How to Maintain Diesel Particulate Filters

As the beating heart of every machine, the engine and all of its components require proper care to prevent costly downtime. The aftertreatment system plays a critical role in optimizing the performance of the engine, but it often doesn’t get the attention it deserves. In particular, equipment owners should understand the importance of diesel particulate filters (DPFs) and their service lives.

The main function of the DPF is to trap soot and ash from exhaust fumes, which is critical for reducing emissions and ensuring compliance with regulatory standards.

DPFs collect and filter out two different particulates: soot and ash. Soot is generated by the incomplete combustion of diesel fuel, which is typical in normally operating diesel engines.

Through a process called regeneration, soot that has accumulated in the DPF’s ceramic substrate is heated and converted into carbon dioxide gas, which flows through the DPF and exits through the exhaust stack.

Residue left behind after regeneration is ash, which consists of metallic compounds originating from a number of sources: lubricant additives, trace elements in diesel fuel, and by-products of engine wear and corrosion.

Although soot can be oxidized and removed as a gas during regeneration, ash does not combust and becomes trapped in the walls of the DPF substrate. As it accumulates, the ash tends to harden, limiting the collection of soot to only a portion of the filter channels. An obstructed DPF can also restrict exhaust flow and increase backpressure, which degrades engine performance and increases fuel consumption.

Operators may note some warning signs when the DPF begins to fail. A DPF alert may light up on the instrument panel, and they may detect noises, vibrations and reduced engine performance. Other more subtle signs of failure can include frequent regenerations and increases in fuel consumption.

How to preserve optimal functioning of DPFs

First, it’s imperative that equipment owners follow the specific oil and fuel recommendations from the manufacturer. Low-ash engine oil is recommended for most engines meeting Tier 4-F and Tier 4-I emission standards.

Leading engine manufacturers follow robust formulation and testing processes to make sure their approved lubricants excel in every way, including oxidation control, soot handling, deposit prevention, low-temperature pumpability, cleanliness, and shear stability, among others. The American Petroleum Institute (API) sets standards for engine oil performance, and oils for engines with DPF systems should be clearly labeled as meeting or exceeding API’s CK-4 criteria.

Beyond the engine oil service, DPFs have standard maintenance service intervals specified by the manufacturer as well. This means the DPF should be removed, inspected, cleaned, reinstalled, and tested by a trained service professional.  

During this service, technicians note that the DPF will almost always be black with accumulated soot at the inlet, but a properly functioning filter has a clean, smooth surface at the outlet with no indication of soot tracking or any other build up. If otherwise, then the DPF may be damaged and need to be replaced.

When considering the maintenance intervals for your DPF, it’s critical to factor engine idle time into this equation. An idling engine passes more oil past the piston rings than it does at normal operating speeds, which accelerates the deposit of ash downstream in the DPF and can significantly decrease service intervals.