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Understanding Diesel Particulate Filters

Diesel engines offer an unmatched combination of power and fuel economy, and that makes diesel-powered trucks the most popular choice for heavy duty hauling. However, unregulated diesel combustion can contribute to poor air quality and create other environmental concerns.

As a result, diesel engine manufacturers have created innovations over the years in an effort to reduce harmful emissions. One such innovation is the diesel particulate filter, a device that has made profound reductions in diesel-caused pollution.

Below is more information about diesel particulate filters, including how they work, as well as what drivers should know about their care and maintenance.

Why Diesel Particulate Filters Are Necessary

When diesel is burned inside an engine, it produces several gaseous byproducts, including carbon dioxide, water vapor, nitrogen, and carbon monoxide. Solid byproducts are also produced, including unburned hydrocarbons, which are also known as soot.

Soot consists of fine, black particles and can cause serious long-term health problems in humans, including lung cancer, heart disease and asthma. In addition, soot poses an ecological threat, since its production is also associated with acid rain.

At one time, soot was not regulated as a pollutant, but stricter environmental laws and regulations now mandate its control. Diesel particulate filters are a means of reducing soot output and make compliance with regulations easily attainable.

How Diesel Particulate Filters Work

Diesel particulate filters capture soot, but they are capable of doing much more than simply trapping unburned hydrocarbons. In addition to catching soot, a diesel particulate filter initiates a chemical reaction that changes soot into harmless gases. These gases include carbon dioxide, water vapor and oxygen.

A diesel particulate filter lies within the engine exhaust stream and consists of a metal canister filled with a filter media. The media type can vary, depending on the specific application, but most trucks are equipped with ceramic filter media.

The ceramic media are filled with tiny holes and passageways that permit exhaust to enter and pass; however, the media will not allow soot to pass through, and the tiny particles become lodged within the filter as a result.

If the ceramic media become clogged with soot, the exhaust will no longer be able to pass through, and engine performance will suffer as a result. The key to preventing this from occurring is regeneration, a process that permits the filter to be used for lengthy periods of time before replacement is needed. 

Understanding Filter Regeneration

Regeneration occurs whenever soot is heated to a sufficiently hot temperature, and the hydrocarbons are consumed in the ensuing reaction. The soot essentially "disappears into thin air" and leaves room for new particles to be trapped.

While soot is burned via regeneration, ash, which is a non-combustible byproduct of oil combustion, is retained inside diesel particulate filters. Ash must be manually removed by disassembling the filter on a periodic basis.

For the truck driver, regeneration is either an active or passive process, depending on the type of engine and diesel particulate filter in use. Drivers should have a firm grasp of the process and know their specific responsibilities; otherwise, there is a real risk of damage being caused to the engine.

If regeneration is passive, or automatic, then drivers serve more of an oversight role than anything. They monitor regeneration to ensure the process proceeds well and only intervene if regeneration fails due to insufficient operating speed or other inhibiting factors.

With active regeneration, the driver will be involved as an active participant in regeneration. That means the truck may need to be parked, for example, and the driver will need to send a command to the engine to begin regeneration. As such, there is a heightened need for drivers to be more alert and trained in their duties, if active regeneration is used.