How Diesel Emission Aftertreatment Works

By: Rob

Video Transcript


Hi. I’m Rob Melanson. I’m the field trainer here at Parts for Trucks. And today we’re going to be talking about aftertreatment systems.

So what is exhaust aftertreatment? This system is very similar to the catalytic converter which have been on our vehicles for decades, and they are both designed to reduce harmful emissions. Our vehicles produce hydrocarbons and carbon monoxide, which are both contributors to global warming, providing our system is properly working,
these pollutants are converted to harmless nitrogen and water vapor, so where do we start? The first component in the system is the DOC. Just like the catalytic converters, the DOC uses precious metals to create a chemical reaction. This removes most of the hydrocarbons and carbon monoxide from the exhaust. Next in line would be the DPF. This is one area that does not resemble our converter system.

The filters in the system are designed to trap any un-burnt fuel in the form of soot. These wall flow filters store the soot until they are full.

So how does the regen process work? The system monitors the inlet and outlet pressures to determine the amount of soot or restriction through the filter. When a determined value has been reached, this triggers a burn or regen by injecting diesel fuel into the exhaust.

Before the DOC. This condensing of the soot particles allows the filters to continue collecting more soot until they fill up again. The last component is the SCR. When we perform a region or burn and create those high temperatures to reduce the soot and ash, we actually create a lot more NOx. To combat this, we inject the DEF into the exhaust stream.
The two mix and enter the SCR, where another chemical reaction occurs, reducing the level of NOx down to nitrogen and water vapor. Thanks for watching. If you’d like to learn more, visit us at or any of our locations.