The CTS Diesel Particulate Filter (DPF) Knowledge Base contains a compilation of technical articles summarizing particulate filter operation, ash sources and accumulation in the filter, the manner in which ash affects filter performance, and the importance of diesel particulate filter cleaning and inspection.
The image above provides a close-up view of ash deposits coating the walls of the DPF cells and completely plugging many of the filter channels. Image was obtained from a DPF cross-section analyzed at CTS’ Boston Innovation Office.
CTS Diesel Particulate Filter (DPF) Knowledge Base Technical Articles:
Basics of Diesel Particulate Filter Operation
Diesel particulate filters operate by trapping soot particles from the engine exhaust, preventing them from reaching the environment. Unlike a catalytic converter which is designed to reduce gas-phase emissions flowing through the catalyst, the particulate filter is designed to trap and retain the solid particles until the particles can be oxidized or burned in the DPF itself. READ MORE
Understanding the Differences Between Ash and Soot
Ash and soot are fundamentally different materials, but both accumulate in the DPF. Removing each of these materials from the DPF requires completely different processes. Soot is normally removed from the DPF through regeneration on the vehicle, which burns off the soot, leaving the incombustible ash behind. Ash, on the other hand, by definition is incombustible and must be cleaned from the DPF. READ MORE
Ash Sources and Chemical Composition
For most DPFs in on-highway applications with a properly functioning engine, there is only one major source of ash – engine lubricant oil. Specifically, it is only certain additives in the oil that contribute to ash in the DPF. Other sources of ash, which contribute to a lesser extent, include certain elements in the fuel, engine wear metals, exhaust system corrosion products, and ambient sources. READ MORE
Ash Accumulation and Distribution in Diesel Particulate Filters
Ash accumulation occurs in the DPF over thousands of hours and tens of thousands of miles. The ash may lodge in the filter pores, form a layer along the filter surface, or pack in plugs toward the back of the filter channels. In some cases, ash bridging may also occur where ash blockages form near the middle of the filter, effectively blocking flow through the remainder of the channel. The location of these deposits plays an important role in determining the best method of DPF cleaning to remove the ash. READ MORE
Factors Impacting Ash Properties and Ease of Ash Removal
Due to the long time ash spends in the DPF between filter cleanings, the ash properties and the manner in which the ash deposits are formed in the filter are affected by a number of factors. The primary factors impacting the nature of the ash include: lubricant chemistry, exhaust temperature and flow conditions, and DPF regeneration processes, which vary significantly for different vehicles and applications. READ MORE
Ash Impact on Filter and Engine Performance
Ash build-up is the primary reason for premature DPF failure and is the most important factor controlling the service life of the filter. Ash accumulation restricts exhaust flow, increasing back pressure, and making it harder for the engine to breathe. This negatively impacts fuel economy. In addition, the ash occupies some of the filter volume, reducing the filtration area for soot, which results in more frequent regenerations and additional fuel consumed, as well as thermal aging of the DPF. READ MORE
DPF Ash Cleaning Processes and Filter Cleaning Intervals
A number of ash cleaning systems exist, with the most common being pneumatic, utilizing reverse flow of air through the DPF to blow out the accumulated material. The frequency of filter cleaning is generally specified by the engine or equipment manufacturer based on pre-determined maintenance intervals. The actual frequency of DPF ash cleaning will depend on many factors, including the effectiveness of previous cleanings (i.e. residual ash), engine oil consumption, and the vehicle drive cycle. READ MORE
Ash Handling and Disposal
Ash contains a complex mixture of engine lubricant additives, wear metals, and many other non-combustible materials that have made their way through the engine and exhaust system. In many cases, ash, once freed from the DPF, may exists as a loose powder. Care must be exercised when handling loose ash powders, and handling and disposal of the ash and aftertreatment system components which have reached the end of their useful life must follow all local, state, and federal guidelines. READ MORE