| 摘要 |
The invention relates to a method for, by means of a reducing agent, purifying exhaust gas in an exhaust gas flow from an engine (230) in an SCR system comprising two SCR catalyst configurations (260, 265) arranged in series in said exhaust gas flow, comprising the steps of: - continuously determining a content of ammonia in said exhaust gas downstream of a first SCR catalyst configuration (260); - continuously determining a content of NOx in said exhaust gas downstream of a second SCR catalyst configuration (265), which is arranged downstream of said first SCR catalyst configuration; - performing said purifying partly in a first state (State 1) comprising evident overdosing of said reducing agent in said first SCR catalyst configuration (260) and partly in a second state (State 2) comprising evident underdosing of said reducing agent in said first SCR catalyst configuration (260); and - shifting between said first state (State 1) and said second state (State 2) on the basis of said determined content of ammonia and said content of NOx in said exhaust gas. The invention relates also to a computer programme product comprising programme code (P) for a computer (200; 210) for implementing a method according to the invention. The invention relates also to an SCR system and a motor vehicle which is equipped with the SCR system. |
