Assignment

The exhaust gas treatment is supposed to regulate the air-fuel mixture in the Otto-cycle engine in such a way that the catalyst is able to convert a maximum of pollutants into harmless exhaust gases. Harmless exhaust gases are CO₂ (carbon dioxide) and H₂O (water), where water leaves the exhaust system as 'white smoke' with less than 70°C.

Function

While the engine is running, the lambda probe delivers signals to the control unit regarding the air-fuel mixture.For most ranges it uses the data to regulate the ideal mixture of 14.8 kg air with 1 kg fuel (lambda = 1).In this case the ratio of pollutants (CO,CH and NO_X) is such that with simultaneous oxidation and reduction they can be offset against each other. NO_X carries too much oxygen, which is compensated by the need for oxygen of CO and CH. Just in the ranges of cold starting, accelerating, and (for most cars) full load, relatively more fuel is used for the mixture.