In order to achieve and even exceed the requirements of the stringent Euro 4 exhaust emission standard with an efficient and clean engine with petrol direct injection, the vehicle concept must include an expensive exhaust gas aftertreatment system. This is due to the fact that during layer-by-layer mixing (see chapters «Engine management and petrol injection system») a large amount of nitrogen oxides are produced, which must be converted into harmless nitrogen on their way to the exhaust pipe.
Therefore, in the 2.0l FSI engine, in addition to a small three-way catalytic converter, which is located directly behind the engine and therefore starts immediately after a cold start, there is an additional NO storage converter, and (for the first time in the world) NOx sensor. In the mode of layered mixing, nitrogen oxides are retained in the accumulative neutralizer by barium molecules. The sensor determines the moment when the capacity of the neutralizer is exhausted, and it threatens «overflow». This happens approximately every 60 seconds. After that, the sensor generates a pulse that enters the central control unit of the engine. The control unit switches the engine to regeneration mode for approximately two seconds with a richer mixture and a higher exhaust gas temperature.
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