Catalyst operation
In a car, a catalyst is a ceramic particle coated with noble metals - platinum and rhodium, placed in a special container. The exhaust gases, passing through this container, flow around particles that have a very large total active surface. The total amount of noble metals contained in the catalyst is 2-3 grams. Thanks to the three-stage catalyst, it is possible to get rid of such harmful substances as CO, CH and CNx.
CO and CH, oxidized by oxygen, turn into harmless carbon dioxide CO₂.
To neutralize NOx, a chemical reaction is used to remove oxygen. This produces nitrogen (N2O) and CO2O. Both substances are harmless.
The catalyst only works under certain conditions. For this to happen, there must be a certain ratio of fuel to air. The biggest difficulty is to maintain this proportion constant as 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 900°C its efficiency drops sharply. At a temperature of 1200°C it can be destroyed.
Note: If a catalytic converter is present, unleaded petrol is required. When using leaded gasoline, after 2-3 refills the catalyst stops working.
Operating mode with a catalyst
When operating a vehicle with a catalytic converter, the remains of unburned mixture are especially dangerous, as they can ignite inside the hot catalytic converter, and the temperature can exceed the critical level. As a result, the catalyst may partially melt and cease to function.
That's why:
- Rolling, idling and towing the vehicle are all possible without problems if the starter is unable to start the engine due to a discharged battery.
- Push starting of the engine is not allowed, since it will cause 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 enters 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 multi-day drought, you should not park your car on dry grass. Under unfavorable conditions, a fire may occur under the vehicle.
- 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 that the heat shields are not damaged or missing.
What else is useful to know:
- High oil consumption is not harmful to the catalytic converter. Because oil consists essentially of the same elements as gasoline. Burnt oil is deactivated by the catalyst in the same way as burnt fuel.
- Additives added to fuel and motor oil do not harm the catalyst.
- Defects in the catalytic converter or lambda probe can only be detected by properly performing exhaust gas testing. A catalyst damaged by high temperature can be identified by a knocking sound, since the ceramic filler, when partially melted, crumbles and begins to roll around inside the metal container.