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

ENGINE 156.980 in MODEL 164, 251 

ENGINE 156.982 in MODEL 209 

ENGINE 156.983 in MODEL 211, 219 

ENGINE 156.984 in MODEL 216, 221 

Location on model 164, 216, 221, 251 

Fig 1: Identifying Three-Way Catalytic Converter Components Location On Model 164, 216, 221, 251

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

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

Location on model 209, 211, 219 

Two separate catalytic converters each are used per exhaust chain.

Fig 2: Identifying Three-Way Catalytic Converter Components Location On Model 209, 211, 219

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Task 

Reducing the exhaust gas emissions:

• Nitrogen oxides (NO_X )
• Hydrocarbon (HC)
• Carbon monoxide (CO)

Body (schematic) 

Fig 3: Identifying Three-Way Catalytic Converter Body (Schematic) Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

There are two ceramic monoliths (ceramic body) in each firewall catalytic converter which are penetrated by 600 channels each. 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 increases the active surface of the catalytic converter by an approximate factor of 7000.

The active catalytic layer coated on the substrate is available in three-way catalysts primarily out of platinum and rhodium. Platinum accelerates oxidation of hydrocarbons (HC) and carbon monoxide (CO), whereas rhodium accelerates the reduction of nitrogen oxide (NO_x ).

The O₂ sensors on the left or right downstream of TWC (G3/5, G3/6) are located on the side on the firewall catalytic converters and jut into the space between both monoliths.

Function (schematic) 

Fig 4: Identifying Three-Way Catalytic Converter Function (Schematic) Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Exhaust gases flow through the three way catalytic converter and hence come into contact with the rare metals, platinum and rhodium.

• Through oxidation, carbon monoxide (CO) is converted into carbon dioxide (CO₂ ) and hydrocarbons (HC) into water (H₂ O) + carbon dioxide (CO₂ ).
• Through reduction, nitrogen oxides (NO_x ) are converted into nitrogen (N₂ ) + carbon dioxide (CO₂ ).

The remaining oxygen content in the exhaust is a crucial factor in the conversion of pollutants. The best pollutant conversion is obtained at λ=1.

Operating conditions 

As is the case for the O₂ sensor, the operating temperature also plays a very important role in the case of the catalytic converter. Appreciable conversion of the pollutants does not commence until an operating temperature of approx. 250°C.

Ideal operating conditions for high conversion rates and a long life prevail at temperatures between around 450 to 800°C.

The temperature of the three way catalytic converter can increase beyond 1400°C due to malfunctioning of the engine such as misfiring etc. These high temperatures can lead to destruction of the catalytic converter, by melting the ceramic monoliths.

Another requirement for reliable long-term operation is that only unleaded fuel be used. Lead compounds form a deposit on the 6 of 43 active surface and as a result prevent the exhaust gases from coming into contact with the catalytic layer.

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