Importance of DPF and DOC Cleaning
Did you know that aftertreatment systems, designed to eliminate pollutants from truck exhaust, were not introduced to diesel trucks until 2007? While diesel engines are known for their efficiency and power, they unfortunately emit harmful pollutants such as particulate matter (PM), carbon monoxide, hydrocarbons, and nitrogen oxides (NOx). These pollutants can pose risks to both humans and the environment.
To mitigate diesel emissions, trucks manufactured post-2007 are equipped with an aftertreatment system consisting of a diesel particulate filter (DPF) and a diesel oxidation catalyst (DOC). These components function by trapping pollutants and removing them from the exhaust system.
Since the aftertreatment system retains these pollutants, the DPF and DOC may become obstructed or rendered ineffective over time, necessitating periodic cleaning to prevent complications. We'll guide you through how the DPF and DOC operate and the proper methods for cleaning them to extend their lifespan.
What do the DPF and DOC do for the Truck?
The DOC and DPF in an engine's exhaust system collaborate to prevent harmful diesel particulate matter (PM) and gases from escaping into the environment. Their joint efforts not only enhance fuel efficiency, but also ensure compliance with emissions standards set by the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB).
Diesel Oxidation Catalyst
Initially, the exhaust flows through the DOC, where a chemical reaction occurs, breaking down harmful pollutants. Precious metals like platinum, palladium, and rhodium, which are coated on a ceramic honeycomb structure, facilitate the catalytic reaction that converts carbon monoxide and hydrocarbons into carbon dioxide and water.
DOCs that are verified by the EPA and CARB typically reduce PM by 20–40%, hydrocarbons by 40–75%, and carbon monoxide by 10–60%. Next, the exhaust gases continue through the DPF, which captures and oxidizes soot and remaining particulates, transforming them into ash. DPFs consist of a honeycomb structure with microscopic pores that effectively trap and retain PM and ash, thus purifying the exhaust and decreasing emissions.
Diesel Particulate Filter
Verified DPFs generally reduce particulate matter emissions by 85–90%, while also lowering hydrocarbon and carbon monoxide emissions by 70–90%. However, it is important to note that the accumulation of debris over time can lead to clogged pores in the DPF. Additionally, the precious metal coating in the DOC may become contaminated or degraded, resulting in malfunctions.
The Importance of cleaning the DPF and DOC
A clogged DPF or malfunctioning DOC can cause engine issues, reduced fuel efficiency, and increased emission levels of harmful pollutants. Therefore, adhering to the manufacturer's maintenance schedule and cleaning or replacing the DPF or DOC when necessary is crucial to ensure proper functionality and prevent future problems.
Ultimately, regular cleaning of both the DPF and DOC is beneficial as it prolongs the engine's lifespan and optimizes its performance.
On-Truck DPF Regeneration
To remove trapped soot from the Diesel Particulate Filter (DPF), a built-in cleaning process in diesel engines called DPF regeneration is used. DPF regeneration burns off accumulated soot and ash at high temperatures, preventing clogging of the DPF. The effectiveness of DPF regeneration depends on various factors like the engine make, DPF type, and driving conditions. There are three types of regeneration: passive, active, and manual.
What is Passive Regeneration?
Passive regeneration occurs naturally during driving, without requiring the driver to initiate the cleaning process. For successful passive regeneration, the vehicle must be driven at speeds of 70 mph or above for at least 45 minutes, enabling exhaust gases to reach temperatures greater than 350°C (662°F) to burn off the soot and ash.
In cases where passive regeneration is not possible due to low temperatures, active regeneration is necessary. Active regeneration is a controlled cleaning process initiated automatically by the vehicle's Engine Control Unit (ECU) when the filter reaches a certain soot capacity. The ECU triggers post-combustion fuel injection, raising exhaust temperatures to approximately 550–650°C (1,000–1,200°F) to burn off trapped soot and ash.
What is Manual Regeneration?
Manual regeneration requires driver intervention when the DPF becomes clogged and cannot self-clean, indicated by a DPF warning light on the dashboard. In such cases, the driver should park the vehicle and initiate manual regeneration. This process increases engine RPM and injects additional fuel to generate the necessary regeneration temperatures, typically taking about 30 minutes.
Importance of Professional DPF and DOC Cleaning
Regrettably, the process of on-truck regeneration does not completely eliminate all substances from the DPF. To completely remove noncombustible materials and ash, periodic removal of the filter from the engine is necessary. Additionally, when the DPF is taken out for cleaning, it is important to inspect and clean the DOC as well.
It is not advisable to attempt cleaning the DPF or DOC independently, as it could result in damage that requires complete replacement of the parts. Skilled technicians can effectively and safely clean both DPFs and DOCs using specialized cleaning devices, ensuring proper airflow and compliance with EPA standards. Generally, truck repair shops employ three cleaning methods to properly restore and clean DPFs and DOCs: air, thermal, and aqueous.
Pneumatic Air Cleaning – In certain cases, compressed air is used exclusively to clean the DPF. This process loosens and expels contaminants from the filter.
Thermal Cleaning – Air cleaning alone is often insufficient, requiring the application of heat to eliminate contaminants. The DPF is heated to high temperatures (typically 500–600°C or 932–1,112°F) in a specialized oven device to evaporate and oxidize accumulated soot and PM. Thermal cleaning generally takes about a day, including heating and cooling periods.
Aqueous Cleaning – This method involves utilizing a non-destructive cleaning solution that envelops ash particles, facilitating their removal from the pores of the DPF. The DPF is subsequently dried in a specialized drying cabinet and can be reinstalled within approximately two hours.
How often should I have my DFP and DOC Cleaned?
Most diesel vehicles are equipped with an onboard filter service monitor that provides indications about the condition of the filter. This monitor can help determine when it's necessary to clean the filter. Most engine Original Equipment Manufacturers (OEMs) recommend cleaning the Diesel Particulate Filter (DPF) every 120,000 to 200,000 miles or every six to twelve months. Retrofit DPFs may require more frequent cleanings every 60,000 miles. Regular cleaning is crucial to prevent the accumulation of hardened soot and ash, which can be challenging to remove. Neglecting regular cleanings can lead to the need for filter replacement.
The frequency of DPF and Diesel Oxidation Catalyst (DOC) cleanings depends on the truck's vocation and application. Trucks primarily used for highway driving and carrying heavy loads, allowing for passive regeneration, can have longer intervals between cleanings compared to trucks used for applications that involve frequent starting, stopping, or off-road work.
If you notice issues like increased frequency of regeneration cycles, decreased engine performance, strong exhaust odors, reduced efficiency, or activated cooling fans, these may indicate a clogged DPF that requires professional cleaning.
How long does a DPF and DOC Last In A Truck?
A well-maintained and clean, or new Diesel Particulate Filter (DPF) and Diesel Oxidation Catalyst (DOC) can typically remain effective for around five to 10 years, or 10,000 or more hours of operation. However, engine problems related to fuel control or oil consumption can significantly reduce performance and necessitate the earlier replacement of these components. In fact, about 80% of DOC and DPF failures occur prematurely due to engine-related issues. On the other hand, since DOCs do not have any moving parts, they generally have a longer lifecycle if properly maintained and cleaned.
When the time does come to replace a DPF, the cost usually ranges from $5,000 to $15,000 or more, depending on factors such as engine size, filter technology, and installation requirements. Meanwhile, the cost of DOC replacement generally falls between $600 and $2,000.
Time for a DPF Cleaning?
Westrux has 4 convenient dealership service locations serving customers throughout the Southern California region. Contact our Santa Fe Springs, Fontana, Colton or Montebello service teams today to schedule your DPF and DOC cleaning!