Pollution control system present in the exhaust line, which transforms, by reaction with the oxygen present in the gases, the pollutants resulting from combustion into harmless components. It is usually placed not far from the engine, allowing it to quickly reach operating temperature.
However, a few minutes are still necessary before it plays its role. Recently, the catalytic converter has been mandatory on all gasoline engines since 90s and on diesel engines since 2000.
On gasoline cars, three-way catalysts are most often found, capable of transforming three toxic substances, hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). They convert them into water vapour, carbon dioxide (CO2) and nitrogen.
Diesels generally make do with two-way catalysts, which do not deal with nitrogen oxides. To overcome this drawback, some models use NOx/DeNOx catalysts capable of converting NOx. Particle filters are also frequently used to burn the toxic particles emitted by diesel engines.
The catalyst uses a process called catalysis to accelerate the chemical reaction of converting pollutants. It consists of a support, usually ceramic, which has a honeycomb structure made up of multiple channels, in which there are microscopic particles of precious metals (platinum, palladium, etc.). There is also another meaning of catalyst which is used in chemistry.
It is the reaction between these metals and the pollutants that accelerates the transformation of toxic substances. The catalytic converter, on the other hand, requires the use of low-sulphur fuels and unleaded gasoline to preserve its lifespan.
It also required the installation of a lambda sensor, which continuously measures the oxygen level at the engine outlet. A computer is then responsible for adapting the fuel injection into the engine, to obtain the air/fuel mixture that is most conducive to the proper functioning of pollution control.
