Diesel Particulate Filters (DPFs) play an important role in diesel engines. They’re designed to trap and store particulate matter (soot) that is produced by the diesel engine during driving. The DPF allows exhaust gases with particulate material to enter the DPF where the soot is trapped inside the filter, allowing cleaner exhaust gases to exit into the atmosphere, which then reduces the exhaust emissions from the engine.
I love clean air. I appreciate the way it smells after rain, especially out in the countryside. On the other hand, the smell of exhaust fumes is sickening and potentially deadly. We have all probably seen a vehicle blowing black smoke as it accelerates. If it happened to be a semi-truck, we would see the smoke roll, then stop when the driver shifts gears, to then roll again. Whether the engine is gas or diesel, air pollution has drastically driven major changes in the transportation industry over the last 60 years.
In the 1960s, there was a substantial smog problem in Los Angeles, California. In response to this, the US enacted the first automobile emission standards in 1963. It wasn’t long until other nations followed in similar footsteps. Japan enacted their first emission rules three years later and, between 1970 and 1972, several European nations followed suit.
As a result of California’s emission laws, the Positive Crankcase Ventilation (PCV) valve was the first component created to help reduce emissions in 1961. In a nutshell, it removes gasses called blow-by from the crankcase.
Fast forward to the 2000s, the DPF first appeared on Mercedes-Benz® sold in California. By the late 2000s, they were becoming common on both passenger cars and commercial trucks around the world.
DPF’S LIFE CYCLE
A DPF should typically last for around 100,000 miles before needing to be replaced. The DPF’s level of maintenance will have a big impact on how much this figure varies. While a well-maintained DPF may even go 150,000 miles before needing to be replaced, a badly kept DPF may last a much shorter time. To help extend the life and maintain performance of a DPF, a process known as DPF regeneration can be used to clean the filter and restore its performance.
DPF regeneration refers to the procedure of cleaning and emptying the DPF of soot that is created by the process of combustion. Burning off the soot particles requires heating the diesel particulate filter to a very high temperature. Active regeneration and passive regeneration are two methods that can be used to accomplish this.
There are several factors that can affect the effectiveness of DPF regeneration:
- The make of engine
- The type of DPF
- The driving conditions the vehicle has been put through
For example, engines that are used primarily for short trips or in stop-and-go traffic may require more frequent regeneration to prevent the DPF from becoming clogged. Moreover, certain DPF systems are more likely than others to clog, meaning they may need more frequent maintenance.
Passive DPF regeneration occurs naturally during normal driving conditions when the temperature of the exhaust gas is high enough to burn off the particulate matter. However, this process is not always effective, especially for vehicles that are used for short trips or in cold weather conditions.
Active DPF regeneration is a more controlled process that is initiated by the engine control unit (ECU) when the DPF reaches a certain level of saturation. The ECU uses various sensors to monitor the exhaust gas temperature, pressure, and flow rate to determine when active regeneration is necessary. When the DPF is ready for regeneration, the ECU injects additional fuel into the engine to increase the temperature of the exhaust gas and initiate the cleaning process.
During active regeneration, the temperature of the exhaust gas must reach a certain level to burn off the soot. This temperature is typically around 1100 to 1300 degrees, which is much higher than the normal operating temperature of the engine. To achieve this, the engine may run in a high-idle mode or the vehicle may be driven at higher speeds for a period of time to increase the temperature of the exhaust gas.
Manual regeneration is often required when vehicles are driven at insufficient speed to allow regeneration to be carried out automatically by their engine management control software. The vehicle is already suffering with drivability and lack of power problems. At this point, as long as the DPF is not severely blocked (over 90% filled), a scan tool can be used to perform a static or (up to 60% filled) dynamic regeneration to clear the soot levels in the DPF.
How to perform manual DPF regeneration:
- Connect the scan tool to the vehicle’s diagnostic port and follow the manufacturer’s instructions for accessing the DPF regeneration function
- Ensure that the engine is fully warmed up and that the DPF is not excessively clogged. The scan tool may provide diagnostic information on the DPF’s condition
- Follow the prompts on the scan tool to initiate the manual regeneration process. This typically involves commanding the engine to run at a higher temperature to burn off the accumulated soot
- Perform a test drive and confirm that the DPF warning light is no longer illuminated
- Some OEMs require a special function “Replace or Reset DPF” after the replacement of the filter
DPF regeneration is a critical procedure that lowers harmful emissions while maintaining the performance of diesel engines. While active regeneration is a more controlled process that’s started by the engine control unit, passive regeneration happens naturally while driving normally. To make sure the DPF keeps working well over time, proper maintenance is required, which could involve performing a manual DPF regeneration or replacing the DPF filter entirely.
ABOUT THE AUTHOR
Keith Wray has over 45 years of experience in the automotive industry as a technician/automotive machinist and service manager for an OEM dealership. He currently serves as the national training manager for Snap-on Diagnostics, where he co-develops training materials and conducts technical courses for franchisees, employees, end-users, and vocational students. For more, visit www.snapon.com/diagnostics.