The uses of catalytic converters reduces the emission from the exhaust system. Its primary function is to reduce the harmful emissions produced during the combustion process in the engine. Inside the catalytic converter are catalysts, usually made of precious metals such as platinum, palladium, and rhodium. In this article, I will discuss the uses of catalytic converts in a vehicle.
Uses of Catalytic Converter
A catalytic converter uses a catalyst to convert harmful exhaust emissions into harmless gases and liquids. It is a cylindrical unit about the size of a small silencer and is installed into the exhaust system of a vehicle such as a car, scooter, moped, motorcycle, or auto-rickshaw.
It is placed between the exhaust manifold and the silencer. Inside the converter, there is a honeycomb structure of a ceramic or metal that is coated with alumina base materials and thereafter a second coating of precious metals platinum, palladium, rhodium, or combinations of the same.
This second coating serves as a catalyst A catalyst is a substance that causes a chemical reaction that normally does not happen in the given conditions. As a result of the catalytic reaction, when the exhaust gases pass over the converter substrate, toxic gases such as CO. HC and Ox are converted into harmless C02, H2, and N2.
These are two types of catalytic converters:
- A two-way converter is used to control CO and HC emissions by oxidation.
- A three-way converter, which is used almost in all petrol. It controls CO and HC by oxidation as well as NOx by reduction.
Three-way converters (TWC) as shown in Fig. 37.6 (b) are now commonly being used for petrol engines and operate in two states. The first converter stage uses radium to reduce the NOx in the exhaust into nitrogen and oxygen. In the second converter stage, platinum or palladium acts as an oxidation catalyst to change HC and CO into harmless water and C02.
To supply the oxygen required in the second stage, air is fed into the exhaust after the first stage. The catalyst allows the oxidation of the exhaust gases at a much lower temperature than in the combustion chamber. With temperature exceeding 300°C, the steady state conversion efficiencies of the new converter are about 98% for carbon monoxide and about 95% for hydrocarbons.
What is Catalyst
Catalysts are used in catalytic converters to convert harmful emissions of automobiles into harmless compounds. Catalysts used in catalytic converters are in the form of coating of precious metals such as platinum, palladium, or rhodium or combinations of the same.
It promotes a chemical reaction called catalytic reaction which converts toxic gases such as CO, HC, and NO” into C02, H2, and N2• The catalyst in a converter should have low thermal inertia and should warm up rapidly. The warm-up time should be preferably 30 seconds, but not more than one minute.
Placing the converter very close to the exhaust manifold shall help in the rapid warm-up, but too close a placement can cause the exhaust gases under certain conditions, to exceed the safe working temperature, thereby reducing drastically the converter life.
Uses of Catalytic Converter in a Diesel Engine
The catalytic converter used in diesel engines operates in a different manner than the 3-way catalytic converter in petrol engines. The diesel engine catalytic is a pure oxidation catalytic convener, which oxidises hydrocarbons and carbon monoxide i nto water and carbon dioxide.
It cannot reduce nitrogen oxides. Such a catalytic converter is used on a Mercedess-Benz car. The particulate matter can be removed by passing the exhaust gas through a filter, wherein the particles are retained on the filter element, which is periodically removed by their oxidation using h exhaust gases, either at elevated temperature or in the presence of a catalyst.
In this way, the filter is kept clean automatically. Such filter traps are effective for small diesel engines wherein exhaust temperatures are high. In the case of large diesel engines, wherein exhaust gases are at lower temperatures and the particulate matter is also large, the process of removal of particulate matter from the exhaust is relatively difficult.
Variation of Catalytic Converter Efficiency with Air-Fuel Ratio
The efficiency of catalytic converter varies considerably with air-fuel ratio. Lean mixtures will provide lower H and CO levels and the converter is quite efficient in oxidizing these, but these ratios produce higher cylinder temperatures and consequently higher NOx levels to reduce for which converter efficiency is very low.
On the other hand, rich air-fuel ratios would provide low NOx emission levels, which are reduced quite efficiently by the converter. Yet these also cause high emissions of HC and CO and extremely low converter efficiency for oxidizing these. Thus, for the catalyst to operate at nearly 90 percent efficiency, the air-fuel ratio should be exactly stoichiometric. The slight change in the air-fuel ratio within which the converter may be allowed to work is called the catalyst operating window.
Advantages of Catalytic Converter
Catalytic converters offer several advantages in the context of automotive and industrial applications, primarily related to environmental and health considerations. Here are some key advantages:
- The primary function of a catalytic converter is to reduce harmful emissions from the exhaust gases of an internal combustion engine.
- By minimizing the release of pollutants into the atmosphere, catalytic converters contribute to the reduction of air pollution.
- Many countries have stringent emission standards and regulations in place to control air pollution.
- Reduced emissions lead to improved air quality, which, in turn, has positive effects on public health.
- Catalytic converters operate at relatively low temperatures, enhancing their efficiency in promoting chemical reactions that convert harmful gases into less toxic substances.
- Catalytic converters are widely used around the world, making them a global solution to address the environmental impact of internal combustion engines.
In summary, catalytic converters play a vital role in reducing harmful emissions from vehicles, contributing to cleaner air and environmental conservation. Despite their environmental benefits, catalytic converters can face issues, such as clogging due to the accumulation of deposits or damage from impacts.
Frequently Asked Questions(FAQ’S)
Why are catalytic converters important?
Catalytic converters are crucial for reducing air pollution by minimizing the emission of harmful gases from vehicles and industrial processes. They play a key role in meeting environmental regulations and improving air quality.
Can catalytic converters wear out or become damaged?
Yes, catalytic converters can face issues such as clogging, catalyst poisoning, or physical damage. Factors like engine misfires, oil or coolant contamination, and impacts can contribute to the degradation of catalytic converter performance.
Are catalytic converters recyclable?
Yes, catalytic converters contain valuable metals, making them recyclable. Recycling facilities can extract and reuse precious metals from old or damaged converters, contributing to sustainability efforts.