Catalyst operation
In a car, ceramic particles coated with noble metals - platinum and rhodium, placed in a special container, are called catalysts. 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, being oxidized by oxygen, turn into harmless carbon dioxide CO2.
To neutralize NOx, a chemical reaction is used to remove oxygen. 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 city 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.
Attention: Unleaded gasoline is required if a catalytic converter is present. When using leaded gasoline, after 2-3 refuellings, the catalyst ceases to function.
Operating mode with catalytic converter
When operating a car with a catalyst, unburned mixture residues are especially dangerous, which can ignite inside the hot catalyst, and the temperature may 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 are carried out without problems if the starter cannot start the engine due to a discharged battery.
- Starting the engine with «pusher» is unacceptable, as 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 unburned mixture are not dangerous, especially if they enter 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, with the vehicle jacked up, check for damage or loss of heat shields.
Other useful things to know:
- High oil consumption is harmless to the catalyst. Because oil is basically made up 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 engine oil do not harm the catalyst.
- 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, crumbles and begins to roll inside the metal container.