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The research and development activities on diesel injection systems have focused some key-factors that improve the solenoid actuated injector performance, especially in the frame of the multi-event injection strategies. This paper deals with a 3-D numerical investigation that highlights the nozzle flow features of different injector layouts. A comparison between a last generation standard injector and an optimized unit characterized by an improved dynamics, different number of holes and reduced maximum lift is performed. By means of transient numerical simulations, the behavior of the fuel flows, the tendency to cavitation development and the response to the deviation from the standard operating conditions (highlighted by introducing a radial perturbation on the lift motion) are investigated.

The injection strategy as well as the overall efficiency of the diesel engine are tightly related to the performance of the high-pressure injection pump. The paper deals with the modeling of a latest generation Common Rail injection pump, aiming at the characterization of its performance in terms of volumetric- and torque-efficiency. A lumped parameter approach is adopted; with reference to a commercial pump widely used in the field of light diesel engines, a dynamic model of the piston-cylinder pair is built, taking its mechanical drive, the hydraulic supply and delivery systems into account. Based on in-depth experimental activities that provide the performance diagrams of pump, the lumped-parameter model is built and assessed. Given the current strong interest in the use of alternative fuels that limit CO2 emissions, the pump model has been implemented to simulate, beside the standard diesel, the use of biofuel.

Relatively recent investigations, basing on experiments as well as on modeling, have highlighted that the needle displacement in common-rail diesel injectors is affected by radial components. The effects of such “off-axis” needle displacement on fuel flow features have been so far investigated within the nozzle, only. The objective of this work is to extend the attention towards the formation of fuel sprays, when needle off-axis condition is encountered. In such a viewpoint, the development of each fuel spray has been modeled taking into account the hole-to-hole variations induced by the needle misalignment. The investigation has been carried out basing on 3D-CFD campaigns, in AVL FIRE environment. The modeling of diesel nozzle flow has been interfaced to the spray simulation, initializing the break-up model on the basis of the transient flow conditions (fuel velocity, turbulence and vapor fraction) at each hole outlet section.