Diesel particulate filter

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, 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. 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. 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. 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. With an optimal diesel particulate filter (DPF), soot emissions may be decreased to or less. == History ==

Diesel particulate filtering was first considered in the 1970s due to concerns regarding the impacts of inhaled particulates. Particulate filters have been in use on non-road machines since 1980, and in automobiles since 1985. 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. Since then, progressively tighter standards have been introduced for light- and heavy-duty roadgoing 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. 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. 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 fulfill 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. 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). • 2008 – Milan Ecopass area traffic charge – a hefty entrance tax on all diesel vehicles except those with a particulate filter, either stock or retrofit. • 2008 – London low emission zone charges vehicles that do not meet emission standards, encouraging retrofit filters. Inadequately maintained particulate filters on vehicles with diesel engines are prone to soot buildup, which can cause engine problems due to high back pressure. 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; 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. 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. 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. 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. 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. Metal fiber flow-through filters Some cores are made from metal fibers – generally the fibers are "woven" into a monolith. Such cores have the advantage that an electrical current can be passed through the monolith to heat the core for regeneration purposes, allowing the filter to regenerate at low exhaust temperatures and/or low exhaust flow rates. Metal fiber cores tend to be more expensive than cordierite or silicon carbide cores, and are generally not interchangeable with them because of the electrical requirement. Paper Disposable paper cores are used in certain specialty applications, without a regeneration strategy. Coal mines are common users – the exhaust gas is usually first passed through a water trap to cool it, and then through the filter. Paper filters are also used when a diesel machine must be used indoors for short periods of time, such as on a forklift being used to install equipment inside a store. Partial filters There are a variety of devices that produce over 50% particulate matter filtration, but less than 85%. Partial filters come in a variety of materials. The only commonality between them is that they produce more back pressure than a catalytic converter, and less than a diesel particulate filter. Partial filter technology is popular for retrofit. ==Maintenance==

Filters require more maintenance than catalytic converters. Ash, a byproduct of oil consumption from normal engine operation, builds up in the filter as it cannot be converted into a gas and pass through the walls of the filter. This increases the pressure before the filter. Heavy duty pickup trucks have less stringent requirements for all three parameters, and Class 8 trucks significantly less. If the vehicle is often driven in cities the DPF may become clogged, causing a reduction in power and acceleration either passively due to increased exhaust pressure or actively due to vehicle going into "limp/turtle mode" as it tries to prevent engine and turbo damage. Once clogged both passive and active regeneration may become ineffective. DPF may be unclogged by high temperature pressure washing (not officially recommended) and/or burn-off oven. ==Safety==

In 2011, Ford recalled 37,400 F-Series trucks with diesel engines after fuel and oil leaks caused fires in the diesel particulate filters of the trucks. No injuries occurred before the recall, though one grass fire was started. A similar recall was issued for 2005-2007 Jaguar S-Type and XJ diesels, where large amounts of soot became trapped in the DPF In affected vehicles, smoke and fire emanated from the vehicle underside, accompanied by flames from the rear of the exhaust. The heat from the fire could cause heating through the transmission tunnel to the interior, melting interior components and potentially causing interior fires. ==Regeneration==

and its selective catalytic reduction (SCR) next to the DPF with regeneration process by the late fuel injection to control exhaust temperature to burn off soot. Regeneration is the process of burning off (oxidizing) the accumulated soot from the filter. This is done either passively (from the engine's exhaust heat in normal operation or by adding a catalyst to the filter) or actively introducing very high heat into the exhaust system. On-board active filter management can use a variety of strategies: This advancement is significant because it allows the cleaning reaction to take place at the standard operating temperature of most diesel engines, removing the requirement for burning extra fuel or otherwise artificially heating the engine. The family of Mg doped catalysts, named Grindstaff catalysts after the chemist who started the work, has been the subject of much investigation across industry and academia with the tightening of emissions regulations on particulate matter world wide. == Removal or tampering ==

Intentionally removing or tampering with a DPF is prohibited by the EPA. The act of removing emission control devices, such as a DPF, is commonly referred to as "deleting." Several manufacturers and retailers of diesel emissions defeat devices have been fined up to $1 million. == See also ==