| 摘要 |
The invention relates to a procedure for purifying exhaust gas in the exhaust gas duct of a combustion engine with an exhaust gas purification system and a SCR-catalyzer that is arranged in the exhaust gas purification system for a selective catalytic reduction of nitrous gases (SCR), whereby reducing agents for the selective catalytic reduction of nitrous gases can be added to the exhaust gas in direction of the flow before the SCR-catalyzer. According to the invention it is provided that the exhaust gas is led through a catalyzer for converting nitrous gases with hydrocarbons and subsequently through the SCR-catalyzer and that the operating parameters are adjusted in a first operating phase in such a way, that nitrous gases are mostly converted at the catalyzer for converting nitrous gases with hydrocarbons and that the operating parameters are adjusted in a second operating phase in such a way, that nitrous gases are mostly converted at the SCR-catalyzer. The adjustments for the first operating phase are selected at the start of the combustion engine. The catalyzer is heated to its operating temperature in this operating phase for the conversion of nitrous gases with hydrocarbons. Because it is arranged before the SCR-catalyzer and a particle filter that is usually arranged in front of it, its heating takes place very fast and the output of nitrous gases in the starting phase of the combustion engine can be reduced as opposed to the state of the art. The normal operation of the combustion engine is characterized by a lean mixture composition and therefore by an oxygen-rich exhaust gas. This is adjusted in the second operating phase, in which nitrous gases are converted in the SCR-catalyzer that is now heated to its operating temperature.
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