General information about the exhaust system

Skoda cars of the Octavia type series are equipped with several types of exhaust systems depending on the installed engine. Gasoline vehicles always have an adjustable triple acting catalytic converter installed in the exhaust tract, diesel vehicles always have an oxidizing catalyst installed.

Mostly exhaust systems consist of two parts.

First, I would like to acquaint readers in detail with the catalysts used in gasoline engines.

The installation, which is simply called a catalyst, is not quite correctly and accurately called a variable catalyst, or triple action. None of the above names fully reveal the way it works. It is called triple action, as it destroys three harmful components. Through chemical reactions, it changes the harmful constituents in exhaust gases into harmless chemical compounds or elements. There is a change in CO (carbon monoxide), О2 (oxygen) and NOx (nitrogen dioxide) on CO2 (carbon dioxide), N2 (nitrogen) and H2O (water). Reactions take place only in the presence of noble metals (platinum, palladium and rhodium), that have a catalytic effect in a chemical process. At the same time, a high temperature is also required.

To ensure high efficiency, said metals should 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 catalyst is installed in the exhaust tract, leaded gasoline should not be used, since the products resulting from the combustion of fuel with lead cover the active layer of the catalyst relatively quickly and thereby disable it. Likewise, unburned fuel in the engine may ignite towards the catalyst and melt it, or fuel accumulated there may explode and destroy the catalyst. Therefore, a prerequisite should be the combustion of fuel only in the engine. Therefore, the engine must not be started by accelerating the vehicle on the rope or by pushing it.

The catalyst must be shielded both on the floor side and on the chassis side.

The catalyst is an integral part of the electronically controlled injection and ignition system. Electronics works by receiving information from several sensors (e.g. intake air temperature and pressure, engine speed, coolant temperature, etc). One of the sensors is an oxygen sensor or a lambda probe. He and the whole group of other sensors and actuators, among other things, have 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 14.7 parts of air accounted for one part of the fuel.