A system for injecting an air/fuel mixture into a turbomachine combustion chamber, including a hollow tubular structure for the flow of the air/fuel mixture into the combustion chamber; a fuel injection device placed at an upstream end of the hollow tubular structure, and an air injection device placed downstream of the fuel injection device. The system also includes a cold plasma generator placed downstream of the air injection device so as to generate active species in the flow of the air/fuel mixture and to cause prefragmentation of the molecules of the air/fuel mixture. The system further includes a device for controlling the cold plasma generator depending on the speed of operation of the turbomachine.