Catalytic converter on a Dodge Ram Van.

Catalytic converter on a Saab 9-5.

A catalytic converter (colloquially, "cat" or "catcon") is a device used to reduce the toxicity of emissions from an internal combustion engine. First widely introduced on series-production automobiles in the US market for the 1975 model year to comply with tightening EPA regulations on auto exhaust, catalytic converters are still most commonly used in motor vehicle exhaust systems. Catalytic converters are also used on generator sets, forklifts, mining equipment, trucks, buses, trains, and other engine-equipped machines. A catalytic converter provides an environment for a chemical reaction wherein toxic combustion by-products are converted to less-toxic substances. Image File history File links Metadata Size of this preview: 637 × 600 pixelsFull resolution (720 × 678 pixel, file size: 111 KB, MIME type: image/jpeg) OEM Catalytic Converter on a 1996 Dodge Ram B2500 van. ... Image File history File links Metadata Size of this preview: 637 × 600 pixelsFull resolution (720 × 678 pixel, file size: 111 KB, MIME type: image/jpeg) OEM Catalytic Converter on a 1996 Dodge Ram B2500 van. ... The Dodge Ram Van is a full-size van marketed under the Dodge brand by DaimlerChrysler. ... Image File history File linksMetadata Download high-resolution version (2560x1920, 2408 KB) Other versions Originally from en. ... Image File history File linksMetadata Download high-resolution version (2560x1920, 2408 KB) Other versions Originally from en. ... 2000 Saab 9-5 sedan 2006 Saab 9-5 station wagon The Saab 9-5 is an executive car produced by the Swedish automaker Saab. ... The internal combustion engine is an engine in which the combustion of fuel and an oxidizer (typically air) occurs in a confined space called a combustion chamber. ... Mass production is the production of large amounts of standardised products on production lines. ... Motto: (traditional) In God We Trust (official, 1956–present) Anthem: The Star-Spangled Banner Capital Washington, D.C. Largest city New York City Official language(s) None at the federal level; English de facto Government Federal Republic  - President George W. Bush (R)  - Vice President Dick Cheney (R) Independence - Declared - Recognized... Year 1975 (MCMLXXV) was a common year starting on Wednesday (link will display full calendar) of the Gregorian calendar. ... The model year of a product is a number used to describe approximately when a product was produced. ... EPA redirects here. ... Automobile exhaust Exhaust gas is flue gas which occurs as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel, fuel oil or coal. ... This article is about machines that produce electricity. ... US airman operates forklift at a truck A forklift is a powered industrial truck used to hoist and transport materials by means of steel forks inserted under the load. ... For other uses, see Truck (disambiguation). ... “Autobus” redirects here. ... For other uses, see Train (disambiguation). ... For other uses, see Chemical reaction (disambiguation). ...

Functions

Three-way catalytic converters

A three-way catalytic converter has three simultaneous tasks:

1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NO_x → xO₂ + N₂
2. Oxidation of (toxic) carbon monoxide to carbon dioxide: 2CO + O₂ → 2CO₂
3. Oxidation of unburnt carcinogenic hydrocarbons (HC) to carbon dioxide and water: 2C_xH_y + (2x+y/2)O₂ → 2xCO₂ + yH₂O

These three reactions occur most efficiently when the catalytic converter receives exhaust from an engine running slightly above the stoichiometric point. This is between 14.8 and 14.9 parts air to 1 part fuel, by weight, for gasoline (the ratio for LPG, natural gas and ethanol fuels is slightly different, requiring modified fuel system settings when using those fuels). When there is more oxygen than required, then the system is said to be running lean, and the system is in oxidizing condition. In that case, the converter's two oxidizing reactions (oxidation of CO and hydrocarbons) are favoured, at the expense of the reducing reaction. When there is excessive fuel, then the engine is running rich. The reduction of NO_x is favoured, at the expense of CO and HC oxidation. If an engine could be held at the strict stoichiometric point for the fuel used, it is theoretically possible to reach 100% conversion efficiencies. Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... Nitrogen has six different oxides: Nitric oxide (NO) Nitrous oxide (N2O) Nitrogen dioxide (NO2) Dinitrogen trioxide (N2O3) Dinitrogen tetroxide (N2O4) Dinitrogen pentoxide (N2O5) The term nitrogen oxide is imprecise and can be used to refer to any of these or to a mixture of them. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... The most fundamental reactions in chemistry are the redox processes. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... In chemistry, stoichiometry is the study of the combination of elements in chemical reactions. ... “Petrol” redirects here. ... Autogas is the common name for liquified petroleum gas when it is used as a fuel in internal combustion engines in vehicles. ... This article is about the fossil fuel. ... “Grain alcohol” redirects here. ...

Since 1981, three-way catalytic converters have been at the heart of vehicle emission control systems in North American roadgoing vehicles, and have been used on "Large Spark Ignition" engines since 2001 in California, and from 2004 in the other 49 states. LSI engines are used in forklifts, aerial boom lifts, ice resurfacing machines and construction equipment. The converters used in these are three-way types designed to reduce combined NO_x+HC emissions from 12 gram/BHP-hour to 3 gram/BHP-hour or less, per the United States Environmental Protection Agency (EPA) 2004 regulations. A further drop to 2 gram/BHP-hour of NO_x+HC emissions is mandated in 2007 (note: NO_x is the industry standard short form for nitric oxide (NO) and nitrogen dioxide (NO₂) both of which are smog precursors. HC is the industry short form for hydrocarbons). The EPA intends to introduce emissions rules for stationary Spark Ignition engines, to take effect in January 2008. This article or section should include material from Spark gap A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed aerosol gasoline by means of an electric spark. ... The ignition system of an internal-combustion engine is an important part of the overall engine system that provides for the timely burning of the fuel mixture within the engine. ... US airman operates forklift at a truck A forklift is a powered industrial truck used to hoist and transport materials by means of steel forks inserted under the load. ... Vehicle emissions inspection station Automobile emissions control covers all the technologies that are employed to reduce the air pollution-causing emissions produced by automobiles. ... BIC pen cap, about 1 gram. ... This article is about a unit of measurement. ... EPA redirects here. ... R-phrases , , , , S-phrases , , , Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Nitric oxide or Nitrogen monoxide is a chemical compound with chemical formula NO. This gas is an important signaling molecule in the body of... [1] R-phrases , S-phrases , , , , , Supplementary data page Structure and properties n, εr, etc. ...

Two-way catalytic converters

A two-way catalytic converter has two simultaneous tasks:

1. Oxidation of carbon monoxide to carbon dioxide: 2CO + O₂ → 2CO₂
2. Oxidation of unburnt hydrocarbons (unburnt and partially-burnt fuel) to carbon dioxide and water: 2C_xH_y + (2x+y/2)O₂ → 2xCO₂ + yH₂O

This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. They were also used on spark ignition (gasoline) engines in USA market automobiles up until 1981, when they were replaced by three-way converters due to regulatory changes requiring reductions on NO_x emissions. The most fundamental reactions in chemistry are the redox processes. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... This article is about the fuel. ... Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... “Petrol” redirects here. ... Look up nox, Nox in Wiktionary, the free dictionary. ...

Reduction of the NO_x emissions requires an additional step. Platinum catalysis can be used. Instead of catalysis, a true reactant — diesel fuel or ammonia pyrolyzed in situ from urea — can be used to reduce the NO_x into nitrogen. General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... For other uses, see Ammonia (disambiguation). ... Urea is an organic compound with the chemical formula (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Nonproprietary Names (rINN) in use in Europe. ...

Curiously, the regulations regarding hydrocarbons vary according to the engine regulated, as well as the jurisdiction. In some cases, "non-methane hydrocarbons" are regulated, while in other cases, "total hydrocarbons" are regulated. Technology for one application (to meet a non-methane hydrocarbon standard) may not be suitable for use in an application that has to meet a total hydrocarbon standard. Methane is not toxic, but is more difficult to break down in a catalytic converter, so in effect a "non-methane hydrocarbon" standard can be considered to be looser. Since some theorists maintain that methane might be a greenhouse gas, interest is rising in how to eliminate emissions of it. Methane is a chemical compound with the molecular formula CH4. ... Top: Increasing atmospheric CO2 levels as measured in the atmosphere and ice cores. ...

Catalyst poisoning and deactivation

Catalytic converters become ineffective in the presence of lead due to catalyst poisoning. Therefore, vehicles equipped with catalytic converters must only be run on unleaded gasoline, and it is this fact, as much as concerns about the possibly harmful effects of lead emissions, which caused the end of pump-available leaded gasoline in countries where catalytic converters have been in common use for many years. Leaded "race only" fuel is still used for non-catalyst vehicles in some countries. Catalyst poisoning occurs when a substance in the engine exhaust coats the surface of the catalyst, preventing further exhaust access to the catalytic materials. Poisoning can sometimes be reversed by running the engine under a very heavy load for an extended period of time to raise exhaust gas temperature, which may cause liquefaction or sublimation of the catalyst poison. Common catalyst poisons are lead, sulfur, zinc, manganese, silicon and phosphorus. For Pb as an abbreviation, see PB. General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ... Catalyst poisoning refers to the effect that a catalyst can be poisoned if it reacts with another compound that bonds chemically (similar to an inhibitor) but does not release, or chemically alters the catalyst. ... Tetra-ethyl lead (also known as TEL, lead tetraethyl and tetraethyllead) is a toxic organometallic chemical compound, with formula (CH3CH2)4Pb, which was once used as a gasoline (petrol) additive. ... It has been suggested that this article or section be merged into Catalysis. ... This article is about the chemical element. ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... General Name, symbol, number manganese, Mn, 25 Chemical series transition metals Group, period, block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... Not to be confused with Silicone. ... General Name, symbol, number phosphorus, P, 15 Chemical series nonmetals Group, period, block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ...

Zinc, phosphorus and sulfur originate from lubricant antiwear additives such as ZDDP; sulfur and manganese primarily originate from fuel impurities or from additives such as Methylcyclopentadienyl Manganese Tricarbonyl (MMT), respectively. Silicon poisoning in automotive applications is the result of engine damage, such as a faulty cylinder head gasket or cracked casting, admitting silicate-containing coolant into the combustion chamber. In stationary engines silicon poisoning is more often caused by the use of methane landfill gas as a fuel. A lubricant (colloquially, lube) is a substance (often a liquid) introduced between two moving surfaces to reduce the friction and wear between them. ... AW additives, or antiwear additives, are additives for lubricants with role to prevent metal-to-metal contact between parts of the gears. ... Zinc dialkyl dithio phosphate Zinc dialkyl dithio phosphate (ZDDP, ZnDTP, or ZDP) is a family of zinc salts of dithio organophosphates. ... Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organometallic compound with the formula (CH3C5H4)Mn(CO)3. ... Not to be confused with Silicone. ... The cylinder head from a GMC van. ... Some seals and gaskets 1. ... A man pouring antifreeze into his vehicle. ... Look up landfill in Wiktionary, the free dictionary. ...

Removal of sulfur from a catalyst surface by running heated exhaust gases over the catalyst surface is often successful; however, removal of lead deposits in this manner is usually not possible because of lead's high boiling point. In particularly bad cases of catalyst poisoning by lead, the catalytic converter can actually become completely plugged with lead residue.

A variety of conditions may cause the catalyst to overheat (heat deactivation) and potentially to melt down. Some factors that can cause this are:

• lubricating oil in the exhaust system (caused by engine wear, or by damaged rings or valves)
• an engine misfire or ignition failure (causing unburnt fuel to enter the exhaust)
• a cracked exhaust valve (again, causing unburnt fuel in the exhaust)

Overly rich fuel mixtures are not usually a problem - there is too little unused oxygen for the exothermic reaction to be large enough to cause damage. A slightly lean of stoichiometric mix is far more dangerous, as the oxygen level is elevated, allowing a very large exotherm, and many engine manufacturers design "rich excursions" as a catalyst protection measure in the engine control software. In the early days of catalyst-equipped cars, (primarily in the USA) before the advent of sophisticated engine management systems, it was necessary for fuel/air mixtures to be significantly richer than had hitherto been the case to allow the catalyst to work effectively. This contributed to the very poor fuel consumption figures achieved by such cars. It has been suggested that this article or section be merged into Catalysis. ... An electronic control unit (ECU) (also known as an engine management system) is an electronic device, basically a computer, in an internal combustion engine that reads several sensors in the engine and uses the information to control the fuel injection and ignition systems of the engine. ...

Engine misfires can overheat and destroy the converter as the excessive amounts of unburned fuel are broken down within it, especially when the engine is under heavy loads. Vehicles equipped with OBD-II diagnostic systems are designed to alert the driver of a misfire condition, along with other malfunctions, using the Malfunction Indicator Lamp or "Check Engine" light. If the misfire and engine load can produce heating severe enough to cause catalyst damage, the MIL will flash until the misfire or engine load is reduced. OBD-II (OnBoard Diagnostics version 2) is a common hardware diagnostics interface that is present on all cars sold in the United States after 1996. ...

Technical details

Cross section of a Metal-core Converter

The catalytic converter consists of several components: Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

1. The core, or substrate. In modern catalytic converters, this is most often a ceramic honeycomb, however stainless steel foil honeycombs are also used. The purpose of the core is to "support the catalyst" and therefore it is often called a "catalyst support". The ceramic substrate was invented by Rodney Bagley, Irwin Lachman and Ronald Lewis at Corning Glass for which they were inducted into the National Inventors Hall of Fame in 2002.
2. The washcoat. In an effort to make converters more efficient, a washcoat is utilized, most often a mixture of silica and alumina. The washcoat, when added to the core, forms a rough, irregular surface which has a far greater surface area than the flat core surfaces, which is desirable to give the converter core a larger surface area, and therefore more places for active precious metal sites. The catalyst is added to the washcoat (in suspension) before application to the core.
3. The catalyst itself is most often a precious metal. Platinum is the most active catalyst and is widely used. However, it is not suitable for all applications because of unwanted additional reactions and/or cost. Palladium and rhodium are two other precious metals that are used. Platinum and rhodium are used as a reduction catalyst, while platinum and palladium are used as an oxidization catalyst. Cerium, iron, manganese and nickel are also used, though each has its own limitations. Nickel is not legal for use in the European Union (due to reaction with carbon monoxide). While copper can be used, its use is illegal in North America due to the formation of dioxin.

Fixed Partial Denture, or Bridge The word ceramic is derived from the Greek word κεραμικός (keramikos). ... The 630 foot high, stainless-clad (type 304L) Gateway Arch defines St. ... Irwin Lachman is a scientist and artist born in Brooklyn, NY in 1930 and who grew up in Jersey Homesteads, NJ (now called Roosevelt). ... Corning Glass Works (NYSE: GLW) is a U.S. manufacturer of glass, ceramics and related materials, primarily for technical and scientific applications. ... Exterior of the National Inventors Hall of Fame museum, 2005 The National Inventors Hall of Fame is an organization that honors important inventors from the whole world. ... Also see: 2002 (number). ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... For other uses, see Palladium (disambiguation). ... General Name, Symbol, Number rhodium, Rh, 45 Chemical series transition metals Group, Period, Block 9, 5, d Appearance silvery white metallic Standard atomic weight 102. ... General Name, Symbol, Number cerium, Ce, 58 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 140. ... For other uses, see Iron (disambiguation). ... General Name, symbol, number manganese, Mn, 25 Chemical series transition metals Group, period, block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... For other uses, see Nickel (disambiguation). ... Nickel carbonyl (IUPAC name: tetracarbonylnickel) is a colorless organometallic complex that is a versatile reagent, first described in 1890 by Ludwig Mond. ... For other uses, see Copper (disambiguation). ... Dioxin is the common name for the group of compounds classified as polychlorinated dibenzodioxins (PCDDs). ...

Conventional spark ignition engines

Catalytic converters are used on spark ignition (gasoline; liquified petroleum gas (LPG); flexible fuel vehicles burning varying blends of E85 and gasoline; compressed natural gas (CNG)) engines; and compression ignition (diesel) engines. “Petrol” redirects here. ... 45 kg LPG cylinders Spherical Gas Container typically found in Refineries. ... A flexible-fuel vehicle or dual-fuel vehicle is an automobile or truck (lorry) that can accept a range of fuel mixtures. ... Logo used in the United States for E85 fuel E85 is an alcohol fuel mixture that typically contains a mixture of up to 85% denatured fuel ethanol and gasoline or other hydrocarbon by volume. ... Typical North America vehicles carry this diamond shape symbol, meaning it is running on compressed natural gas fuel. ... This article is about the fuel. ...

For spark ignition engines, the most commonly used catalytic converter is the three-way converter, which gets its name by dint of acting to convert the three main pollutants of concern — CO, HC, and NO_x— to less-toxic substances. The control of NO_x involves a reduction process that releases oxygen and the control of CO and HC involves an oxidation process that consumes oxygen. Therefore, a 3-way converter contains two catalyst-coated stages: The first catalyst stage encountered by the exhaust is for reduction of NOx, which produces oxygen employed by the second stage to oxidize CO and HC. 3-way converters work most efficiently with exhaust from engines operated on a stoichiometric air-fuel mixture. Generally, such engines are equipped with closed-loop feedback fuel mixture control employing one or more oxygen (lambda) sensors. While a 3-way catalyst can be used in an open-loop system, NO_x reduction efficiency is low. Since NO_x emissions are now regulated throughout the world, open-loop fuel systems are obsolete in many jurisdictions. Closed-loop maintenance of the stoichiometric air-fuel ratio is most often attained by means of an engine management system with computer-controlled fuel injection, though early in the deployment of 3-way converters, carburetors equipped for feedback mixture control were used during the transition to fuel injection. Within a narrow ratio band surrounding stoichiometry, conversion of all three pollutants is very complete, sometimes approaching 100%. However, outside of that band, conversion efficiency falls off very rapidly. Two-way (or oxidation) converters act only to control CO and HC, and have therefore been abandoned on conventional spark ignition engines in most jurisdictions due to an inability to control NO_x. Stoichiometry (sometimes called reaction stoichiometry to distinguish it from composition stoichiometry) is the calculation of quantitative (measurable) relationships of the reactants and products in chemical reactions (chemical equations). ... A Proportional-Integral-Derivative controller is a standard feedback loop component in industrial control applications. ... // An oxygen sensor is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed. ... An Engine Control Unit (ECU) is an electronic control unit which controls various aspects of an internal combustion engines operation. ... // Fuel injection is a means of metering fuel into an internal combustion engine. ... Bendix-Technico (Stromberg) 1-barrel downdraft carburetor model BXUV-3, with nomenclature The carburetor, carburettor, or carburetter (see spelling differences), also called carb (in North America) or carbie (chiefly in Australia) for short, is a device that blends air and fuel for an internal combustion engine. ... The graph of the probability density function of the normal distribution is sometimes called the bell curve or the bell-shaped curve; see normal distribution. ...

A three-way catalyst reduces emissions of CO (carbon monoxide), HC (hydrocarbons), and NO_x (nitrogen oxides) simultaneously when the oxygen level of the exhaust gas stream is below 1.0%, though performance is best at below 0.5% O₂. Unwanted reactions, such as the formation of H₂S (hydrogen sulfide) and NH₃ (ammonia), can occur in the three-way catalyst. Formation of each can be limited by modifications to the washcoat and precious metals used. It is, however, difficult to eliminate these side products entirely. Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ... The term nitrogen oxide is a general term and can be used to refer to any of these oxides (oxygen compounds) of nitrogen, or to a mixture of them: Nitric oxide (NO), nitrogen(II) oxide Nitrogen dioxide (NO2) Dinitrogen monoxide (N2O) (Nitrous oxide) Dinitrogen trioxide (N2O3) Dinitrogen tetroxide (N2O4) Dinitrogen... Hydrogen sulfide (hydrogen sulphide in British English) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs and flatulence. ... For other uses, see Ammonia (disambiguation). ...

For example, when control of H₂S (hydrogen sulfide) emissions is desired, nickel or manganese is added to the washcoat - both substances act to block the adsorption of sulfur by the washcoat. H₂S is formed when the washcoat has adsorbed sulfur during a low temperature part of the operating cycle, which is then released during the high temperature part of the cycle and the sulfur combines with HC. For "lean burn" spark ignition engines (e.g. compressed natural gas, or compressed natural gas with diesel fuel pilot injection), an oxidation catalyst is used in the same manner as in a compression ignition engine.

Recently, many systems have used a pre-catalyst in the system to reduce startup emissions and burn off hydrocarbons from the extra-rich mixture used in a cold engine. Upstream and downstream parts are now often separated in the system to provide an optimum temperature and space for extra oxygen sensors. The converter needs to be placed close enough to the engine to quickly reach operating temperature but far enough away to avoid heat damage.

Many three-way catalytic converters utilize an air injection tube between the first (NO_x reduction) and second (HC and CO oxidation) biscuits of the converter. This tube is fed by either an air pump or by an aspirator. The injected air provides oxygen for the catalyst's oxidizing reaction. These systems also sometimes include an upstream air injector to admit oxygen to the exhaust system before it reaches the catalytic converter. This precleans the extra-rich exhaust from a cold engine, and helps bring the catalytic converter quickly up to operating temperature. A very early automobile emissions control system, the Air injection reactor (AIR) reduces the products of incomplete combustion (hydrocarbons and carbon monoxide) by injecting fresh air into the exhaust manifolds of the engine near to the exhaust valves. ... Pulse Air is a system used by American Motors and other manufacturers during the eighties and early nineties. ...

Most newer systems do not employ air injection. Instead, they provide a constantly varying mixture that quickly and continually cycles between lean and rich to keep the first catalyst (NO_x reduction) from becoming oxygen loaded, and to keep the second catalyst (CO oxidization) sufficiently oxygen-saturated. They also utilize several oxygen sensors to monitor the exhaust, at least one before the catalytic converter for each bank of cylinders, and one after the converter. Some systems contain the reduction and oxidation functions separately rather than in a common housing.

Diesel engines

For compression ignition (i.e., Diesel) engines, the most commonly used catalytic converter is the diesel oxidation catalyst. The catalyst uses excess O₂ (oxygen) in the exhaust gas stream to oxidize CO (Carbon Monoxide) to CO₂ (Carbon Dioxide) and HC (hydrocarbons) to H₂O (water) and CO₂. These converters often reach 90% effectiveness, virtually eliminating diesel odor and helping to reduce visible particulates (soot), however they are incapable of reducing NO_x as chemical reactions always occur in the simplest possible way, and the existing O₂ in the exhaust gas stream would react first. This article is about the fuel. ... Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... Soot, also called lampblack, Pigment Black 7, carbon black or black carbon, is a dark powdery deposit of unburned fuel residues, usually composed mainly of amorphous carbon, that accumulates in chimneys, automobile mufflers and other surfaces exposed to smoke—especially from the combustion of carbon-rich organic fuels in the...

To reduce NO_x on a compression ignition engine it is necessary to change the exhaust gas - two main technologies are used for this - selective catalytic reduction (SCR) and NOx (NO_x) traps (or NOx Adsorbers). Selective Catalytic Reduction (SCR): Gaseous or liquid ammonia is added to the flue gas stream and is absorbed onto a catalyst. ... The NOx Adsorber or NOx Trap is a device that is use to reduce NOx (NO and NO2) emissions from a lean burn internal combustion engine. ...

Another issue for diesel engines is particulate (soot). This can be controlled by a soot trap or diesel particulate filter (DPF), as catalytic converters are unable to affect elemental carbon (however they will remove up to 90% of the soluble organic fraction). A clogging soot filter creates a lot of back pressure decreasing engine performance. However, once clogged, the filter goes through a regeneration cycle where diesel fuel is injected directly into the exhaust stream and the soot is burned off. After the soot has been burned off the regeneration cycle stops and injection of diesel fuel stops. This regeneration cycle should not affect performance of the engine. A diesel particulate filter (top left) in a Peugeot A diesel particulate filter, sometimes called a DPF, is device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine, most of which are rated at 85% efficiency, but often attaining efficiencies of over 90...

All major diesel engine manufacturers in the USA (Ford, Caterpillar, Cummins, Volvo, MMC) starting January 1, 2007 are required to have a catalytic converter and a soot filter inline, as per new EPA legislation. http://www.epa.gov/otaq/highway-diesel/regs/2007-heavy-duty-highway.htm

Oxygen storage in three-way converters

In order to oxidize CO and HC, the catalytic converter also has the capability of storing the oxygen from the exhaust gas stream, usually when the air fuel ratio goes lean. When insufficient oxygen is available from the exhaust stream the stored oxygen is released and consumed. This happens either when oxygen derived from NO_x reduction is unavailable or certain maneuvers such as hard acceleration enrich the mixture beyond the ability of the converter to compensate.

Note that diesel catalysts do not use this feature as there is sufficient O2 in the exhaust gas stream to handle the CO & HC reductions needed.

Regulations

Emissions regulations vary considerably from jurisdiction to jurisdiction, as do what engines are regulated. In North America any spark ignition engine of over 19 kW (25 hp) power output built later than January 1, 2004 probably has a three-way catalytic converter installed. In Japan a similar set of regulations came into effect January 1, 2007, while the European Union has not yet enacted analogous regulations. Most automobile spark ignition engines in North America have been fitted with catalytic converters since the mid-1970s and the technology used in non-automotive applications is generally based on automotive technology. North America North America is a continent[1] in the Earths northern hemisphere and (chiefly) western hemisphere. ... For other uses, see Watt (disambiguation). ... This article is about a unit of measurement. ... is the 1st day of the year in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... is the 1st day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ...

Diesel engine regulations are similarly varied, with some jurisdictions focusing on NO_x (Nitric Oxide and Nitrogen Dioxide) emissions and others focusing on particulate (soot) emissions. This can cause problems for the engine manufacturers as it may not be economical to design an engine to meet two sets of regulations.

Note that no jurisdiction has specific legislation mandating the use of catalytic converters, however with spark ignition engines a catalytic converter is usually the only practical way to meet regulatory requirements.

An important issue is that fuel quality varies widely from place to place, even within jurisdictions, as do the regulations covering fuel quality. In North America, Europe, Japan, and Hong Kong both gasoline and diesel fuel are highly regulated and there are campaigns under way to regulate CNG and LPG as well. In most of Asia and Africa this is not true - in some places sulfur content of the fuel can reach 20,000 parts per million (2%). Any sulfur in the fuel may be oxidized to SO₂ (sulfur dioxide) or even SO₃ (sulfur trioxide) in the combustion chamber. If sulfur passes over a catalyst it may be further oxidized in the catalyst, i.e. (SO₂ may be further oxidized to SO₃). Sulfur oxides are precursors to sulfuric acid, a major component of acid rain. While it is possible to add substances like vanadium to the catalyst wash coat to combat sulfur oxide formation, this will reduce the effectiveness of the catalyst—the best solution is further refinement of the fuel at the refinery to remove the sulfur. Regulations in Japan, Europe and —by 2007— North America tightly restrict the amount of sulfur permitted in motor fuels. However, the expense is such that this is not practical in many developing countries. As a result cities in these countries with high levels of vehicular traffic suffer damage to buildings due to acid rain eating away the stone/woodwork, and acid rain has deleterious effects on the local ecosystem. This article is about the chemical element. ... Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ... “SO3” redirects here. ... A combustion chamber is part of an engine in which fuel is burned. ... R-phrases S-phrases , , , Flash point Non-flammable Related Compounds Related strong acids Selenic acid Hydrochloric acid Nitric acid Related compounds Hydrogen sulfide Sulfurous acid Peroxymonosulfuric acid Sulfur trioxide Oleum Supplementary data page Structure and properties n, εr, etc. ... The term acid rain Since the industrial revolution, emissions of sulfur and nitrogen oxides to the atmosphere have increased. ... General Name, symbol, number vanadium, V, 23 Chemical series transition metals Group, period, block 5, 4, d Appearance silver-grey metal Standard atomic weight 50. ...

Regulatory agencies

The agencies charged with regulating engine emissions vary from jurisdiction to jurisdiction, even in the same country. For example, in the United States, overall responsibility belongs to the United States Environmental Protection Agency (EPA), but due to special requirements of the State of California, emissions in California are regulated by the Air Resources Board. In Texas, the Texas Railroad Commission is responsible for regulating emissions from LPG fueled rich burn engines (but not gasoline fueled rich burn engines). EPA redirects here. ... State nickname: The Golden State Other U.S. States Capital Sacramento Largest city Los Angeles Governor Arnold Schwarzenegger Official languages English Area 410,000 km² (3rd)  - Land 404,298 km²  - Water 20,047 km² (4. ... California Air Resources Board (CARB) is the clean air agency of the state of California in the United States. ... The Texas Railroad Commission was a government agency created in the 1930s to regulate the petroleum industry in the state of Texas. ... LPG might be an initialism or abbreviation for: Liquified petroleum gas Laboratoire de Planetologie, Grenoble, France Literary Press Group of Canada Landwirtschaftliche Produktionsgenossenschaft (German, obsolete/historical) Long period grating This page concerning a three-letter acronym or abbreviation is a disambiguation page — a navigational aid which lists other pages that...

• California Air Resources Board - California, United States (most sources)
• Environment Canada - Canada (most sources)
• Environmental Protection Agency - United States (most sources)
• Texas Railroad Commission - Texas, United States (LPG fueled engines only)
• Transport Canada - Canada (trains and ships)

California Air Resources Board (CARB) is the clean air agency of the state of California in the United States. ... Environment Canada is the department of the government of Canada with responsibility for coordinating environmental policies and programs as well as preserving and enhancing the natural environment and conservation of wildlife. ... EPA redirects here. ... The Texas Railroad Commission was a government agency created in the 1930s to regulate the petroleum industry in the state of Texas. ... Transport Canada is the department within the government of Canada which is responsible for developing regulations, policies and services of transportation in Canada. ...

Criticisms

Catalytic converters have proven to be reliable devices and have been successful in reducing noxious tailpipe emissions. However, they may have some adverse environmental impacts in use:

• The requirement for a rich burn engine to run at the stoichiometric point means it uses more fuel than a "lean burn" engine running at a mixture of 20:1 or less. This increases the amount of fossil fuel consumed and the carbon dioxide emissions of the vehicle. However NOx control on lean burn engines is problematic at best, and many lean burn engine manufacturers are considering rich burn variations. Another solution is to increase the amount of biofuels used - if 100% biofuel was used the engines would be CO₂ neutral, presuming no fossil fuels were consumed in production of the biofuels, which currently is far from the case (see energy balance of biofuels).
• Catalytic converters are "estimated" to account for 50% of total nitrous oxide (dinitrogen oxide, 'laughing gas') emissions to atmosphere. While N₂O emissions in these concentrations are not harmful to human health, it is a potent greenhouse gas, accounting for around 7% of the overall greenhouse effect despite its small concentration in the atmosphere. The California Air Resources Board is investigating this issue, and will introduce legislation to address it if necessary.
• The manufacturing of catalytic converters requires palladium and/or platinum; a portion of the world supply of these precious metals is produced near the Russian city of Norilsk (about 15%), with significant negative environmental effects due to the lack of environmental protection legislation. [2]

It can be argued that catalytic converters have reduced toxic emissions and smog at the expense of increased greenhouse gases, however anyone making this argument should consider the California Air Resources Board reports on improvements in Air Quality that have been achieved over the last 30 years. For a fuel to oxidize, or burn, it must have a reagent or oxidizer with which it can react. ... This article does not cite any references or sources. ... Fossil fuels are hydrocarbons, primarily coal and petroleum (fuel oil or natural gas), formed from the fossilized remains of dead plants and animals[1] by exposure to heat and pressure in the Earths crust over hundreds of millions of years[2]. The theory that hydrocarbons were formed from these... Biofuel is any fuel that derives from biomass _ recently living organisms or their metabolic byproducts, such as manure from cows. ... For other uses, see Nitrous oxide (disambiguation). ... For other uses, see Palladium (disambiguation). ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... A gold nugget A precious metal is a rare metallic chemical element of high economic value. ... Norilsk downtown was designed in a typical Stalinist style. ... It has been suggested that Haze be merged into this article or section. ... Greenhouse gases are gaseous components of the atmosphere that contribute to the greenhouse effect. ...

Catalytic converter theft

Due to the use of precious metals including platinum, which is worth up to $1,200 an ounce; palladium, which can fetch $320 an ounce; and rhodium, which can go for up to $6,400 an ounce on the market, catalytic converter theft is on the rise. (Note, however, that the loading of precious metals in a converter is low, and seldom over $50 per converter at 2007 spot prices). The problem is especially common among mid-90s to present Toyota sport-utility vehicles and trucks, due to their high ground clearance and bolt on catalytic converters, which are easy to remove. Welded-in converters are also at risk of theft from SUVs and trucks, as they can be removed within five minutes by means of a battery powered reciprocating saw. ^[1], General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... For other uses, see Palladium (disambiguation). ... General Name, Symbol, Number rhodium, Rh, 45 Chemical series transition metals Group, Period, Block 9, 5, d Appearance silvery white metallic Standard atomic weight 102. ... This article is about the automaker. ... Reciprocating saws are saws with a straight blade mounted at the end of a gun-like body. ...

Diagnostics

Various jurisdictions now legislate on-board diagnostics to monitor the effectiveness of the emissions control system, including the catalytic converter and such diagnostics are often included in aftermarket retrofit kits as a matter of course, even if legislation does not directly require them. Retrofitting is a term used in e. ...

On-board diagnostics take several forms, depending upon the legislation and the type of emissions control product being monitored, the three main types are:

• temperature
• oxygen
• NO_x

Temperature sensors

Temperature sensors are used for two purposes. The first is as a warning system, typically on obsolete 2-Way catalytic converters such as are still sometimes used on LPG forklifts. The function of the sensor is to warn of temperature excursions above the safe operating temperature of 750°Celsius of the 2-Way catalytic converter. Note that modern catalytic converters are not as susceptible to temperature damage, many modern 3-Way platinum based converters can handle temperatures of 900°C sustained, while many modern 3-way palladium based converters can handle temperatures of 925°C sustained. Temperature sensors are also used to monitor catalyst functioning - usually two sensors will be fitted, one before the catalyst and one after to monitor the temperature rise over the catalytic converter core. For every 1% of CO in the exhaust gas stream the exhaust gas temperature will rise by 100°C. Not to be confused with censure, censer, or censor. ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ...

Oxygen sensors

The Oxygen sensor or "lambda sensor" is the basis of the closed loop control system on a spark ignited rich burn engine, however it is also used for diagnostics. Oxygen sensors only work when at operating temperature, when they output a voltage based on the O₂ level in the exhaust gas to the computer. Typically a single wire oxygen sensor will take 3-5 minutes to reach operating temperature. The more expensive heated sensors (3 to 5 wires) can reach operating temperature in 1 minute. // An oxygen sensor is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed. ... ...

The simplest sort of diagnostic an oxygen sensor can perform is related to the closed loop control system. If the system makes a change to the air-fuel ratio based on oxygen sensor readings, and the readings do not change the sensor will light an indicator on the instrument panel warning the operator that there is a problem with the vehicle. There is always a delay before this happens, usually 5 minutes of engine operation. Most systems do not store the state, so turning off the engine and turning it back on will reset the system, and if the error is transient (i.e. fuel filter is partially blocked) the light will not come back on. However, if the problem is recurring the light will come on as soon as the sensor reaches operating temperature and a manufacturer-defined driving pattern known as a drive-trace is completed. Until this procedure has finished, the diagnostic computer will set a parameter called a readiness monitor to "unready". The readiness monitor system was implemented in order to ensure that diagnostic computers would not falsely report working emissions systems in vehicles whose computer's error memory had recently been cleared. Such diagnostics have been factory fitted to automobiles since 1985 in North America and factory fitted to off-road Spark Ignition engines since 2004 (however such systems have been available as retrofit kits for off-road SI engines since 1997).

The second sort of diagnostic is more complex and is a result of the California OBD-II rule (though temperature sensors are sometimes used for this). In vehicles with OBD-II, a second oxygen sensor is fitted after the catalytic converter to monitor the O₂ levels. The on-board computer makes comparisons to the readings of the two sensors. If both sensors give the same output, the catalytic converter is non-functioning, and must be replaced. It will also spot less serious damage to a catalytic converter, such as the use of racing fuel in an on-road vehicle. Lead is still legal in racing fuel, and use of as little as half a tank of leaded fuel will cause enough damage for the computer to notice, and warn the operator that the converter is not functioning properly. OBD-II (OnBoard Diagnostics version 2) is a common hardware diagnostics interface that is present on all cars sold in the United States after 1996. ...

NO_x sensors

NO_x sensors are extremely expensive and are generally only used when a compression ignition engine is fitted with a Selective Catalytic Reduction Converter, or a NO_x Adsorber Catalyst in a feedback system (though many SCR systems do not use a NO_x sensor, but instead rely on the engine map being programmed into the Engine Control Unit or computer). When fitted to an SCR system there may be one or two sensors. When one sensor is fitted it will be pre-catalyst, when two are fitted the second one is post catalyst. They are utilized for the same reasons, and in the same manner as an Oxygen Sensor - the only difference is the substance being monitored.

See also

• Exhaust system
• Automobile emissions control
• Diesel particulate filter
• SCR
• NOx Adsorbers
• Roadway air dispersion modeling
• Catalysis

Exhaust pipe of a car An exhaust pipe is usually tubing used to guide waste exhaust gases away from a controlled combustion inside an engine or stove. ... Vehicle emissions inspection station Automobile emissions control covers all the technologies that are employed to reduce the air pollution-causing emissions produced by automobiles. ... A diesel particulate filter (top left) in a Peugeot A diesel particulate filter, sometimes called a DPF, is device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine, most of which are rated at 85% efficiency, but often attaining efficiencies of over 90... Selective Catalytic Reduction (SCR): Gaseous or liquid ammonia is added to the flue gas stream and is absorbed onto a catalyst. ... The NOx Adsorber or NOx Trap is a device that is use to reduce NOx (NO and NO2) emissions from a lean burn internal combustion engine. ... Roadway air dispersion is applied to highway segments Roadway air dispersion modeling is the study of air pollutant transport from a roadway or other linear emitter. ... In chemistry and biology, catalysis is the acceleration (increase in rate) of a chemical reaction by means of a substance, called a catalyst, that is itself not consumed by the overall reaction. ...

Notes

1. ^ [1]

External links

• Johnson Matthey plc - The Inventors of the Catalytic Converter
• Howstuffworks: "How Catalytic Converters Work"
• Source for Electronic Catalytic Convertor Info
• Detecting Clogged Converter

Patents

• Keith, C. D., et al., -- U.S. Patent 3,441,381  -- "Apparatus for purifying exhaust gases of an internal combustion engine" -- April 29, 1969
• Lachman, I. M. et al., -- U.S. Patent 3,885,977  -- "Anisotropic Cordierite Monolith" (Ceramic substrate) -- November 5, 1973
• Srinivasan Gopalakrishnan -- GB patent 2397782 -- "Process And Synthesizer For Molecular Engineering Of Materials" -- March 13, 2002