M62 TU Exhaust System
The M62 TU is equipped with two additional catalytic converters known as "warm-up converters". This configuration positions the forward mounted warm-up catalytic converters closer to the hot exhaust gasses immediately exiting the combustion chambers. The closer location heats the catalytic converters to the point of light-off faster than previous systems. Earlier light-off reduces cold start emissions by allowing the gas conversion (HC to H2O, CO to CO2 and NOx by reduction to N2 and O2) to occur more rapidly just after cold start.
The system also contains two main catalytic converters. The main exhaust gas conversion process occurs further downstream in the main catalytic converters.
OVERVIEW OF COMPONENTS:
The forward mounted warm-up catalytic converters are made of thin-wall ceramics. They are mounted in a pliable material called silicatex which isolates them from vibrations ensuring a long service life.
For their relatively small size, the catalyst volume of 878 cm3 provides a large conversion surface area. Use of the thin-wall ceramic design also minimizes exhaust back pressure.
Both pre-catalytic converter oxygen sensors are positioned forward of each warm-up catalyst.
The Bosch LSH 25 oxygen sensors are carried over from the M62 engine and provide the familiar "swinging" voltage signal (0.2 - max lean to 0.8 - max rich) representing oxygen content in the exhaust gas.
The main catalytic converters are also made of thin-wall ceramics. The post catalytic converter oxygen sensors are positioned just behind the main catalytic converters to monitor the catalytic converter function.
The pipes of the exhaust system up to the rear main catalytic converters are made from dual wall stainless steel. This design insulates exhaust noise as well as insulating the thermal energy in the hot exhaust gasses to light-off the converters as quickly as possible.