Function of the catalytic converter
A catalyst as a concept from the field of chemistry is a substance that controls a chemical reaction or speeds it up. At the same time, the composition and structure of the catalyst remain unchanged. In cars, it is part of the exhaust system.
Vectra has a ceramic catalyst. We are talking about a ceramic body, coated, along with its shell, noble metals - platinum and rhodium. The ceramic part, located in a wire mesh, is penetrated by several thousand parallel channels. An intermediate layer is applied to the walls of the channels, which serves to increase the outer surface (the so-called wash-coat). It increases the active surface of the catalyst to about the size of a football field.
The catalysts in both designs are platinum and rhodium. These noble metals in the catalytic converter contain 2-3 g, while platinum supports oxidation, and rhodium - lowering the level of nitrogen oxide.
With the help of a catalytic converter, harmful substances such as carbon monoxides, hydrocarbons and nitrogen oxides are converted (hence the name - triple action catalyst).
- Carbon monoxide and hydrocarbons are converted by oxidation with oxygen into carbon dioxide (CO2).
- To break down nitrogen oxides, a means is used that takes oxygen from them. This agent can be a harmful substance - carbon monoxide. This produces nitrogen (N2) and again CO2. Both are not dangerous.
Tips: Individually, the reduction of harmful substances in a controlled catalytic converter is: carbon monoxide by 85%, hydrocarbons by 80%, nitrogen oxides by 70%. This takes into account that as the mileage increases, the catalytic converter loses some of its effectiveness.
In combination with a catalytic converter, other concepts often appear: «nested» catalytic converter means that the ceramic body of the catalytic converter is enclosed in a closed housing (with metallic wool lining). catalytic converter «dual purpose» can neutralize only two harmful substances in the exhaust gases, the catalytic converter «triple use» (installed in the Vectra), on the contrary, three.
Action range
The catalytic converter functions with a high degree of efficiency only in a narrow range: at «stoichiometric» the ratio of fuel and air in the combustible mixture (λ=1). The biggest challenge in catalytic converter technology is to maintain this ratio under all vehicle operating conditions through lambda control. A deviation of even 1% has a significant effect on the degree of efficiency of the catalytic converter.
In order for the catalytic converter to start working, the initial temperature must reach approximately 300°C. This usually happens after 25-80 seconds; in urban areas, it may take even three minutes before the required temperature is reached. At the same time, the ceramic catalyst is sensitive to overheating. If the temperature in the catalytic converter rises above 900°C, accelerated aging of the device begins. From 1200°C, its effectiveness is destroyed for a long time.
The catalytic converter requires unleaded gasoline. Lead would quickly clog the surface of the catalytic converter, and the exhaust gases would no longer be able to come into contact with substances that have a catalytic effect. Experiments have shown that even after one refueling of the fuel tank with leaded gasoline, carbon monoxide is almost not split. After 2-3 refills, the remaining harmful substances no longer break down. The catalyst is poisoned.
Tip: Noble metals in a catalytic converter can be removed after it has served its purpose. German Society for the Disposal of Automotive Catalytic Converters (DAR) collects old automotive catalytic converters from auto repair shops and other firms in order to prepare them for other uses, such as jewelry making. Some workshops pay a small fee for used catalytic converters.
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