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Temperature variations due to compressibility effects of the liquid fuel were evaluated, for the first time in high-pressure injection system simulation, by employing the energy conservation equation, in addition to the mass-continuity and momentum-balance equations, as well as the constitutive state equation of the liquid. To that end, the physical properties (bulk elasticity modulus, thermal expansivity, kinematic viscosity) of the fluid were used as analytic functions of pressure and temperature obtained by interpolating carefully determined experimental data. Consistent with negligible thermal effects of heat transfer and viscous power losses involved in the flow process, the equation of energy was reduced to a state relation among the fluid thermodynamic properties, leading to a barotropic flow model.

A challenging task that is required to modern injection systems is represented by the enhanced control of the injected quantities, especially when small injections are considered, such as, pilot and main shots in the context of multiple injections. The propagation of the pressure waves triggered by the nozzle opening and closure events through the high-pressure hydraulic circuit can influence and alter the performance of the injection apparatus. For this reason, an investigation of the injection system fluid dynamics in the frequency domain has been proposed. A complete lumped parameter model of the high-pressure hydraulic circuit has been applied to perform a modal analysis. The visualization of the main vibration modes of the apparatus allows a detailed and deep comprehension of the system dynamics. Furthermore, the possible resonances, which are induced by the action of the external forcing terms, have been identified.

A numerical-experimental analysis of a new generation Common Feeding (CF) fuel injection system, equipped with last generation solenoid injectors that feature pressure-balanced pilot-valves, has been developed. The main feature of the CF system is that it removes the accumulator from the high-pressure layout of the standard Common Rail (CR). In the CF apparatus, the high-pressure pump is connected directly to the injectors, and a small accumulation volume is integrated in the pump high-pressure circuit. The hydraulic performance of the CF system, including the injectors with the pressure-balanced pilot-valve, has been compared with that of the standard CR system in terms of injected masses, fuel leakages, high-pressure and injected flow-rate time histories. A previously developed advanced one-dimensional code for CR type systems has been adapted for the simulation of the CF high-pressure layout.