| 摘要 |
A method and system for controlling the injection of reducing agent upstream of an SCR catalyst (4). The injection is controlled according to an accumulation actual value and an accumulation set-point value which are calculated on the basis of information from a computation model. The computation model divides the catalyst in its longitudinal direction into a tank series with a plurality of tanks one after another, and said actual value and set-point value refer respectively to current and required accumulations of ammonia in a tank (4ref), herein called reference tank, situated upstream of the last tank (4K). A given slip value representing maximum permissible ammonia concentration in the exhaust gases leaving the catalyst serves as basis for calculating for each tank, using information from said computation model, a reference value representing the equilibrium accumulation of ammonia which has to be present in the tank in order to achieve the slip value. Such a reference value is calculated sequentially for each tank, starting with the last tank and proceeding thereafter tank by tank upstream right up to the reference tank. The reference value determined for the reference tank is used as said set-point value or as a maximum permissible upper limit for it. |
