Abstract: An aftertreatment system comprises a housing defining an internal volume. The housing includes an inlet, an outlet and a first sidewall. A sleeve is positioned within the internal volume and protrudes through the first sidewall. An inner shell is positioned within an inner region defined by the sleeve and defines a recess therein. The inner shell spaced apart from the sleeve so as to define a channel therebetween. A base is positioned within the recess and includes an injection port which is in communication with the internal volume. An injector is disposed on the base and is disposed completely within the recess. The injector is in fluidic communication with the internal volume via the injection port. The injector is configured to inject an exhaust reductant into the internal volume via the opening. A cover plate can be disposed over the recess and structured to prevent objects from impacting the injector.