Dynamic Rise of Pressure in the Common-Rail Fuel Injection System

The dynamic behavior of the injection pressure in a common-rail system for Diesel engines is considered. A CFD code has been developed for simulating the unsteady flow in the pipes connecting the rail with the injection holes and with the control volume. Computed numerical results have shown a good agreement with available experimental data, referring to a single injection of a single injector, thus proving the reliability of the code. The experimental data have also shown that the injection pressure is significantly lower than the rail pressure in most of the injection phase. Numerical investigations have shown that such a pressure decrease is mainly due to dynamic effects, namely to the sudden acceleration of the fuel, rather than to friction losses. As a consequence, the pressure gap will never be recovered by minimizing the friction losses. Further numerical investigations have also shown that these dynamic phenomena can be used to increase the injection pressure by hundreds of bar, without increasing the rail pressure.