A fuel electro-injector for a fuel injection system for an internal combustion engine, the electro-injector comprising: - an atomizer comprising: a) a nozzle defining a sealing seat; b) a valve needle extending in said nozzle along a longitudinal axis and axially sliding from a closed position, in which it is coupled to said sealing seat, for performing an opening stroke in an outward direction and opening said nozzle; said sealing seat and said valve needle defining a discharge section, which is annular and has a width that continuously increases as the opening stroke of said valve needle proceeds; - an electric actuator suitable for being excited by an electric command signal to cause the opening stroke of said valve needle and defining an axial displacement that is proportional to the magnitude of said electric command signal; - an inlet suitable for being connected to a high-pressure fuel supply; - a high-pressure environment (16,18) for supplying fuel from said inlet to said discharge section; - an outlet suitable for being connected to a low-pressure return system, and - a low-pressure environment directly communicating with said outlet; - a hydraulic connection arranged between said electric actuator and said valve needle and comprising a pressure chamber, which is axially delimited, on one side, by said valve needle and, in use, is filled with fuel that, once compressed, exerts an axial thrust on said valve needle to cause said opening stroke; said high-pressure environment comprising an annular passageway defined between a lateral outer surface of said valve needle and an inner surface of said nozzle and axially ending at said sealing seat; characterized in that: - said low-pressure environment comprises a portion that is arranged axially between said hydraulic connection and said annular passageway and is separated from said high-pressure environment (16,18) by means of a dynamic seal, defined by a coupling zone between said valve needle and a fixed guide portion; - said hydraulic connection is arranged in said low-pressure environment, such that said pressure chamber communicates only with said low-pressure environment. - an atomizer comprising: a) a nozzle defining a sealing seat; b) a valve needle extending in said nozzle along a longitudinal axis and axially sliding from a closed position, in which it is coupled to said sealing seat, for performing an opening stroke in an outward direction and opening said nozzle; said sealing seat and said valve needle defining a discharge section, which is annular and has a width that continuously increases as the opening stroke of said valve needle proceeds; a) a nozzle defining a sealing seat; b) a valve needle extending in said nozzle along a longitudinal axis and axially sliding from a closed position, in which it is coupled to said sealing seat, for performing an opening stroke in an outward direction and opening said nozzle; said sealing seat and said valve needle defining a discharge section, which is annular and has a width that continuously increases as the opening stroke of said valve needle proceeds; - an electric actuator suitable for being excited by an electric command signal to cause the opening stroke of said valve needle and defining an axial displacement that is proportional to the magnitude of said electric command signal; - an inlet suitable for being connected to a high-pressure fuel supply; - a high-pressure environment (16,18) for supplying fuel from said inlet to said discharge section; - an outlet suitable for being connected to a low-pressure return system, and - a low-pressure environment directly communicating with said outlet; - a hydraulic connection arranged between said electric actuator and said valve needle and comprising a pressure chamber, which is axially delimited, on one side, by said valve needle and, in use, is filled with fuel that, once compressed, exerts an axial thrust on said valve needle to cause said opening stroke; said high-pressure environment comprising an annular passageway defined between a lateral outer surface of said valve needle and an inner surface of said nozzle and axially ending at said sealing seat; - said low-pressure environment comprises a portion that is arranged axially between said hydraulic connection and said annular passageway and is separated from said high-pressure environment (16,18) by means of a dynamic seal, defined by a coupling zone between said valve needle and a fixed guide portion; - said hydraulic connection is arranged in said low-pressure environment, such that said pressure chamber communicates only with said low-pressure environment.