Exhaust system for FSI engines (Audi A4 B6)

In order to achieve and even exceed the stringent Euro 4 exhaust emission standard in the case of an efficient and clean direct petrol injection engine, the vehicle concept must include an expensive exhaust gas aftertreatment system. This is due to the fact that during stratified mixture formation (see Chapters "Engine management and petrol injection system") a large amount of nitrogen oxides is produced, which must be converted into harmless nitrogen on the way to the exhaust pipe.

Therefore, in the 2.0 l FSI engine, in addition to a small three-way catalytic converter, which is located directly behind the engine and therefore begins to work immediately after a cold start, there is an additional NO storage converter, and (for the first time in the world) nOx sensor. In the stratified mixture formation mode, nitrogen oxides are retained in the accumulating neutralizer by barium molecules. The sensor determines the moment when the capacity of the neutralizer is exhausted and it threatens to "overflow". This happens approximately every 60 seconds. After that, the sensor produces a pulse that goes to the central control unit of the engine. The control unit switches the engine to regeneration mode for approximately two seconds, forming a richer mixture and a higher exhaust gas temperature.