An injector for delivering a working fluid into a working environment is disclosed. According to one embodiment of the present invention, the injector includes a pre-metering chamber with a control valve controlling fluid delivery rate and a swirl chamber, in which a swirling flow is created and atomization is achieved at low injector pressure when it is released. In another embodiment, the injector includes a swirl chamber and an atomization element with a bore, through which a control valve is positioned. The control valve forces a working fluid flow through the atomization element when the injector is energized to create a metered swirling flow. To avoid issues with deteriorated working fluid, a purging apparatus is used for emptying working fluid residue in the injector, and a special control method is used when the injector works in a high-temperature working environment.