A diesel particulate filter (DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.Tom Nash (May 2003) "Diesels: The Smoke is clearing", Motor Vol.199 No. 5, p. 54, Hearst Business Publishing Inc.
Mode of action Wall-flow diesel particulate filters usually remove 85% or more of the soot, and under certain conditions can attain soot removal efficiencies approaching 100%. Some filters are single-use, intended for disposal and replacement once full of accumulated ash. Others are designed to burn off the accumulated particulate either passively through the use of a catalyst or by active means such as a fuel burner which heats the filter to soot combustion temperatures. This is accomplished by engine programming to run (when the filter is full) in a manner that elevates exhaust temperature, in conjunction with an extra fuel injector in the exhaust stream that injects fuel to react with a catalyst element to burn off accumulated soot in the DPF filter,Jong Hun Kim et al. (November 2010) "NO2-Assisted Soot Regeneration Behavior in a Diesel Particulate Filter with Heavy-Duty Diesel Exhaust Gases", Numerical Heat Transfer Part A Vol.58 No.9 pp.725–739, Chonbuk National University, Korea or through other methods. This is known as . Cleaning is also required as part of periodic maintenance, and it must be done carefully to avoid damaging the filter. Failure of fuel injectors or turbochargers resulting in contamination of the filter with raw diesel or engine oil can also necessitate cleaning."DPF Maintenance" (January 2010) HDT Trucking Info The regeneration process occurs at road speeds higher than can generally be attained on city streets; vehicles driven exclusively at low speeds in urban traffic can require periodic trips at higher speeds to clean out the DPF. If the driver ignores the warning light and waits too long to operate the vehicle above , the DPF may not regenerate properly, and continued operation past that point may spoil the DPF completely so it must be replaced."DPFs reduce diesel soot emissions by 80% but they're not suitable for everyone" (5 December 2013) The Automobile Association Some newer diesel engines, namely those installed in combination vehicles, can also perform what is called a Parked Regeneration, where the engine increases RPM to around 1400 while parked, to increase the temperature of the exhaust.
Diesel engines produce a variety of particles during the combustion of the fuel/air mix due to incomplete combustion. The composition of the particles varies widely dependent upon engine type, age, and the emissions specification that the engine was designed to meet. Two-stroke diesel engines produce more particulate per unit of power than do four-stroke diesel engines, as they burn the fuel-air mix less completely."Study: 'Clean fuel' not always successful" (March 1, 2011) UPI NewsTrack, Vancouver, British Columbia"Canadian researchers say a program by one of the world's largest cities [New Delhi] to switch its vehicles to clean fuel has not significantly improved emission levels."
Diesel particulate matter resulting from the incomplete combustion of diesel fuel produces soot (black carbon) particles. These particles include tiny nanoparticles—smaller than one micrometre (one micron). Soot and other particles from diesel engines worsen the particulate matter pollution in the air and are harmful to health. New particulate filters can capture from 30% to greater than 95% of the harmful soot.Barone et al. (August 2010) "An analysis of field-aged diesel particulate filter performance: particle emissions before, during, and after regeneration", Journal of the Air & Waste Management Association Vol. 60 No.8 pp. 968-76 With an optimal diesel particulate filter (DPF), soot emissions may be decreased to or less.DPF - Diesel Particulate Filters, Axces.eu
History Diesel particulate filtering was first considered in the 1970s due to concerns regarding the impacts of inhaled particulates.Vincent D. Blondel: Recent Advances in Learning and Control, p. 233, Springer Science & Business Media, 2008, Particulate filters have been in use on non-road machines since 1980, and in automobiles since 1985.Diesel Particulate Regeneration Historically medium and heavy duty diesel engine emissions were not regulated until 1987 when the first California Heavy Truck rule was introduced capping particulate emissions at 0.60 g/BHP Hour.Bahadur et al. (2011) "Impact of California’s air pollution laws on black carbon and their implications for direct radiative forcing", Atmospheric Environment Vol. 45 pp. 1162–1167, Scripps Institution of Oceanography, University of California San Diego Since then, progressively tighter standards have been introduced for light- and heavy-duty road-going diesel-powered vehicles and for off-road diesel engines. Similar regulations have also been adopted by the European Union and some individual European countries, most Asian countries, and the rest of North and South America.Worldwide emission standards for diesel vehicles and engines
Whilst few jurisdictions have explicitly made filters mandatory, the increasingly stringent emissions regulations that engine manufacturers must meet mean that eventually all on-road diesel engines will be fitted with them. In the European Union, filters are highly recommended and effectively necessary to meet the Euro 6 Heavy-Duty emissions standards for vehicles such as lorries. In 2000, in anticipation of the future Euro 5 regulations PSA Peugeot Citroën became the first company to make filters standard on passenger cars.James Scoltock (June 2014) "Diesel Particulate Filter: PSA Peugeot Citroën was the first to bring in particulate filters to help make diesels cleaner", Automotive Engineer p. 9 Euro 5 regulations, fully coming into force in January 2011, require that diesel cars must have a diesel particulate filter.
As of December 2008, the California Air Resources Board (CARB) established the 2008 California Statewide Truck and Bus Rule which—with variance according to vehicle type, size and usage—requires that on-road diesel heavy trucks and buses in California be retrofitted, repowered, or replaced to reduce particulate matter (PM) emissions by at least 85%. Retrofitting the engines with CARB-approved diesel particulate filters is one way to fulfil this requirement. In 2009 the American Recovery and Reinvestment Act provided funding to assist owners in offsetting the cost of diesel retrofits for their vehicles.American Recovery and Reinvestment Act Other jurisdictions have also launched retrofit programs, including: 2001 – Hong Kong retrofit program. 2002 – In Japan the Prefecture of Tokyo passed a law banning trucks without filters from entering the city limits. 2003 – Mexico City started a program to retrofit trucks. 2004 – New York City retrofit program (non-road)."New York City passes diesel emissions rules" (Apr 21, 2005) FleetOwner 2008 – Milan Ecopass area traffic charge – a hefty entrance tax on all diesel vehicles except those with a particulate filter, either stock or retrofit."Milan’s Ecopass To Evolve" (September 2, 2011) Italy Chronicles 2008 – London low emission zone charges vehicles that do not meet emission standards, encouraging retrofit filters.Low Emission Zone, Transport for londonFit a Filter, Transport for london
Inadequately maintained particulate filters on vehicles with diesel engines are prone to soot buildup, which can cause engine problems due to high back pressure.
In 2018, the UK made changes to its MOT test requirements,"Pass Your 2018 MOT - New Rules Regulations including tougher scrutiny of diesel cars. One requirement was to have a properly fitted and working DPF. Driving without a DPF could incur a £1000 fine.
Variants of DPFs
Unlike a catalytic converter which is a flow-through device, a DPF retains bigger exhaust gas particles by forcing the gas to flow through the filter material before exiting;Diesel particulate Matter – Emission Reduction Methods (2009) Mine Safety and Health Administration (MSHA), U.S. Department of Labor] however, the DPF does not retain small particles. Maintenance-free DPFs oxidise or burn larger particles until they are small enough to pass through the filter, though often particles "clump" together in the DPF reducing the overall particle count as well as overall mass.Particulate emissions from diesel engines: correlation between engine technology and emissionsDPF (Diesel Particulate Filters) Explained There are a variety of diesel particulate filter technologies on the market. Each is designed around similar requirements: Fine filtration Minimum pressure drop Low cost Mass production suitability Product durability
Cordierite wall flow filters The most common filter is made of cordierite (a ceramic material that is also used as catalytic converter supports (cores)). Cordierite filters provide excellent filtration efficiency, are relatively inexpensive, and have thermal properties that make packaging them for installation in the vehicle simple. The major drawback is that cordierite has a relatively low melting point (about 1200 °C) and cordierite substrates have been known to melt during filter regeneration. This is mostly an issue if the filter has become loaded more heavily than usual, and is more of an issue with passive systems than with active systems, unless there is a system breakdown."Technical Papers" (2013) Corning Environmental Technologies
Cordierite filter cores look like catalytic converter cores that have had alternate channels plugged – the plugs force the exhaust gas flow through the wall and the particulate collects on the inlet face."Cordierite" (2009) Diesel Emission Technologies Inc.
Silicon carbide wall flow filters The second most popular filter material is silicon carbide, or SiC. It has a higher (2700 °C) melting point than cordierite, however, it is not as stable thermally, making packaging an issue. Small SiC cores are made of single pieces, while larger cores are made in segments, which are separated by a special cement so that heat expansion of the core will be taken up by the cement, and not the package. SiC cores are usually more expensive than cordierite cores, however they are manufactured in similar sizes, and one can often be used to replace the other. Silicon carbide filter cores also look like catalytic converter cores that have had alternate channels plugged – again the plugs force the exhaust gas flow through the wall and the particulate collects on the inlet face."Silicon Carbide (SiC)" (2009) Diesel Emission Technologies Inc.
The characteristics of the wall flow diesel particulate filter substrate are:
broad band filtration (the diameters of the filtered particles are 0.2–150 μm) high filtration efficiency (can be up to 95%) high refractory high mechanical properties high boiling point.
Ceramic fiber filters