The catalytic converter looks like a muffler. It contains a ceramic structure consisting of a huge number of small cells. The surface of these cells is treated with a thin layer of precious metals. Diesel engine: the catalytic converter affects both harmful substances (carbon monoxide and hydrocarbon compounds). The catalyst oxidizes up to 50% of these substances to harmless compounds such as carbon and water vapor. Of particular importance is the reduction of hydrocarbons, since (although the catalytic converter is not a soot filter) it helps reduce the soot content in the exhaust. The reason for this is that the gaseous hydrocarbon settles on the solid soot particles and thus increases the amount of emitted soot. If the hydrocarbon is oxidized in the catalyst, it can no longer combine with the soot.
Gasoline engines: The most effective method to date for neutralizing exhaust gases in cars with a gasoline engine is a triple-action catalytic converter.
The adjustment occurs in the range from l = 0.8 to l = 1.2 in a rapidly changing order: increasing the air supply for combustion of hydrocarbons, decreasing the air supply to reduce the emission of nitrogen oxides. The gaseous waste formed from this mixture enters the catalyst, where they are almost completely (with a new catalyst, approximately up to 90%) converted into harmless compounds such as carbon dioxide, water vapor and nitrogen. During engine warm-up, the device does not work, and then, when switched on, it maintains the average value of l. The same thing happens when the throttle valve is fully opened.
Operating temperatures
Before the catalyst starts working, it must reach a temperature of about 300°C. This temperature is reached in 25-270 seconds. The lambda probe reaches its operating temperature a little faster, as it is additionally heated by electricity.
The catalytic converter and the lambda probe are very sensitive to overheating. If the temperature of the catalytic converter exceeds 900°C, its wear increases significantly, starting from a temperature of 1200°C and above, the catalytic converter stops working. The same applies to the lambda probe. When the catalytic converter overheats, its ceramic structure is destroyed and it begins to dangle in its housing. This can be determined by the characteristic knocking in the exhaust system. In this case, the catalytic converter must be replaced.
Precautions for vehicles with a catalytic converter
The operating manual contains a lot of recommendations for cars with a catalytic converter. Particularly dangerous is the unburned working mixture, which oxidizes in the hot catalytic converter, which can lead to a critical increase in temperature when starting the engine.
Below we provide the most important recommendations:
- If there are interruptions in the ignition, check its serviceability.
- In summer, when the air temperature is high, when there is no rain for a long time, be careful, because when parking the car after a long trip, dry grass or leaves may catch fire from the hot catalytic converter housing.
- Check the condition of your vehicle's heat-insulating covers regularly.
(Material is located on the source website: RENAULTBOOK.ru)