Why is a new diesel engine smoking?

When a car in front of you on the highway suddenly starts spewing gray-white smoke from its exhaust pipe, the first thought that comes to mind is usually that the engine is failing. This is also often the case with diesel vehicles — which is exactly what we're talking about here. However, there is likely no reason to panic — and here's why.

Diesel exhaust gases contain large carbon particles, also known as soot. It is the soot that gives the exhaust its black color — on old diesel trucks from the last century, this was always noticeable. In addition to the smell, such exhaust was dangerous due to its carcinogenic nature — this has been taken seriously for some time now. In the early 2000s, the first diesel particulate filters were introduced, capable of capturing up to 90% of harmful particles.

Typically, a layer of catalyst is applied to the walls of the channels of these filters, which provides oxidation of hydrocarbons. However, it is clear that the efficiency of any filter is limited over time. Soot settling inside it impairs the flow of exhaust gases, which is monitored by special sensors linked to the engine control unit. Filters become clogged with soot quite quickly — they cannot last for more than a thousand kilometers. This is precisely why another mode was invented — regeneration. It can be passive or active. In both cases, the soot is oxidized and exits the filter harmlessly.

Passive regeneration occurs during intensive driving on the highway. The particulate filter is burned out by the high temperature of the exhaust, but the smoke from the pipe is almost imperceptible as it quickly dissipates. Soot particles react with nitrogen dioxide to become carbon dioxide gas. However, during city driving, that is, when there is little load on the engine, the temperature for passive regeneration is too low. The destruction of particles becomes impossible, and soot accumulates in the filter.

During active regeneration of the exhaust gas cleaning system in diesel cars, the electronic control unit sharply increases the supply of diesel fuel. This leads to a rise in temperature, a flash of soot in the exhaust system, and the appearance of a gray-white cloud of smoke. To maintain the burning of the soot, the electronics increase the idle speed, allowing the engine to pass more air. When the temperature reaches around 600-650°C, the soot particles are burned, resulting in the release of carbon dioxide gas.

Usually, active regeneration of the system occurs every 1000 kilometers. If the car rarely travels on country roads and passive regeneration is insufficient, the process can take several tens of minutes. It is important not to interrupt this process and even continue driving after it is completed to avoid possible problems when parking.

Some factors can affect the activation of the regeneration system. If it is cold outside or the trips are short, it is desirable to go on the autobahn to increase the duration of the trip and raise the temperature of the exhaust gas. This will help start the regeneration system.

If white-gray clouds of smoke appear behind your car, there is no need to panic and turn off the engine. This is a normal process, and if the car is smoking, it means it is being cleaned. However, black smoke or smoke when idling may be a cause for concern and indicate that the engine needs to be diagnosed.

In conclusion, it is important for all novice diesel drivers to remember the proper functioning of the exhaust gas cleaning system and the ability to recognize different types of smoke. This will help keep the car in good condition and avoid serious problems.

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Author`s name Pavel Morozov