What Is a Diesel Particulate Filter (DPF)?

A diesel particulate filter (DPF) is an exhaust treatment device used to remove small particles such as soot from diesel engine emissions. Learn what a diesel particulate filter does, how it works, and why it’s essential for regulatory compliance in trucking operations. 

Understanding DPF Systems

DPF systems include a ceramic filter unit with porous walls and a diesel oxidation catalyst (DOC) with a catalytic coating of rhodium, platinum, or palladium. The exhaust system forces smoke from fuel combustion through the filter, where soot, ash, and other particulates are filtered out and burned away. 

A pressure differential sensor monitors pressure on either side of the DPF to identify soot buildup. If soot starts to affect exhaust flow, the engine control unit (ECU) automatically initiates cleaning through active regeneration. The result is cleaner emissions consistent with regulatory requirements.

How a Diesel Particulate Filter Works

The DPF traps particulate matter like soot and ash. With prolonged use, particles accumulate in the DPF, increasing backpressure and reducing fuel efficiency. Regeneration is the process of eliminating the buildup on the filter when backpressure builds. Depending on the type of driving you do, your vehicle might use passive regeneration, active regeneration, or a combination of both. 

Soot Trapping

The DPF uses a ceramic filter with an internal honeycomb structure. Thousands of parallel channels run through the filter from end to end. These channels are open at one end to allow exhaust from the engine into the filter. They are closed at the other end, which forces the exhaust through the filter’s porous walls. Soot, ash, and other solid carbon particles get stuck in the filter, while the filtered gases continue through the exhaust system.

Passive Regeneration

Passive regeneration uses elevated temperatures generated by the engine during sustained highway travel to burn off soot and clear the filter. The precious metals coating the DOC reduce the soot’s ignition temperature, making it easier to passively burn off particulate matter during regular operation. 

Passive regeneration works best if you’re driving long distances at sustained highway speeds. For shorter runs or stop-and-go urban traffic, it can be hard to keep the exhaust temperature high enough for passive regeneration. If your ECU detects backflow due to soot buildup, it may initiate active regeneration to clear the DPF.

Active Regeneration 

With active regeneration, the ECU injects additional fuel after combustion in the engine or through a dedicated injector in the exhaust system. The fuel vaporizes instead of combusting and collects on the DOC, boosting catalytic surface temperatures. The extreme heat from the injected fuel incinerates the trapped soot, clearing the filter without manual intervention.

Active regeneration is best for local and regional hauls, where the engine does not operate at sustained temperatures high enough for passive regeneration.

The Importance of DPFs for Pollution Reduction

Diesel particulate filters are a critical tool for reducing particulate emissions, especially soot, in diesel exhaust. They trap over 90% of soot and other harmful particles, which reduces dangerous environmental pollution.

Regulatory standards for diesel emissions vary between states, and federal rules are also in flux. To keep your truck compliant across state lines, it’s best to incorporate pollution reduction measures like DPFs right away. Failure to meet emission standards during a cross-country drive could result in higher fines and other penalties. 

Common DPF Issues and How to Address Them

Although DPF filters self-regulate in many ways, you should watch for the following common issues. 

Clogged Filters

When there isn’t enough sustained driving for your DPF, the particulate filter can get clogged and prevent regeneration. You might notice that the engine doesn’t have as much power, and you’re using more fuel than you used to. A clogged filter and poor regeneration won’t allow air to move through the exhaust as efficiently, creating backflow that diminishes fuel efficiency.

You can usually correct this issue by driving at a sustained highway speed for about half an hour. This elevates the exhaust temperature enough to encourage passive regeneration and clear the filter. If this doesn’t work, deep-clean your DPF or have it professionally serviced to avoid more expensive long-term issues.

Faulty Sensors

If you notice your DPF light coming on frequently, even when driving at sustained speeds, you might have a damaged or defective temperature or exhaust gas recirculation (EGR) sensor. A faulty sensor can trigger active regeneration even when you don’t need it, wasting fuel and creating unnecessary wear on your system.

Regular maintenance checks can help you catch sensor faults before they affect your DPF system. If you think a sensor is damaged, have it repaired or replaced as soon as possible. 

Black Smoke

Black smoke typically arises when there is too much fuel and not enough airflow. It’s the visible sign of soot in your exhaust. You might see black smoke from your exhaust if your DPF is blocking airflow or triggering unnecessary fuel injection for active regeneration. 

Black smoke isn’t always a DPF issue. You might get it from soot buildup in other parts of the engine. It can also happen with a bad turbocharger, faulty fuel injector, damaged charge air cooler (CAC) hoses, or EGR valve disruption.

Wrong Oil Use

DPF vehicles need a different type of oil from traditional diesel vehicles. Make sure you’re using oils low in Sulphated Ash, Phosphorus, and Sulfur (SAPS). While SAPS oil is great for lubrication in standard vehicles, it leaves behind non-combustible ash that can clog up your DPF. The ash doesn’t oxidize or burn off like soot, so it continues to accumulate until your DPF is completely blocked.  

Using the wrong oil can cause serious damage to your DPF and your engine as a whole. Avoid these issues by using low-SAPS oil specifically rated for DPF vehicles. If you aren’t sure which oil to use, check your owner’s manual for manufacturer recommendations.

Get Expert Advice and Quality DPF Parts From Truck Pipes USA

Truck Pipes USA is a leading supplier of high-quality aftermarket exhaust components for the transportation industry. If you need a DPF system or other diesel exhaust parts, we are here to help. Shop DPF filters and components today or call to discuss your needs with a seasoned expert.