Patent attributes
Exhaust gas post treatment system for nitrogen oxide reduction of internal combustion engines operated with excess air. A partial exhaust gas stream is branched off upstream of an SCR catalytic converter for reducing nitrogen oxides. A metering device delivers to the partial exhaust gas stream reduction agent, which is ammonia or a material that releases ammonia downstream of the supply location as a result of the hot exhaust gas. The partial exhaust gas stream is returned to the exhaust gas stream downstream of the supply location and upstream of the SCR catalytic converter, which reduces the 1J nitrogen oxides in the exhaust gas stream with the aid of the ammonia or released ammonia, by selective catalytic reduction, to nitrogen and water vapor. At engine operating conditions at which reversal of the exhaust gas stream toward the engine occurs, an oxidation catalytic converter, disposed in the partial exhaust gas stream upstream of the supply location for the reduction agent, oxidizes ammonia and/or reduction agent decomposition products that flow back.
