GF49.10-P-2010AMG Component Description For the Three-Way Catalytic Converter
GF49.10-P-2010AMG Component Description For The Three-way Catalytic Converter
ENGINE 156.980 in MODEL 164, 251 up to Model Year 8
ENGINE 156.982 in MODEL 209
ENGINE 156.983 in MODEL 211, 219
ENGINE 156.984 in MODEL 216, 221 up to Model Year 8
Location on model 164, 216, 221, 251
157 Firewall catalytic converter
157/1 Catalytic converter insert
Two types of catalytic converter inserts are used respectively in near-engine mounted firewall catalytic converters.
Location on model 209, 211, 219
157 Firewall catalytic converter
158 Underfloor catalytic converter
Two separate catalytic converters each are used per exhaust chain.
Task
Reducing the exhaust gas emissions:
^ Nitrogen oxides (NOX)
^ Hydrocarbon (HC)
^ Carbon monoxide (CO)
Body (schematic)
1 Ceramic monolith
2 Wire mesh (embedded)
3 Double-walled housing (insulation)
4 Substrate (washcoat) with a coating of platinum and rhodium
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 (Al2O3) 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 (NOx).
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)
A Unpurified exhaust
B Purified exhaust
F Rich mixture
M Lean mixture
Lambda (air/fuel ratio)
CO Carbon monoxide
CO2 Carbon dioxide
HC Hydrocarbon
H2O Water
N 2 nitrogen
NOX Nitrogen oxides
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 (H2O)+ carbon dioxide (CO2).
^ Through reduction, nitrogen oxides (NOx)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 lambda equals 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 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.