catalytic converter is a gas emission control tool that converts toxic gases and pollutants in the exhaust from internal combustion engines to less toxic pollutants by catalyzing redox reactions (oxidation and reduction reactions). Catalytic converters are commonly used with internal combustion engines fueled by gasoline or diesel - including lean-burn engines and kerosene heaters and stoves.
The introduction of the first catalytic converter is vast in the US car market. To comply with strict regulations on exhaust emissions from the US Environmental Protection Agency, most gasoline-powered vehicles starting with the 1975 model must be equipped with a catalytic converter. This "two-way" converter combines oxygen with carbon monoxide (CO) and unburned hydrocarbons (HC) to produce carbon dioxide (CO 2 ) and water (H 2 O ). In 1981, a two-way catalytic converter was made obsolete by a "three-way" converter which also reduced nitrogen oxide (NO x ); However, a two-way converter is still used for lean-burn machines. This is because the three-way converter requires rich burning or stoichiometric to successfully reduce NO x .
Although catalytic converters are most often applied to automobile exhaust systems, they are also used in electric generators, forklifts, mining equipment, trucks, buses, locomotives, and motorcycles. They are also used on some wood stoves to control emissions. This is usually in response to government regulations, either through direct environmental regulations or through health and safety regulations.
Video Catalytic converter
History
The catalytic converter prototype was first designed in France at the end of the 19th century, when only a few thousand "oil cars" were on the road; it consists of an inert material coated with platinum, iridium and palladium, sealed into a double metal cylinder.
A few decades later, a catalytic converter was patented by Eugene Houdry, a French mechanical engineer and expert in catalytic oil refinement, who moved to the United States in 1930. When the initial haze study results in Los Angeles were published, Houdry became concerned with the role of pile smoke exhaust and exhaust cars in air pollution and set up a company called Oxy-Catalyst. Houdry first developed a catalytic converter for a smoke pile called "cat" for short, and then developed a catalytic converter for warehouse forklifts that uses low-grade unleaded gasoline. In the mid-1950s, he began research to develop a catalytic converter for gasoline engines used on cars. He was awarded United States Patent 2,742,437 for his work.
Extensive adoption of catalytic converters does not occur until stricter emissions control regulations force the removal of tetraethyl anticnock agents from most types of gasoline. Lead is a "catalyst poison" and will effectively disable the catalytic converter by forming a coating on the surface of the catalyst.
The catalytic converter was further developed by a series of engineers including John J. Mooney, Carl D. Keith, Antonio Eleazar, and Phillip Messina at Engelhard Corporation, creating the first catalytic converter production in 1973.
William C. Pfefferle developed a catalytic burner for gas turbines in the early 1970s, allowing combustion without significant nitrogen oxide and carbon monoxide formation.
Maps Catalytic converter
Construction
Construction of catalytic converter is as follows:
- Support catalyst or substrate. For automotive catalytic converters, the core is usually a ceramic monolith that has a honeycomb structure (generally square, not hexagonal). (Prior to the mid-1980s, catalyst materials were deposited on packed pellet beds, especially in early GM applications.) Monolithic metallic foil made of Kanthal (FeCrAl) is used in applications requiring extremely high heat resistance. The substrate is structured to produce large surface area. The cordierite ceramic substrate used in most catalytic converters was created by Rodney Bagley, Irwin Lachman, and Ronald Lewis at Corning Glass, which was then inducted into the National Inventors Hall of Fame in 2002.
- The washcoat. A washcoat is a carrier for the catalytic material and is used to disperse the material over a large surface area. Aluminum oxide, titanium dioxide, silicon dioxide, or a mixture of silica and alumina may be used. The catalytic material is suspended in washcoat before it is applied to the core. Washcoat materials are selected to form a rough, irregular surface, which greatly increases the surface area compared to the fine surface of the bare substrate. This in turn maximizes the surface of the active catalyst available to react with the engine exhaust. The coating must retain its surface area and prevent sintering of catalytic metal particles even at high temperatures (1000 Â ° C).
- Cheerful or cheerful-zirconia. This oxide is mainly added as an oxygen storage promoter.
- The catalyst itself is most often a precious metal alloy. Platinum is the most active and widely used catalyst, but it is not suitable for all applications due to additional unwanted reactions and high costs. Palladium and rhodium are the other two precious metals used. Rhodium is used as a reduction catalyst, palladium is used as an oxidation catalyst, and platinum is used both for reduction and oxidation. Cerium, iron, manganese, and nickel are also used, although each has its limitations. Nickel is not legal for use in the EU because its reaction with carbon monoxide becomes tetracarbonyl toxic nickel. Copper can be used anywhere except Japan.
After failure, the catalytic converter can be recycled to scrap. Precious metals in converters, including platinum, palladium, and rhodium, are extracted.
Placement catalytic converter
The catalytic converter requires a temperature of 800 degrees Fahrenheit (426 ° C) to efficiently convert harmful flue gases into inert gases, such as carbon dioxide and water vapor. Therefore, the first catalytic converter is placed close to the engine to ensure rapid heating. However, these placements cause some issues, such as the steam lock. It happens a few minutes after the engine is turned off, because the heat from the catalytic converter affects the fuel in the fuel line, which makes it boil first and then aerated. This fuel condition produces a non-starting condition that lasts until the engine and fuel on the line cool off.
Alternatively, the catalytic converter is moved to a third of the way back from the engine, and then placed under the vehicle.
Type
Two way
A 2-way (or "oxidation", sometimes called catalytic converter "oxi-cat") has two simultaneous tasks:
- Oxidation of carbon monoxide to carbon dioxide: 2 CO < 2 -> 2 CO 2
- Oxidation of hydrocarbons (unburned and partially burned fuel) to carbon dioxide and water: C x H 2x 2 [(3x1)/2] O < sub> 2 -> x CO 2 (x 1) H 2 O (burning reaction)
This type of catalytic converter is widely used in diesel engines to reduce emissions of hydrocarbons and carbon monoxide. They were also used on petrol engines in American and Canadian market cars until 1981. Due to their inability to control nitrogen oxides, they were replaced by a three-way converter.
Three way
The three-way catalytic converter (TWC) has the additional advantage of controlling the emission of nitric oxide (NO) and nitrogen dioxide (NO 2 ) (both abbreviated as NO x and do not be confused with nitrous oxide (N 2 O)), which is a precursor for acid rain and smog.
Since 1981, "three-way" (oxidation-reduction) catalytic converters have been used in vehicle emission control systems in the United States and Canada; many other countries have also adopted strict vehicle emission regulations that essentially require a three-way converter on gasoline-powered vehicles. Reduction and oxidation catalysts are typically contained in one general housing; However, in some cases, they can be placed separately. Three-way catalytic converter has three simultaneous tasks:
Pengurangan nitrogen oxides of nitrogen (N 2 ) 2
Oxidation of carbon monoxide to carbon dioxide
- 2 CO O 2 -> 2 CO 2
Oxidation of unburned hydrocarbons (HC) to carbon dioxide and water, in addition to the above NO reaction.
- hydrocarbons O 2 -> H 2 O CO 2
These three reactions occur most efficiently when the catalytic converter receives exhaust from a machine that runs slightly above the stoichiometric point. For gasoline combustion, this ratio is between 14.6 and 14.8 parts of air into one part fuel, based on weight. The ratio for autogas (or LPG liquid gas), natural gas, and ethanol fuel is slightly different for each, requiring adjustment of modified fuel systems when using such fuel. In general, machines equipped with 3-way catalytic converters are equipped with a computerized feedback loop feedback system using one or more oxygen sensors, although at the start of the three-way converter, a carburetor equipped with feedback mix control is used.
The three-way converter is effective when the engine is operated in a narrow range of air-fuel ratio near the stoichiometric point, so the exhaust gas composition oscillates between rich (excess fuel) and lean (oxygen excess). The conversion efficiency goes down very quickly when the machine is operated outside of this band. Under the operation of a sleek machine, the exhaust contains excess oxygen, and a reduction of NO x is not preferred. In rich conditions, excess fuel will deplete all available oxygen before the catalyst, leaving only oxygen stored in the catalyst available for the oxidation function.
A closed-loop engine control system is required for the operation of an effective three-way catalytic converter due to the continuous balancing required for effective NO reduction x and HC oxidation. The control system should prevent NO x reduction catalysts from fully oxidizing, but recharging the oxygen storage material so that its function as an oxidation catalyst is maintained.
A three-way catalytic converter can store oxygen from the flue gas stream, usually when the air-fuel ratio becomes lean. When sufficient oxygen is not available from the discharge stream, stored oxygen is released and consumed (see cerium (IV) oxide) . The lack of sufficient oxygen occurs either when oxygen comes from a reduction of NO x is not available or when certain maneuvers such as hard acceleration enrich the mixture beyond the ability of the converter to supply oxygen..
Unwanted reaction
Unwanted reactions may occur in a three-way catalyst, such as the formation of hydrogen sulfide and ammonia that smell. Each formation may be limited by modification to the washcoat and precious metal used. It is difficult to remove this by-product completely. Sulfur-free or low sulfur material removes or reduces hydrogen sulfide.
For example, when the hydrogen-sulphide emission control is desired, nickel or manganese is added to the washcoat. Both of these substances serve to block the absorption of sulfur by washcoat. Hydrogen sulfide is formed when the washcoat has absorbed sulfur during low temperature parts of the operating cycle, which is then released during the high temperature part of the cycle and the sulfur combines with HC.
Diesel Engine
For compression ignition (ie, diesel engines), the most commonly used catalytic converter is diesel oxidation catalyst ( DOC ). DOC contains palladium, platinum, and aluminum oxide, all of which catalytically oxidize hydrocarbons and carbon monoxide with oxygen to form carbon dioxide and water.
- 2 CO O 2 -> 2 CO 2
- C x H 2 x 2 [(3 x 1) 2 -> x CO 2 ( x 1) H 2 O
These converters often operate at 90 percent efficiency, virtually eliminating the smell of diesel and helping to reduce visible particles (soot). The catalyst is inactive for the reduction of NO x because each present reductant will react first with a high concentration of O 2 in the diesel exhaust gas.
The reduction in NO x emissions from the previous compression ignition engine has been handled by the addition of exhaust gas to the incoming air charge, known as exhaust gas recirculation (EGR). In 2010, most light-duty diesel manufacturers in the US added a catalytic system to their vehicles to meet new federal emissions requirements. There are two techniques that have been developed for the catalytic reduction of NO x emissions under the lean exhaust conditions: selective catalytic reduction (SCR) and lean NO x trap or NO x adsorber. Instead of valuable NO silencers, most manufacturers opt for metal-based SCR systems that use reagents such as ammonia to reduce NO x <$ var> /sub> to nitrogen. Ammonia is supplied to the catalyst system by urea injection into the exhaust, which then undergoes thermal decomposition and hydrolysis to ammonia. One of the trademark products of urea solutions, also referred to as Diesel Exhaust Fluid (DEF), is AdBlue.
Diesel exhaust has a relatively high particulate content (carbon black), which is composed mostly of carbon elements. The catalytic converter can not clean the carbon element, although they remove up to 90 percent of the dissolved organic fraction, so the particulate is cleaned by a soot particle filter (DPF). Historically, DPF consists of a cordierite substrate or silicon carbide with a geometry that forces the flow of flue through the substrate walls, leaving the soot particles trapped. Contemporary DPFs can be made from a variety of rare metals that provide superior performance (at a greater cost). Because the amount of soot that is trapped in the DPF increases, so does the back pressure in the exhaust system. Periodic regeneration (high temperature visits) is required to initiate the burning of trapped soot and thereby reducing the exhaust back pressure. The amount of soot that is loaded in the DPF before regeneration can also be limited to prevent extreme extremes from damaging traps during regeneration. In the US, all light, medium and heavy-duty diesel-powered road vehicles built after January 1, 2007 must meet the emission limits of diesel particles, meaning that they should effectively be equipped with a 2-way catalytic converter and diesel particle filter. Note that this applies only to diesel engines used in vehicles. As long as the machine was manufactured before January 1, 2007, the vehicle is not required to have a DPF system. This led to a runup inventory by machine manufacturers at the end of 2006 so they could continue to sell pre-DPF vehicles until 2007. During the re-generation cycle, most systems require the engine to consume more fuel in a relatively short period of time in order. to produce the high temperature required to complete the cycle. This adversely affects the overall fuel economy of vehicles equipped with DPF systems, especially in vehicles driven largely by city conditions where acceleration often requires more fuel to be burned and therefore more soot to be collected in the exhaust system.
The ignition spark ignition engine
For a non-firing spark-ignition engine, the oxidation catalyst is used in the same way as in a diesel engine. The emissions from the ignition ignition engine are very similar to emissions from the diesel ignition ignition engine.
Installation
Many vehicles have a near-pair catalytic converter located near the engine exhaust manifold. The converter heats up rapidly, due to its exposure to a very hot exhaust gas, enabling it to reduce unwanted emissions during the heating period of the machine. This is achieved by burning the excess hydrocarbons generated from the very rich mixture needed to start the cold.
When the catalytic converter was first introduced, most vehicles use carburetors that provide relatively rich fuel-air ratio. The level of oxygen (O 2 ) in the flue stream is therefore generally not sufficient for the catalytic reaction to occur efficiently. Most design times therefore include secondary air injection, which injects air into the discharge stream. This increases the oxygen available, allowing the catalyst to function as intended.
Some three-way catalytic converter systems have air injection systems with air injected between the first reduction step (NO x ) and the second (HC and CO oxidation) of the converter. As with the two-way converter, the injected air provides oxygen for the oxidation reaction. The point of the upstream air injection, in front of the catalytic converter, is sometimes also present to provide additional oxygen only during the heating period of the machine. This causes unburned fuel to ignite in the drain, thus preventing it from reaching the catalytic converter at all. This technique reduces the engine working time required for a catalytic converter to achieve "light-off" or operating temperature.
Most new vehicles have an electronic fuel injection system, and do not require an air injection system in the exhaust. Instead, they provide a precisely controlled air-fuel mixture that quickly and continuously rotates between sleek and rich combustion. The oxygen sensor monitors the oxygen content of the exhaust before and after the catalytic converter, and the machine control unit uses this information to adjust the fuel injection thereby preventing the first (NO x reduction) catalyst to oxygen being loaded, while ensuring the second catalyst (HC and CO oxidation) is sufficiently saturated with oxygen.
Damage
Catalyst poisoning occurs when catalytic converters are exposed to exhausts containing substances that coat the work surface, so they can not contact and react with the exhaust. The most important contaminant is lead, so a vehicle equipped with a catalytic converter can run only on unleaded fuel. Other common catalyst catalysts include sulfur, manganese (mainly derived from MMT gasoline additives), and silicon, which can enter the drainage stream if the engine has a leak that allows the coolant to enter the combustion chamber. Phosphorus is another catalyst contaminant. Although phosphorus is no longer used in gasoline, it (and zinc, other low-level catalyst contaminants) is widely used in anti-engine oil additives such as zinc dithiophosphate (ZDDP). Beginning in 2004, the limits of phosphorus concentration in engine oils were adopted in API specifications BC and ILSAC GF-4.
Depending on the contaminants, the catalyst poisoning can sometimes be reversed by running the machine under a very heavy load for a long time. Increased exhaust temperatures can sometimes vaporize or sublimate the contaminants, removing them from the catalytic surface. However, the removal of lead deposits in this way is usually not possible because of the high lead boiling point.
Any condition that causes an abnormally unburned hydrocarbon level - burned or partially burned fuel - to reach the converter will tend to increase the temperature significantly, carrying the risk of substrate destruction and resulting in catalytic deactivation and severe restriction of disposal. Typically the upstream components of the exhaust system (associated head and clamp manifolds are susceptible to rust/corrosion and/or fatigue eg exhaust manifold splits after recurring heat cycles), eg ignition systems. (eg distributor lid, cable, ignition coil and spark plugs) and/or faulty fuel system components (fuel injectors, fuel pressure regulators, and related sensors) - since 2006 ethanol has been frequently used with blend fuels in which an incompatible ethanol fuel system component can damage the catalytic converter - this also includes using a thicker oil viscosity not recommended by the manufacturer (especially with ZDDP content - this includes "high mileage" without inhaling if the oil is conventional or synthetic), leakage of oil and/or coolant (eg wind-blown gaskets including overheated engines). Vehicles equipped with the OBD-II diagnostic system are designed to alert the driver to a misfire condition by lighting the check engine light on the dashboard, or flash it if the current misfire condition is severe enough to potentially damage the catalytic converter.
Rule
Emission regulations vary from jurisdiction to jurisdiction. Most of the car spark-ignition engines in North America have been fitted with catalytic converters since 1975, and technologies used in non-automotive applications are generally based on automotive technology.
The regulations for diesel engines also vary, with some jurisdictions that focus on emission NO x (nitric oxide and nitrogen dioxide) and others focus on particulate emissions (soot). This regulatory diversity is challenging for engine manufacturers, as it may be uneconomical to design machines to meet two sets of regulations.
Rules of fuel quality vary across jurisdictions. In North America, Europe, Japan and Hong Kong, gasoline and diesel are highly regulated, and natural gas and LPG compressed (autogas) are being reviewed for regulation. In most of Asia and Africa, regulation is often loose: in some places the sulfur content of fuel can reach 20,000 parts per million (2%). Each sulfur in the fuel can be oxidized to SO 2 (sulfur dioxide) or even SO 3 (sulfur trioxide) in the combustion chamber. If the sulfur passes through a catalyst, it can be further oxidized in the catalyst, that is, SO 2 can be further oxidized to SO 3 . Sulfur oxide is a precursor for sulfuric acid, a major component of acid rain. While it may be possible to add a substance such as vanadium to a catalyst cleaning cloth to combat sulfur-oxide formation, the addition will reduce the effectiveness of the catalyst. The most effective solution is to further refine the fuel at the refinery to produce ultra-low sulfur diesel. Regulations in Japan, Europe and North America strictly limit the amount of sulfur allowed in motor fuel. However, direct financial costs for producing such clean fuels can make it impractical for use in developing countries. As a result, cities in these countries with high traffic levels suffer acid rain, which destroys stones and wood from buildings, poisoning humans and other animals, and destroying local ecosystems, at very high financial costs.
Negative aspects
The catalytic converter limits the free flow of exhaust, which negatively affects vehicle performance and fuel economy, especially in older cars. Since the car's car's carburetor was unable to properly control the air fuel mixture, the car's catalytic converter can heat and burn combustible material under the car. A 2006 test in 1999 Honda Civic showed that removing the catalytic converter stocks netted a 3% increase in horsepower; the new metal core converter consumes only 1% power horsepower, compared to no converter. For some performance enthusiasts, this simple power increase at a surprisingly low cost encourages the removal or "blocking" of the catalytic converter. In this case, the converter may be replaced by a welded section on a plain pipe or a "test tube" flanged, intended to check whether the converter is blocked, by comparing how the engine runs with and without a converter. This facilitates a temporary reinstallation of the converter to pass the emissions test. In many jurisdictions, it is illegal to remove or disable the catalytic converter for any reason other than immediate and immediate replacement. In the United States, for example, is a violation of Article 203 (a) (3) (A) of the 1990 Clean Air Act amended for a vehicle repair shop to remove the converter from a vehicle, or cause the converter to be removed from the vehicle, except to replace it with other converters, and Section 203 (a) (3) (B) make it illegal for anyone to sell or install any portion that will cut, defeat or otherwise make any emissions control system, device or design element. Vehicles without a working catalytic converter generally fail emissions inspection. Automotive aftermarket supplies high flow converters for vehicles with upgraded engines, or owners preferring a disposal system with a larger capacity than stock.
HEATING PERIOD
Vehicles equipped with catalytic converters emit most of their total pollution during the first five minutes of machine operation; for example, before the catalytic converter has been sufficiently hot to be fully effective.
In 1995, Alpina introduced an electrically heated catalyst. Called "E-KAT," it's used in Alpina's B12 5.7 E-KAT based on BMW 750i. The heating coil in the catalytic converter is fed by the electric current after the ignition, bringing the catalyst up to very fast operating temperature to qualify the vehicle for the determination of low emission vehicle (LEV). BMW then introduced the same heat catalyst, co-developed by Emitec, Alpina, and BMW, at 750i in 1999.
Some vehicles contain pre-paint, a small catalytic converter upstream of the main catalytic converter that heats up faster at vehicle start-up, reducing emissions associated with cold start. Pre-cats are most often used by car manufacturers when trying to achieve an Ultra Low Emissions Vehicle (ULEV) rating, such as the Toyota MR2 Roadster.
Environmental impact
The catalytic converter has been proven to be reliable and effective in reducing harmful exhaust emissions. However, they also have some deficiencies in use, as well as adverse environmental impacts in production:
- A machine equipped with a three-way catalyst must be run at a stoichiometric point, which means more fuel is consumed than in a lean-burn machine. This means about 10% more CO 2 emissions from the vehicle.
- The production of catalytic converters requires palladium or platinum; part of the world supply of this precious metal was produced near Norilsk, Russia, where the industry (among others) has caused Norilsk to be added to the magazine's list of Time of the most polluted places.
- Catalytic converter pieces can cause wildfires, especially in dry areas
Theft
Due to the external location and the use of precious metals including platinum, palladium, rhodium, and gold, the catalytic converter is a thief target. The problem is very common among the final model trucks and SUVs, due to the high ground clearance and is easily released in the catalytic converter bolts. Welded converters are also at risk of theft, as they can easily be cut. Thieves that quickly remove catalytic converters, such as portable reciprocating saws, can often damage other components of the car, such as fuel cables or ducts, and thus can have dangerous consequences. The rising cost of metals in the US over the past few years has led to a huge increase in converter theft. The catalytic converter can cost over $ 1,000 to replace.
Diagnostics
Various jurisdictions now require on-board diagnostics to monitor the functions and conditions of emissions control systems, including catalytic converters. The on-board diagnostic system takes several forms.
Temperature sensors are used for two purposes. The first is as a warning system, usually on a two-way catalytic converter as it is sometimes still used on LPG forklifts. The function of the sensor is to warn the temperature of the catalytic converter above the safe limit of 750 ° C (1.380 ° F). Newer catalytic-converter designs are not susceptible to temperature damage and can withstand a continuous temperature of 900 ° C (1,650 ° F). Temperature sensors are also used to monitor catalyst function: usually two sensors will be installed, with one before the catalyst and another to monitor the temperature rise above the catalytic-converter core.
Oxygen sensors are the basis of closed-loop control systems in rich combustion engines triggered by sparks; However, it is also used for diagnostics. In vehicles with OBD II, a second oxygen sensor is installed after the catalytic converter to monitor the level of O 2 . Level O 2 is monitored to see the efficiency of the combustion process. The on-board computer makes a comparison between the readings of the two sensors. The readings are taken by voltage measurement. If both sensors show the same output or rear O <2> is "switching", the computer recognizes that the catalytic converter is not working or has been removed, and will operate the malfunction indicator light and affect the engine. performance. A simple "oxygen sensor simulator" has been developed to avoid this problem by simulating changes in catalytic converters with plans and pre-assembled devices available on the Internet. While this is not legitimate for use on the go, they have been used with mixed results. A similar tool implements offsets on the sensor signal, allowing the engine to run a more economical fuel-slim combustion that can damage the engine or catalytic converter.
Sensors NO x are very expensive and are generally only used when compression ignition engines are installed with selective catalytic-reduction (SCR) converters, or NO x catalyst absorber in the feedback system. When mounted to an SCR system, there may be one or two sensors. When one sensor is installed it becomes pre-catalyst; when two are installed, the second will be a post-catalyst. They are used for the same reason and in the same way as oxygen sensors; the only difference is the substance being monitored.
See also
- Catalytic heater
- Serium (III) oxide
- NOT x adsorber
- Airway dispersion modeling
References
Further reading
- Keith, C. D., et al. US. Patent 3.441.381 : "Equipment to purify the exhaust from the internal combustion engine". April 29, 1969
- Lachman, I. M. et al. US. Patent 3,885,977 : "Anisotropic Cordierite Monolith" (Ceramic substrate). 5 November 1973
- Charles H. Bailey. US. Patent 4,094,645 : "Combination muffler and catalytic converter have low back pressure". June 13, 1978
- Charles H. Bailey. US. Patent 4,250,146 : '"Monolithic catalytic catalytic converter". February 10, 1981
- Srinivasan Gopalakrishnan. GB 2397782 : " Process And Synthesis For Molecular Material Engineering ". March 13, 2002 .
External links
- Catalytic converter in HowStuffWorks
- Automotive applications of high temperature insulation wool
- Photo catalytic Converter
Source of the article : Wikipedia
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