Aftertreatment system for an internal combustion engine

A mixing space for exhaust gas includes a canister having an inlet and an outlet. A partition disposed downstream from the inlet to define an exhaust chamber consolidation. An opening in the partition wall permits entry of the exhaust gas in a U-shaped line which is configured to direct the exhaust gas from a downstream direction to an upstream direction before the exhaust gas downstream back into the room is released the partition wall. An injection device is configured in the exhaust gas that enters conduit to inject fluid. A cable outlet which is placed at a distance "E" from the downstream side of the partition, allows leaving the gas / fluid mixture from the pipe into a larger discharge volume of the compact mixing box in the manner of an expansion chamber, its velocity slows and takes place, a further mixing of the fluid / waste gas, and leaves the compact mixing box through the outlet flange.