What is a Diesel Particulate Filter?

Mary McMahon

A diesel particulate filter is a device used to filter out harmful substances in diesel exhaust before venting the exhaust to the environment. Such devices can be fitted on trucks, buses, and other vehicles along with stationary diesel engines to comply with air quality mandates or to address more general concerns about air quality. Use of such filters is not mandated by law in most regions, but often, air quality standards necessitate their use, as it may be impossible to run a diesel engine cleanly enough to meet standards without using a filter.

Some diesel vehicles feature a diesel particulate filter.
Some diesel vehicles feature a diesel particulate filter.

On an engine equipped with a diesel particulate filter, exhaust gases are passed through the filter before being vented. The filter traps particulates like soot along with unburned hydrocarbons and gases like nitrogen oxides. Filter efficiency varies, depending on design, but can be very high in some filters, making an engine burn much more cleanly and reducing the overall amount of pollution in the air, especially when filters are used on entire fleets of engines and vehicles, like municipal buses.

Inhaling diesel exhaust fumes may cause breathing difficulties.
Inhaling diesel exhaust fumes may cause breathing difficulties.

Sometimes, a diesel particulate filter is designed to simply be replaced when it clogs, as will happen over time with the deposition of layers of trapped particulates. Other filters are self cleaning, using tools like a catalyst or incineration of the components to break them down into less harmful byproducts. Other diesel particulate filters must be cleaned by the operator, requiring periodic removal and servicing.

Companies that design diesel engines also develop diesel particulate filter products designed to work with their engines and associated components. It is also possible to purchase third party products for diesel exhaust filtration although using such products may void an equipment warranty, and it is important to select products designed to work safely and effectively with a given piece of equipment. Installation and maintenance can be performed by technicians or the operator, depending on the level of complexity involved and the operator's comfort level with mechanical work.

The diesel particulate filter is one among a range of products designed to address concerns about engine emissions. Designing engines to burn more cleanly involves a cooperative effort from a number of different perspectives to address different sources of pollution. Even the best designs cannot compensate for poor maintenance and it is critical to maintain diesel engines as recommended to keep them as safe and efficient as possible. For engines used in commercial applications, maintenance logs may be required for health and safety reasons.

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