Catalytic Converters
The Catalytic Converter is an exhaust emission control device. Its function involves the reduction of carbon monoxide (CO), oxides of nitrogen (NOx) and hydrocarbons (HC). The converter, mounted in the exhaust stream works as a gas reactor by speeding up the chemical reaction between the exhaust gas components with the goal of reducing the amount of pollutants in the engine exhaust.
The combustion reaction, aided by the catalyst, causes a temperature increase in the area of the reactor. Heat shields and carefully located components are essential for safe operation. DO NOT remove shields or reroute exhaust system.
On some models, a Three Way Catalyst (TWC) is used in conjunction with a Conventional Oxidation Catalyst (COC) contained in the same canister. Working with this, there often is an air injection pipe that injects air between these 2 beds to help further oxidize the exhaust gases. This is a dual bed converter. See Fig 1 .
On some models, the first converter in the exhaust system is a Light Off Converter (LOC). This is a single bed type converter designed to control exhaust emissions during engine warm-up when the main converter is not at temperature required for maximum efficiency.
On all other dual bed converter models, the first converter (3-way) in the exhaust system reduces hydrocarbons (HC) and carbon monoxide (CO), but mainly deals with oxides of nitrogen (NOx). The second converter (oxidation type), with help of the air pump, reduces hydrocarbons (HC) and carbon monoxide (CO).