DPF – to clean, or not to clean

Majority of drivers already are familiar with the term DPF ( Diesel Particulate Filter). Most of the time it is associated with costly and not pleasant experience: vehicle went to local mechanic, who offered take it to the dealer or “knock it out and forget about it”. As you know roughly now that this part is “completely not required for your car”, lets see why manufacturers designing such systems and governments implementing more and more low emission requirements for new diesel cars.
A diesel particulate filter (DPF) is a device fitted to a diesel vehicle which filters particulate matter (PM) from exhaust gases. It does this by trapping solid particles while letting gaseous components escape. This type of filter has been in use for over 20 years, and many variants exist. These filters enable reductions in emissions which help meet European emission standards, improving air quality and thereby health standards.

What is PM

PM is made up of a complex mixture of solid and liquid particles, including carbon, complex organic chemicals, sulphate, nitrates, ammonium, sodium chloride, mineral dust, water and a series of metals, which is suspended in the air. PM10 refers to particles with a diameter smaller than 10μm and PM2.5 to particles with a diameter smaller than 2.5μm. They may be produced directly from a source such as an engine – or formed from reactions between other pollutants (e.g. NO2, SO2, NH3) in the air (secondary PM)

Legal requirements and the MoT test

From February 2014 the inspection of the exhaust system carried out during the MoT test will include a check for the presence of a DPF. A missing DPF, where one was fitted when the vehicle was built, will result in an MoT failure. A vehicle might still pass the MoT visible smoke emissions test, which is primarily intended to identify vehicles that are in a very poor state of repair, whilst emitting illegal and harmful levels of fine exhaust particulate. It is an offence under the Road vehicles (Construction and Use) Regulations (Regulation 61a(3))1 to use a vehicle which has been modified in such a way that it no longer complies with the air pollutant emissions standards it was designed to meet. Removal of a DPF will almost invariably contravene these requirements, making the vehicle illegal for road use. The potential penalties for failing to comply with Regulation 61a are fines of up to £1,000 for a car or £2,500 for a light goods vehicle.

Social Implications

Air pollution causes an estimated 29,000 early deaths in the UK, and has annual health costs of roughly £15 billion. The health effects of PM are more significant than those of other air pollutants. Chronic exposure contributes to the risk of developing cardiovascular diseases and lung cancer. Current evidence suggests that there is no “safe” limit for exposure to fine particulate matter. The Report of the Committee on the Medical Effects of Air Pollutants (COMEAP) from 2008 concluded that, although there had been improvements in pollutant levels, the average reduction in life expectancy as a result of airborne particulate matter across the population was 6 months3
Furthermore, PM has negative environmental impacts. It comprises nitrates, sulphates and ammonium which are the main drivers for acidification and eutrophication – two extremely damaging processes to natural ecosystems, which can cause habitat loss and affect biodiversity. PM also contains black carbon, a known contributor to global warming. DPFs are essential in reducing current PM emissions in order to prevent these processes occurring.diesel-particulate-filter-pollution

What can be done regarding DPF once it’s flagged as faulty.

If your vehicle developed DPF related fault, it needs to be booked to the workshop to be checked and repaired ASAP as continues driving even with limited power will negatively affect diesel particulate filter and more expensive treatment will be required. A special test is required to complete components condition evaluation. Then based on results, mileage and new components costs most effective solution is offered to vehicle owner.

DPF system related faults

like intermittent faulty operation of DPF back pressure measuring sensor due to fault in pipe connections, wiring connector or sensor it self. With faulty sensor if addressed on time, DPF normally does not need any treatment after fault elimination and memory reset.

Active DPF regeneration

procedure that is normally programmed in engines control module as option to trigger and complete regeneration by vehicle technician. Usually can be applied to cars and vans that failed multiple regeneration attempts due to required parameters not met like not being driven long enough at stable speed at right engine temperature with minimum required amount of fuel in tank. Required conditions for active regeneration do differ from one manufacturer to another but vehicle steady speed, engine temperature and fuel amount in tank generally applies to all.

Forced regeneration

– a special complex procedure most of the time applies to DPF (Diesel Particulate Filter) that has blockage values way above maximum allowed values but not reaching 0.7 BAR of back pressure.

Chemical cleaning & active / forced regeneration

– this procedure is called also DPF cleaning but regeneration needs to be achieved afterwards in order no to waste the effort. DPF cleaning is most of the time applied by technician to DPF (Diesel Particulate Filter) that has high blockage values. Back pressure read is usually close to 0.9 Bar.

DPF removal, chemical cleaning & forced regeneration

– this procedure is offered to DPF ( Diesel particulate Filter) which has excessive blockage readings with back pressure values exceeding 0.9 Bar. Mileage of the car is usually above 100k miles. Chemical more intense pressure cleaning applied. Replacement option of old DPF is also addressed at this stage as treatment might not be long lasting due to excessive wear of original DPF.

New DPF installation

– this is usually offered to vehicles with high mileage of 110k-120k miles and regularly driven on motorways yet still developing DPF related faults.


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