An exhaust treatment system for an internal combustion engine having improved mixing of an injected fluid comprises an exhaust gas conduit configured to receive exhaust gas from an internal combustion engine and to deliver the exhaust gas to the exhaust treatment system. A fluid injector in fluid communication with the exhaust gas conduit configured delivers a fluid into the exhaust gas and an evaporation volume disposed in the exhaust conduit downstream of the fluid injector is configured to slow the bulk velocity of the fluid and exhaust gas mixture to thereby increase the residence time of the exhaust gas mixture therein. An exhaust treatment device is configured to receive the fluid and exhaust gas mixture.