Operation of the catalytic converter (Scorpio 2)

Gasoline engines with regulated catalytic converter

The connection of the electronically controlled injection system and the oxygen sensor allows precise dosing of the amount of fuel for combustion so that the catalytic converter can reduce the emission of harmful substances. The oxygen sensor is located in the exhaust pipe in front of the catalytic converter and is washed by the exhaust gas flow. The oxygen sensor is an electrical sensor that displays the residual oxygen content in the exhaust gas through fluctuations in the electrical voltage and allows conclusions to be drawn about the composition of the air-fuel mixture. In a fraction of a second, the oxygen sensor can transmit a corresponding signal to the injection system control unit and thus constantly change the quality of the mixture. Firstly, this is necessary, since the operating conditions (idle, full load) are constantly changing, and secondly, optimal combustion in the catalytic converter only occurs when there is still a sufficient proportion of gasoline in the exhaust gases.

So, in order for combustion to occur at all in a catalytic converter at a temperature of +300 to +800°C, the fuel-air mixture must contain more fuel than would be necessary for complete combustion.

The regulated catalytic converter in question is a three-way converter. This means that in this catalytic converter, due to the regulation of the excess air coefficient, the oxidation of carbon monoxide (CO) and hydrocarbons (CH) and the reduction of nitrogen oxides (NOx) are carried out simultaneously.





The catalytic converter consists of a ceramic honeycomb housing, which is covered with a carrier layer. The carrier layer contains salts of noble metals, which affect the processes of chemical transformations. In the housing, the catalytic converter is fixed with an elastic insulating protective cushion, which also compensates for temperature expansion. The insulating protective cushion is an extremely heat-resistant weave of ceramic fibers.

Catalytic converter for diesel engines

A diesel engine can also have a catalytic converter. No control of the mixture composition is possible here. The catalytic converter for diesel engines is oxidizing and unregulated. The oxidizing catalytic converter reduces the emission of harmful carbon monoxide and hydrocarbons to a level that is significantly lower than that of gasoline engines with a regulated catalytic converter. In addition, it reduces the smoke typical of a diesel engine.

Exhaust gas recirculation system (EGR system) for diesel engines and DOHC engines

The EGR system maintains the proportion of nitrogen oxides at an insignificant level already before the catalytic converter. Depending on the engine load mode, the recirculation system directs a certain portion of the exhaust gas to the engine intake via an adjustable valve.



This allows to reduce the temperature of the combustion process and, as a result, the proportion of harmful nitrogen oxides in the exhaust gas.

[Information for this article was taken from the website: FordBook]