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The effect of cavitation plays a fundamental role in the hydraulic components design and the capability of predicting its causes and characteristics is fundamental for the optimization of fluid systems. In this paper, a multidimensional CFD approach is used to analyze the cavitating phenomena typical of hydraulic components using water as operating fluid. An open source fluid-dynamics code is used and the original cavitation model (based on a barotropic equation of state and homogeneous equilibrium assumption) is extended in order to account also for gases dissolved in the liquid medium. The effect of air dissolution into liquid water is modeled by introducing the Henry law for the equilibrium condition, and the time dependence of solubility is calculated on a Bunsen Coefficient basis. Furthermore, a simplified approach to turbulence modeling for compressible flows is coupled to the cavitation model and implemented into the CFD code.

This paper studies the dependency of the total efficiency of a multiple actuation hydraulic system on the operating conditions as well as on the control strategies applicable to control valves. In particular, with respect to the parallel connection among hydraulic actuators managed by proportional control valves, a general structure of the functional relationship correlating the hydraulic power provided by the supply unit and the mechanical power exerted by actuators is proposed and used to determine the operating point and the system overall efficiency. Afterwards, the dependency of the system behavior on external load variations and on valves control is assessed, and the influence of a modification of the operating conditions on the overall efficiency is highlighted. Finally, the validity limits of some compensating corrections are determined.

The internal flow field of a low pressure common rail type multi-fuel injector is analyzed by means of numerical simulation and particular attention is devoted to the cavitation and aeration phenomena when using different fuel mixtures. The fluid-dynamics open source OpenFOAM code is used; and the original cavitation model (based on a barotropic equation of state and homogeneous equilibrium assumption) is extended in order to account also for gases dissolved in the liquid medium. The effect of air dissolution into liquid is determined by introducing the Henry law for the equilibrium condition and the time dependence of solubility is calculated on a Bunsen Coefficient basis. A preliminary study of test cases available in literature is carried out to address the model predictive capabilities and grid dependency. The calculated pressure distribution and discharge coefficient for different nozzle shapes and operating conditions are compared with the referenced experimental measurements.

In this paper, the dependency on fuel blends of a four stroke, four cylinder SI engine equipped with a low pressure common rail type injection system is analyzed. With reference to an operating condition using E21 (21% ethanol, 79% gasoline) as a fuel, the experimental performance of the engine are firstly introduced, and the brake power, the specific fuel consumption, the total efficiency, the heating combustion power and the injected mass per stroke dependency on shaft speed are introduced. Then, the multi-fuel injection system actual behavior is predicted by means of a properly tailored lumped and distributed numerical model, whose general reliability is defined mainly in terms of injected mass per stroke. Afterward, the engine performance variation with the fuel mixture is determined, and the adaptation of the PWM control applied to injectors is proposed to compensate the engine operating characteristics.

The paper focuses on the mixing process of different fuels in a multi-fuel low pressure common rail injection system for a four stroke SI engine. The study is devoted to the prediction of the fuel mixture delivered by the injectors during a transient in which gasoline is being replaced by ethanol or a gasoline/ethanol blend. An integrated approach of different numerical tools is used to model the rail dynamic behavior under actual operating conditions. First, the 1D model of the injection system is constructed and the time varying conditions at the accumulator inlet and at the injectors' boundaries are assessed. The second step of the study is centered on the CFD analysis of the mixing process within the rail. The effects of the different engine operations on the fuels mixing are investigated and the injected fuel distribution among the cylinders is calculated. An open source computational fluid dynamics code is used in the simulations.

This paper presents a multidimensional approach to the hydraulic components design by means of an open-source fluid dynamics code. A preliminary study of a basic geometry was carried out by simulating the efflux of an incompressible fluid through circular pipes. Both laminar and turbulent conditions were analyzed and the influence of the grid resolution and modeling settings were investigated. A qualitative description of the internal flow-field distribution, and a quantitative comparison of pressure and velocity profiles along the pipe axis were used to asses the multidimensional open-source code capabilities. Moreover the results were compared with the experimental measurements available in literature and with the theoretical trends which can be found in well-known literature fundamentals (Hagen-Poiseuille theory and Nikuradse interpolation). Further comparison was performed by using a commercial CFD code.

Flexibility in running with different fuel is becoming an important issue in the Internal Combustion Engine design due to the increasingly wider use of alternative fuels. The injection systems must deal with fuels having different properties and effects on engine behavior and take proper adjustments in the control strategy. Particularly the transient during which one fuel is being replaced by the second one is a critical point of the injection system operation, and its capability of recognizing the fuel mixture currently available is a fundamental matter in the engine control development. This paper focuses on the multidimensional CFD analysis of a Common Rail type multi-fuel injection system accumulator during the gasoline - ethanol shift. An open source computational fluid dynamics code was used in the modeling.

This paper focuses on the preliminary design of a proportional solenoid aimed at controlling the low pressure stage of a two stage pressure regulator for CNG applications. In particular, the dynamic performance of a two stage pressure regulator is firstly studied in the whole operational field of a four stroke, four cylinder spark ignition engine, equipped with a simplified low-pressure Common Rail type collector serving four PWM actuated single stage injectors. Then, with the aim of developing an electro-magnetic direct actuation, the dynamic performance of the second stage needle is adopted to drive the design of a spires type, cylindrical coil proportional solenoid. In particular, both the steady and the transients steps needed to complete the preliminary design are highlighted, and the influence of some relevant design parameters (such as the coil geometry and the air gap) on the actuation characteristics are evidenced.

For the simultaneous evaluation of the influence on engine knock of both chemical conditions and global operating parameters, a combined tool was developed. Thus, a two-zone kinetic model for SI engine combustion calculation (Ignition) was implemented into an engine cycle simulation commercial code. The combined model predictions are compared with experimental data from a single-cylinder test engine. This shows that the model can accurately predict the knock onset and in-cylinder pressure and temperature for different lambda conditions, with and without EGR. The influence of nitric oxide amount from residual gas in relation with knock is further investigated. The created numerical tool represents a useful support for experimental measurements, reducing the number of tests required to assess the proper engine control strategies.

The purpose of this paper is to compare different methodologies of CFD analysis, applied to the intake plenum of a turbocharged HSDI Diesel engine. The study is performed by using both an engine cycle simulation code and a 3D-CFD code. Experiments at the engine dynamometer and at a steady flow bench support the theoretical study. The most promising simulation technique presented in the paper is the integrated 1D and 3D-CFD simulation. This numerical approach showed itself to be particularly suitable for analysing complex engine components where the flow patterns are fully transient.