Contents: Petrol engines ⇓ Catalytic converter in diesel engines ⇓ Exhaust gas recirculation system ⇓
All engines are equipped with a catalytic converter to clean exhaust gases.
The catalyst consists of a ceramic honeycomb element (3), which is located inside a protective fastening layer. On the fastening layer are salts of noble metals, which ensure the conversion process. In the housing (1), the catalyst is fixed with the help of an insulating protective layer (2), which also compensates for thermal expansion.
Petrol engines
The electronic injection system and the lambda probe work together to precisely dose the fuel for combustion so that the catalytic converter can reduce the concentration of toxic substances. The lambda probe is located in the exhaust pipe in front of the catalytic converter and is surrounded by the exhaust gas flow here. The lambda probe is an electrical measuring sensor that determines the residual oxygen content in the exhaust gas by means of fluctuations in the electrical voltage and makes it possible to correct the composition of the fuel-air mixture. In a fraction of a second, the lambda probe can send a corresponding signal to the injection system control unit and, thanks to this, the ratio between fuel and air is corrected. On the one hand, this is necessary, because the operating conditions (idle, full load) are constantly changing, but, on the other hand, optimal afterburning in the catalytic converter occurs only when the exhaust gases contain a sufficient amount of gasoline.
In order for afterburning to begin at all in the catalytic converter at temperatures between 300 and 800°C, there must be more oxygen in the fuel-air mixture than is required for clean combustion.
The catalyst used is a so-called 3-way catalyst. This means that this catalyst, thanks to lambda regulation, simultaneously oxidizes carbon monoxide (CO) and hydrocarbons (CH), and reduces the concentration of nitrogen oxide (NOx).
(The original text is published on: Mazbook.ru)
Catalytic converter in diesel engines
In cars with diesel engines, the catalytic converter is installed as standard. However, in this case, the fuel-air mixture is not corrected. The catalytic converter, however, reduces emissions of toxic carbon monoxide and hydrocarbons to a level that is significantly lower than the level for gasoline engines with controlled catalytic converters. In addition, the characteristic noise from the operation of the diesel engine is reduced.
Exhaust gas recirculation system
The exhaust gas recirculation system is installed to maintain the concentration of nitrogen oxides already before the catalytic converter at a low level. Depending on the engine operating mode, exhaust gas recirculation directs a certain amount of exhaust gases back into the flow of air entering the engine via a controlled valve. This reduces the combustion temperature. The lower it is, the less toxic nitrogen oxides are formed in the exhaust gases.