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The Scorpio is fitted with a 3 way Catalytic Converter (Cat) on all models except for the 24V which has 2 - one for each downpipe. There are also 2 associated Lambda (Heated Oxygen Sensors) mounted before and after  each Cat. The first one measures the amount of Oxygen in the exhaust gas and is used by the EEC-V to adjust the mixture between rich and lean and the other monitors the efficiency of the Cat but is not used by the EEC-V. How the Catalytic Converter works

There are millions of cars on the road that are potential sources of air  pollution. In a major effort to reduce vehicle emissions, carmakers have developed an interesting device called a catalytic converter, which treats the exhaust before it leaves the car and removes a lot of the pollution. Pollutants Produced the Engine

In order to reduce emissions, modern cars have been designed to carefully control the amount of fuel they burn. The goal is to keep the airto-fuel ratioideal veryratio closeoftoairthe point, which is the calculated to "stoichiometric" fuel. Theoretically, at this ratio, all of the fuel will be burned using all of the oxygen in the air. [For petrol, the stoichiometric ratio is about 14.7 to 1, meaning that for each pound of  fuel, 14.7 pounds of air will be burned. The fuel mixture actually varies from the ideal ratio quite a bit during driving. Sometimes the mixture can be "lean" (an air-to-fuel ratio higher than 14.7); and other times the mixture can be "rich" (an air-to-fuel ratio lower than 14.7).] The main emissions of a car engine are: Nitrogen gas: Air is 78 percent nitrogen gas, and most of this passes right through the car engine. Carbon Dioxide: This is one product of combustion. The carbon in the fuel bonds with the oxygen in the air. Water vapor: This is another product of combustion. The hydrogen in the fuel bonds with the oxygen in the air.

These emissions are mostly benign (although carbon dioxide emissions are believed to contribute to global warming), however because the combustion process is never perfect, some smaller amounts of more harmful emissions are also produced in car engines:

 

Carbon monoxide: A poisonous gas that is colorless and odorless. Hydrocarbons or volatile organic compounds (VOC's): Produced mostly from unburned fuel that evaporates. Sunlight breaks these down to form oxidants, which react with oxides of nitrogen to cause ground level ozone, a major  component of pollution. Oxides of nitrogen: Contributes to smog and acid rain, and also causes irritation to human mucus membranes.

These are the three main regulated emissions, and also the ones that catalytic converters are designed to reduce. How Catalytic Converters Reduce Pollution

Most modern cars are equipped with three-way catalytic converters. "Three-way" refers to the three regulated emissions it helps to reduce carbon monoxide, unburnt hydrocarbons and nitrogen oxide molecules. The converter uses two different types of catalysts, a reduction catalyst and an oxidization catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. The is to create a structure that exposes theminimising maximumthe surface area of theidea catalyst to the exhaust stream, while also amount of  catalyst required (they are very expensive). There are three main types of structures used in catalytic converters ceramic honeycomb, metal plate and ceramic beads (now almost obsolete) - the Scorpio like most cars today use a ceramic honeycomb structure. The Reduction Catalyst

The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the nitrogen oxide emissions. When such molecules come in contact with the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. The Oxidization Catalyst

The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. The Control System

 

The third stage is a control system that monitors the exhaust stream, and uses this information to control the fuel injection system. There is a heated oxygen sensor (also called a Lambda Sensor) mounted upstream of the catalytic converter, meaning it is closer to the engine than the converter. This sensor tells the EEC-V PCM how much oxygen is in the exhaust. The EEC-V can increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This control scheme allows the EEC-V to ensure that the engine is running at close to the stoichiometric point, while also making sure that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and carbon monoxide. Other Ways to Reduce Pollution

The catalytic converter does a great job of reducing pollution, but there is room for improvement. One of the catalytic converter's biggest shortcomings is that it only works at a fairly high temperature. When you start your car cold, the catalytic converter does almost nothing to reduce the pollution in your exhaust. This is anhad important when car for its MOT - make sure that it has a goodnote steady runtaking to heatyour  up the Cats to working temperature or you could fail your emissions test. One simple solution to this problem is to move the catalytic converter  closer to the engine. This means that hotter exhaust gases reach the converter and it heats up faster, but this may also reduce the life of the converter by exposing it to extremely high temperatures. Most carmakers position the converter under the front passenger seat, far enough from the engine to keep the temperature down to levels that will not harm it. Preheating the catalytic converter could be a good way to reduce emissions using electric resistance heaters. Unfortunately, the 12-volt electrical systems on most cars just doesn't provide enough energy or  power to heat the catalytic converter fast enough. Most people won't wait a few minutes for the catalytic converter to heat up before starting their  car. Electric/Fuel Hybrid cars that have big, high-voltage battery packs can provide enough power to heat up the catalytic converter very quickly which contributes to their green claims of lower emissions. The Scorpio Cats form part of a relatively complex exhaust arrangement and can be expensive to replace at £300 apiece plus installation so well worth getting them checked by an emission test before purchase of a new

 

vehicle.  

The rear most Lambda sensors are not used to adjust the engine mixture but simply to identify the performance of the Catalytic Converters. In ideal conditions they should show a constant output indicating that the Cats are working as intended. Ripple which mirrors the output of the pre-CAT sensors indicates Cats that are starting to fail.

The front sensors (pre-CAT) monitor the engine mixture and report back to the EEC-V which then adjusts the mixture accordingly. Cats work best when the mixture varies between weak and rich every few seconds.

There is an excellent article on Lambda Sensors Here There are millions of cars on the road in the United States, and each one is a source of air  pollution. Especially in large cities, the amount of pollution that all the cars produce together can create big problems. To solve those problems, cities, states and the federal government create clean-air laws that restrict the amount of pollution that cars can produce. Over the years, automakers have made many refinements to car engines car engines  and fuel systems to keep up with these laws. One of these changes came about in 1975 with an interesting device called a catalytic converter . The job of the catalytic converter is to convert harmful pollutants into less harmful emissions before they ever  leave the car's exhaust system. Catalytic converters are amazingly simple devices, so it is incredible to see how big an impact they have. In this article, you will learn which pollutants are produced by an engine and how a catalytic converter deals with each of these pollutants to help reduce vehicle emissions. We all know that pushing down on the brake pedal slows a car to a stop. But how does this happen? How does your car transmit the force from your leg to its wheels? How does it multiply the force so that it is enough to stop something as big as a car?

 

When you depress your brake pedal, your car transmits the force from your foot to its brakes through a fluid. Since the actual brakes require a much greater force than you could apply with your  leg, your car must also multiply the force of your foot. It does this in two ways: •

Mechanical advantage(leverage)

•

Hydraulic force multiplication

The brakes transmit the force to the tires using friction, and the tires transmit that force to the road using friction also. Before we begin our discussion on the components

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How Disc Brakes Work by Karim Nice

 

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Image Gallery: Brakes Image Gallery: Brakes

Most modern cars have disc brakes on the front wheels, and some have disc brakes on all four  wheels. This is the part of the brake system that does the actual work of stopping the car. The most common type of disc brake on modern cars is thesingle-piston floating caliper . In this article, we will learn all about this type of disc brake design.

How Anti-Lock Brakes Work by Karim Nice 313 

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Location of anti-lock brake components. See more  brakes. more  pictures of brakes.

Stopping a car in a hurry on a slippery road can be very challenging. Anti-lock braking systems (ABS) take a lot of the challenge out of this sometimes nerve-wracking event. In fact, on slippery surfaces, even professional drivers can't stop as quickly without ABS as an average driver can with  ABS..  ABS In this article, the last in a six-part series on brakes, we'll learn all about anti-lock braking systems -why you need them, what's in them, how they work, some of the common types and some associated problems.

How Power Brakes Work by Karim Nice

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Brake Image Gallery

If you've ever opened the hood of your car, you've probably seen the brake booster . It's the round, black cannister located at the back of the  the  engine compartment on the driver's side of the car. Back in the day, when most cars had  had drum brakes, brakes, power brakes were not really necessary -- drum brakes naturally provide some of their own power assist. Since most cars today have disc brakes, brakes, at least on the front wheels, they need power brakes. Without this device, a lot of drivers would have very tired legs.

How Catalytic

Converters Work by Karim Nice and Charles W. Bryant

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How Catalytic Converters Reduce Pollution In chemistry, a catalyst is a substance that causes or accelerates a chemical reaction without itself  being affected. Catalysts participate in the reactions, but are neither reactants nor products of the reaction they catalyze. In the human body, enzymes are naturally occurring catalysts responsible for many essential biochemical reactions [source: Chemicool Chemicool]].

In the catalytic converter, there are two different types of catalyst at work, a reduction catalyst and anoxidation catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. The idea is to create a structure that exposes the maximum surface area of catalyst to the exhaust stream, while also minimizing the amount of  catalyst required, as the materials are extremely expensive. Some of the newest converters have even started to use gold mixed with the more traditional catalysts. Gold is cheaper than the other  materials and could increase oxidation, the chemical reaction that reduces pollutants, by up to 40 percent [source: Kanellos Kanellos]. ]. Most modern cars are equipped with three-way catalytic converters. This refers to the three regulated emissions it helps to reduce. The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example: 2NO => N2 + O2 or 2NO2 => N2 + 2O2 2NO => N2 + O2 or 2NO2 => N2 + 2O2

 

Ceramic honeycomb catalyst structure.

The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example: 2CO + O2 => 2CO2 There are two main types of structures used in catalytic converters -- honeycomb and ceramic beads. Most cars today use a honeycomb structure. In the next section, we'll look at the third stage of the conversion process and how you can get the most from your catalytic converter.

Catalytic converter  From Wikipedia, the free encyclopedia

Catalytic converter converter on a 1996 Dodge Ram Van

 

 A catalytic converter  (colloquially, "cat" or "catcon") is a  a  vehicle emissions control device which converts  toxic byproducts of  combustion in the exhaust of an  converts an  internal combustion engine to less toxic substances by way of  catalysed chemical reactions. The specific reactions vary with the type of  catalyst installed. Most present-day vehicles that run on gasoline  gasoline are fitted with a "three way" converter, so named because it converts the three main pollutants in automobile exhaust: hydrocarbons  (HC), and an  an oxidizing reaction converts carbon monoxide (CO) and unburned hydrocarbons a reduction reaction converts  converts oxides of nitrogen (NOx) to produce carbon dioxide (CO2), nitrogen  nitrogen (N2), and  water (H and water  (H2O).[1] The first widespread introduction of catalytic converters was in the United States market, where gasoline-powered -powered automobiles were so equipped to comply with tightening  tightening U.S. 1975 model year  gasoline Environmental Protection Agency  Agency regulations on automobile exhaust emissions. [2][3][4][5] These were hydrocarbons  (HC) to "two-way" converters which combined carbon monoxide (CO) and unburned hydrocarbons produce carbon dioxide (CO2) and  and water  (H2O). Two-way catalytic converters of this type are now considered obsolete, having been supplanted except on lean burn  burn engines[citation needed ] by "three-way" converters which also reduce oxides of nitrogen (NOx).[2] Catalytic converters are still most commonly used in  in exhaust systems in automobiles, automobiles, but are also generator sets, sets,  forklifts forklifts,, mining used on  on generator  equipment,trucks,, buses, equipment,trucks buses, locomotives locomotives,, motorcycles motorcycles,, airplanes airplanes  and other engine fitted devices. They are also used on some wood stoves to control emissions.[6]This is usually in response to  to government government  regulation regulation,, either through direct environmental regulation or through health and safety regulations. Catalytic oxidization is also used, but for the purpose of safe, flameless generation of heat rather than destruction of pollutants, in catalytic heaters. heaters.

 

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History  [ e edit  dit   ] History 

Yamaha 100  modification  A modern catalytic catalytic converte converterr used for Y amaha RX 100

The catalytic converter was invented by Eugene Houdry, Houdry, a French mechanical engineer and expert in of smog smog in catalytic oil refining[7] who lived in the U.S. around 1950. When the results of early studies of  Los Angeles were published, Houdry became concerned about the role of smoke stack exhaust and automobile exhaust in air pollution and founded a company, Oxy-Catalyst. Houdry first developed catalytic converters for smoke stacks called cats for short. Then he developed catalytic converters for 

 

warehouse fork lifts that used low grade non-leaded non-l eaded gasoline.[8] Then in the mid 1950s he began research to develop catalytic converters for gasoline for  gasoline engines used on cars. He was awarded United States Patent 2742437 for his work. work.[9] Widespread adoption of catalytic converters didn't occur until more stringent emission control regulations forced the removal of anti-knock of  anti-knock agent  tetraethyl lead from most gasoline, because lead was a 'catalyst poison' and would inactivate the converter by forming a coating on the catalyst's surface, effectively disabling it.[10] Catalytic converters were further developed by a series of engineers including  including John J. Mooney and Carl D. Keith at the Engelhard Corporation, Corporation,[11] creating the first production catalytic converter in 1973. [12]  ] Construction Construction [ e edit  dit 

Metal-core converter 

Ceramic-core converter 

The catalytic converter consists of several components:

1.

The catalyst core, or substrate or  substrate.. For automotive catalytic converters, the core is

usually a  a ceramic monolith with a honeycomb structure. Metallic foil monoliths made of  FeCrAl are used in some applications. This is partially a cost issue. Ceramic cores are inexpensive when manufactured in large quantities. Metallic cores are less expensive to build in small production runs, and are used in sportscars where low back pressure and reliability under continuous high load is required. Either material is designed to provide a high surface [citation

area to support the catalyst washcoat, and therefore is often called a ""catalyst support". catalyst support". needed ] The cordierite ceramic substrate used in most catalytic converters was invented

 

byRodney byRodney Bagley, Bagley, Irwin Lachman and Ronald Lewis at  at Corning Glass, Glass, for which they were inducted into the National Inventors Hall of Fame in 2002.[citation needed ]

2.

The washcoat. A washcoat is a carrier for the catalytic materials and is used to

 Aluminum oxide, dioxide, silicon disperse the materials over a high surface area. area. Aluminum oxide,titanium dioxide, dioxide,, or a mixture of silica dioxide of silica  and  and alumina can be used. The catalytic materials are suspended in the washcoat prior to applying to the core. Washcoat materials are selected to form a rough, irregular surface, which greatly increases the surface area compared to the smooth surface of the bare substrate. This in turn maximizes the catalytically active surface available to react with the engine exhaust. The coat must retain its surface area and prevent sintering of the catalytic metal particles even at high temperatures (1000 °C). [13]

3.

The catalyst itself is most often a  a precious metal. metal . Platinum  Platinum is the most active catalyst

and is widely used, but is not suitable for all applications because of unwanted additional cost.  Palladium  Palladium and  and rhodium are two other precious metals used. reactions[vague] and high cost.  Rhodium is used as areduction areduction catalyst, palladium is used as an oxidation catalyst, and platinum is used both for reduction and oxidation. Cerium Cerium,, iron iron,, manganese manganeseand and  nickel are also used, although each has its own limitations. Nickel is not legal for use in the European tetracarbonyl). ). Copper can Copper can Union (because of its reaction with carbon monoxide into nickel tetracarbonyl clarification needed ] be used everywhere except  except  North America America,,[clarification where its use is illegal because of the

formation of  dioxin. dioxin. [ e edit  dit   ] Types Types [edit edit]]Two-way  A two-way (or "oxidation") "oxidation") catalytic converter has two simultaneous simultaneous tasks:

1. 2.

Oxidation of  carbon monoxide monoxide  to  to carbon dioxide dioxide:: 2CO + O2 → 2CO2 Oxidation of  hydrocarbons (unburnt and partially burnt fuel) to carbon dioxide

and water : CxH2x+2 + [(3x+1)/2] O2 → xCO2 + (x+1) H2O (a combustion reaction) This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. They were also used on gasoline engines in American- and Canadian-market nitrogen,, they were superseded automobiles until 1981. Because of their inability to control oxides of nitrogen by three-way converters. [edit edit]]Three-way 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

 

stringent vehicle emission regulations that in effect require three-way converters on gasoline-powered vehicles. The reduction and oxidation catalysts are typically contained in a common housing, however  in some instances they may be housed separately. A three-way catalytic converter has three simultaneous tasks:

1. 2.

to nitrogen and oxygen oxygen:: 2NOx → xO2 + N2 Reduction of nitrogen oxides to  Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2

3.

Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and and  water : CxH2x+2 +

[(3x+1)/2]O2 → xCO2 + (x+1)H2O. These three reactions occur most efficiently when the catalytic converter receives r eceives exhaust from an engine running slightly above the  the stoichiometric point. This point is between 14.6 and 14.8 parts air to (or liquefied liquefied petroleum gas  gas (LPG)), natural 1 part fuel, by weight, for gasoline. The ratio for  Autogas  Autogas (or  gas  and  gas and ethanol fuels is each slightly different, requiring modified fuel system settings when using those fuels. In general, engines fitted with 3-way catalytic converters are equipped with feedback  fuel injection system using one or more  more  oxygen sensors sensors,, though a computerized  computerized closed-loop feedback early in the deployment of three-way converters,  converters,  carburetors carburetors  equipped for feedback mixture control were used. Three-way catalysts are effective when the engine is operated within a narrow band of air-fuel ratios near stoichiometry, such that the exhaust gas oscillates between rich (excess fuel) and lean (excess oxygen) conditions. However, conversion efficiency falls very rapidly when the engine is operated outside of that band of air-fuel ratios. Under lean engine operation, there is excess oxygen and the reduction of NOx is not favored. Under rich conditions, the excess fuel consumes all of the available oxygen prior to the catalyst, thus only stored oxygen is available for the oxidation function. Closed-loop control systems are necessary because of the conflicting requirements for effective NOx reduction and HC oxidation. The control system must prevent the NO xreduction catalyst from becoming fully oxidized, yet replenish the oxygen storage material to maintain its function as an oxidation catalyst. Three-way catalytic converters can store oxygen from the exhaust gas stream, usually when the  the  airfuel ratio  ratio goes lean.[14] When insufficient oxygen is available from the exhaust stream, the stored oxygen is released and consumed (see cerium(IV) oxide ). A lack of sufficient oxygen occurs either  when oxygen derived from NO x reduction is unavailable or when certain maneuvers such as hard acceleration enrich the mixture beyond the ability of the converter to supply oxygen. edit]]Unwanted [edit

reactions

Unwanted reactions can occur in the three-way catalyst, such as the formation of odoriferous odoriferous  hydrogen hydrogen   sulfide  and  sulfide and ammonia. ammonia . Formation of each can be limited by modifications to the washcoat and precious

 

metals used. It is difficult to eliminate these byproducts entirely. Sulfur-free or low-sulfur fuels eliminate or reduce hydrogen sulfide. For example, when control of hydrogen-sulfide emissions is desired, nickel or  or manganese manganese  is added to sulfur by by the washcoat. Hydrogen sulfide the washcoat. Both substances act to block the absorption of  sulfur  is formed when the washcoat has absorbed 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. [edit] edit]Diesel

engines

engines), ), the most commonly used catalytic converter is the For compression-ignition (i.e., diesel engines Diesel Oxidation Catalyst (DOC). This catalyst uses O2 (oxygen) in the exhaust gas stream to convert CO (carbon monoxide) to CO2 (carbon dioxide) and HC (hydrocarbons) to H2O (water) and CO2. These converters often operate at 90 percent efficiency, virtually elimi eliminating nating diesel odor and helping to reduce visible particulates (soot). soot). These catalysts are not active for NOx reduction because any reductant present would react first with the high concentration of O 2 in diesel exhaust gas. Reduction in NOx emissions from compression-ignition engines has previously been addressed by the addition of exhaust gas to incoming air charge, known as exhaust gas recirculation (EGR) ( EGR).. In 2010, most light-duty diesel manufacturers in the U.S. added catalytic systems to their vehicles to meet new federal emissions requirements. There are two techniques that have been developed for the catalytic reduction of NOx emissions under lean exhaust conditions -  - selective catalytic reduction (SCR) and the lean NOx trap or  NOx adsorber . Instead of precious metal-containing NOx adsorbers, most manufacturers selected base-metal SCR systems that use a  a reagent such as ammonia to reduce the NOx into nitrogen. Ammonia is supplied to the catalyst system by the injection of urea of  urea into the exhaust, which then undergoes thermal decomposition and hydrolysis into ammonia. One trademark product of  urea solution, also referred to as Diesel Emission Fluid (DEF), is  is  AdBlue. AdBlue. Diesel exhaust  exhaust contains relatively high levels of particulate matter (soot), consisting in large part of  elemental carbon. carbon. Catalytic converters cannot clean up elemental carbon, though they do remove up to 90 percent of the soluble organic fraction[citation needed ], so particulates are cleaned up by a soot trap or  or diesel filter  (DPF). Historically, a DPF consists of a Cordierite or Silicon Carbide diesel particulate filter (DPF). substrate with a geometry that forces the exhaust flow through the substrate walls, leaving behind trapped soot particles. Contemporary DPFs can be manufactured from a variety of rare metals that provide superior performance (at a greater expense).[15] As the amount of soot trapped on the DPF increases, so does the back pressure in the exhaust system. Periodic regenerations (high temperature excursions) are required to initiate combustion of the trapped soot and thereby reducing the exhaust back pressure. The amount of soot loaded on the DPF prior to regeneration r egeneration may also be limited to prevent extreme exotherms from damaging the trap during regeneration. In the U.S., all on-road light,

 

medium and heavy-duty vehicles powered by diesel and built after January 1, 2007, must meet diesel particulate emission limits that means they effectively have to be equipped with a 2-Way catalytic converter and a diesel particulate filter. Note that this applies only to the diesel engine used in the vehicle. As long as the engine was manufactured before January 1, 2007, the vehicle is not required to have the DPF system. This led to an inventory runup by engine manufacturers in late 2006 so they could continue selling pre-DPF vehicles well into 2007. [16] [edit edit]]Lean

burn spark-ignition engines

For lean For  lean burn burn  spark-ignition engines, an oxidation catalyst is used in the same manner as in a diesel engine. Emissions from Lean Burn Spark Ignition Engines are very similar to emissions from a Diesel Compression Ignition engine.  ] Installation Installation edit  [ e dit  manifold.. This unit Many vehicles have a close-coupled catalysts located near the engine's engine's  exhaust manifold heats up quickly due to its proximity to the engine, and reduces cold-engine emissions by burning off  hydrocarbons from the extra-rich mixture used to start a cold engine. When catalytic converters were rich air-fuel ratio ratio.. Oxygen first introduced, most vehicles used carburetors that provided a relatively rich  (O2) levels in the exhaust stream were generally insufficient for the catalytic reaction to occur  efficiently, so most installations included secondary air injection which injected air into the exhaust stream to increase the available oxygen and allow the catalyst to function. Some three-way catalytic converter systems have air injection systems with the air injected between the first (NOx reduction) and second (HC and CO oxidation) stages of the converter. As in the two-way converters, this injected air  provides oxygen for the oxidation reactions. An upstream air injection point, ahead of the catalytic converter, is also sometimes present to provide oxygen during engine warmup, which causes unburned fuel to ignite in the exhaust tract before reaching the catalytic converter. This reduces the engine runtime needed for the catalytic converter to reach its "light-off" or  operating temperature. Modern vehicles do not have air injection systems. Instead, they provide a constantly varying air-fuel mixture that quickly and continually cycles between lean and rich exhaust. Oxygen sensorsare sensorsare used to monitor the exhaust oxygen content before and after the catalytic converter and this information is used by the Electronic control unit to adjust the fuel injection so as to prevent the first (NOx reduction) catalyst from becoming oxygen-loaded while ensuring the second (HC and CO oxidization) catalyst is sufficiently oxygen-saturated.  ] Damage Damage [ edit  edit  Catalyst poisoning occurs when the catalytic converter is exposed to exhaust containing substances that coat the working surfaces, encapsulating the catalyst so that it cannot contact and treat the

 

exhaust. The most-notable contaminant is lead, lead, so vehicles equipped with catalytic converters can be run only on unleaded fuels. Other common catalyst poisons include fuel sulfur ,manganese (originating primarily from the gasoline additive additive  MMT), MMT), and silicone silicone,, which can enter the exhaust stream if the coolant  into the combustion chamber .Phosphorus Phosphorus  is another catalyst engine has a leak that allows  allows  coolant zinc,, another low-level contaminant. Although phosphorus is no longer used in gasoline, it (and zinc catalyst contaminant) was until recently widely used in engine oilantiwear oil antiwear additives such as zinc dithiophosphate (ZDDP). Beginning in 2006, a rapid phaseout of ZDDP in engine oils began.[citation needed ] Depending on the contaminant, catalyst poisoning can sometimes be reversed by running the engine under a very heavy load for an extended period of time. The increased exhaust temperature can sometimes liquefy or sublimate the contaminant, removing it from the catalytic surface. However, removal of lead deposits in this manner is usually not possible because of lead's high boiling point.  Any condition that causes causes abnormally high level levels s of unburned hydrocarbons—raw or partially burnt burnt fuel —to reach the converter will tend to significantly elevate its temperature, bringing the risk of a meltdown of the substrate and resultant catalytic deactivation and severe exhaust restriction. Vehicles equipped with  with OBD-II  OBD-II diagnostic systems are designed to alert the driver to a misfire condition by means of flashing the "check engine" light on the dashboard. edit   ] Regulations Regulations [ e dit  This section needs additionallcitations for additiona for  verification. (January 2012)

Emissions regulations vary considerably from jurisdiction to jurisdiction. Most automobile spark-ignition 4][5] 5] engines in North America have been fitted with catalytic converters since 1975, 1975, [2][3][4][ and the

technology used in non-automotive applications is generally based on automotive technology. While the regulatory requirement was for the 1975 model year, General Motors is documented as having fitted catalytic converters to the 1974 Camaro Type LT [17] fitted with the 5.7L L65 and LM1 engines. Regulations for diesel engines are similarly varied, with some jurisdictions focusing on NO x (nitric oxide and nitrogen dioxide) emissions and others focusing on particulate (soot) emissions. This regulatory diversity is challenging for manufacturers of engines, as it may not be economical to design an engine to meet two sets of regulations. Kong,,  Regulations of fuel quality vary across jurisdictions. In North America, Europe, Japan and Hong Kong gasoline and diesel fuel are highly regulated, and compressed natural gas gas  and LPG (Autogas) are being reviewed for regulation. In most of Asia and Africa, the regulations are often lax: in some places sulfur  content of the fuel can reach 20,000 parts per million (2%). Any sulfur in the fuel can be

 

oxidized to SO2 (sulfur dioxide dioxide)) or even SO 3 (sulfur trioxide) trioxide) in the  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, acid, a major component of acid of acid rain rain.. While it is possible to add substances such as vanadium  vanadium to the catalyst washcoat to combat sulfur-oxide formation, such addition will reduce the effectiveness of the catalyst. The most effective solution is to further refine fuel at the refinery to produce  produce  ultra-low sulfur diesel. diesel . Regulations in Japan, Europe and North America tightly restrict the amount of sulfur permitted in motor fuels. However, the expense of producing such clean fuel may make it impractical for use in developing countries. As a result, cities in these countries with high levels of vehicular traffic suffer from acid rain, which damages stone and woodwork of  ecosystems.. buildings, poisons humans and other animals, and damages local ecosystems [ e dit  edit   ] Negative Negative

aspects This article's Criticism or Controversy or Controversy section may compromise the article's  neutral point of view of the subject. Please  article's Please integrate the section's contents into the article as a whole, or rewrite the material. (July 2012)

Some early converter designs greatly restricted the flow of exhaust, which negatively affected vehicle performance, driveability, and fuel economy. [18] Because they were used with carburetors incapable of  precise fuel-air mixture control, they could overheat and set fire to flammable materials under the car. [19]

 Removing a modern catalytic converter in new condition will not increase vehicle performance

without retuning,[20] but their removal or "gutting" continues.[18] [21] In such cases, the converter may be replaced by a welded-in section of ordinary pipe or a flanged "test pipe" ostensibly meant to check if  the converter is clogged by comparing how the engine runs with versus without the converter, which facilitates reinstallation of the converter in order to pass an emission test.[20] In many jurisdictions, it is illegal to remove or disable a catalytic converter for any reason other than its direct and immediate replacement. In the United States, for example, it is a violation of Section 203(a)(3)(A) of the 1990 Clean Air Act for a vehicle repair shop to remove a converter from a vehicle, or cause a converter to be removed from a vehicle, except in order to replace it with another converter., [22] and Section 203(a)(3) (B) makes it illegal for any person to sell or to install any part that would bypass, defeat, or render  inoperative any emission control system, device, or design element. Vehicles without functioning catalytic converters generally fail emission inspections. The automotive aftermarket supplies high-flow converters for vehicles with upgraded engines, or whose owners prefer an exhaust system with largerthan-stock capacity.[23] [edit edit]]Warm-up

period

Vehicles emit most of their pollution during the first five minutes of engine operation before the catalytic [24]

converter has warmed up sufficiently to be effective. effective.

 

BMW  introduced an electrically heated catalyst, which they called "E-CAT", in In 1999, BMW their 750iL  sedan. Heating coils inside the catalytic converter assemblies are electrified just after  their 750iL engine start, bringing the catalyst up to operating temperature very quickly to qualify the vehicle for  low emission vehicle (LEV) designation. designation. [25] [edit edit]]Environmental

impact

Catalytic converters have proven to be reliable and effective in reducing noxious tailpipe emissions. However, they also have some shortcomings and adverse environmental impacts in production:



 Although catalytic converters converters are effective at rem removing oving hydrocarbons and other harmf harmful ul

emissions, they do not reduce the emission of carbon dioxide (CO2) produced when fossil fuels the  greenhouse gases indicated are burnt.[26] Carbon dioxide produced from fossil fuels is one of the by the Intergovernmental Panel on Climate Change Change  (IPCC) to be a "most likely" cause of  global warming.[27] Additionally, the  warming. the U.S. Environmental Protection Agency (EPA) has stated catalytic converters are a significant and growing cause of global warming, because of their release of n itrous oxide (N2O), a greenhouse gas over three hundred times more potent than carbon nitrous dioxide. The EPA states that motor vehicles contribute approximately 50% of nitrous oxide emissions, nitrous oxide makes up 7.2% of greenhouse gases. [28] 

 An engine equipped with with a three-way catalyst must must run at the stoichiometric point point,, which

means more fuel is consumed than in a  a  lean-burn engine. This, in turn, means relatively more CO2emissions from the vehicle. Nevertheless, catalyst-equipped engines produce cleaner exhaust than lean-burn engines. 

Catalytic converter production requires  requires  palladium or platinum or platinum;; part of the world supply of 

near  Norilsk,, Russia, Russia, where the industry (among others) has these precious metals is produced near Norilsk caused Norilsk to be added to  to  Time magazine's list of most-polluted places. [29] [ e edit  dit   ] Theft  Theft  Because of the external location and the use of valuable precious metals including platinum platinum,, palladium, palladium, and rhodium rhodium,, converters are a target for thieves. The problem is especially common among late-model trucks and SUVs, because of their high ground clearance and easily removed bolt-on catalytic converters. Welded-in converters are also at risk of theft, as they can [30][31] 31][32] be easily removed with a reciprocating saw. [30][  Theft removal of the converter can often

inadvertently damage the car's wiring or fuel line resulting r esulting in dangerous consequences. Rises in metal costs in the U.S. during recent years have led to a large increase in theft incidents of the converter, [33]

[34]

 which can then cost well over $1,000 to replace.

 

edit   ] Diagnostics Diagnostics [ e dit  Various jurisdictions now legislate on-board diagnostics to monitor the function and condition of the emissions-control system, including the catalytic converter. On-board diagnostic systems take several forms. Temperature sensors sensors  are used for two purposes. The first is as a warning system, typically on two-way catalytic converters such as are still sometimes used on LPG forklifts. The function of the sensor is to warn of catalytic converter temperature above the safe limit of 750 °C (1,380 °F). More-recent catalytic-converter designs are not as susceptible to temperature damage and can withstand sustained temperatures of 900 °C (1,650 °F).[citation needed ] Temperature sensors are also used to monitor catalyst functioning: usually two sensors will be fitted, with one before the catalyst and one after to monitor the temperature rise over the catalytic-converter core. The oxygen sensor is sensor is the basis of the closed-loop control system on a spark-ignited rich-burn engine; II,, a second oxygen sensor is fitted after  however, it is also used for diagnostics. In vehicles with OBD II the catalytic converter to monitor the O 2 levels. The O2 levels are monitored to see the efficiency of the burn process. The on-board computer makes comparisons between the readings of the two sensors. The readings are taken by voltage measurements. If both sensors show the same output or the rear  O2 is "switching", the computer recognizes that the catalytic converter either is not functioning or has been removed, and will operate a malfunction indicator lamp and affect engine performance. Simple "oxygen sensor simulators" have been developed to circumvent this problem by simulating the change across the catalytic converter with plans and pre-assembled pre- assembled devices available on the Internet.  Although these are not legal legal for on-road use, they have been been used with mixed mixed results results..[35] Similar  devices apply an offset to the sensor signals, allowing the engine to run a more fuel-economical lean burn that may, however, damage the engine or the catalytic converter .[36] NOx sensors are extremely expensive and are in general used only when a compression-ignition engine is fitted with a selective catalytic-reduction (SCR) converter, or a NOx absorber catalyst in a feedback system. 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 will be post-catalyst. They are used for the same reasons and in the same manner as an oxygen sensor: the only difference is the substance being monitored.

 

The brake booster uses vacuumfrom the engine to multiply the force that your foot applies to themaster the master cylinder . In this article, we'll see what's inside the black cannister that provides power  braking. HIT THE BRAKES!