel directly to the solenoid valves, is used in the majority of new diesel-powered vehicles. It will be difficult for any emissions or black smoke to escape employing this high-tech injection technique. So, if you’re looking for a diesel vehicle, look for one that has common rail fuel injection. Then you won’t have to worry about black exhaust smoke any longer.

Use Fuel Additives

In the fuel injectors and cylinder chambers, combustion debris and deposits will progressively accumulate. Fuel efficiency and engine performance will be reduced as a result of the mixing of fuel and deposits, resulting in black smoke released from the exhaust pipe. Fortunately, you can remove these hazardous deposits by mixing diesel fuel with a detergent ingredient. After you do that, the black smoke will go away after a few days.

Get The Engine Rings Checked And Replaced If Damaged

Due to the fact that damaged piston rings might generate black exhaust smoke when accelerating, you should inspect them and replace them if necessary to eliminate black exhaust smoke.

Furthermore, it would be great if you repair your vehicle on a regular basis. If you’ve been driving for a long time, you should give your vehicle a break. When the engine has cooled down, resume your journey.

After reading this article, you should have a better understanding of what creates black smoke and how to get rid of it. If you have any questions about this issue, please leave them in the comments below and one of our car specialists will respond as soon as possible.

Is diesel soot bad for the environment?

The most common fuel used to move commodities across the United States is diesel. Diesel fuel is heavier and oilier than gasoline, and consumers found their automobiles covered with soot when it was first utilized in cars during the 1970s oil crisis. When diesel engines burn diesel fuel, they can generate a lot of nitrogen compounds and particulate matter. These elements combined to give diesel fuel a bad reputation in the environmental community, despite the fact that it emits less carbon monoxide, hydrocarbons, and carbon dioxide than gasoline.

Diesel fuel demand continues to climb, particularly in China, as the country’s construction needs grow. The European Union is also searching for ways to make diesel fuel more environmentally friendly by lowering overall particulate emissions per kilometer. Researchers have improved engine performance and made diesel fuel cleaner during the last three or four decades, making it more environmentally friendly.