Sustainable mobility has become a major issue for internal combustion engines and has led to increasing research efforts in the field of alternative fuels, such as bio-fuel, CNG and hydrogen addition, as well as into engine design and control optimization. To that end, a thorough control of the air-to-fuel ratio appears to be mandatory in SI engine in order to meet the even more stringent thresholds set by the current regulations. The accuracy of the air/fuel mixture highly depends on the injection system dynamic behavior and to its coupling to the engine fluid-dynamic. Thus, a sound investigation into the mixing process can only be achieved provided that a proper analysis of the injection rail and of the injectors is carried out.The present paper carries out a numerical investigation into the fluid dynamic behavior of a commercial CNG injection system by means of a 0D-1D code. The model has been validated by comparing the experimental readings to the numerical outputs in terms of injection system pressure profiles versus time. The model has hence been applied to the prediction of the pressure waves produced by the injection event and of their effect on the actually injected fuel.Experimental results have shown the effectiveness of the predictive model. A general good match between the predicted values and the measured rail pressure and injected fuel mass flow rates has been observed over a wide range of engine operation conditions. Moreover, the dynamic simulations have brought out a reduced independence of the injected fuel mass on the average rail pressure level, which further reduced for increasing engine power outputs. Moreover, the results have proved that the correct simulation of the system behavior relies on the consistent characterization of the pressure regulator functioning. It is worth observing that the full fluid dynamic characterization of the rail allows for the design of optimal control strategies so as to meet the engine requirements.