CATALYTIC CONVERTER FOR AUTOMOBILE

CHAPTER 1INTRODUCTION

Air pollution generated from mobile sources such as automobiles contributes major air quality problems in rural as well as in urban and industrial areas in both developed and developing countries.

Vehicle population is projected to grow close to 1300 million by the year 2030. A large amount of vehicle transportation relies on combustion of diesel, gasoline, jet fuels with large amount of emission of carbon monoxide (CO), Unburned hydrocarbons (HC), Nitrogen oxide (NOx) and particulate matters (PM) are specially concern. HC, CO occur because the combustion efficiency < 100%. The NOx is formed during the very high temperatures (>1500 C) of the combustion process resulting in thermal fixation of nitrogen in the air which forms NOx. Typical exhaust gases compositionat the normal engine operating conditions are: Carbon monoxide (CO, 0.5 Vol. %), unburned Hydrocarbon (HC, 350vppm), Nitrogen Oxides (NOx, 900ppm), Hydrogen (H2, 0.17vol. %), Water (H2O,10 vol. %),Carbon dioxide( CO2, 10 vol.. %),Oxygen ( O2, 0.5 vol.%). Carbon monoxide isnoted poison that has an affinity for Hemoglobin in the blood 210 times more than the Oxygen. The reduction of toxic substances emission from the combustion can be seen in the form of two measures: [1]. Primary measures(Inside Engine): Here many different technical methods are used to reduce the exhaust emission i.e. Combustion of lean air fuel mixture, Exhaust gas recirculation etc. [2].Secondary measures Outside Cylinder): After the primary measures are used, there is an oxidation, reduction, and 3 way catalytic converter based on adsorption procedure. This enables the reduction of CO, HC, And NOx, that is Desirable.

CHAPTER 2

CATALYTIC CONVERTER

 A Catalytic Converter is an emissions control device that converts Toxic gases and Pollutants in exhaust gases to less Toxic pollutants by catalyzing a Redox reaction (an oxidation and a reduction reaction). Catalytic converters are used with Internal Combustion Engine fueled by either petrol (Gasoline) or Diesel- including lean burn engines as well as Kerosene Heaters and Stoves.

2.1 Position of Catalytic Converter Vehicle The Catalytic Converter is placed inside the tail pipe through which deadly exhaust gases containing unburntfuel, CO, NOx etc. are emitted.

CHAPTER 3

WORKING OF CATALYTIC CONVERTER

The function of the Catalytic Converter is to convert the pollutants into CO2, Water, N2, O2, These are less harmful gases. A mixture of residual quantity of HC, CO, NOx are left over after combustion, consequently, a Catalytic Converter uses precious metal like - Platinum( PT), Palladium ( PD)as a catalyst to convert harmful pollutants into less harmful gases like- CO2, O2, H20 etc. Although catalytic converters are most commonly applied to exhaust systems in automobiles, they are also used on electrical generators, forklifts, mining equipment, trucks, buses, locomotives and motorcycles. They are also used on some wood stoves to control emissions. This is usually in response to government regulation, either through direct environmental regulation or through health and safety regulations.

CHAPTER 4

HISTORY OF CATALYTIC CONVERTER

The catalytic converter was invented by Eugene Houdry, a French mechanical engineer and expert in catalytic oil refining, who moved to the United States in 1930. When the results of early studies of smog in Los Angeles were published, Houdry became concerned about the role of smoke stack exhaust and automobile exhaust in air pollution and founded a company called Oxy-Catalyst. Houdry first developed catalytic converters for smoke stacks called "cats" for short, and later developed catalytic converters for warehouse forklifts that used low grade, unleaded gasoline In the mid-1950s, he began research to develop catalytic converters for gasoline engines used on cars. He was awarded United States Patent 2,742,437 for his work. Widespread adoption of catalytic converters did not occur until more stringent emission control regulations forced the removal of the anti-knock agent tetraethyl lead from most types of gasoline. Lead is a "catalyst poison" and would effectively disable a catalytic converter by forming a coating on the catalyst's surface. Catalytic converters were further developed by a series of engineers including John J. Mooney and Carl D. Keith at the Engelhard Corporation,creating the first production catalytic converter in 1973.William C. Pfefferle developed a catalytic combustor for gas turbines in the early 1970s, allowing combustion without significant formation of nitrogen oxides and carbon monoxide.

CHAPTER 5

CONSTRUCTION

The Construction of a Catalytic Converter can be seen in terms of its basic parts as following:

5.1 Substrate

For automotive catalytic converters, the core is usually a ceramic monolith with a honeycomb structure. Metallic foil monoliths made of Kanthal (FeCrAl) are used in applications where particularly high heat resistance is required.Either material is designed to provide a large surface area 

5.2 The Wash coat

A wash coat is a carrier for catalytic materials and used to disperse the material over a large surface area. Aluminum oxide, Titanium oxide, Silicon dioxide, or a mixture of silica and alumina can be used. Catalytic materials are suspended in wash coat prior to applying to the core. The coat must retain its surface area and prevent sintering of the Catalytic metal particles even at the high temperature (1000 C).

CHAPTER 6

TYPES OF CATALYTIC CONVERTER

Generally catalytic converter are classified into two categories-

6.1 Two –Way

A 2-way (or "oxidation", sometimes called an "oxi-cat") catalytic converter has two simultaneous tasks:

1. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2 2. Oxidation of hydrocarbons (unburned and partially burned 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 automobiles until 1981. Because of their inability to control oxides of nitrogen, they were superseded by three-way converters

6.2 Three – way

Three-way catalytic converters (TWC) have the additional advantage of controlling the emission of nitric oxide and nitrogen dioxide (both together abbreviated with NOx and not to be confused with nitrous oxide), which are precursors to acid rain and smog.Since 1981, "three-way" (oxidation- reduction) catalytic converters have been used in vehicle emission control systems in the United States and Canada; many other countries have also adopted 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) Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2

2) Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2C 3) Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water:

CxH2x+2 + [(3x+1)/2] O2 → xCO2 + (x+1)H2O.

These three reactions occur most efficiently when the catalytic converter receives exhaust from an engine running slightly above the stoichiometric point. For gasoline combustion. This ratio is between 14.6 and 14.8 parts air to one part fuel, by weight

Comparison between Two-way and Three- way catalytic converter:

 Three ways catalytic converter are better than the two ways in terms of efficiency and effectiveness as we can see from the following chart

CHAPTER 7

CATALYSTS USED IN CATALYTIC CONVERTER

 There are mainly three catalysts that are used in a catalytic converter

 [1] Palladium (pd)- It is used in Oxidation Reactions

[2] Rhodium ( Rh) – It is used in Reduction Reactions

[3] Platinum ( pt. ) – It is used in both Oxidation and Reduction Reactions as well. 

CHAPTER 8

AIR TO FUEL RATIO

There is a narrow range of air- fuel ratio near stoichimetry in which high conversion efficiencies for all three pollutants are achieved. The width of this window is narrow about 0.1 airfuel ratio for catalyst with high mileage use and depends on catalyst formulation and engine operating conditions.Conversion efficiency of NO, CO and HC as a function of the air-fuel in a three way catalytic converter. Fig.5 shows the conversion efficiency of NO, CO and HC as function of the air- fuel ratio.

8.1 When the A/F ratio is leaner than stoichiometry

The oxygen content of the exhaust stream rises and the carbon monoxide content falls. This providesa high efficiency operating environment for the oxidizing catalysts (platinum and palladium). During this lean cycle the catalyst (by using cerium) also stores excess oxygen which will be released to promote better oxidation during the rich cycle.

8.2 When the A/F ratio is richer than stoichiometry

The carbon monoxide content of the exhaust rises and the oxygen content falls. This provided a high efficiency operating environment for the reducing catalyst (rhodium). The oxidizing catalyst maintains its efficiency as stored oxygen is released A closed loop feedback fuel management system with an oxygen sensor in the exhaust is used for precise control of air-fuel ration. To obtain an efficient control of the A/F ratio the amount of air is measured and the fuel injection is controlled by a computerized system which uses an oxygen (λ ) sensor located at the inlet of the catalytic converter. The signal from this λ sensor is used as a feedback for the fuel and air injection control loop. A second λ sensor is mounted at the outlet of the catalytic converter (Fig. 4). This configuration constitutes the basis of the so-called engine onboard diagnostics (OBD). By comparing the oxygen concentration before and after the catalyst, A/F fluctuations are detected. Extensive fluctuations of A/F at the outlet signal

system failure. Effect of A/F ratio on the conversion efficiency of three-way catalysts narrow A/F window at the stoichiometric point is the fingerprint of an effective TWC system. A simple closed loop feedback engine fuel management system is shown schematically in fig. 9

     CHAPTER 9

LIMITATIONS OF CATALYTIC CONVERTER

With the temperature up to 1000 c the metal in the catalyst is prone to deactivation by sintering

Emissions control targets is simply to increase the amount of PGM(platinum group metals)in the auto catalyst

Can not function well beyond 80000 km

CHAPTER 10

CONCLUSION

Today’s automobiles are meeting emission standards that require reductions of up to 99% of HC, CO and NOx compared to the uncontrolled levels of automobiles sold in the 1960s. Environmental, Ecological and Health concern result in increasingly stringent emissions regulations of pollutant emissions from vehicle engines. Use of metal monolith type catalytic converters are the best way to control the auto exhaust emissions. The economic reasons, limited resources of platinum group (Noble Group) metal and some operating limitations of platinum group metal based catalytic converters have motivated towards the investigation of alternative catalyst materials. This type of catalytic converters have also been developed for the use on trucks, buses and motorcycles as well as on construction equipment lawn and garden equipment etc. In 2005, 100% of the new cars sold in the U.S. were equipped with a catalytic converter , and Worldwide over 90% of the new cars sold had a metal monolith type Catalyst

CHAPTER 11

REFERENCES

1. A Technical Review of Automobile Catalytic Converter: Current Status and                   Perspectives S.K.Sharma 1, P.Goyal 2, S. Maheshwari 3, A.Chandra 4

2. A Review paper on Catalytic Converter for Automotive Exhaust Emission

    Prof. BHARAT S PATEL1, Mr KULDEEP D PATEL

3. Review Paper on Catalytic Converter for Automobile Exhaust Emission Prashant           Katara