Abstract: A mixing device for mixing a gas and a liquid in an exhaust system has an injector for injecting the liquid, a shell, an inlet, an outlet and an exhaust gas flow path between the inlet and the outlet. The mixing device defines an axis, and the flow path has a first part, a second part and a third part. The first part extends generally parallel to the axis to direct a flow in a generally forward direction, the first part extending up to a first axial position. The second part extends generally parallel to the axis to direct flow in a generally reverse direction. The third part extends generally parallel to the axis to direct a flow in the generally forward direction. The third part is a volume that allows mixing and extends past the first axial position.