Catalytic Converter: Description and Operation

PURPOSE
Three-way Catalytic Converter reduces the emission of Carbon Monoxide (CO), Hydrocarbons (HC) and Oxides of Nitrogen (NOx), by up to 90%.

OPERATION
Oxidation Reaction
^ As exhaust gasses pass through converter, the platinum in the converter triggers an oxidation (burning) reaction.

^ During this process the HC and CO combine with oxygen, forming water vapor (H2O) and Carbon Dioxide (CO2).

^ This process has no effect on NOx emissions.

Reduction Reaction
^ The Rhodium in the converter converts the NOx into nitrogen and oxygen, in a "reduction" (removal of oxygen), reaction.

Converter Efficiency VS. Stoichiometric Fuel/Air Ratio:

Optimum performance of the catalytic converter is obtained, with a fuel-air mixture ratio of 14.7 to 1 ± 1%, and exhaust gas temperatures between 400 to 800 degrees C (750 to 1500 degrees F).

CAUTION: Engine malfunctions such as misfiring can result in exhaust temperatures exceeding 1400 degrees C (2500 degrees F). These extreme high temperatures can cause the substrate to melt, destroying the converter.

CAUTION: The use of leaded fuels will coat the catalyst preventing catalytic action. Excessive oil residues in the exhaust have the same effect.

CONSTRUCTION

Fig. 38 Underfloor Catalytic Converter:

The converter has a monolythic type, ceramic honeycomb. Platinum and rhodium catalysts cover the surface.