A mixing system includes a pipe having a longitudinal axis, in which exhaust gases can flow in a flow direction, a nozzle designed to inject a fluid inside the pipe from an injection inlet arranged in the pipe wall, according to an injection direction, a first mixing device positioned inside the pipe upstream from the injection inlet, the first mixing device including a peripheral portion including blades capable of creating a peripheral swirl along the pipe wall, and a central portion designed to create substantially no turbulence, and a second mixing device positioned inside the pipe downstream from the injection inlet, the second mixing device including a central portion including blades capable of creating a swirl inside the pipe.