A fuel injector for fuel injection systems in internal combustion engines, including an actuator, a valve needle operable by the actuator for operating a valve-closure member, which, together with a valve-seat surface forms a sealing seat and a swirl device including at least one swirl channel, through which fuel flows with a tangential component relative to a longitudinal axis of the fuel injector. The axial position of a plunger element determines a cross-section of at least one bypass channel that bypasses the at least one swirl channel without a tangential component.