A deep dive into DPFs
European Exhaust and Catalyst Technical Trainer, Stuart Still, provides an educational piece on the diesel particulate filter (DPF), its continued role in the aftermarket and why and how they fail.
As governments tighten the reins on vehicle emissions, MOT emissions testing is becoming increasingly rigorous too. The push to reduce harmful pollutants means stricter limits on what can come out of a vehicle’s exhaust; for example, modern Euro 6 diesel emissions systems require exhaust gases to journey through a series of four sophisticated filters and catalysts, including an oxidation catalyst, DPF, diffuser and selective catalytic reduction (SCR).
DPFs are the unsung heroes of modern diesel engines, designed to trap and dispose of sooty particles – formally known as particulate matter. Think of them as high-tech sieves, catching harmful particles before they can escape into the atmosphere.
Under ideal combustion conditions, a diesel engine would emit only carbon dioxide, water and nitrogen – but real world conditions are far from perfect! The incomplete combustion of diesel results in a cocktail of emissions, comprising nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC) and particulate matter laden with soot, ash and even traces of engine oil debris.
Particulate matter falls into two categories – particles between 2.5 and 10 microns and sub-2.5 micron particles. Shockingly, over 99% of diesel particulates are smaller than 2.5 microns – tiny but incredibly dangerous.
These particles are carcinogenic, posing severe health risks. Fortunately, wall-flow DPFs can capture at least 85% of these harmful particles, with some systems achieving nearly 100% efficiency under highload conditions.
A DPF is a marvel of engineering, but it’s not invincible. Excessive particulate matter production usually points to upstream issues:
- Faulty fuel injectors
- Malfunctioning glow plugs
- Contaminated or incorrect oil
- A clogged air filter
- Problems with turbos or EGR valves
Routine maintenance is key. Using high-quality fuel additives – like our 6-in-1 – can prevent carbon buildup, protect components and assist with DPF regeneration.
Signs of trouble…
If a DPF warning light illuminates, it shouldn’t be ignored. A professional should check the engine oil for diesel contamination. Neglecting the issue could lead to costly repairs, including a DPF or turbocharger replacement – did you know that 90% of turbo failures are linked to oil issues and a failed turbo can damage your DPF?
How DPF regeneration works
DPFs don’t just trap particulate matter, they also clean themselves through a process called regeneration. When levels reach about 60%, the ECU initiates regeneration, injecting additional fuel to heat the DPF to over 550°C. This burns off the accumulated particulate matter; however, regeneration is unlikely to occur if the vehicle is experiencing certain symptoms (see table below).
To ensure proper regeneration, a technician should inspect pressure pipes for damage or debris, verify the EGR system is functioning correctly, use the manufacturer-recommended engine oil, check for diesel contamination in the engine oil, ensure the active system fuel additive is sufficient, and ensure the fuel vaporiser is working correctly. If a DPF fills beyond 90% capacity – or 45g of particulate matter – it may be irreparable.
DPFs and the law
Tampering with a DPF is a big no-no. Under MOT regulations, a modified or removed DPF is an automatic failure. Worse yet, it could invalidate motor insurance under the Road Vehicles (Construction & Use) Regulations 61A(3).
At EEC, we’re committed to helping your workshop customers tackle emission challenges. With a growing range of high-quality DPFs and an in- house wash-coating facility in Denmead, we prioritise excellence for both domestic and export markets. Our education and training seminars provide industry professionals with the confidence and ability to handle these issues confidently.
