Diesel particulate filter

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The articles diesel soot particle filter and sintered metal filter overlap thematically. Help me to better differentiate or merge the articles (→  instructions ) . To do this, take part in the relevant redundancy discussion . Please remove this module only after the redundancy has been completely processed and do not forget to include the relevant entry on the redundancy discussion page{{ Done | 1 = ~~~~}}to mark. Little Red Riding Hood ( discussion ) 13:52, 10 Jun. 2014 (CEST)
Diesel particulate filter (top left) in a Peugeot
Hino Motors truck with SCR catalytic converter with diesel exhaust fluid tank and diesel particulate filter
Diesel soot particle filter made of silicon carbide (right) plus oxidation catalytic converter (left) including sensors and metal housings for cars

A diesel soot particle filter (DRPF), often also referred to as a diesel particulate filter (DPF), soot particle filter (RPF) or particle filter , is a device for reducing the particles present in the exhaust gas of diesel engines .

Background and introduction

Especially the carbon-containing fine dust has long been considered harmful, as it is not a matter of soot particles made of pure carbon, but mostly agglomerations (caking) of soot particles with other harmful substances such as PAH ( polycyclic aromatic hydrocarbons ) and the like. a. m. acts. The modern diesel engine technology with common rail injection also ensures finer and therefore more respirable fine particles. These extremely small fine particles are particularly harmful to health.

Environmental groups had therefore been calling for a diesel particulate filter for decades. However, since this technology is very complex and expensive, it was only around the turn of the millennium that a reliably working system could be developed to series production readiness .

A distinction is made between wall-flooded ceramic modules (on which the channel ends are alternately closed with plugs), sintered metal filters , which instead of porous ceramics have closed and folded pockets made of porous sintered metal , and bypass deep-bed filters, which remove the soot particles through flow dynamics - targeted flow deflections - virtually from the exhaust gas flow fish out. The wall-flooded filters are often incorrectly referred to as "closed filter systems", while the bypass deep-bed filters are often incorrectly referred to as "open filter systems".

Diesel soot particle filters with wall-flooded ceramic modules are used in 99% of the automotive series. The reason is that they can filter out more than 98% of the particle mass - and until 2015 (Euro 5), the exhaust gas limit values ​​for particles only required mass and not particle number. In the case of the particularly harmful fine particles, however, these have system-related weaknesses; especially after each regeneration until a filter cake has built up again . Bypass-flow deep-bed filters, on the other hand, can only filter out around 40% of the particle mass, but up to around 80% of the finest particles.

The visible soot on vehicles, locomotives and ships mainly contributes to the less health-critical particle mass and does not necessarily have to contain a high number of fine particles.

In the case of the wall-flooded diesel particulate filters, the collected soot must be burned regularly (approximately every 500 to 1000 km). A small amount of incombustible ash remains. This adds up, so that one day the filter is completely full (the limit in 2015 was around 200,000 km). Since the soot only burns at higher temperatures around 500 ° Celsius and the exhaust gas from the diesel engine is quite cold, a filter can also become clogged with soot. Both types of blockage (soot or ash) have different reasons. The process of regeneration (the soot burn-off) takes place at medium-high temperatures, at which chemical conversions also take place. Most DPFs are catalytically coated, which supports such chemical reactions. This can then lead to other poisonous substances, which get into the environment with the exhaust gas.

The soot emitted by diesel engines and direct-injection gasoline engines is only a small part of the measured and discussed particulate matter pollution, since dust from natural and industrial sources is also recorded. In addition, building heating systems with solid fuels generate soot-containing fine dust.


The first experiments with exhaust gas cleaning systems took place during the First World War, but not for the purpose of environmental protection, but for camouflage . The first diesel-powered ships and submarines were revealed by soot plumes that were visible from afar. For this purpose, acetone was sprayed into the exhaust system . The resulting exhaust gas mixture was then fed back into the combustion process. However, the successes were moderate.

Diesel soot filters in diesel engines and vehicles - used in mining, underground or in large halls - have been common since the 1970s.

The diesel soot particle filter was first used in passenger cars in 1985 in the Mercedes-Benz S-Class (W 126 series) . However, this model, which was exclusively intended for the American market, had serious problems with the durability of the filter. Therefore the production was stopped in 1987.

After leading automobile manufacturers refrained from introducing filters for years, the breakthrough for the technology came in 2000, when Peugeot equipped the 406 and 607 and Citroën the C5 with a filter as standard. The manufacturer of the ready-to-sell filter (French abbreviation FAP for F iltre à p articules ) was, in addition to the German-based company Tenneco, the supplier Faurecia , which is majority owned by the PSA group . It was a wall-flow filter with additive-supported regeneration. The filter elements themselves consist of cordierite , silicon carbide or aluminum titanate and are manufactured by the ceramic companies Saint-Gobain , Ibiden , NGK Insulators and Corning (only aluminum titanate). Despite the filter, the Peugeot 607 did not yet meet the Euro 4 emissions standard , which has been in force since January 1, 2005 . The limit values ​​of the Euro 4 standard for soot particles were undershot many times over, but the nitrogen oxide and hydrocarbon emissions were still too high. In 2003 Tenneco and Faurecia brought a new generation of filters onto the market, now with catalytic regeneration. These filters already complied with the Euro 4 standard, so HDi diesel engines equipped with them (High Pressure Direct Injection, here common rail injection ) were presented by Peugeot at the 2003 IAA . Due to the sharp rise in demand, there were capacity bottlenecks in filter production in 2004. As a result, the manufacturers of the filter elements multiplied their production capacities at the urging of the automobile manufacturers.

Formation of diesel soot

Particle size distribution in the unfiltered exhaust gas of a diesel engine

Diesel soot is created due to the properties of the fuel and the combustion process. Particles in diesel exhaust mainly consist of soot and unburned hydrocarbons . The particle size distribution (PGV) generated by the diesel engine is mostly multimodal and can be approximated as normally distributed in the respective mode (plotted logarithmically) . The maximum value of the distribution occurs in the range of around 50-100 nm (depending on the motor used). Deviations from the normal distribution in the range of the smaller modes (smaller than 20 nm) are mostly caused by the sampling to determine the PGV and represent so-called artifacts. These modes can be attributed, for example, to the recondensation of volatile hydrocarbons (droplet formation, nucleation) which then appear in the particle spectrum and can lead to misinterpretations. This nucleation is due to homogeneous or heterogeneous condensation, as occurs with highly concentrated saturated vapors. If small particle nuclei (for example soot particles) appear in the gas phase, one speaks of heterogeneous nucleation. Also sulfur in the fuel leads to such increased droplet formation, for example when the engine oil is operated. Larger modes in the range of several micrometers arise in the course of movement through the exhaust system through agglomeration of smaller particles.


There are two modes of operation that differ fundamentally: wall-flow filters , in which the exhaust gas penetrates a porous wall in the filter , and side- flow filters , in which the exhaust gas flows through the filter along its inner surface.

Wall-flow filter


Wall-flow filters made of silicon carbide are glued together from individual cuboid segments, turned round and the jacket plastered

With a wall-flow filter ( marketing names: CERACLEAN® , HONEYCERAM® , Wall-Flow , incorrectly also called a closed system ), the exhaust gas mixed with soot particles is filtered when it penetrates a porous filter wall.

With surface filters, the particles mainly stick to the surface of the filter wall or remain inside the filter wall by means of deep filtration. Larger particles cannot pass the filter wall and are thus deposited on its surface. In this way, layers up to 200 µm thick can form on the canal surface by the time of regeneration. The physically effective mechanism for adhering the particles to the porous filter wall is based on adhesion . The movement of the particles to the filter wall is mainly caused by the mechanism of diffusion and is superimposed by the flow of the exhaust gas through the filter.

With surface filters, too, depth filtration takes place at the beginning. When the inner filter surfaces are covered, the particles are deposited on the surface. A layer of particles forms with the so-called filter cake . With depth filters , the particles are only deposited in the internal filter structure.

Diesel soot particle filter (monolith) on the left made of Cordierite ceramic, on the right made of aluminum titanate ceramic

The filter walls themselves can consist of different porous materials, which are usually made up of fibers or powder. The fibers or the powder itself consist of ceramics or metals. Classic ceramics are mullite, cordierite , silicon carbide (SiC) and aluminum titanate . In some cases, different materials are combined in more recent developments.

Diesel particulate filter made from silicon carbide

The porous walls can be arranged in different ways in the filter. In the case of fibers and metal powder, flat filter walls are built up, which are arranged in tubes, pockets or bellows. In the case of filters made of ceramic powder, a channel structure is used, with the channels being alternately closed. The exhaust gas is thereby forced to flow through the porous wall. Different geometries or properties of the filter material can be created through the production process. The wall thickness, cell density, mean pore size and pore volume are particularly important.

As the particles are deposited on the surface or inside the filter wall, the differential pressure generated by the exhaust gas volume flow across the filter increases. When a threshold value is reached - i.e. when a certain amount of soot is stored - the regeneration of the filter is initiated.

Usual filters have a pore size of 10 µm in the substrate. This means that the pores are indeed significantly larger than the particle spectrum to be filtered, but the particles are deposited on the porous wall when they pass through, creating a surface filtrate on which the so-called filter cake is formed from further separated particles.

The efficiencies, based on the particle mass and number distribution, are therefore in the range of 90 to 99.9% even for ultrafine nanoparticles with particle sizes of more than 20 nm.

All areas relevant to the fine dust discussion, such as PM 10 , PM 2.5 , PM 1 and PM 0.1 (see fine dust ), are effectively reduced with a wall-flow filter.


The filter is regenerated by burning the embedded particles. The regeneration is necessary if a high exhaust gas back pressure due to the particle load impairs exhaust gas emissions too much. The differential pressure across the filter is a measurable variable that is easy to record and that allows the level of filter loading to be recognized. Since this differential pressure varies depending on the engine speed, load condition and load quantity, these parameters must be recorded in a map. The monitoring of the differential pressure and the initiation and control of the regeneration are carried out by the engine control of the diesel engine.

Diesel soot particle filter made of sintered metal loaded with soot

The regeneration takes place depending on the driving profile in a cycle of several hundred kilometers. Under favorable circumstances (motorway operation), with exhaust gas temperatures in the range of the burn-off temperature of the soot particles, a regeneration initiated by the engine control unit is only necessary after significantly higher mileage or not at all. Under unfavorable circumstances (short-distance traffic) problems can arise with the loading of the filter and with reaching the regeneration temperature. Depending on the vehicle type, this is displayed to the driver. The driver does not notice the regeneration, the engine performance is not affected. In the filter, the diesel soot is converted into CO 2 during regeneration .

As with any chemical reaction , a certain temperature is required for the accumulated particles to burn . Since soot is a modification of the carbon, the regeneration is an exothermic oxidation, which under favorable circumstances can enable it to burn off further independently after the ignition of the soot. The necessary exhaust gas temperature for a regeneration is (depending on the implementation "additively supported" or "catalytically supported", see below) at least 500–550 ° C. The exhaust gas temperature in diesel engines is normally relatively low; compared to temperatures of 700 to 800 ° C at nominal power, it can drop to values ​​below 200 ° C in city traffic, for example. To carry out the regeneration over a sufficiently high exhaust gas temperature, there are, among others, the following different, also combinable techniques:

Post-injection (internal engine and exhaust system)

During the expansion during the work cycle, fuel is injected. Because of the late position of this injection in the combustion process, this injection is called, among other things, "late post-injection". Because the combustion gases are no longer expanded as much during this injection, the exhaust gas temperature rises. It is also increased by a downstream oxidation catalytic converter . As an alternative to engine-internal injection, there are system solutions that introduce the fuel by means of a diesel metering pump via an atomizing nozzle in front of the oxidation catalytic converter - regardless of the current driving situation. The latter has the great advantage that there is no risk of engine oil dilution ( which is problematic especially with increasing proportions of the admixture of biofuels ) and the driving behavior or the engine response does not change during regeneration. Another possibility for post-injection is the introduction of fuel vapor via a fuel evaporator (vaporizer) . This has the advantage that the fuel does not first have to be vaporized over a relatively long distance in the exhaust system, but is introduced as vapor just before the oxidation catalytic converter. This significantly reduces the risk of damage to the oxidation catalytic converter from impacting fuel drops.

Oxidation catalyst

An oxidation catalytic converter can significantly increase the exhaust gas temperature under certain conditions. The factors influencing this are the amount of catalytic coating and the composition of the exhaust gas. In order to achieve a significant increase in the temperature of the exhaust gas at the oxidation catalytic converter, in addition to a high concentration of unburned hydrocarbons (HC) and carbon monoxide (CO), a sufficient residual oxygen content is necessary. In particular, the HC concentration can be greatly increased, for example, by post-injection inside the engine or by introducing fuel into the exhaust system using a metering valve arranged upstream of the oxidation catalytic converter.

Diesel injection systems based on common rail , in particular, allow the fuel injection to be controlled independently. For regeneration purposes, fuel is therefore injected in some engines in the exhaust stroke (4th stroke). This burns in the downstream oxidation catalytic converter and can raise the exhaust gas temperature to such an extent that it is sufficient to ignite the soot deposits in the following diesel soot particle filter.

Heating coil

The exhaust gas can also be heated sufficiently by using a heating coil installed in front of the filter. However, this is only practicable for stationary systems (e.g. generator operation or heat pumps) with mains voltage supply. The feasibility in the car does not make sense because of the performance of the usual 12 V on-board network. Heating power in the single-digit kW range is required to heat the exhaust gas mass flow, which would require major modifications to the vehicle electrical system due to the high electrical currents.

Additive-supported regeneration

With the help of an additive to the fuel ( additive ), the temperature required to burn the particles in the filter is reduced from more than 600 to 450 to 550 ° C. The additive is carried in a separate tank (e.g. 5 liters for vehicles from the PSA Group) in the vehicle; it must be topped up at long intervals (approx. 120,000 km) as part of maintenance .

With the systems commonly used in passenger cars (FAP), the additive is automatically added to the diesel fuel using a metering pump during the refueling process, depending on the amount of fuel used . The impregnated particles created during fuel combustion and stored in the filter enable a significantly lower regeneration temperature of the filter due to the permanent enrichment of the diesel fuel with the Cerin solution of the FAP additive, which enables the regeneration process even under driving conditions such as in city traffic.
Another method is to install a metering system, for example using a metering pump, which adjusts the mixing ratio to the current exhaust gas pressure in front of the filter. This means that only the amount of additive that is required for successful regeneration is added to the diesel . The ash storage in the filter is reduced by this technique, and the maintenance intervals are prolonged. Nevertheless, more ash is produced in additive-based systems than in systems that manage without additives.

In addition to vehicles from Peugeot and Citroën as well as Ford , Mazda and Volvo with FAP technology of the first generation (French: FAP = F iltre à p articules), this technology was also used in agricultural and construction machinery , forklifts , permanently installed units and some trucks . A disadvantage of additive technology is that, for example, the frequently used ferrocene itself is oxidized to microfine particles during regeneration, which are themselves respirable and - according to the latest findings - just as dangerous as the diesel soot particles themselves. A requirement for use is that the particle filter never loses its deposit and then blows out the collected iron oxide particles again.

Catalytic regeneration
Diagram of the course of a catalytic regeneration

Catalytically assisted regeneration has established itself as an alternative method for additive-assisted regeneration in cars. The filter is catalytically coated, similar to an oxidation catalytic converter. This filter is referred to as “coated” DPF, “coated” RPF, CSPF or CSF (Catalysed Soot (Particle) filter).

These work in two ways:

  • With passive regeneration, if the temperatures and NO 2 concentrations are sufficiently high - especially when driving on the motorway, the soot is permanently converted to CO 2 and nitrogen monoxide (NO). This process occurs in a temperature range of 350 to 500 ° C and runs without special measures according to the principle of continuous regeneration (particle) case (engl .: C ontinuously R egenerating T rap (CRT)). For this purpose, an upstream oxidation catalytic converter or the catalytically active filter coating converts the nitrogen monoxide (NO) present in the exhaust gases together with the residual oxygen (O 2 ) into nitrogen dioxide (NO 2 ). This nitrogen dioxide then enables continuous combustion of the soot that has accumulated in the particle filter (soot oxidation) to form carbon dioxide (CO 2 ) and nitrogen monoxide (NO). Chemical: 2NO 2 + C → 2NO + CO 2 . The nitrogen monoxide (NO) formed is broken down in a subsequent SCR catalytic converter .
  • During longer periods of operation with a low load - such as in city traffic - active regeneration takes place every 1,000 to 1,200 kilometers or with a maximum load level determined by appropriate sensors by increasing the exhaust gas temperature to 600 ° C via post-injection.

The advantages of this process are lower secondary CO emissions, much less ash residue in the particle filter, the elimination of the additional tank for the additive and a further improved degree of efficiency with less additional consumption compared to a normal wall-flow filter. This is also known as a regulated closed system and is now favored by most manufacturers ex works.

Effectiveness and efficiency

What all wall-flow filters have in common is a long-term stable, very high separation rate (more than 95%) of the total particle mass and a slight increase in fuel consumption . This additional consumption results on the one hand from the regeneration process, which results in additional consumption through the post-injection of fuel or additional consumption through the generation of electrical energy for the electrical heating coil, as well as from the increased exhaust gas back pressure caused by the particles stored in the filter.

Bypass filter

Bypass filters , or more precisely: Bypass deep bed filters , incorrectly also flow filters or open systems , called open filters , usually work according to the principle of deep bed filtration in the bypass flow . Due to design details, part of the exhaust gas flow is  diverted into the adjacent ducts, for example by a fleece , and the soot particles are filtered out. However, the exhaust gas flow is not forced to penetrate the fine-pored wall. In the event of overloading with diesel soot particles, the partial exhaust gas flow is diverted through the normal longitudinal ducts. The partial flow filters mostly work according to the CRT principle (CRT = Continuously Regeneration Trap), which was patented by Johnson Matthey . Since these filters are coated with washcoat and precious metals , they are often called particle catalysts .

Particle catalyst

A particle catalyst is a continuously catalytically regenerating particle reduction system. The term is mostly used for bypass filters. Such filters from Emitec have been used by MAN under the name PM-Kat since 2004 and are offered by Twintec as retrofit filters with their own coating. Several competitors, including Eberspächer and HJS , offer similar systems.

The PM- Metalit filter from Emitec consists of thin, corrugated steel foils with shovel-shaped sub-structures and interposed layers of sintered metal fleece, which serve as a storage medium for the particles. In particle catalysts , when the temperatures and NO 2 concentrations are high enough, the particles deposited there are oxidized and the filter is continuously regenerated according to the so-called CRT principle (CRT: "Continuous Regenerating Trap" = continuously regenerating (particle) trap = particle catalyst). The nitrogen dioxide is produced from nitrogen oxide in the upstream oxidation catalytic converter and possibly on catalytically coated surfaces in the filter. Volatile and soluble organic substances are oxidized on the catalytic coating.

The bypass deep-bed filters are continuously operating systems that do not need to be actively regenerated after a certain driving cycle of around 400 to 1000 kilometers. Especially the regeneration cycle, as it is necessary for filters according to the wall flow principle (wall flow filter), requires various sensors as well as extensive intervention in the existing engine control units of the vehicles. For this reason, conventional diesel particulate filters from the original equipment can only be retrofitted with considerable effort and expense. Since the reduction in diesel soot particles takes place continuously during operation, bypass deep-bed filters are much more reliable. A sudden significant increase in exhaust gas back pressure and possibly resulting engine damage cannot take place. The only slight increase in the exhaust gas back pressure has an advantageous effect , which means that the fuel consumption is not or only slightly increased. Compared to other systems, these are also much more compact in size. In addition, they are maintenance-free over the entire service life of a vehicle.

Compared to the wall-flow filter

Since the exhaust gas flow of a bypass deep-bed filter is not forced completely through a fine-pore wall, the filtration efficiency is significantly lower. The reduction in the total particle mass is 30 to 40%, sometimes even more. However, since a large part of the exhaust gas flow is led past the fleece layer in the longitudinal direction, bypass flow deep-bed filters mainly reduce the particularly harmful, ultra-fine particles (diameter <400 nm) by around 80% due to diffusions / adhesions. When vehicles are retrofitted with a bypass deep-bed filter, no further changes to the vehicle are necessary in addition to the installation of the exhaust gas aftertreatment system in the exhaust system, because the exhaust gas back pressure cannot reach any impermissible values ​​with conventional systems. The filter efficiency is strongly dependent on the filter design, vehicle, operating conditions and states (also over time) and the interaction of these influences.


The combustion of the particles in the diesel particulate filter does not take place without leaving any residue. The additives contained in engine oil and diesel fuel lead to an accumulating ash deposit in the filter. The metal abrasion from the engine also leads to storage in the filter (comparatively low compared to the chemically formed ash). Many manufacturers prescribe engine oils with a low proportion of ash formation (so-called low SAPS oils). These are oils with a specified proportion of ash-forming sulfates ( sulfated ash), phosphorus and sulfur . After a long vehicle mileage , the ash increases the exhaust gas back pressure of the filter and thus fuel consumption. Today's (status: 2011) modern wall-flow filters enable mileage of up to 180,000 km until the ash fill level is so high that the diesel soot particle filter (DPF) has to be replaced with a new part or the previous filter has to be cleaned. Since new DPFs cost between 1,500 and even 4,500 euros for the vehicle customer, depending on the vehicle model, many companies offer diesel particle filter cleaning as a cost-effective service .

Retrofitting for non-road vehicles

Retrofitting for construction vehicles or similar
Particle filter for retrofitting
Data logger / data logger for monitoring diesel soot particle filters
Control display from the manufacturer CPK Automotive

In principle, every diesel engine can be retrofitted with a filter. The decisive factors, however, are the engine's raw emissions, the exhaust gas values ​​to be achieved and the costs of the exhaust gas cleaning system. In Switzerland and Sweden, there has been a filter requirement for mobile “off-highway” diesel vehicles such as construction machinery for years, but this is controversial. In Europe, manufacturers of such vehicles with combustion engines must comply with the exhaust gas regulations in accordance with Directive 97/68 / EC. Operators of off-highway vehicles with internal combustion engines must comply with UVV VBG 36 industrial trucks §21 exhaust gases, TRGS 900 (MAK / TRK values), TRGS 554 DME, UVV VBG 21 Use of liquefied gas §29 and §37 vehicles Consider combustion engine. Among other things, these stipulate the use of such vehicles in open and closed halls. For the use of diesel and LPG forklifts in completely or partially closed rooms, the air limit values ​​according to TRGS 900 apply in Germany. These are made up of the MAK values ​​(maximum workplace concentrations) and the TRK values ​​(technical guideline concentrations). For gaseous pollutants such as CO x , NO x and HC, the MAK values ​​for diesel engine emissions (DME) apply TRK values ​​of max. 0.1 mg / m³.

Retrofitting cars and trucks

Bypass-flow deep-bed filters and "open" wall-flow filters based on the CRT principle do not require any sensors or changes to the vehicle's engine control unit for regeneration. For this reason they are ideal for retrofitting. Conventional diesel soot particle filters based on the wall through-flow principle, as is customary in original equipment, can theoretically also be used for retrofitting, but only with considerable effort and expense. They do not occur in retrofitting practice.

Numerous manufacturers offer retrofit filters for cars and trucks. There are several manufacturers of retrofit systems in Germany. These companies offer different concepts for reducing soot immissions. From sintered metal filters (HJS, Mann + Hummel) to ceramic or metal sponges (GAT) to metal foil / metal fleece PM-Kat (Twintec) and combination filter - catalyst and filter in one component - a large number of concepts have been implemented.

The General Operating Permit (ABE) of the German Federal Motor Transport Authority (ABE) for its metal sponge filters was withdrawn from GAT catalysts GmbH after it was proven that they did not achieve the degree of efficiency or separation required for retrofitting. The offense was the forged test certificate for issuing the operating license.

The companies Baumot, HUSS, HJS, PURItech, Tehag and Twintec in particular have an extensive range of products for retrofitting commercial vehicles, especially for trucks. Baumot Deutschland GmbH in Recklinghausen, Tehag Deutschland GmbH in Moers, and HUSS Umwelttechnik GmbH in Nuremberg offer them In addition, we offer a wide variety of diesel particulate filter systems for off-road and heavy-duty vehicles. The spectrum ranges from systems that regenerate continuously during operation to particle filters that work when the engine is not running. The legislator prescribes electronic monitoring of the built-in particle filters. This is to ensure that the specified pollutant values ​​are adhered to and that the systems function properly. CPK Automotive or DEC, for example, are manufacturers of such electronic controls. With their help, diesel particulate filters are monitored and the vehicle driver is informed of error messages. All recorded data are logged and are available for evaluation on the PC. These monitoring systems can usually be used regardless of the engine manufacturer and type, exhaust system and additive.

The budget committee of the Bundestag has made available 30 million euros for the 2012 budget year to support retrofitting with particulate filters. This means that around 90,000 retrofits can be funded. For 2015, the federal government is making available 30 million euros to fund the retrofitting of particle filters. Diesel cars with first registration up to 12/2006 as well as mobile homes and light commercial vehicles up to 3.5 t each and first registration up to 16 December 2009 are eligible for funding.

Effects on Taxation


In Germany, the retrofitting of diesel-powered cars with particle filters is tax-subsidized. The fourth law amending the Motor Vehicle Tax Act (BT-Drs. 16/4010) came into force on April 1, 2007. Subsequently installed diesel soot particle filters were funded retrospectively until January 1, 2006. For diesel cars that were registered for the first time by the end of 2006 and which can be shown to comply with certain limit values ​​for fine dust emissions after installing a filter, a vehicle tax rebate of up to 330 euros was granted until the end of 2010.

From April 1, 2007, the vehicle tax increased by 1.20 euros for every 100 cc or part thereof for diesel cars that were not converted and registered for the first time until December 31, 2006. For the owner of a diesel car with 2000 cm³ displacement, this is an additional annual cost of 24 euros. The tax surcharge was initially limited to March 31, 2011.

New diesel vehicles without a particle filter registered on January 1, 2007 or later were also subject to the tax surcharge, unless they comply with the future Euro 5 limit value for particle mass of 0.005 g / km.

Only the subsequent installation of a soot particle filter was subsidized by taxes. Vehicles that were already equipped with a corresponding filter ex works were not subject to the law and were therefore not tax-subsidized.

Diesel vehicles without a filter suffered lower sales proceeds due to tax disadvantages and possible driving restrictions.


In Austria, since July 1, 2005, there has been state funding for vehicles with filters. The standard consumption tax ( NoVA ) is reduced by 300 euros for all diesel vehicles with filters that are registered by June 30, 2007. This last-mentioned reduction was extended by one year (thus still valid for all registrations until June 30, 2008). For diesel cars without a filter, the NoVA increased by 0.75% (but not more than 150 euros). On July 1, 2006, this penalty was doubled and is now 1.5% (but no more than 300 euros). The bonus is only granted if certain limit values ​​are adhered to, which as a rule cannot be adhered to when retrofitting. However, this is partly supported by the federal states and municipalities.

Particulate reduction levels

With the introduction of the so-called fine dust ordinance , the labeling of motor vehicles according to the level of their particulate emissions is standardized nationwide. According to this, diesel cars can reach certain limit values ​​by retrofitting particle filters, which lead to a classification in a particle reduction level and which are used as a criterion for the issuing of stickers (green, yellow or red) in Germany. The limit values ​​PM1 to PM3 are achieved by the so-called "open" particle filter systems, which by far do not lower the particle mass emissions to the level of 0.001 g / km as with closed particle filter systems.

  • PM1: Euro 1 and Euro 2 diesel cars can thus reach the limit values ​​for Euro 3, namely a particle mass emission of less than 0.05 g / km.
  • PM2: Euro 3 diesel cars can reach the limit values ​​for Euro 4, namely particle mass emissions of less than 0.025 g / km.
  • PM3: Euro-4 diesel cars that previously complied with a limit value of 0.025 g / km now achieve the halved Euro-4 limit value of 0.0125 g / km.
  • PM4: This level is given to retrofitted Euro 4 diesel cars that were appropriately pre-equipped at the factory, but could not be equipped with the "regulated particle filters" due to a lack of production capacities, which achieve a reduction rate of more than 90%. PM4 vehicles comply with the limit values ​​for Euro 5 with a particle mass emission of less than 0.005 g / km.
  • PM5: Only new vehicles in emission classes Euro 3 and Euro 4 receive the Euro 5 limit of 0.005 instead of a PM limit value of 0.050 g / km according to Euro 3 or 0.025 g / km according to Euro 4 from the date of first registration Observe g / km.

Current discussion about particulate matter

The filter is often considered to be the best solution to massively reduce the carcinogenic particles in the emissions of diesel engines . Nevertheless, the potential for improvement in fine dust pollution through the filter should not be overestimated, since the share of road traffic (cars and commercial vehicles ) in fine dust pollution for particles <10 µm is only 17% in the national average.

According to the findings of the federal state of Mecklenburg-Western Pomerania, which were published in the document "Fine dust immissions in Mecklenburg-Western Pomerania" from 2004, the proportion of fine dust in all motor vehicles (road, i.e. cars and trucks, as well as other: construction machinery, industrial trucks such as forklifts or forestry and agricultural machinery as well as locomotives and ships) just 0.1%. For this reason, scientists like the epidemiologist H.-Erich Wichmann differentiate between general fine dust and fine dust on a carbon basis. According to H.-Erich Wichmann, the latter is the health-critical fine dust.

A vehicle with a diesel particulate filter cannot be operated with pure biodiesel ( RME ) or only to a limited extent. A CO 2 reduction can only be achieved by adding RME or BTL to the mineral diesel, which is already carried out in the refinery with up to 7% according to the corresponding EU directive.

Exceeding limits in cities

There are various reasons for exceeding the limit values ​​specified by the European Union. In the case of fine dust (PM), the main causes (without taking natural fine dust into account) are brake and tire wear and, above all, the swirling up of the dust (suspension) that is already on the ground. The share of diesel soot (cars and trucks) makes up around a third of the anthropogenic fine dust share. In addition to traffic, there is also house fires (especially wood-burning stoves), power plants, raw material handling (sand, gravel, coal, etc.) and other industrial fine dust emissions as well as other incinerations (e.g. Easter fires in Northern Germany).

According to the Federal Environment Agency , this (trucks and cars together) contributes over 58% of the PM 10 pollution in Berlin . So far, however, mostly only the PM 10 values have been measured and not the even finer carcinogenic and exhaust-gas-typical particles. In some cities, for example in Vienna, the smaller particles with 2.5 µm are also measured at some measuring points.

In terms of nitrogen oxide values, on the other hand, motor vehicle traffic (including that of non-road vehicles such as construction machinery, forklifts, tractors etc .; but also lawnmowers, power chainsaws, dust / leaf blowers, etc.) is the main cause. The nitrogen oxide emissions of all these internal combustion engines are well over 50% of the total nitrogen oxide emissions.


There are many municipal ways to mitigate local particulate matter pollution, such as driving bans. In Greece and Italy, for example, temporary driving bans are in place across all vehicle classes in the major cities. Athens, for example, only allows vehicles with even or odd numbers of license plates to enter the city center on a daily basis . The city ​​toll systems that have been set up in Europe to date ( e.g. London ) differentiate between emission classes.

In Germany z. B. for Munich: Since October 1, 2010, cars with a yellow or green sticker are only allowed to drive within the middle ring, since October 1, 2012, only cars with a green sticker are allowed.

Since January 1, 2010, the Berlin inner city ring may only be used with a green sticker. Exceptions are only allowed to a very limited extent and must be approved.

The scrapping bonus has drastically reduced the particulate matter problem on the part of car diesel engines, but the overall particulate matter emissions have only been reduced slightly. The background to this is that the diesel internal combustion engines in passenger cars contribute only little to fine dust emissions - see above: “Limit values ​​exceeded in cities”. Lower toll payments for low-emission trucks as well as de minimis subsidies for haulage companies have drastically reduced the fine dust problem on the part of truck diesel engines; but this also does not generally solve the fine dust problem. Until the root causes are addressed, there is no improvement in sight. Natural sources of fine dust cannot be influenced at all, be it pollen or volcanic ash, for example . The particulate matter emitted by volcanoes is distributed worldwide across the stratosphere and can be identified as particulate matter.

For measures see also fine dust reduction .

Environmental aspects of the filters

  • Filters (wall-flow filters; often, incorrectly also called closed systems ) reduce the particle mass by well over 90%, but the fine particles that can penetrate the lungs are not completely reduced (sometimes only by 50%).
  • Wall-flow filters produce considerably harmful pollutants, especially so-called polycyclic aromatic hydrocarbons (PAH) such as benzo [ a ] pyrene - according to VDI report 714, 1988, over 300 times as much as a vehicle without a filter (during regeneration).
  • As with every component, resources are required for manufacture and disposal, and thus pollute the environment.
  • Filters increase fuel consumption by up to 9%, especially during regeneration, as the fuel mixture is “enriched” for burning the soot particles.
  • In city traffic, the exhaust gas temperatures required for regeneration are not reached at the low engine speeds, so that the filters clog faster than average. This means unnecessary trips at high engine speed at regular intervals in order to clean the filter.

Application of biodiesel

The particle filter manufacturers HJS , Eberspächer and Twintec (Freie Werkstätten) have approved their retrofit particle filters for operation with biodiesel . For operation with biodiesel, it is therefore crucial whether the vehicle is approved for this fuel - this is the case with many VW, Škoda and Seat vehicles according to the operating instructions. Nothing stands in the way of retrofitting and thus continued operation with biodiesel.

European emission standards

To reduce soot particles from diesel engines in passenger cars, the European Union (EU) has been tightening the emission standards for particles in the NEDC test cycle since 1993 as follows:

  • Euro 1 (1993): 140 mg particles / km
  • Euro 2 (1997): 80/100 mg particles / km (diesel engines with direct injection 100 mg / km, with indirect injection 80 mg / km)
  • Euro 3 (2001): 50 mg particles / km
  • Euro 4 (2005): 25 mg particles / km
  • Euro 5 (2009): 5 mg particles / km
  • Euro 6 (2014): 4.5 mg particles / km

The European Parliament approved the Euro 5 and Euro 6 emission standards on December 13, 2006 in Strasbourg.

The particle limit of 5 mg / km should also apply to lean-burn and direct-injection gasoline engines from Euro 5 onwards. Lean here means that during combustion (as in a diesel engine) there is more air available in the combustion chamber than is necessary for complete combustion (lambda> 1). Conventional gasoline engines, on the other hand, are usually operated with a constant lambda of 1. This particle limit for gasoline engines could mean that such vehicles would also have to be equipped with a filter for certification according to Euro 5.

Motor vehicles with filters ex works

Larger diesel engines have been offered with filters for a long time, although the exhaust gas limit values ​​in accordance with Euro 4 and, in some cases, Euro 5 would have been possible without a diesel particulate filter. For political reasons alone, however, the diesel particulate filter has largely gained acceptance. Only for small cars did some automobile manufacturers forego the use of a diesel particulate filter for reasons of cost. The limit values ​​of Euro level 6 can probably not be met without a diesel particulate filter. This does not only apply to diesel engines, but also to gasoline engines, especially direct-injection petrol engines, which also have soot problems.

The strived for strict particle number limit of 6 × 10 11 particles per kilometer at Euro 6 was rejected in 2011 by manufacturers of wall-flow filters as not being compliant.


Doubts about the effectiveness for the environment

Diesel particulate filters are a lot more complex than catalytic converters. The reason for this is that the highly efficient wall-flow particle filters have to burn off the collected soot regularly (regeneration). This requires complex control technology and the use of temperature-reducing processes. In addition, the soot burn-off also creates secondary emissions. Opel development engineers have proven that diesel soot particle filters produce polycyclic aromatic hydrocarbons (PAHs, especially benzo [ a ] pyrene ) in greatly increased concentrations and release them during regeneration. These should actually be removed with an additional catalyst after the DPF. When PAHs are burned at a low temperature, as is the case with the regeneration temperature of around 250 to 500 ° C, dioxins and furans may even be formed. This has been proven by several research institutions: Swiss Federal Office for the Environment (FOEN); Federal Materials Testing and Research Institute (EMPA, Analytical Chemistry Department), the Engl. Institut Ricardo on behalf of the EU on the subject: Particle Measurement Program (PMP).

Other experts and even manufacturers doubt the promised effect of the diesel particulate filter. In the book "Minimizing Particle Emissions from Internal Combustion Engines", measurements by Heinz Burtscher from the Aargau / Windisch University of Applied Sciences in Switzerland show that particle filters through the wall do not have the desired and required high separation efficiency of 99%, especially in the 10 to 500 nanometer range. On the contrary: these fine particle numbers are even increasing. These are aerosols that are more or less broken down by the filter. In turn, the American company Corning, itself a large manufacturer of wall-flow particle filters , showed at an SAE conference in Chicago that these filters can sometimes have a separation efficiency of only 43%, depending on their porosity and pore size. After the regeneration, which is known to take place every 500 to 1000 km, the separation efficiency is only less than 60%.

German automobile manufacturers only use coated diesel particulate filters. For reasons of cost, some manufacturers have dispensed with an upstream oxidation catalyst that supports the burning off of the soot particles. The result: When driving at low speed, such as constant city trips or driving on very winding roads, the particle filter can no longer burn off the collected soot and the front part of the filter in particular quickly clogs. A control lamp on the dashboard with the inscription “Dieselparticulate filter” then prompts the driver to take a special “regeneration drive”. Even those who live in the middle of a big city have to drive at least 60 km / h for more than 15 minutes. If you ignore the indicator light and start the car five more times, you can only drive to the workshop at a limited speed, where the filter has to be cleaned manually or the soot burnt off.

There are also criticisms of bypass deep-bed filters and of "open" wall-flow filters based on the CRT principle. Above all, the low separation efficiency of 30 to 40% is emphasized. However, this is the total particle mass. The separation efficiency in relation to the number of particles is quite high at 80%. Technicians from the Eidgenössische Materialprüfungs- und Forschungsanstalt (EMPA) in Dübendorf (Switzerland) tested a VW Touran 1.9 TDI before and after it was fitted with a so-called "open" filter system. As Spiegel Online reported on January 29, 2007, the soot load in the exhaust gases was reduced by almost 40 percent due to the filter installation - but this corresponds to the specifications, since it is a retrofit filter (see under “Comparison to wall-flow filter”).

Nitrogen dioxide

CRT diesel particulate filters can increase the proportion of nitrogen dioxide (NO 2 ) in total nitrogen oxide (NO x ) emissions . The UBA reports that the use of CRT particle filters increases NO 2 emissions from 5% to 60%. This in turn leads to increased, inner-city NO 2 emissions in narrow urban canyons. This effect is particularly significant when introducing CRT particle filters in EuroIV vehicles and when retrofitting old vehicles (before EuroV) with high NOx emissions, as this increases the absolute NO 2 emissions significantly. The effect can be demonstrated in the immission measurements, which increase significantly around 2003, when the CRT filter was introduced. Currently, however, the filters are mostly combined with SCR systems ( selective catalytic reduction ) in order to reduce total NOx emissions, which also reduces absolute nitrogen dioxide emissions.

Increase in fuel consumption

Long-term tests have shown that the particle filter can lead to additional consumption of 3 to 8 percent. For example, Škoda states on its website an additional consumption of around 0.2 liters for models with a particle filter. The increased consumption results, among other things, in the necessary regeneration of the diesel particulate filter, which requires additional fuel. The combustion provides the necessary increase and maintenance of the exhaust gas temperature, which is necessary for the ignition of the accumulated soot until complete regeneration.

Shorter maintenance intervals

Depending on the manufacturer, car models with particle filters may require shorter maintenance intervals; For models of the Mercedes-Benz A-Class with a particle filter, this is only around 15,000 km, as only certain engine oils that are listed in the manufacturer's specifications sheet 229.31 or 229.51 may be used in connection with the particle filter. If these oils are also used in A-Class models without a particle filter, the interval for these is also reduced to 15,000 km.

See also


  • David Krahlisch: Lobbyism in Germany - Using the example of the diesel particulate filter. VDM Verlag Dr. Müller, Saarbrücken 2007, ISBN 978-3-8364-2316-8 .
  • Andreas Mayer and others: Minimizing particle emissions from internal combustion engines. Expert Verlag, Renningen 2004, ISBN 3-8169-2430-1 .
  • H. Berendes, H. Eickhoff: Development of a regeneration system for exhaust particle filters of diesel engines. VDI reports No. 765-1989, VDI Verlag 1989, ISBN 3-18-090765-7 .

Sources and individual references

  1. Citroën workshop documents: C5 (X7) - B1HAAVP0 - Function: Additive supply of fuel (SIEMENS SID 201). and C5 (X7) - D4EA02TZP0 - Function: Additive supply of the fuel (Bosch EDC17CP11).
  2. http://www.stahlgruber.de/Kataloge/chemie/data/pdf/ford_1.pdf Technical Bulletin Ford
  3. Andreas Döring, Eberhard Jacob: Method and apparatus for separating fine particulate matter from exhaust gas of an internal combustion engine . Ed .: European Patent Office. EP1072765, 2000 ( googleapis.com [PDF]).
  4. Imprisonment for former GAT managing director. at: www.autoservicepraxis.de , accessed on November 6, 2013.
  5. Retrofitting with particle filters will be funded again in 2012 - budget committee clears the way. In: Press release No. 139/11. Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB), November 11, 2011, accessed on March 31, 2014 .
  6. DPF retrofitting: Funding 2015. February 18, 2015, accessed on February 18, 2015 .
  7. Retrofitting with particle filters should also be funded in 2010. In: Press release No. 362/09. Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB), December 16, 2009, accessed on March 31, 2014 .
  8. Federal Law Gazette for the Republic of Austria No. 65/2007 of July 31, 2007 (individual evidence for the extension of the tax break until June 2008)
  9. The fine dust ghost. (= Der Spiegel . 14/05).
  10. wien.gv.at
  11. Working Group Quality Management Biodiesel eV - FAQ: Retrofit particle filters and biodiesel. ( Memento from July 26, 2009 in the Internet Archive )
  12. VDI reports No. 714, 1988: F. Indra: Particle filter for passenger car diesel engines by F. Indra
  13. "Soot particle filter without side effects"
  14. There are good filters and there are bad filters.
  15. The Cost of the Diesel Boom. (PDF; 93 kB)
  16. Andreas Mayer and others: Minimizing particle emissions from internal combustion engines. Expert Verlag, Renningen 2004, ISBN 3-8169-2430-1 .
  17. Fine dust filter: Doubtful miracle weapon. Retrieved September 29, 2009 .
  18. Statement on the CRT soot filter. Federal Environment Agency , archived from the original on April 11, 2013 ; Retrieved April 4, 2011 .
  19. Federal Environment Agency: nitrogen dioxide pollution. Retrieved March 1, 2020 .
  20. Retrofit particle filter being tested. ADAC , archived from the original on July 5, 2010 ; Retrieved June 15, 2010 .
  21. Soot particle filters increase fuel consumption. In: Hamburger Abendblatt. October 5, 2005.