A diesel particulate filter (DPF) is a device designed to remove diesel particulate matter [ broken anchor ] or soot from the exhaust gas of a diesel engine. [1] [2]
A diesel particulate filter (DPF) is a device designed to remove diesel particulate matter [ broken anchor ] or soot from the exhaust gas of a diesel engine. [1] [2]
Wall-flow diesel particulate filters usually remove 85% or more of the soot, and under certain conditions can attain soot removal efficiencies approaching 100%. Some filters are single-use, intended for disposal and replacement once full of accumulated ash. Others are designed to burn off the accumulated particulate either passively through the use of a catalyst or by active means such as a fuel burner which heats the filter to soot combustion temperatures. This is accomplished by engine programming to run (when the filter is full) in a manner that elevates exhaust temperature, in conjunction with an extra fuel injector in the exhaust stream that injects fuel to react with a catalyst element to burn off accumulated soot in the DPF filter, [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 the warning light and waits too long to operate the vehicle above 60 km/h (40 mph), 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.
Diesel engines produce a variety of particles during the combustion of the fuel/air mix due to incomplete combustion. The composition of the particles varies widely dependent upon engine type, age, and the emissions specification that the engine was designed to meet. Two-stroke diesel engines produce more particulate per unit of power than do four-stroke diesel engines, as they burn the fuel-air mix less completely. [7]
Diesel particulate matter resulting from the incomplete combustion of diesel fuel produces soot (black carbon) particles. These particles include tiny nanoparticles—smaller than one micrometre (one micron). Soot and other particles from diesel engines worsen the particulate matter pollution in the air and are harmful to health. [8] New particulate filters can capture from 30% to greater than 95% of the harmful soot. [9] With an optimal diesel particulate filter (DPF), soot emissions may be decreased to 0.001 g/km or less. [10]
The quality of the fuel also influences the formation of these particles. For example, a high sulphur content diesel produces more particles. Lower sulphur fuel produces fewer particles, and allows use of particulate filters. The injection pressure of diesel also influences the formation of fine particles.
Diesel particulate filtering was first considered in the 1970s due to concerns regarding the impacts of inhaled particulates. [11] Particulate filters have been in use on non-road machines since 1980, and in automobiles since 1985. [12] [13] 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. [14] Since then, progressively tighter standards have been introduced for light- and heavy-duty roadgoing diesel-powered vehicles and for off-road diesel engines. Similar regulations have also been adopted by the European Union and some individual European countries, most Asian countries, and the rest of North and South America. [15]
Whilst few jurisdictions have explicitly made filters mandatory, the increasingly stringent emissions regulations that engine manufacturers must meet mean that eventually all on-road diesel engines will be fitted with them. [14] 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. [16]
As of December 2008, the California Air Resources Board (CARB) established the 2008 California Statewide Truck and Bus Rule which—with variance according to vehicle type, size and usage—requires that on-road diesel heavy trucks and buses in California be retrofitted, repowered, or replaced to reduce particulate matter (PM) emissions by at least 85%. Retrofitting the engines with CARB-approved diesel particulate filters is one way to fulfill this requirement. [17] In 2009 the American Recovery and Reinvestment Act provided funding to assist owners in offsetting the cost of diesel retrofits for their vehicles. [18] Other jurisdictions have also launched retrofit programs, including:
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]
In 2018, the UK made changes to its MOT test requirements, [26] including tougher scrutiny of diesel cars. One requirement was to have a properly fitted and working DPF. Driving without a DPF could incur a £1000 fine. [27] [28]
Unlike a catalytic converter which is a flow-through device, a DPF retains bigger exhaust gas particles by forcing the gas to flow through the filter material before exiting; [2] [29] however, the DPF does not retain small particles. Maintenance-free DPFs oxidise or burn larger particles until they are small enough to pass through the filter, though often particles "clump" together in the DPF reducing the overall particle count as well as overall mass. [30] [31] There are a variety of diesel particulate filter technologies on the market. Each is designed around similar requirements:
The most common filter is made of cordierite (a ceramic material that is also used as catalytic converter supports (cores)). Cordierite filters provide excellent filtration efficiency, are relatively inexpensive, and have thermal properties that make packaging them for installation in the vehicle simple. The major drawback is that cordierite has a relatively low melting point (about 1200 °C) and cordierite substrates have been known to melt during filter regeneration. This is mostly an issue if the filter has become loaded more heavily than usual, and is more of an issue with passive systems than with active systems, unless there is a system breakdown. [2] [32]
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. [33]
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. [2] [34]
The characteristics of the wall flow diesel particulate filter substrate are:
Fibrous ceramic filters are made from several different types of ceramic fibers that are mixed together to form a porous medium. This medium 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. Fibrous ceramic filters remove carbon particulates almost completely, including fine particulates less than 100 nanometres (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 particulate burn-off forms water and CO2 in small quantities amounting to less than 0.05% of the CO2 emitted by the engine. [2]
Some cores are made from metal fibers – generally the fibers are "woven" into a monolith. Such cores have the advantage that an electrical current can be passed through the monolith to heat the core for regeneration purposes, allowing the filter to regenerate at low exhaust temperatures and/or low exhaust flow rates. Metal fiber cores tend to be more expensive than cordierite or silicon carbide cores, and are generally not interchangeable with them because of the electrical requirement. [2] [35]
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. [36] 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. [2] [37]
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. [38]
Filters require more maintenance than catalytic converters. Soot, 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. [39] This increases the pressure before the filter. [4]
DPF filters go through a regeneration process which removes this soot and lowers the filter pressure. There are three types of regeneration: passive, active, and forced. Passive regeneration takes place normally while driving, when engine load and vehicle drive-cycle create temperatures that are high enough to regenerate the soot buildup on the DPF walls. Active regeneration happens while the vehicle is in use, when low engine load and lower exhaust gas temperatures inhibit the naturally occurring passive regeneration. Sensors upstream and downstream of the DPF (or a differential pressure sensor) provide readings that initiate a metered addition of fuel into the exhaust stream. There are two methods to inject fuel, either downstream injection directly into the exhaust stream, downstream of the turbo, or fuel injection into the engine cylinders on the exhaust stroke. This fuel and exhaust gas mixture passes through the Diesel Oxidation Catalyst (DOC) creating temperatures high enough to burn off the accumulated soot. Once the pressure drop across the DPF lowers to a calculated value, the process ends, until the soot accumulation builds up again. This works well for vehicles that drive longer distances with few stops compared to those that perform short trips with many starts and stops. If the filter develops too much pressure then the last type of regeneration must be used – a forced regeneration. This can be accomplished in two ways. The vehicle operator can initiate the regeneration via a dashboard mounted switch. Various signal interlocks, such as park brake applied, transmission in neutral, engine coolant temperature, and an absence of engine related fault codes are required (vary by OEM and application) for this process to initiate. When the soot accumulation reaches a level that is potentially damaging to the engine or the exhaust system, the solution involves a garage using a computer program to run a regeneration of the DPF manually.
When a regeneration occurs, the soot is turned to gasses and ash of which some remains in the filter. This will increase restriction through the filter and can result in a blockage. Warnings are given to the driver before filter restriction causes an issue with driveability or damage to the engine or filter develop. Regular filter maintenance is a necessity to remove ash build up, either through cleaning or replacement of the filter.
Regeneration typically requires the vehicle to be driven continuously at 50-60mph (80-100km/h) for 30 to 45 minutes every few hundred miles/kilometers of city driving. [40] Heavy duty pickup trucks have less stringent requirements for all three parameters, and Class 8 trucks significantly less. [41] [42] If the vehicle is often driven in cities the DPF may become clogged, causing a reduction in power and acceleration either passively due to increased exhaust pressure or actively due to vehicle going into "limp/turtle mode" as it tries to prevent engine and turbo damage. [43] [44] Once clogged both passive and active regeneration may become ineffective. DPF may be unclogged by high temperature pressure washing (not officially recommended) and/or burn-off oven. [45] [46]
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. [47] 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. [48]
Regeneration is the process of burning off (oxidizing) the accumulated soot from the filter. This is done either passively (from the engine's exhaust heat in normal operation or by adding a catalyst to the filter) or actively introducing very high heat into the exhaust system. On-board active filter management can use a variety of strategies: [9]
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 °C are attained. This temperature can be reduced to somewhere in the range of 350 to 450 °C by use of a fuel-borne catalyst. The actual temperature of soot burn-out will depend on the chemistry employed. In the mid-2010s, scientists at 3M developed a magnesium doped version of traditional iron based catalysts which lowered the temperature required for particulate matter oxidation to just over 200 °C. The lower reaction temperature is made possible by the dopant allowing the Fe lattice to hold more oxygen. [51] This advancement is significant because it allows the cleaning reaction to take place at the standard operating temperature of most diesel engines, removing the requirement for burning extra fuel or otherwise artificially heating the engine. The family of Mg doped catalysts, named Grindstaff catalysts after the chemist who started the work, has been the subject of much investigation across industry and academia with the tightening of emissions regulations on particulate matter world wide. [52] [51]
In some cases, in the absence of a fuel-borne catalyst, the combustion of the particulate matter can raise temperatures so high, that they are 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). [53]
Intentionally removing or tampering with a DPF device, known as variously as "deleting", "defeating" or "tuning", is prohibited by the EPA. Several manufacturers and retailers of diesel emissions defeat devices have been fined up to $1 million dollars. [54]
In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The exhaust gas displaces atmospheric air and reduces O2 in the combustion chamber. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The actual amount of recirculated exhaust gas varies with the engine operating parameters.
A catalytic converter is an exhaust emission control device which converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually used with internal combustion engines fueled by gasoline or diesel, including lean-burn engines, and sometimes on kerosene heaters and stoves.
Vehicle emissions control is the study of reducing the emissions produced by motor vehicles, especially internal combustion engines. The primary emissions studied include hydrocarbons, volatile organic compounds, carbon monoxide, carbon dioxide, nitrogen oxides, particulate matter, and sulfur oxides. Starting in the 1950s and 1960s, various regulatory agencies were formed with a primary focus on studying the vehicle emissions and their effects on human health and the environment. As the worlds understanding of vehicle emissions improved, so did the devices used to mitigate their impacts. The regulatory requirements of the Clean Air Act, which was amended many times, greatly restricted acceptable vehicle emissions. With the restrictions, vehicles started being designed more efficiently by utilizing various emission control systems and devices which became more common in vehicles over time.
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack, or propelling nozzle. It often disperses downwind in a pattern called an exhaust plume.
The Duramax V8 engine is a family of 6.6-liter diesel V8 engines produced by DMAX, a wholly owned subsidiary of General Motors in Moraine, Ohio. The Duramax block and heads are supplied from reliable vendors of General Motors. This engine was initially installed in 2001 Chevrolet and GMC trucks, and has since become an option in pickups, vans, and medium-duty trucks. In 2006, production at Moraine was reportedly limited to approximately 200,000 engines per year. On May 9, 2007, DMAX announced the production of the 1,000,000th Duramax V8 at its Moraine facility, followed by the 2,000,000th on March 24, 2017.
Mazda has a long history of building its own diesel engines, with the exception of a few units that were built under license.
Power Stroke, also known as Powerstroke, is the name used by a family of diesel engines for trucks produced by Ford Motor Company and Navistar International for Ford products since 1994. Along with its use in the Ford F-Series, applications include the Ford E-Series, Ford Excursion, and Ford LCF commercial truck. The name was also used for a diesel engine used in South American production of the Ford Ranger.
Engine braking occurs when the retarding forces within an internal combustion engine are used to slow down a motor vehicle, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes.
Diesel exhaust is the exhaust gas produced by a diesel engine, plus any contained particulates. Its composition may vary with the fuel type, rate of consumption or speed of engine operation, and whether the engine is in an on-road vehicle, farm vehicle, locomotive, marine vessel, or stationary generator or other application.
A particulate air filter is a device composed of fibrous, or porous materials which removes particulates such as smoke, dust, pollen, mold, viruses and bacteria from the air. Filters containing an adsorbent or catalyst such as charcoal (carbon) may also remove odors and gaseous pollutants such as volatile organic compounds or ozone. Air filters are used in applications where air quality is important, notably in building ventilation systems and in engines.
An exhaust system is used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes. Depending on the overall system design, the exhaust gas may flow through one or more of the following:
Selective catalytic reduction (SCR) means converting nitrogen oxides, also referred to as NO
x with the aid of a catalyst into diatomic nitrogen, and water. A reductant, typically anhydrous ammonia, aqueous ammonia, or a urea solution, is added to a stream of flue or exhaust gas and is reacted onto a catalyst. As the reaction drives toward completion, nitrogen, and carbon dioxide, in the case of urea use, are produced.
Diesel exhaust fluid is a liquid used to reduce the amount of air pollution created by a diesel engine. Specifically, DEF is an aqueous urea solution made with 32.5% urea and 67.5% deionized water. DEF is consumed in a selective catalytic reduction (SCR) that lowers the concentration of nitrogen oxides in the diesel exhaust emissions from a diesel engine.
BlueTEC is Mercedes-Benz Group's marketing name for engines equipped with advanced NOx reducing technology for vehicle emissions control in diesel-powered vehicles. The technology in BlueTec vehicles includes a selective catalytic reduction (SCR) system that uses diesel exhaust fluid, and a system of NOx adsorbers the automaker calls DeNOx, which uses an oxidizing catalytic converter and diesel particulate filter combined with other NOx reducing systems.
Secondary air injection is a vehicle emissions control strategy introduced in 1966, wherein fresh air is injected into the exhaust stream to allow for a fuller secondary combustion of exhaust gases.
The Cummins X-series engine is an Inline (Straight)-6 diesel engine produced by Cummins for heavy duty trucks and motorcoaches, replacing the N14 in 2001 when emissions regulations passed by the EPA made the engine obsolete. Originally called the "Signature" series engine, the ISX uses the "Intellect System" to further improve the engine. This engine is widely used in on highway and vocational trucks and is available in power ranging from 430 hp all the way to 620 hp 2050 lb-ft. The QSX is the off-highway version of the ISX with the Q standing for Quantum. The QSX is used for industrial, marine, oil & gas and other off-highway applications. Cummins also produced a 650 hp and 1950 lb-ft version for the RV market.
Monolithic catalyst supports are extruded structures that are the core of many catalytic converters, most diesel particulate filters, and some catalytic reactors. Most catalytic converters are used for vehicle emissions control. Stationary catalytic converters can reduce air pollution from fossil fuel power stations.
Dan Luss is an American chemical engineer, who is the Cullen Professor of Chemical Engineering at the University of Houston. He is known for his work in chemical reaction engineering, complex reacting systems, multiple steady-states reactor design, dynamics of chemical reactors, and combustion.
Berlin’s Environmental Zone, also known as Berlin’s Umweltzone, refers to a region within the city of Berlin and has been deemed a low-emissions zone. This zone permits only vehicles that have an environmental badge, or a green sticker, to enter. The policy was put into place in January 2008 due to the high density of Berlin’s inner city being affected by pollutants such as fine dust (PM 10) and nitrogen dioxide (NO2) threatening human health.
AIR-INK is a proprietary brand of ink and composites products made by condensing carbon-based gaseous effluents generated by air pollution due to incomplete combustion of fossil fuels. Founded by Graviky Labs, a spin-off group of MIT Media Lab, AIR-INK produces its materials through a step-by-step process which primarily involves capturing of emissions, separation of carbon from the emissions, and then mixing of this carbon with different types of oils and solutions to achieve advanced material properties. It uses a patented device and technique called 'KAALINK' to carry out the filtration of soot, which contains carbon and other polluting agents like heavy metals and polycyclic aromatic hydrocarbon.
