A light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode, which emits light when activated.[4]When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor.
An LED is often small in area (less than 1 mm2) and integrated optical components may be used to shape its radiation pattern.[5]
Appearing as practical electronic components in 1962,[6] the earliest LEDs emitted low-intensity infrared light. Infrared LEDs are still frequently used as transmitting elements in remote-control circuits, such as those in remote controls for a wide variety of consumer electronics. The first visible-light LEDs were also of low intensity, and limited to red. Modern LEDs are available across the visible,ultraviolet, and infrared wavelengths, with very high brightness.
Early LEDs were often used as indicator lamps for electronic devices, replacing small incandescent bulbs. They were soon packaged into numeric readouts in the form of seven-segment displays, and were commonly seen in digital clocks.
Recent developments in LEDs permit them to be used in environmental and task lighting. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are now used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, camera flashes and even LED wallpaper. As of 2015, LEDs powerful enough for room lighting remain somewhat more expensive, and require more precise current and heat management, than compact fluorescent lampsources of comparable output.
LEDs have allowed new text, video displays, and sensors to be developed, while their high switching rates are also useful in advanced communications technology.

Discoveries and early devices[edit]

Green electroluminescence from a point contact on a crystal of SiCrecreates H. J. Round's original experiment from 1907.
Electroluminescence as a phenomenon was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector.[7][8] Soviet inventor Oleg Losev reported creation of the first LED in 1927.[9] His research was distributed in Soviet, German and British scientific journals, but no practical use was made of the discovery for several decades.[10][11]Kurt Lehovec, Carl Accardo and Edward Jamgochian, explained these first light-emitting diodes in 1951 using an apparatus employing SiCcrystals with a current source of battery or pulse generator and with a comparison to a variant, pure, crystal in 1953.[12] [13]
Rubin Braunstein[14] of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955.[15] Braunstein observed infrared emission generated by simple diode structures using gallium antimonide(GaSb), GaAs, indium phosphide (InP), and silicon-germanium (SiGe) alloys at room temperature and at 77 kelvins.
In 1957, Braunstein further demonstrated that the rudimentary devices could be used for non-radio communication across a short distance. As noted by Kroemer[16] Braunstein".. had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away. This signal was fed into an audio amplifier, and played back by a loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup." This setup presaged the use of LEDs for optical communication applications.

Diagram of a light emitting diode constructed on a zinc diffused area of gallium arsenide semi-insulating substrate
In October 1961, while working at Texas Instruments in Dallas, TX, James R. Biard and Gary Pittman discovered infrared light emission from a tunnel diode they had constructed on a GaAs substrate.[17] Later that month, they were able to demonstrate efficient light emission and signal coupling between a GaAs p-n junction light emitter and an electrically-isolated semiconductor photodetector.[18] On August 8, 1962, Biard and Pittman filed a patent titled "Semiconductor Radiant Diode" based on their findings, which described a zinc diffused p–n junction LED with a spaced cathode contact to allow for efficient emission of infrared light under forward bias.
After establishing the priority of their work based on engineering notebooks predating submissions from G.E. Labs, RCA Research Labs, IBMResearch Labs, Bell Labs, and Lincoln Lab at MIT, the U.S. patent office issued the two inventors the patent for the GaAs infrared (IR) light-emitting diode (U.S. Patent US3293513), the first practical LED.[19] Immediately after filing the patent, Texas Instruments began a project to manufacture infrared diodes. In October 1962, they announced the first LED commercial product (the SNX-100), which employed a pure GaAs crystal to emit a 900 nm light output.
The first visible-spectrum (red) LED was developed in 1962 by Nick Holonyak, Jr., while working at General Electric Company.[6] Holonyak first reported his LED in the journal Applied Physics Letters on the December 1, 1962.[20][21] M. George Craford,[22] a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972.[23] In 1976, T. P. Pearsall created the first high-brightness, high-efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.
About LED Lighting
LED light bulbs are carefully packaged arrays of light emitting diodes (LEDs). These simple LEDs are solid state devices which produce light through a process called "electroluminescence." They do this by moving electrons across a very special gap within their internal construction that gives off photons when electrons enter the gap. These photons are the light we see and are different colors based on what materials are used to make the LED. LED bulbs use arrays of multiple LEDs along with special reflectors to replicate the patterns and brilliance of standard lights in many shapes and sizes.
This method not only produces far less heat, but it generates an equivalent amount of light for roughly 80% less energy than a traditional incandescent lamp. Without a filament or glass bulb, an LED light bulb is also more durable and longer lasting than any incandescent can be.
LEDs are one of today's most promising lighting technologies. The best claims made by LEDs are: * No mercury, making them a cleaner alternative to fluorescent and CFL lamps. * The lowest energy consumption of any lighting product to date. * Light quality equal or superior to traditional lighting products. * Life that is 20 times than some traditional lighting products.
LEDs or Fluorescents - Which is More Efficient?
When it comes to purchasing energy-efficient lighting, LEDs exceed CFLs by a wide margin. LEDs have a faster start time, work well in cold weather, and are substantially more durable since they're made from plastic rather than glass. From standard bulbs to fluorescent tubes, LEDs can replicate the same lighting conditions found in fluorescents while lasting longer and using less energy. As an added bonus, all LEDs are RoHS compliant and do not use mercury, a claim that can't be made by fluorescent lamps.

A diesel particulate filter (or DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.[1][2]
Contents
[hide] * 1 Mode of action * 2 History * 3 Variants of DPFs * 3.1 Cordierite wall flow filters * 3.2 Silicon carbide wall flow filters * 3.3 Ceramic Fiber Filters * 3.4 Metal fiber flow-through filters * 3.5 Paper * 3.6 Partial filters * 4 Maintenance * 5 Safety * 6 Regeneration * 7 Notes * 7.1 Citations * 8 See also * 9 External links
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Mode of action[edit]
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 and convert it to ash where it is stored in the DPF filter,[3] or through other methods. This is known as "filter regeneration". 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.[4] 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.[5] If the driver ignores thewarning light and waits too long to operate the vehicle above 40 miles per hour (64 km/h), the DPF may not regenerate properly, and continued operation past that point may spoil the DPF completely so it must be replaced.[6] 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.
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History[edit]
Diesel engines produce a variety of particles during 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.[7]
Diesel particulate matter resulting from the incomplete combustion of diesel fuel produces soot (black carbon) particles. These particles include tiny nanoparticles—smaller than a thousandth of a millimeter (one micron). Soot and other particles from diesel engines worsen the particulate matter pollution in the air and are harmful to health[citation needed].
New particulate filters can capture from 30% to greater than 95% of the harmful soot.[8] With an optimal diesel particulate filter (DPF), soot emissions may be decreased to 0.001 g / km or less.[9]
The quality of the fuel also influences the formation of these particles. For example, a high sulfur content diesel produces more particles. Lower sulfur fuel produces fewer particles, and allows use of particulate filters. The injection pressure of diesel also influences the formation of fine particles.
Particulate filters have been in use on non-road machines since 1980, and in automobiles since 1985.[10] [11] 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.[12] 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 theEuropean Union and some individual European countries, most Asian countries, and the rest of North and South America.[13]
While no jurisdiction has explicitly 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. [12] In the European Union, filters are expected to be necessary to meet the Euro.VI heavy truck engine emissions regulations currently under discussion and planned for the 2012-2013 time frame. In 2000, in anticipation of the future Euro 5 regulations PSA Peugeot Citroën became the first company to make filters standard on passenger cars.[14]
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—require 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.[15] In 2009 the American Recovery and Reinvestment Act provided funding to assist owners in offsetting the cost of diesel retrofits for their vehicles.[16] Other jurisdictions have also launched retrofit programs, including: * 2001 - Hong Kong retrofit program.[17] * 2002 - In Japan the Prefecture of Tokyo passed a law banning trucks without filters from entering the city limits.[18] * 2003 - Mexico City started a program to retrofit trucks.[19] * 2004 - New York City retrofit program (non-road).[20] * 2008 - Milan Ecopass area traffic charge – a hefty entrance tax on all diesel vehicles except those with a particulate filter, either stock or retrofit.[21] * 2008 - London Low Emission Zone charges vehicles that do not meet emission standards, encouraging retrofit filters.[22][23]
Inadequately maintained particulate filters on vehicles with diesel engines are prone to soot buildup, which can cause engine problems due to high back pressure.[4]
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Variants of DPFs[edit]

Cordierite Diesel Particulate Filter on GM 7.8 Isuzu
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;[2][24] however, the DPF does not retain small particles and maintenance-free DPFs break larger particles into smaller ones. There are a variety of diesel particulate filter technologies on the market. Each is designed around similar requirements: 1. Fine filtration 2. Minimum pressure drop 3. Low cost 4. Mass production suitability 5. Product durability
Cordierite wall flow filters[edit]
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 break down.[25][2]
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.[26]
Silicon carbide wall flow filters[edit]
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.[27][2]
The characteristics of the wall flow diesel Particulate filter substrate are as follows: 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.[27]
Ceramic Fiber Filters[edit]
Fibrous ceramic filters are made from several different types of ceramic fibers that are mixed together to form a porous media. This media can be formed into almost any shape and can be customized to suit various applications. The porosity can be controlled in order to produce high flow, lower efficiency or high efficiency lower volume filtration. Fibrous filters have an advantage over wall flow design of producing lower back pressure. Ceramic wall-flow filters remove carbon particulates almost completely, including fine particulates less than 100 nanometers (nm) diameter with an efficiency of greater than 95% in mass and greater than 99% in number of particles over a wide range of engine operating conditions. Since the continuous flow of soot into the filter would eventually block it, it is necessary to 'regenerate' the filtration properties of the filter by burning-off the collected particulate on a regular basis. Soot particulates burn-off forms water and CO2 in small quantity amounting to less than 0.05% of the CO2 emitted by the engine.[2]
Metal fiber flow-through filters[edit]
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 generally not interchangeable with them because of the electrical requirement.[28][2]
Paper[edit]
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.[29] 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.[30][2]
Partial filters[edit]
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. [31]
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Maintenance[edit]
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. Warnings are given to the driver before filter restriction causes an issue with drive-ability or damage to the engine or filter develop. Regular filter maintenance is a necessity.[4]
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Safety[edit]
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.[32] 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.[33]
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Regeneration[edit]

Metering pump for Diesel or additive injection, 3 L/h at 5 bar

Diagram of the regeneration

Hino truck 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.[34][35]
Regeneration is the process of removing 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:[8] 1. Engine management to increase exhaust temperature through late fuel injection or injection during the exhaust stroke 2. Use of a fuel borne catalyst to reduce soot burn-out temperature 3. A fuel burner after the turbo to increase the exhaust temperature 4. A catalytic oxidizer to increase the exhaust temperature, with after injection (HC-Doser) 5. Resistive heating coils to increase the exhaust temperature 6. Microwave energy to increase the particulate temperature
All on-board active systems use extra fuel, whether through burning to heat the DPF, or providing extra power to the DPF's electrical system, although the use of a fuel borne catalyst reduces the energy required very significantly. Typically a computer monitors one or more sensors that measure back pressure and/or temperature, and based on pre-programmed set points the computer makes decisions on when to activate the regeneration cycle. The additional fuel can be supplied by a metering pump. Running the cycle too often while keeping the back pressure in the exhaust system low will result in high fuel consumption. Not running the regeneration cycle soon enough increases the risk of engine damage and/or uncontrolled regeneration (thermal runaway) and possible DPF failure.
Diesel particulate matter burns when temperatures above 600 degrees Celsius are attained. This temperature can be reduced to somewhere in the range of 350 to 450 degrees Celsius by use of a fuel borne catalyst. The actual temperature of soot burn-out will depend on the chemistry employed. The start of combustion causes a further increase in temperature. In some cases, in the absence of a fuel borne catalyst, the combustion of the particulate matter can raise temperatures above the structural integrity threshold of the filter material, which can cause catastrophic failure of the substrate. Various strategies have been developed to limit this possibility. Note that unlike a spark-ignited engine, which typically has less than 0.5% oxygen in the exhaust gas stream before the emission control device(s), diesel engines have a very high ratio of oxygen available. While the amount of available oxygen makes fast regeneration of a filter possible, it also contributes to runaway regeneration problems.
Some applications use off-board regeneration. Off-board regeneration requires operator intervention (i.e. the machine is either plugged into a wall/floor mounted regeneration station, or the filter is removed from the machine and placed in the regeneration station). Off-board regeneration is not suitable for on-road vehicles, except in situations where the vehicles are parked in a central depot when not in use. Off-board regeneration is mainly used in industrial and mining applications. Coal mines (with the attendant explosion risk from coal damp) use off-board regeneration if non-disposable filters are installed, with the regeneration stations sited in an area where non-permissible machinery is allowed.
Many forklifts may also use off-board regeneration - typically mining machinery and other machinery that spend their operational lives in one location, which makes having a stationary regeneration station practical. In situations where the filter is physically removed from the machine for regeneration there is also the advantage of being able to inspect the filter core on a daily basis (DPF cores for non-road applications are typically sized to be usable for one shift - so regeneration is a daily occurrence).[36]

The exhaust emissions standards for new cars have effectively required fitment of a DPF in the exhaust of diesel cars since 2009 when the 'Euro 5' standard came into force. In fact, many cars registered before 2009 will have had one fitted too in anticipation of the change in standards.

Standards aim to deliver an 80% reduction in diesel particulate (soot) emissions but the technology's not without problems – AA patrols are regularly called to cars with the particulate filter warning light on indicating a partial blockage of the filter.

Even if your driving isn't mainly urban/stop-start, changes to driving style may be required to keep these systems working properly.
If you're buying a new car and plan to use it mainly for town-based, stop/start driving it would be wise to avoid a diesel car fitted with a Diesel Particulate Filter (DPF) because of the possible hassle of incomplete 'DPF regeneration'.

dpf warning light
How do they work?
Diesel Particulate filters (DPF) or 'traps' do just that, they catch bits of soot in the exhaust.
As with any filter they have to be emptied regularly to maintain performance. For a DPF this process is called 'regeneration' – the collected soot is burnt off at high temperature to leave only a tiny ash residue.
Regeneration is either passive or active
Passive regeneration
Passive regeneration takes place automatically on motorway or fast A-road runs when the exhaust temperature is high. Because many cars don't get this sort of use vehicle manufacturers have had to design-in 'active' regeneration where the engine management computer (ECU) takes control of the process.
Active regeneration
When the soot loading in the filter reaches a set limit (about 45%) the vehicle's ECU will initiate post combustion fuel injection to increase the exhaust temperature and trigger regeneration. If the journey is too short while the regeneration is in progress, it may not complete and the warning light will come on to show that the filter is partially blocked.
It should be possible to complete a regeneration cycle and clear the warning light by driving for 10 minutes or so at speeds greater than 40mph.
Symptoms of active regeneration
During active regeneration you may notice the following symptoms: * Cooling fans running * Increased idle speed * Deactivation of automatic Stop/Start * A slight increase in fuel consumption * A hot, acrid smell from the exhaust. * Engine note change
If the regeneration is unsuccessful due to an insufficient driving cycle the extra fuel injected into the cylinders will not burn and will drain into the sump. As a result, oil quality will deteriorate and the level will rise. Most DPF equipped engines will have an oil quality/viscosity sensor but it is important that you check that the oil level does not increase above the maximum level on the dipstick as diesel engines can run on their own oil if the level is excessive – often to the point of destruction.
If you ignore the DPF warning light and keep driving in a relatively slow, stop/start pattern, soot loading will continue to build up until around 75% when you can expect to see other dashboard warning lights come on too. At this point driving at speed alone will not be enough and you will need to take the car to a dealer for 'forced' regeneration.
Forced regeneration
Forced regeneration is required where `Active` regeneration criteria have not been met or where soot levels have increased within the DPF to a point where normal regeneration cannot be performed: typically around 70% soot loading. At this point the vehicle will enter a 'restricted performance' mode to prevent further damage. If left the soot loading will keep rising.
At this level of soot loading a diagnostic tool must be used to force regeneration. Above around 85% soot loading regeneration can no longer be performed on the vehicle and the DPF will need removing to be cleaned or replaced.
What can prevent normal regeneration taking place? * Frequent short journeys where the engine does not reach normal operating temperature * Wrong oil type - DPF equipped cars require low ash, low sulphur engine oils * A problem with the inlet, fuel or Exhaust Gas Recirculation (EGR) system causing incomplete combustion will increase soot loading. * A warning light on or diagnostic trouble code logged in the engine management system may prevent active or catalyst regeneration * Low fuel level will prevent active regeneration taking place. As a general rule ¼ tank is required * Oil counter/service interval - exceeding the service interval may prevent regeneration * Additive tank low or empty - if the vehicle uses Eolys™ additive a low level may prevent regeneration.
Expensive repairs
If you continue to ignore warnings and soot loading keeps increasing then the car won’t run properly and the most likely outcome will be that you will have to get a new DPF costing at least £1000 plus labour and diagnostic time.
The ash residue which remains after successful regeneration cannot be removed and will eventually fill the filter. DPFs are designed to last in excess of 100,000 miles but, if the vehicle is operated correctly, many will far exceed this mileage.
DPF additives
The most commonly fitted type of DPF has an integrated oxidising catalytic converter and is located very close to the engine where exhaust gases will still be hot. This heat means that passive regeneration is more likely to be successful.
Some models, across a wide range of manufacturers, use a different type of DPF which relies on a fuel additive (Eolys™ fluid) containing Cerium (III) Oxide. Cerium ignites at a lower temperature and adheres to the soot particles meaning regeneration can occur at a lower temperature.
The additive is stored in a separate tank next to the fuel tank and is automatically mixed with the fuel whenever you fill up. Only very small quantities are used so a litre of additive should treat around 2800 litres of fuel – enough to cover 25,000 miles at 40mpg. It lasts about 70000 miles and is replenished during a service – at extra cost.
You will have to pay to get the additive tank refilled at some time in the car's life – expect to pay between £150 and £200 including fluid and labour
Don't be tempted to ignore a warning light showing that the additive tanks need refilling. It's absolutely essential this tank is refilled as without it regeneration is unlikely to be successful and a new DPF may be needed – at significant cost. Fuel consumption can increase as a result of failed regenerations too.
Check the handbook
If you buy a car with a DPF it’s important to read the relevant section of the vehicle handbook so that you understand exactly what actions to take if the warning light illuminates and how, if at all, your driving style may need to be adjusted to ensure maximum DPF efficiency and life.
In most cases there is only a relatively short time between the dpf being partially blocked and becoming so blocked that it requires manual regeneration.
AA experience
We're seeing some evidence of DPF systems failing to regenerate even on cars used mainly on motorways.
On cars with a very high sixth gear the engine revs may be too low to generate sufficient exhaust temperature for regeneration. Occasional driving in a lower gear to maintain around 2,000rpm should be sufficient to burn off the soot in such cases (refer to the vehicle handbook).
DPF regeneration will be initiated by the ECU every 300 miles or so depending on vehicle use and will take 5 to 10 minutes to complete. You may notice other symptoms and a puff of blue smoke from the exhaust, similar to an engine burning oil, when the process is complete.
There's no evidence in AA breakdown data that the problem's going away – newer car models seem just as likely to suffer DPF problems if not driven 'correctly' as those built when DPF's were introduced.
Removal is not a legal option
It is suggested from time to time that the answer to failed DPF regeneration is get the DPF removed from the exhaust system rather than pay to get it repaired/renewed. Indeed there are companies advertising just such a service including reprogramming of the engine management software, but is it legal?
DPFs are fitted to meet European emissions regulations designed to reduce vehicle emissions of particulate matter (soot) associated with respiratory disease and cancer.
According to the Department for Transport, it is an offence under theRoad vehicles (Construction and Use) Regulations (Regulation 61a(3)) to use a vehicle which has been modified in such a way that it no longer complies with the air pollutant emissions standards it was designed to meet. Removal of a DPF will almost invariably contravene these requirements, making the vehicle illegal for road use.
Insurance
You must notify your insurer if the vehicle is modified but such a modification could in turn invalidate any insurance cover because it makes the vehicle illegal for road use.
MOT
From February 2014 the inspection of the exhaust system carried out during the MOT test will include a check for the presence of a DPF. A missing DPF, where one was fitted when the vehicle was built, will result in an MOT failure.
With an original equipment DPF removed from the exhaust the car may or may not pass an MOT smoke test - a Euro V (September 2009 diesel) is more likely to fail than one designed to comply with earlier emissions standards.