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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.

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.

In this paper, an orifice-based lumped parameter model has been developed and tailored to predict the feeding performances of a single stage, inwardly opening, PWM controlled gas injector for automotive applications. In particular, simplifying the description of injector relevant sections, and adopting a “semi-perfect” approach to depict the gas properties dependency on pressure and temperature, the sub-sonic efflux through the injector metering section is studied involving both an isentropic and a polytropic expansion. Then, considering dry air as fluid medium, the injector feeding characteristics variations with the duty cycle, with the feeding pressure and with temperature are highlighted.

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.

In the present automotive research, increasing efforts are being directed to improve the overall organic efficiency, which, inter alia, means to improve the operational behavior of the auxiliary organs. This paper reports an experimental approach for the determination and analysis of the pressure distribution in a variable displacement vane pump for high speed internal combustion engine lubrication. More in details, an actual application is presented for a seven-blades variable displacement vane pump equipped with a hydraulic geometry variation system. This unit is characterized by a high performance, in terms of rotational speed, delivery pressure and displacement variation. The experimental layout and some relevant facilities are described. An extended test campaign was performed on the pump to characterize its operational behavior.

In this paper a detailed analysis focused on lumped parameters numerical modeling of a variable displacement vane pump for high speed internal combustion engine lubrication is presented and discussed. This particular volumetric unit is characterized by very extreme performance, both in terms of rotational speed, delivery pressure and displacement variation. First of all, a comprehensive description of the simulation environment properly tailored for the numerical modeling of the vane pump operation is introduced and all its geometric, kinematic and fluid-dynamic characteristics are described in depth. Then, the results coming from an exhaustive experimental campaign have been compared with simulations, finding a general good accordance that demonstrates the reliability of this numerical approach.

In this paper a detailed analysis focused on lumped parameters numerical modeling of a variable displacement vane pump for high speed internal combustion engine lubrication is presented and discussed. This particular volumetric unit is characterized by very extreme performance, both in terms of rotational speed, delivery pressure and displacement variation. First of all, a comprehensive description of the simulation environment properly tailored for the numerical modeling of the vane pump operation is introduced and all its geometric, kinematic and fluid-dynamic characteristics are described in depth. Then, the results coming from an exhaustive experimental campaign have been compared with simulations, finding a general good accordance that demonstrates the reliability of this numerical approach.

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.

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.

This paper deals with the study of the dynamic behavior of a F1 car gear selection hydraulic circuit, when involved in different shift transients. In the first part of the paper the actual circuit is described, and the main hypotheses adopted for the numerical modeling of the hydraulic power unit, of the control valves, of hydraulic pipes and of the actuators involved in the gear shift cycles are introduced. Particular attention is devoted to the actuators actual sequences, as applied by the Electronic Control Unit (ECU) to the servo-valves deputed to actuators control. The strategy to define each gear shift cycle in terms of actuators working position in time domain is chosen, using the frequency map of each servo-valve. A numerical vs. experimental comparison of the behavior of the actuators involved in the gear selection (during about 50 ms for an up shifting and 100 ms for a down shifting) is performed, with the target to define the validity limits of the numerical model results.

The aim of this work is to propose modifications to the managing of the 1st generation Common Rail injectors in order to reduce actuation time towards multiple injection strategies. The current Common Rail injector driven by 1st ECU generation is capable of operating under stable conditions with a minimum dwell between two consecutive injections of 1.8 ms. This limits the possibility in using proper and efficient injection strategies for emission control purposes. A previous numerical study, performed by the electro-fluid-mechanical model built up by Matlab-Simulink environment, highlighted different area where injector may be improved with particular emphasis on electronic driving circuit and components design. Experiments carried out at injector Bosch test-bench showed that a proper control of the solenoid valve allowed reducing drastically the standard deviation during the pilot pulses.

This paper studies the influence of the discharge chamber geometrical parameters on the steady-state characteristics behavior of a conical seat valve having compensating profile. More in details, starting from the analysis of the experimental behavior of an actual valve showing inefficient characteristic curves, the metering openings leading to the transition from under to over compensation are individuated. Then, a 3D CFD steady-state, incompressible and isothermal analysis is involved, mainly to evidence the valve discharge coefficient and flow-forces variations with operating conditions. After, two alternative valve configurations, presenting a low pressure region designed to optimize the flow-forces compensation, are characterized through the 3D CFD analysis.

The paper investigates, by means of a 3D, steady-state, incompressible and isothermal CFD analysis, the influence of the notch shape and number on proportional directional control valves metering edge characteristics. The numerical activity is firstly performed for a sharp metering edge, considered as reference case. Then, different configurations of notched metering edges are considered, coming from the adoption of two notch geometrical shapes largely used in proportional directional control valves actual design, and from a symmetrical displacement of two, three and four notches on the spool periphery. For all the cases considered, the qualitative analysis of the internal flow field is performed in order to highlight the fluid efflux main characteristics.

This paper studies the proportional directional control valves design influence on the energetic behavior of a mid-power compact excavator. In particular, with reference to the hydraulic circuit actuating the primary workgroup, in the paper the hydraulic power metering performed with the boom cylinder proportional control valve is studied, and some design solution useful in reducing both the hydraulic power dissipation, and the power absorption from the machinery prime mover are highlighted. The analysis, experimentally performed for different operating conditions, is carried out highlighting the influence of a metering configuration both on the supply pressure modulation and on the flow-rate supplied to the actuator.

In this paper a lumped parameters numerical model is reviewed to study the meshing process of external gear pumps and motors, with the aim of highlighting the influence of some geometrical design parameters and operating conditions on inter-teeth volumes pressures. The inter-teeth space is modeled adopting a two-volume approach, properly tailored both for the pump and for the motor units behavior description. In both cases, the communications between the interconnected inter-teeth volumes and the high and low pressure ports are sketched as variable equivalent turbulent restrictors; flow areas have been determined as functions of the gears and of the meshing grooves main design parameters. The inter-teeth pressures, and the leakage flows, are calculated solving the incompressible and isothermal continuity equation, contemporarily applied to both volumes and properly combined with the classical turbulent orifice equation.

In this paper some design aspects related to external gear pumps balancing surfaces are studied, and some useful guidelines for designing bearing blocks balancing surfaces are suggested. In order to study bearing blocks axial balance, a numerical procedure for the determination of the pressure distribution inside the clearance bounded by gears sides and bearing blocks internal surfaces is firstly presented and applied. After, the influence of bearing blocks geometry and pump operating conditions on the widening thrust is highlighted, considering both constant and variable lateral clearance heights. Then, the computations are performed to evaluate the widening thrust variation as a function of bearing blocks relative tilt with respect to gears lateral sides, and both positive and negative bearing blocks tilts are evidenced and discussed.

This paper deals with the analysis of the interaction between solid contamination and internal geometry in hydraulic conical and spherical poppet valves, performed through a non-dimensional, axis-symmetric CFD analysis of their internal flow. The information coming from the flow field solution is used to identify regions having higher probability to be impacted by particles dragged by the fluid, and to estimate the erosion potential of solid particles having different size. The value of the kinetic energy of particles approaching the walls of the geometric domain is used to estimate the amount of material potentially eroded by impacting particles, and to provide a potential correlation between ISO 4406 and NAS 1638 solid contamination level classification. The long-term target is a numerical estimation of service life in hydraulic components.