The invention relates to a fuel injection system provided with a Common Rail (2) pressure accumulator filled at high pressure and with a multifuel nozzle (3) for bifluid injection of fuel and an adjunctive liquid into an internal combustion engine. The inventive injection system comprises a first 2/2-way valve (MV1) in the injection pipe (6) between the Common Rail pressure accumulator (2) and a pressure chamber (3.5) surrounding the injector pin of the multifuel nozzle, as well as a second 2/2-way valve (MV2), the inlet of which is connected via a supply pipe (7) to the injection line (6) at a point located between the first 2/2-way valve (MV1) and the pressure chamber (3.5), and the outlet of which is connected via a discharge line (8) to the low pressure side of fuel. It is thus possible to replace the usual valves, technicaly much more expensive, i.e. the magnetically operated 3/2-way valves, by 2/2-way valves, which are more economical. The invention also enables the adjunctive liquid dosage to be transferred to a regulating valve which operates a whole series of injectors.