Most exhaust systems consist of two parts.
First, I would like to introduce readers in detail to the catalysts used in gasoline engines.
The installation, simply called a catalyst, is not quite correctly and accurately called a regulated catalyst, or triple-action catalyst. None of the given names fully reveals the method of its action. It is called triple-action, since it destroys three harmful components. With the help of chemical reactions, it changes the harmful components in the exhaust gases into harmless chemical compounds or elements. A change in CO occurs (carbon monoxide), O2 (oxygen) and NOx (nitrogen dioxide) on CO ₂ (carbon dioxide), N₂ (nitrogen) and H2O (water). Reactions occur only in the presence of noble metals (platinum, palladium and rhodium), which have a catalytic effect in the chemical process. At the same time, high temperatures are required.
To ensure high efficiency, the mentioned metals must have as large a surface as possible. Most often, their carrier is a ceramic monolith or a metal carrier with channels. This achieves a large surface of many tens of square meters.
If a catalytic converter is installed in the exhaust system, leaded gasoline must not be used, since the products that arise during combustion of fuel with lead cover the active layer of the catalytic converter relatively quickly and thus disable it. Similarly, unburned fuel in the engine can ignite near the catalytic converter and melt it, or the fuel accumulated there can explode and destroy the catalytic converter. Therefore, it is mandatory that the fuel burns only in the engine. Consequently, the engine must not be started by accelerating the car on a cable or pushing it.
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The catalytic converter must be shielded from both the floor and chassis sides.
The catalyst is a component of the injection and ignition system, controlled by electronics. The electronics work by receiving information from several sensors (for example, temperature and pressure of the intake air, engine speed, coolant temperature and others). One of the sensors is the oxygen content sensor or lambda probe. It and the entire group of other sensors and actuators have, among other things, the task of maintaining such an operating mode of the engine so that the ratio of air and fuel approximately corresponds to the optimal value, i.e. so that there is 14.7 parts of air per one part of fuel.