CO and CH, oxidized by oxygen, turns into harmless carbon dioxide CO.
To neutralize NOx, a chemical reaction is used, with the help of which oxygen is taken away. This produces nitrogen (N 2) and CO2. Both substances are harmless.
The catalyst only works under certain conditions. To do this, there must be a certain ratio of fuel and air. The greatest difficulty lies in maintaining this proportion 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 urban traffic 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 decreases sharply. At a temperature of 1200°C, it may collapse. If a catalytic converter is present, unleaded gasoline is required. When using leaded gasoline, after 2-3 refuellings, the catalyst ceases to function.
Operating mode with catalytic converter
The manual supplied with the vehicle contains numerous instructions for operating a vehicle with a catalytic converter. Especially dangerous are the remains of the unburned mixture, which can ignite inside the hot catalyst and the temperature can exceed the critical one. As a result, the catalyst may partially melt and cease to function.
That's why:
Rolling, driving with forced idling and towing the car is carried out without problems if the starter cannot start the engine due to a discharged battery.
Long distance towing (e.g. in the event of a faulty ignition) is unacceptable, since this will introduce a large amount of unburned fuel into the exhaust system, which can damage the still hot catalyst.
If there are misfires, which may indicate a malfunction, urgent measures must be taken. When driving further, high speeds should be avoided.
Small amounts of unburnt mixture are not dangerous, especially if it gets into a cold catalyst.
Catalyst overheating cannot occur during prolonged driving with "full throttle", because in this mode the catalyst is cooled.
Besides:
In the heat of summer, after many days of drought, you should not put the car on top of dry grass. Under unfavorable conditions, a fire may occur under the vehicle.
When installing protection under the bottom, it must not be allowed to touch the catalyst or heat shields.
From time to time, by propping up the car, check if the heat shields are damaged or lost.
Other useful things to know:
High oil consumption is harmless to the catalyst. Because oil is made up of mostly the same elements as gasoline, burnt oil is deactivated by the catalyst in the same way that burnt fuel is.
Additives added to fuel and engine oil do not harm the catalyst. With complete safety, you can use fuel recommended for use by Audi or Volkswagen.
Defects in the catalytic converter or lambda probe are only detected with properly performed exhaust gas testing. A catalyst damaged by high temperature can be identified by knocking, since the ceramic filler, when partially melted, shrinks in volume and begins to roll inside the metal container.
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