Three Way Catalytic Converters Web example essay topic

Abstract: A catalytic converter is a device that we use now to convert pollutant from the engine's exhaust to less harmful gases. Different catalytic converters have been investigated throughout the years to improve the disadvantages that the existed device has. In this paper, we will talk about the basic structure for each of the catalytic converters, the detail of conversion process from harmful gases to less harmful gases, the advantages and disadvantages for the converters, the solutions for the disadvantages, and how to maintain catalytic converters for longer lifetimes. Also, possible trends for the future catalytic converter will also be briefly discussed. Introduction: The advanced technology in recent decades usually has big impacts on the human society.

Often times, it brings us a much more convenient life. But besides all the benefits we enjoy from the advanced technology, other harmful effects also exist as well. The growth of automobiles in the past half-century brought us great conveniences; it is easier for us to travel between places. Despite all the advantages brought by automobiles, air pollution is the major concern that we have. One attempt to minimize this problem has been the introduction of catalytic converters in car exhaust systems. [1] Types of Pollution: There are three major types of harmful compounds created by the use of automobiles, hydrocarbons, carbon monoxide, and nitrogen oxides.

In a perfect engine, oxygen in the air would convert all the hydrogen in the fuel to water and all the carbon in the fuel to carbon dioxide. [Equation 1] But in the normal combustion, automotive engines emit different types of pollutants [2] [Equation 2] In a perfect engine: Fuel (hydrocarbons) + Air (oxygen and nitrogen) = Carbon Dioxide + water + unaffected nitrogen In normal combustion: Fuel + Air = Unburned Hydrocarbons + Nitrogen Oxides + Carbon monoxide + Carbon Dioxide + water Hydrocarbon emissions result when fuel molecules in the engine do not burn or burn only partially. [2] Under the high pressure and temperature conditions in an engine, nitrogen and oxygen atoms in the air react to form various nitrogen oxides. [2] Carbon monoxide is a product of incomplete combustion and occurs when carbon in the fuel is partially oxidized rather than fully oxidized to carbon dioxide. [2] All these three compounds are harmful to human in different ways. Hydrocarbon produces smog, [1] exposure to nitrogen oxides lead to acute respiratory illnesses, [3] and carbon monoxide is poisonous to any air-breathing animal, and it affects the oxygen-dependent tissues, central nervous system, and many other diseases.

[3] Various ways have been relied on for controlling the air pollution from the growth of automobiles in the late 60's. For example, control of the mixture of gasoline and air; air injection that provides enough oxygen to support combustion; and design of the engine. [4] But in the early 70's, the air pollution was not getting better. The immediate need to solve the pollution crisis that was brought about by the automobile emerged.

The first catalytic converter was invented in early 1970's. [5] Through the years, improvements for catalytic converters have been made to increase conversion efficiency. The development of this device would be briefly discussed in the later section. What is a catalytic converter? A catalytic converter is a stainless steel box mounted in the exhaust system. Inside a stainless steel box is a catalyst on a ceramic or metallic support protected from vibration and shock by a resilient ceramic or metallic 'mat'.

[Figure 1] [6] A catalytic converter is a device that uses a catalyst to convert hydrocarbons, carbon monoxide, and nitrogen oxides into harmless compounds. [1] The location of the catalytic converter is shown as below: The catalytic converter is installed between the exhaust manifold and the baffle box, [Figure 3] and makes use of chemicals that act as a catalyst. A catalyst is a chemical that causes a reaction between other chemicals without being affected itself. In the case of the catalytic converter, the chemicals it contains cause a reaction in the pollutants in the exhaust. [7] The catalytic converter treats the exhaust before it leaves the car and thus removes a lot of the pollution. [8] History and developments of Catalytic Converters: "Early model converters used a pellet ised catalyst, but most modern converters are now designed with a free-flowing honeycomb ceramic catalyst.?

[9] There are three basic types of automotive catalytic converters; Two-Way, Three-Way and Three-Way + Air. [9] Oxidation Catalysis-Two-Way catalysis The earlier catalytic converters used commercially on cars during 1975-1980 were two-way, [10] [Figure 4] [11] which is the monolith oxidation catalyst. In a monolithic-type converter, the exhaust gas passes through a honeycomb ceramic block. The converter beads, or ceramic block, are thinly coated with platinum, palladium, and mounted in a stainless steel container. An oxidation catalyst changes HC and CO to CO 2 and water vapor.

[12] [equation 3] An input of oxygen is needed for this type of catalytic converter; therefore oxygen is usually injected into the cylinder head, or directly into the exhaust header or manifold. [13] [Figure 3] [11] The Chemical reaction for two-way converter: 2 CO + O 2 = 2 CO 2 Hydrocarbon + O 2 = CO 2+ H 2 O There were two primary concerns with the application of an oxidation catalyst. The first concern was the under hood temperatures caused by the exothermic reaction of higher HC and CO emissions. This potential problem was addressed with the use of a heat shield separating the silencer from the rest of the engine compartment. [14] The second concern was catalyst deactivation caused by excessive thermal loading of the catalyst and oil contamination. This problem was solved by the incorporation of a closed loop fuel system to reduce engine out emissions along with using a smaller amount of synthetic oil for lubrication.

[14] Even though two-way converter came to make a lot of differences in the society by the fact that it reduced the amount of hydrocarbon and carbon monoxide, there was still need in removing nitrogen oxides, since that nitrogen oxide is a really harmful substance. With the more advanced technology in the 80's, the invention of a more modern, and more efficient catalytic converter so called "three-way converter? brought a whole new horizon to the modern world. Reduction catalysis- Three-Way Converter The three-way catalytic converter first appeared in Europe, and has since taken over completely. It is called three-way because it helps to reduce three harmful emissions. [15] It not only oxidizes hydrocarbon and carbon monoxide with the use of platinum and palladium like two-way converter, but it also breaks nitrogen oxide down into ordinary nitrogen and oxygen through the action of rhodium. [16] Usually, the three-way converter has separate chambers holding two different types of catalysts, the one upstream handling reduction, and the one downstream handling oxidation.

[17] [Figure 5] [11] The idea is to create a structure that exposes the maximum surface area of the catalyst to the exhaust stream, while also minimizing the amount of catalyst required. [18] There are two types of three-way converters, pelletize d three-way converters and monolith three-way converters. Some early automobiles used pallet ized which was constructed of catalyst-coated pellets tightly packed in a sealed shell. Later on, the monolith three-way converter was developed; it uses a honeycomb shaped catalyst element. The monolith design creates less exhaust back pressure, and provides ample surface area to convert feed gases. [19] Three Basic Components of a modern three-way converter: A monolith is a ceramic or metal honeycomb structure that presents the catalyst to the exhaust stream.

[Figure 8] [20] Wash coat material is a porous ceramic coating applied in a thin layer to the monolith that provides a large area over which the catalytic metals can be deposited. [20] [Figure 6] [15] The catalyst enhances rates of reaction by a substance that promotes a faster chemical reaction at a lower temperature without being consumed in the reaction. [21] The catalyst is generally the precious metals -- platinum, palladium and rhodium compounds, within the porous ceramic coating, and is used to carry out the chemical reactions that purify the exhaust. [20] [Figure 7] [15] The three-way converter is composed of several tubes, which are coated with porous ceramic. [Figure 6] [15] Tiny particles of platinum and rhodium metal are present and serve as catalysts within this coating. [Figure 7] [15] The harmful gases enter this stainless steel container, [13] then are temporarily bound to the catalysts (Platinum and Rhodium) and are then converted into non-toxic chemicals when the exhaust from the engine heats the converter above 300 degrees.

[15] How does it actually work? There are three stages taking place within the three-way catalytic converter, reduction catalyst, oxidation catalyst, and control system. Reduction catalyst is the first stage of the process. Platinum and rhodium were used to help reduce the NOx emissions. Rhodium exhibits excellent activity for the reduction catalyst, and therefore, only a small amount of rhodium is actually required.

[21] Platinum does not work as well in the reduction catalysis as rhodium, because it needs a larger amount of the metals in order to reach the same results. When an NO or NO 2 molecule contacts the catalyst, the catalyst takes the nitrogen atom off from the molecule and holds on to it, freeing the oxygen in the form of O 2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N 2. [Equation 4] [15] Reduction: 2 NO = .

N 2 + O 2 Equation 4 (Reference 15) The second stage of the process is oxidization catalyst. It reduces unburned hydrocarbon (gasoline) and carbon monoxide by oxidizing them over platinum and palladium catalyst. Platinum is the major catalyst that is used in this process. One advantage it has is that it still functions during the warm-up of the converter from a cold start. [21] Palladium also works for the oxidation catalyst, but it does not have the specialty that platinum has. These catalysts aid the reaction of the CO and hydrocarbon under the remaining oxygen from the reduction catalyst in the exhaust gas.

[Equation 5] [18] Oxidation: 2 HC + 5/2 O 2 -- 2 CO 2 + H 2 O 2 CO + O 2 -- 2 CO 2 The final stage of the catalytic converter is the control system that monitors the exhaust stream, and controls the fuel injection system by the information that is received. [18] The closed-loop emission control system consists of an oxygen sensor, an electronic control module, a carburetor, and an air pump. [15] In order to have a "perfect? combustion, it is required to have the stoichiometric air / fuel ratio of 14.7 parts air to one part fuel by weight to complete combustion. [16] An Oxygen sensor that is located upstream of the catalytic converter acts as an instrument that detects the amount of oxygen that exists. [18] The mechanism in most sensors involves a chemical reaction that generates a voltage. The electronic control module looks at the voltage, and compares it to a present voltage.

The electronic control module then generates a correction control signal, which passes to the carburetor. The control signal increases or decreases at a fixed rate until the oxygen sensor shows that the air-fuel mixture has reached a stoichiometric composition. A carburetor can adjust the amount of fuel entering the engine accordingly in an earlier time period. [15] In more recent times, the fuel injection system adjusts the amount of fuel entering an engine in an automobile.

It is crucial to have the oxygen sensor in the process because the fuel injection system would not be able to pump out the right amount of fuel, and the automobile would not work efficiently. With all three stages, the conversion cycles would be completed and convert the pollutant into harmless gases. Three-Way + Air converter The three-way + air converter performs the same functions as the Three-Way converter. But the addition of secondary air between the two internal catalyst substrates improves the oxidation capabilities of the converter. The secondary air is pumped between the two separate catalyst coats with ceramic substrate into the middle of the converter. While the front ceramic performs the reduction, the back ceramic performs the oxidation.

It is like having two converters in one in this device. [9] Lethal conditions for Catalytic Converter No matter how advanced the technology is, failures still occur for the sophisticated invention. The catalytic converter fails to function normally under certain conditions. Being overheated is the most general problem for the catalytic converter. The most common cause of failure is an engine that pumps out too much unburned fuel, which can overheat and melt or carbon-clog the catalyst. [16] The catalytic converter can also be overheated when the engine is misfiring.

Any un-burnt fuel from a misfiring engine collects in the catalytic converter and then ignites in the catalytic converter causing it to overheat. The under body and interior of the car has been known to set fire when the catalytic converter gets so hot under these conditions. [22] The catalytic converter is sensitive toward certain chemicals. In order to maintain the catalytic converter in its good condition, unleaded gasoline must be applied. The catalytic converter becomes overheated when leaded gasoline is used. [23] Tetra ethyl-lead fuel forms and coats the catalyst under increased miles operation when using leaded gasoline [4] High temperatures for extended time periods tend to give "glazing? of the catalyst and reduce surface area.

This decreases the effectiveness of a catalytic converter; the lifetime of a catalytic converter thus decreases according to a time-temperature function. [4] The failure from the past would always turn to success by the more advanced technology that is investigated. Catalytic converters are good at removing most of the pollutants from car exhaust, but they have a big disadvantage, that they work only when the car is warm. [24] Automobiles emit as much as 70 percent of their pollutants in the first two minutes after starting up. It greatly reduces the efficiency of the converter with the fact that the catalytic converter does not start functioning until it is warm. There are two different ways of solving this cold-start problem and making converters more efficient.

Mark Golden proposed the method of heating the converter with the alloy metal hydride. "When a hydride absorbs or releases hydrogen, the reaction creates instant temperature swings -- often dramatic -- that are very predictable", he says. [24] The heater includes two containers of metal hydrides. When the engine starts, the hydride in the pressurized container releases hydrogen, which flows to the low-pressure container and is absorbed. This reaction releases sufficient heat to warm the car's exhaust to a high temperature that is enough for the converter to begin working. [24] The other method for solving this problem is proposed by David Benson and Tom Potter.

They developed a well-insulated catalytic converter that stays warm almost indefinitely. The converter is surrounded by vacuum insulation, two sheets of metal with a vacuum between them, to trap heat. The half-inch space between the insulation and the converter is filled with an aluminum-magnesium alloy, which melts and absorbs heat when the converter gets hot. The alloy solidifies and gives up heat to the converter when the converter cools. [24] Despite all the improvements researchers have done with the three-way catalytic converter, there are still negative effects. The catalytic converter greatly reduces the pollution that is created by the automobile, yet researchers have suspected that the converting process also produces pollution.

[25] The converters sometimes form nitrous oxide, known as laughing gas by rearranging the nitrogen-oxygen compounds. According to experts, nitrous oxide is a potent greenhouse gas that is warming the atmosphere. [25] Environmental Protection Agency also stated that the catalytic converter becomes a significant and growing cause of global warming. Another problem is that when nitrogen oxide from the engine's exhaust is reduced, a complex chemical reaction ensues. Ammonia gas forms in the catalytic converter, which is then emitted from the vehicle's tailpipe, and ammonia gas is haze causing. This suggests that while fixing one problem, the catalytic converter creates a secondary problem.

[23] The BOB magnetic fuel catalytic converter was soon created. BOB stands for "Better Overall Burning.? It is a simple unit that significantly reduces hydrocarbon and carbon monoxide emissions from combustion engines. [26] [Figure 8] Magnetic stimulation will alter the hydrogen state. It is determined that particular magnetic frequencies have a more desirable effect than others. With the turbulence created by the rotation of the magnet, and the magnetic properties that hydrogen has, the hydrogen rapidly switches from its symmetrical para, stable state, to its asymmetrical ortho, active state.

This increases the reactivity, therefore increasing the fuels? ability to take on oxygen molecules. The combustion process will then be more completed. As the result, less unburned fuel would be left, and the pollution brought about by the unburned hydrocarbons will be reduced. [26] Even though the BOB magnetic fuel catalytic converter solved the problem that the three-way catalytic converter has in creating secondary pollution, the magnetic fuel catalytic converter can only reduce the hydrocarbon emission, and this is not enough for the world we are living in. Therefore currently, the three-way catalytic converter is still being used by majority of the automobiles even though negative impacts result from using it. Discussion: There is still a lot of room for improvements for the catalytic converters.

There are several parts that are necessary to be fixed. The three-way catalytic converter is up-to-date the best device to remove the harmful gases from the exhaust, because it removes three of the most common pollutants But the secondary pollution that is created by the process of conversion becomes a problem in the current world. One of the things that should be done now is to reduce the secondary pollution from nitrogen oxides from the three-way converter by some new components as well as keeping all the advantages the catalytic converter has so far. It is also possible to combine BOB magnetic fuel catalytic converter with the reduction catalyst from the three-way catalytic converter.

So this would become another solution for the problem that the converter only works when the engine is warm. There are other minor toxic air pollutants other than unburned hydrocarbon, carbon monoxide and nitrogen oxides, but it is still a problem. Some other metals might act as the catalysts to reduce those minor air pollutants. The final thing to do will be to invent new technology that can actually reduce the energy needed for catalytic converters. Conclusion: The catalytic converter plays an essential role on the automobile. Without it, harmful gases would create ozone, and global warming would result.

Even though the catalytic converter greatly reduced the harmful gases from the automobile, it still has downside characteristics. More research is required to improve the existing problems of this device. It is a requirement to have the catalytic converter in the automobile, but the converter would never be perfect, therefore research on the catalytic converter will continue to be a great interest to many researchers. Reference: [1] What is a catalytic converter and how does it work. web. [2] Automobile Emissions: An Overview. web. [3] Russell, E. Clean Air And Your Car; U.S. Environmental Protection Agency, Washington D.C., 1975.

[4] Morse, R. The automobile & air pollution; U.S. Department of Commerce, Washington D. C, 1967. [5] Anonymous. Motor vehicle pollution; OECD, Paris Cedex, 1995. [6] The Introduction of Catalytic Converters. web.

[7] Brandt, Karl. Karl's Emissions Control Page web. [8] How Catalytic Converters Work. web. [9] In a world full of copycats we have the original. web. [10] Conversion of Exhaust Gases. web. [11] Emission Control Systems web.

[12] Teo, Alvin. Exhaust Flow in an Automobile. web. [13] Exhaust And Cooling Systems (An Overview). web. [14] Hein A, Jagusch J, Mills J. Clean Snowmobile Challenge 2000; International Off-Highway & Powerplant Congress & Exposition, Milwaukee, 2000...

[15] Three-Way Catalytic Converters. web. [16] Catalytic Converters. web. [17] Three-Way Converter (TWC). web. [18] Nice, K. How Catalytic Converters Reduce Pollution. web. [19] Emission Sub System-Catalytic Converter. web. [20] Automotive Catalysis. web.

[21] Types Of Catalysis Used In Three-Way Converters. web. [22] Things to do when you get home / How your car works / Catalytic Converters. web. [23] Problems, Shortcomings, And Failures Associated with Catalytic Converters. web. [24] Mueller, A. Discover.

July 1996. web. [25] Wald, M.E.P.A. Says Catalytic Converter Is Growing Cause of Global Warming; The New York Times. May 29, 1998. [26] The BOB?

Magnetic Fuel Catalytic Converter. web..