Cleaner diesel 38 Understanding DPF and SCR systems: A practical guide for modern workshops As emissions regulations continue to tighten, modern diesel vehicles rely heavily on advanced exhaust aftertreatment technologies. Two systems in particular: Diesel Particulate Filters (DPFs) and Selective Catalytic Reduction (SCR) are now standard across the majority of Euro 6 applications, as Denso explains. For workshops, understanding how Diesel Particulate Filters (DPFs) and Selective Catalytic Reduction (SCR) interact, and how they are influenced by upstream engine components, is essential for accurate diagnostics and successful repairs. DPF: More than just a filter The DPF is designed to trap soot particles generated during combustion, preventing them from entering the atmosphere. However, this is only part of the story. A DPF can only function effectively if the combustion process upstream is controlled and optimised. Factors such as injection timing, fuel atomisation and combustion efficiency all directly influence soot production. Modern common rail systems, including injectors and pumps, play a crucial role here. Precision fuel delivery ensures cleaner combustion, reducing the load on the DPF and extending its service life. Poor injector performance, by contrast, can lead to excessive soot build-up and repeated DPF issues. Regeneration, whether passive or active, is critical to maintaining filter performance. However, repeated failed regenerations often point to underlying engine or sensor-related faults rather than a problem with the filter itself. SCR: Precision control of NOx While the DPF addresses particulate matter, SCR systems are responsible for reducing nitrogen oxide (NOx) emissions. This is achieved through the injection of Diesel Exhaust Fluid (AdBlue) into the exhaust stream, where it reacts within the catalyst. SCR systems rely heavily on accurate
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