Catalytic Converter: Description and Operation

CATALYTIC CONVERTER

Exhaust gases pass through and heat the catalytic converter core which contains a mixture of platinum and rhodium. The combination of materials in the core and extreme temperature promotes chemical reactions that reduce the HC, CO and reduces NOx to harmless Carbon Dioxide (CO2) Nitrogen (N2) and water (H2O).

Precise control of the air/fuel ratio is critical for effective catalyst operation. The chart below shows that once the mixture moves away from stoichiometric, catalyst efficiency suffers.

The two greatest enemies of catalyst life are leaded fuels and overheating. The use of leaded fuels will cause deposits to form in the converter core and reduce its ability to produce the desired chemical reactions.

Excessive core temperatures are produced during misfire situations when raw gas in the exhaust ignites in the catalyst core. This can cause the core to fuse into a solid mass that exhaust gasses cannot pass through. Because of this, the desired chemical reactions cannot take place. Poor engine performance due to high back pressure is often a result of this situation.