Methods and apparatus for injecting reagent, such as an aqueous urea solution, into an exhaust stream in order to reduce emissions from an engine exhaust. The present teachings can use a whirl plate having a plurality of whirl slots surrounding an exit orifice of an injector, which produce a high velocity rotating flow in the whirl chamber. When the rotating flow of reagent is passed through the exit orifice into an exhaust stream, atomization occurs from a combination of centrifugal force and shearing of the reagent by air as it jets into the exhaust stream.