CO and CH, when oxidized by oxygen, turn into harmless carbon dioxide CO.
To neutralize NOx, a chemical reaction is used to remove oxygen. This produces nitrogen (N₂) and CO₂. Both substances are harmless.
The catalyst only works under certain conditions. For this, there must be a certain ratio of fuel and air. The greatest difficulty is to maintain this ratio constant when operating conditions change. This is the task of lambda regulation.
The catalyst can only work when the temperature reaches 300* C. This is usually achieved in 25-28 seconds, but in city traffic conditions it may take up to three minutes. On the other hand, the catalyst is very sensitive to overheating. At a temperature of 900°C, its efficiency drops sharply. At a temperature of 1200°C, it can be destroyed. If there is a catalyst, unleaded gasoline is required. When using leaded gasoline, the catalyst stops working after 2-3 refuelings.
Operating mode with a catalyst
The manual that came with the car contains numerous instructions on how to operate a car with a catalytic converter. Particularly dangerous are the remains of unburned mixture, which can ignite inside the hot catalytic converter and the temperature can exceed the critical value. As a result, the catalytic converter can partially melt and stop functioning.
That's why:
Rolling, driving with forced idling and towing the vehicle is carried out without problems if the starter is unable to start the engine due to a discharged battery.
Long distance towing (for example, if the ignition is faulty) is unacceptable, since this will allow a large amount of unburned fuel to enter the exhaust system, which can damage the still hot catalytic converter.
If there are interruptions in the ignition, which may indicate its malfunction, it is necessary to take urgent measures. When driving further, high revs should be avoided.
Small amounts of unburned mixture do not pose a danger, especially if it gets into a cold catalytic converter.
Overheating of the catalytic converter cannot occur during prolonged driving at full throttle, since in this mode the catalytic converter cools down.
Besides:
In the summer heat after a long drought, do not park your car on dry grass. Under unfavorable conditions, a fire may occur under the car.
When installing underbody protection, do not allow it to touch the catalytic converter or heat shields.
From time to time, support the car and check whether the heat shields are damaged or missing.
What else is useful to know:
High oil consumption is harmless to the catalytic converter. Since oil consists essentially of the same elements as gasoline, burnt oil is deactivated by the catalytic converter in the same way as burnt fuel.
Additives added to fuel and motor oil do not harm the catalyst. It is completely safe to use fuel recommended for use by Audi or Volkswagen.
Defects in the catalytic converter or lambda probe are detected only by properly performing exhaust gas testing. A catalytic converter damaged by high temperatures can be identified by a knocking sound, since the ceramic filler, when partially melted, settles in volume and begins to roll around inside the metal container.