The device comprises a control system (100) commanded by sensing means consisting of at least one optic fibre transmitting a radiation to at least one radiation detector, said sensing means co-operating with a rotating element driven by the engine, which consecutively intercepts the receipt of the radiation. The control system (100) determines the beginning and duration of injection at the injectors (11) incorporated in the fuel-transfer circuit (10), which circuit comprises two pipes, namely a fuel inlet pipe (19) and a fuel outlet pipe (20) which are interconnected and in heat exchange relation and are located at the back of each injector in order to obtain a closed transfer circuit and to ensure continuous circulation of fuel at the back of each injector, thus avoiding in-line vaporization of said fuel.