After treatment system

The utility model discloses an after treatment system, this after treatment system can be including the one or more perforated pipe and at the one or more flange in perforated pipe low reaches. The shell can limit the one or more room with the one or more flange together to thereby the detention time of the mixture of extension exhaust and reductant increases the evaporation, improves the evenness index of ammonia - nitrogen oxide proportion and/or the profile exponent that flows. In some embodiment, first flange can be including passing the one or more opening that first flange formed, and the second flange in first flange low reaches can have a plurality of perforation. The perforation of exhaust and reductant accessible perforated pipe flows in first room, through one or more opening stream to the second room of passing first flange, flows to the third room at the catalysis face upper reaches through a plurality of perforation of second flange.