A mixing plenum for exhaust gas comprises a canister with an inlet and an outlet. A bulkhead is located downstream from the inlet to define an exhaust gas consolidation chamber. An opening in the bulkhead allows exhaust gas to enter a u-shape conduit configured to direct the exhaust gas from a downstream direction to an upstream direction before releasing the exhaust gas back into the plenum downstream of the bulkhead. An injector is configured to inject fluid into the exhaust gas entering the conduit. A conduit exit located a distance “E” from the downstream side of the bulkhead allows the exhaust gas/fluid mixture to exit the conduit into a larger exit volume of the compact mixing can, in the manner of an expansion chamber, where its velocity slows and further mixing of the fluid/exhaust gas occurs and exits the compact mixing can through the outlet flange.