Since the inception of the car, it has gone through lots of changes and is still going through the process of evolution. Now some of the changes have made to boost the performance, some of them are made to enhance the beauty and luxury and then there are few changes which are made to make it more environment-friendly. One very popular of those change brought in is known as a catalytic converter.
This is a pollution control device which is designed to convert the pollutant in the cars exhaust gas to a less much less harmful pollutant. Most of the catalytic converters are used in internal combustion engine.
The introduction of the particular device is made through the stricter rules amended by environment protection agency of US. So the first of its kind was seen in US market back in 1975. Though the converter is mostly used in internal combustion engine but there are different models specified for the generator, mining equipment locomotive engine and many more.
The modern catalytic converter has 3 elements as major construction item.
- First one is the catalyst support for automotive converter the core is a ceramic monolith with the honeycomb structure.
- The second one is the wash coat. It basically carries the catalyst materials and spreads it over a large surface. The catalytic materials are suspended prior to applying to the core. Wash coat 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 third one is the catalytic elements itself. The mixture consists of a range of elements expensive to inexpensive based on their purpose. Platinum is one of the elements used in it and is present only in the high-end models. Rhodium and palladium are two other expensive component used as reduction catalyst and oxidation catalyst respectively.
Modern day converters can be classified in two group
Two-way models were used in diesel engines to reduce hydrocarbon and carbon monoxide emission. Though these models are totally replaced by the three-way successor due to inability to control oxides of nitrogen.
The three-way converter can be seen in most vehicle nowadays. Three-way converters are most popular and well accepted because of its ability to reduce nitrous oxide a prominent greenhouse gas.
Three-way converters are effective when the engine is operated within a narrow band of air-fuel ratios near the stoichiometric point, such that the exhaust gas composition oscillates between rich (excess fuel) and lean (excess oxygen). Conversion efficiency falls very rapidly when the engine is operated outside of this band.
Under lean engine operation, the exhaust contains 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, leaving only stored oxygen available for the oxidation function.
Though three way converter have faced some issues regarding backward reaction but still it is the most reliable and widely used alternatives throughout the world.
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