Exhaust system catalyst functions

All Ford Mondeo engines are equipped with an exhaust gas purification catalyst. The catalyst is located in the front exhaust pipe.



The catalyst consists of a ceramic honeycomb body -A- coated with a carrier. On this carrier are salts of noble metals, which provide the transformation process. The insulating support layer -B- elastically holds the ceramic honeycomb body in the catalyst housing. This backing layer is made of an extremely heat resistant ceramic nonwoven.

Gasoline engines

The injection system and oxygen sensor precisely dose the amount of fuel burned so that the catalyst can reduce the content of harmful substances. The oxygen sensor is located in the front exhaust pipe, past it passes the flow of exhaust gases. As for the oxygen sensor, it is an electrical sensor that indicates the residual oxygen content in the exhaust gases on the basis of voltage fluctuations and allows you to draw conclusions about the chemical composition of the fuel-air mixture. The oxygen sensor can send appropriate signals to the injection control unit within a fraction of a second, resulting in a constant change in the ratio between the amount of fuel and the amount of air. Firstly, this is necessary because operating conditions are constantly changing (idle, full throttle), secondly, optimal neutralization in the catalyst occurs if the exhaust gases of the engine still contain a sufficient amount of gasoline.


In order for the catalyst to neutralize at all at temperatures of 300-800°C, the fuel-air mixture must contain more fuel than is necessary for simple combustion.

With regard to the catalyst, we are talking about the so-called three-way catalyst. This means that carbon monoxide is simultaneously oxidized in this catalyst based on oxygen sensor control (SO), hydrocarbons (NS) and a decrease in the content of nitrogen oxides (NO2).

Catalyst in a diesel engine

Diesel engines use serial catalysts. Here it is impossible to adjust the composition of the fuel-air mixture in the same way as it is done using an oxygen sensor in gasoline engines. The catalyst reduces the content of toxic carbon monoxides and hydrocarbons to the level that is achieved with a regulated catalyst in gasoline engines. In addition, the halls characteristic of diesel engines are reduced. The higher levels of nitrogen oxides inherent in diesel engines are reduced with the help of an additional exhaust gas recirculation system, see point 7.

In vehicles with catalysts, certain operating rules must be strictly observed.