Component description for the three-way catalytic converter - GF49.10-P-2010CY

ENGINE 272.911 in MODEL 204.0 up to Model Year 8

ENGINE 272.921 in MODEL 204.0 /2 up to Model Year 8

ENGINE 272.947 in MODEL 204.0 /2 up to Model Year 8

ENGINE 272.948 in MODEL 204.0 up to Model Year 8

ENGINE 272.961 in MODEL 204.0 /2 up to Model Year 8

ENGINE 272.971 in MODEL 204.0 up to Model Year 8

Location

Two types of catalytic converter inserts are used respectively in near-engine mounted firewall catalytic converters.

Fig 1: Identifying Firewall Catalytic Convertor And Catalytic Convertor Insert

Courtesy of MERCEDES-BENZ USA

Task

Reducing the exhaust gas emissions:

nitrogen oxides (NO_X )
Hydrocarbon (HC)
Carbon monoxide (CO)

Body (schematic)

Fig 2: Identifying Three-Way Catalytic Converter Body Schematic

Courtesy of MERCEDES-BENZ USA

Ceramic monoliths are ceramic bodies through which pass several thousand small passages. The exhaust gas flows through these passages. The ceramic consists of high temperature-resistant magnesium aluminum silicate.

The monolith, which is extremely sensitive to voltages, is embedded in an elastic wire mesh made of high-alloy steel wires and fitted in a double-walled stainless steel housing.

Ceramic monoliths require a substrate (washcoat) of aluminum oxide (Al₂ O₃ ) that expands the active surface of the catalytic converter by an approximate factor of 7000.

The effective catalytic layer of rare metal on the intermediate layer for three-way catalytic converters is made out of platinum, rhodium and palladium.

Platinum and palladium accelerate oxidation of hydrocarbons (HC) and carbon monoxide (CO). Rhodium helps reduction of nitrous oxide (NO_X ).

The high-quality catalytic converter coating allows lowering of fuel grade from 98 to 95 ROM (from premium to normal gasoline).

Function (schematic)

Fig 3: Identifying Three-Way Catalytic Converter Function Schematic

Courtesy of MERCEDES-BENZ USA

The exhaust gases flow through the catalytic converter and, in so doing, come into contact with the rare metals platinum, rhodium and palladium.

Through oxidation, carbon monoxide (CO) is converted into carbon dioxide (CO₂ ) and hydrocarbons (HC) into water (H ₂ O)+ carbon dioxide (CO₂ ).
Through reduction, nitrogen oxides (NO_X ) are converted into nitrogen (N₂ ) + carbon dioxide (CO₂ ).

Decisive for conversion of pollutants is the residual oxygen content in the exhaust gas. The best pollutant conversion is obtained at λLD =1.

Operating conditions

For a catalytic converter the operating temperature is crucial. Significant conversion of pollutants only takes place above an operating temperature of about 250°C.

Ideal operating conditions for high conversion rates and a long life prevail at temperatures between around 400 to 800°C.

A temperature >850°C, as can occur when there are combustion misfires, leads to thermal destruction of the catalytic converter (melting of the monoliths).

Owing to its property of being able to reduce three polluting components simultaneously, it is called a "three-way catalytic converter".