Exhaust System
HINT: The illustration displays the exhaust system for the XC90.
The exhaust system is made of double-layer sheeting to keep the temperature down. The inner sheet is 1.0 mm thick while the outer is 1.5 mm thick. There is 4-8 mm of space between the sheets.
An exhaust system extends from each cylinder bank. Each side consists of a manifold with close-coupled catalytic converter, pipes, bellows and a rear catalytic converter. Both sides join to form a common pipe after the rear catalytic converter.
The pipes are designed in such a way that the gas flow from the cylinders is not disruptive and there is good flow distribution to the catalytic converters. Bellows in front of the two rear catalytic converters absorb engine movements and compensate for manufacturing and assembly tolerances.
A catalytic converter consists of perforated stones of ceramic or metal (known as substrate). These are coated with a surface enlarger (washcoat) on which the precious metals platinum, palladium and rhodium, the catalysts, are applied.
The catalytic converter has an extra heat shield toward the radiator fan to reduce the temperature.
Four oxygen sensors are used to regulate the engine and monitor the catalytic converter. There is an oxygen sensor upstream and downstream of each close-coupled catalytic converter.
The two banks are almost exactly the same length to ensure good sound. The exhaust system provides the engine's characteristic V8 sound.