Diesel particulate filter: Difference between revisions
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[[Image:FAP-Filter Peugeot.jpg|thumb|Diesel Particulate Filter (top left) in a Peugeot]] |
[[Image:FAP-Filter Peugeot.jpg|thumb|Diesel Particulate Filter (top left) in a Peugeot]] |
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A '''Diesel Particulate Filter''', sometimes called a '''DPF''', is |
A '''Diesel Particulate Filter''', sometimes called a '''DPF''', is device designed to remove [[Diesel Particulate Matter]] or [[soot]] from the [[exhaust gas]] of a [[diesel engine]], most of which are rated at 85% efficiency, but often attaining efficiencies of over 90%. A [[diesel]] powered [[vehicle]] with a filter installed will emit no visible smoke from it's exhaust pipe. |
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In addition to collecting the particulate, a method must be designed to get rid of it. Some filters are single use (disposable), while others are designed to burn off the accumulated particulate, either through the use of a catalyst (passive), or through an active technology, such as a fuel burner which heats the filter to soot combustion temperatures, or through engine modifications (the engine is set to run a certain specific way when the filter load reachs a pre-determined level, either to heat the exhaust gasses, or to produce high amounts of No2, which will oxidize the particualte at relatively low temperatures). This procedure is known as "Filter Regeneration." Fuel Sulfur interferes many "Regeneration" strategies, and all jurisdictions that are interested in reduction of particulate emissions, are also passing regulations governing fuel sulfur levels. |
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The DPF has several channels in parallel with the ends plugged, in a [[checkerboard]] pattern. A DPF is usually followed by a lean [[NOx]] [[catalyst]] in a proprietary catalytic converter for diesel engines. By trapping the particulate matter, soot, the DPF allows the lean NOx catalyst to work without being clogged by the soot. Hence the effectiveness of the lean NOx catalyst is not reduced by soot covering the active sites of the catalytic converter. |
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==History== |
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These '''particle filters''' are a new technology: high cost [[catalytic]] [[pollution]] control module added to [[diesel engine]]d cars to eliminate the characteristic black smoke trail. It was first offered as standard by the French manufacturer [[PSA Peugeot Citroën]] in early [[2005]]. Slow adoption by the [[Germany|German]] car industry sparked local protests in [[March 2005]]. Despite costs, the device will be mandatory for all newly built vehicles in the [[EU]] starting in [[2007]] (projected). |
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Particulate filters have been in use on Non-Road machines since 1980, and in automobiles since 1996. Diesel engines during combustion of the fuel/air mix produce a variety of particles generically classified as [[Diesel Particulate Matter]] 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 horsepower output than do [[Four-Stroke]] diesel engines, as they less completely combust the fuel-air mix. |
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Historically 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 both [http://www.dieselnet.com/standards/us/hd.html On-Road] and [http://www.dieselnet.com/standards/us/offroad.html Non-Road] diesel engines. |
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==The filter getting clogged== |
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In most forms the exhaust gas is forced to flow through a material with extremely tiny pores, achieveing very high filtration rates even on nano-particles; however, this type of filter may become blocked by soot if there is not a mechanism to oxidize the accumulation, or if that mechanism fails. In any case, [[engine oil]] ash will build up on the face of the filter, needing periodic cleaning (unlike a [[Diesel Oxidation Catalyst]] which can often last the life of the engine without maintenance). |
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While particulate emissions from Diesel Engines was first regulated in the [[U.S.A.]], simular regulations have also been adopted by the [[European Union]], most Asian countries, and the rest of North and South America [http://www.dieselnet.com/standards/ World List of Standards]. |
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Several forms called "leaky filters" have also been devised, which are supposed to be incapable of being plugged, however their filtration efficiency seldom rises above 60%, and they have a tendency to "blow off" accumulated particulates after some hours of operation. |
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==Technology== |
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Unlike a [[catalytic converter]] which is a flow-through device, a DPF cleans exhaust gas by forcing the gas to flow through the filter. There are a variety of diesel particulate filter technologies on the market. Each is designed around simular requirements: |
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1) Fine Filtration |
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2) Minimum Pressure Drop |
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3) Low Cost |
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4) Suitability for Mass Production |
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5) Product durability |
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=[[Corderite Wall Flow Filters]]= |
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The most common filter is made of [[cordierite]] (a ceramic material that is also used as catalytic converter supports (= cores)). Corderite 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 Corderite has a relatively low melting point (about 1200 degrees Celsius) and Corderite substrates have been known to melt down during filter regeneration. This is mostly an issue if the filter has become loaded more heavily than ususal, and is more of an issue with passive systems than with active systems, unless there is a system break down. |
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Corderite 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. |
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=[[Silicon Carbide Wall Flow Filters]]= |
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The second most popular filter material is [[Silicon Carbide]], or [[SiC]]. It has a higher (1700 degrees celsius) melting point than Corderite, 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 seperated 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 Corderite cores, however they are manufactured in simular sizes, and one can often be used to replace the other. |
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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. |
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=[[Metal Fiber Flow Through Filters]]= |
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Some cores are made from metal fibers - generally the fibers are "woven" into a monolith. Such cores have the advantage that a current can be passed through the monolith to heat the core for regeneration purposes. Metal fiber cores tend to be more expensive than Corderite or Silcon Carbide cores, and not generally not interchangeable with them. |
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=[[Paper]]= |
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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 of a store. |
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=[[Partial Filters]]= |
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There are a variety of devices that produce over 50% particulate matter filtration, but less then 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. |
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==[[Regeneration]]== |
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Regeneration is the process of removing the accumulated soot from the filter. This is done either:- |
Regeneration is the process of removing the accumulated soot from the filter. This is done either:- |
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*Passively (by |
*Passively (by adding a catalyst to the filter). |
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*Actively. Active filter management can use a variety of strategies such as using engine management to increase exhaust temperature or using microwave energy or resistive heating coils to heat the filter core. In this soot burn-off, the DPF is heated to a temperature that fully burns the soot. This lets the DPF be used continuously; however, it uses extra fuel, which is burnt to heat the DPF. A sensor that measures back pressure decides when the DPF needs to be heated. |
*Actively. Active filter management can use a variety of strategies such as using engine management to increase exhaust temperature or using microwave energy or resistive heating coils to heat the filter core. In this soot burn-off, the DPF is heated to a temperature that fully burns the soot. This lets the DPF be used continuously; however, it uses extra fuel, which is burnt to heat the DPF. A sensor that measures back pressure feeds this information to a computer, which decides when the DPF needs to be heated. |
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==Filters in Use== |
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A properly designed filter will have little effect on fuel usage, and an improperly one can be catastrophic, which is why automobile and truck engine manufacturers have avoided the use of filter technology. It was first offered as standard by the French manufacturer [[PSA Peugeot Citroën]] in early [[2005]], and has been a huge success. Slow adoption by the [[Germany|German]] car industry sparked local protests in [[March 2005]]. |
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While no jurisdiction has made filters mandatory, the increasingly stringent emissions regulations that engine manufactures must meet mean that eventually all On-Road diesel engines will be fitted with them. Neither the American 2007 heavy truck engine emissions regulations or the European Union 2007 automobile regulations can meet without filters. PSA [[Peugeot]] was the first company to make them standard fit on passenger cars, in anticipation of the 2007 EU regulations. |
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It is expected that Non-Road diesel engines will be regulated in a simular manner. |
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As of July 2006 the California Air Resources Board is looking at introducing regulations that will require retrofit of all diesel engines operating in the state by the year 2013. Other jurisdictions may also do this. A variety of retrofit programs have been done: |
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Back-pressure should be avoided in a large diesel engine's exhaust system, as the exhaust gas should be allowed to cool down as much as possible by drop in pressure as it leaves the engine's cylinders, else the exhaust valve may get damaged by overheating. |
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*2003 Mexico City started a program to retrofit trucks |
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*2001 Hong Kong retrofit program |
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*2004 New York City retrofit program (non-road) |
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==Maintenance== |
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Filters require more maintenance than catalytic converters. Engine oil ash builds up on the surface of the inlet face of the filter, and will eventually clog the pores. This causes an increase of pressure drop over the filter, which when it reachs 100 inches of water or higher is capable of causing engine damage. Regular maintenace of the filter is a necessity. |
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DPF's are in common use in Europe where [[Peugeot]] introduced them as standard fit on passenger cars. The Peugeot system uses a combination of engine management, and a [[fuel borne catalyst]] to regenerate the filters. |
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In [[North America]] filters are used heavily on diesel-powered underground mining machines, and also on transit buses, and the filters are installed as "[[retro]]fit" devices (i.e. not factory fitted). |
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Increasingly stringent regulations mean that filter technology will soon be fitted as standard to engines worldwide. |
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== See also == |
== See also == |
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Revision as of 19:01, 23 July 2006
A Diesel Particulate Filter, sometimes called a DPF, is device designed to remove Diesel Particulate Matter or soot from the exhaust gas of a diesel engine, most of which are rated at 85% efficiency, but often attaining efficiencies of over 90%. A diesel powered vehicle with a filter installed will emit no visible smoke from it's exhaust pipe.
In addition to collecting the particulate, a method must be designed to get rid of it. Some filters are single use (disposable), while others are designed to burn off the accumulated particulate, either through the use of a catalyst (passive), or through an active technology, such as a fuel burner which heats the filter to soot combustion temperatures, or through engine modifications (the engine is set to run a certain specific way when the filter load reachs a pre-determined level, either to heat the exhaust gasses, or to produce high amounts of No2, which will oxidize the particualte at relatively low temperatures). This procedure is known as "Filter Regeneration." Fuel Sulfur interferes many "Regeneration" strategies, and all jurisdictions that are interested in reduction of particulate emissions, are also passing regulations governing fuel sulfur levels.
History
Particulate filters have been in use on Non-Road machines since 1980, and in automobiles since 1996. Diesel engines during combustion of the fuel/air mix produce a variety of particles generically classified as Diesel Particulate Matter 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 horsepower output than do Four-Stroke diesel engines, as they less completely combust the fuel-air mix.
Historically 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 both On-Road and Non-Road diesel engines.
While particulate emissions from Diesel Engines was first regulated in the U.S.A., simular regulations have also been adopted by the European Union, most Asian countries, and the rest of North and South America World List of Standards.
Technology
Unlike a catalytic converter which is a flow-through device, a DPF cleans exhaust gas by forcing the gas to flow through the filter. There are a variety of diesel particulate filter technologies on the market. Each is designed around simular requirements:
1) Fine Filtration 2) Minimum Pressure Drop 3) Low Cost 4) Suitability for Mass Production 5) Product durability
Corderite Wall Flow Filters
The most common filter is made of cordierite (a ceramic material that is also used as catalytic converter supports (= cores)). Corderite 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 Corderite has a relatively low melting point (about 1200 degrees Celsius) and Corderite substrates have been known to melt down during filter regeneration. This is mostly an issue if the filter has become loaded more heavily than ususal, and is more of an issue with passive systems than with active systems, unless there is a system break down.
Corderite 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 (1700 degrees celsius) melting point than Corderite, 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 seperated 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 Corderite cores, however they are manufactured in simular 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.
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 a current can be passed through the monolith to heat the core for regeneration purposes. Metal fiber cores tend to be more expensive than Corderite or Silcon Carbide cores, and not generally not interchangeable with them.
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 of a store.
Partial Filters
There are a variety of devices that produce over 50% particulate matter filtration, but less then 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.
Regeneration
Regeneration is the process of removing the accumulated soot from the filter. This is done either:-
- Passively (by adding a catalyst to the filter).
- Actively. Active filter management can use a variety of strategies such as using engine management to increase exhaust temperature or using microwave energy or resistive heating coils to heat the filter core. In this soot burn-off, the DPF is heated to a temperature that fully burns the soot. This lets the DPF be used continuously; however, it uses extra fuel, which is burnt to heat the DPF. A sensor that measures back pressure feeds this information to a computer, which decides when the DPF needs to be heated.
Filters in Use
A properly designed filter will have little effect on fuel usage, and an improperly one can be catastrophic, which is why automobile and truck engine manufacturers have avoided the use of filter technology. It was first offered as standard by the French manufacturer PSA Peugeot Citroën in early 2005, and has been a huge success. Slow adoption by the German car industry sparked local protests in March 2005.
While no jurisdiction has made filters mandatory, the increasingly stringent emissions regulations that engine manufactures must meet mean that eventually all On-Road diesel engines will be fitted with them. Neither the American 2007 heavy truck engine emissions regulations or the European Union 2007 automobile regulations can meet without filters. PSA Peugeot was the first company to make them standard fit on passenger cars, in anticipation of the 2007 EU regulations.
It is expected that Non-Road diesel engines will be regulated in a simular manner.
As of July 2006 the California Air Resources Board is looking at introducing regulations that will require retrofit of all diesel engines operating in the state by the year 2013. Other jurisdictions may also do this. A variety of retrofit programs have been done:
- 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
- 2001 Hong Kong retrofit program
- 2004 New York City retrofit program (non-road)
Maintenance
Filters require more maintenance than catalytic converters. Engine oil ash builds up on the surface of the inlet face of the filter, and will eventually clog the pores. This causes an increase of pressure drop over the filter, which when it reachs 100 inches of water or higher is capable of causing engine damage. Regular maintenace of the filter is a necessity.