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Technical Paper

Design and Optimization of a Variable Displacement Vane Pump for High Performance IC Engine Lubrication: Part 1 - Experimental Analysis of the Circumferential Pressure Distribution with Dynamic Pressure Sensors

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.
Technical Paper

The Influence of Cavitation and Aeration in a Multi-Fuel Injector

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.
Technical Paper

Mechanical Cushion Design Influence on Cylinder Dynamics

The paper deals with the simulation and the experimental verification of the dynamic behaviour of a linear actuator equipped with different configurations of mechanical cushion. A numerical model, developed and tailored to describe the influence of different modulation of the discharged flow-rate (and of the correspondent discharging orifice design) on the cushioning characteristics variation is firstly introduced. Then, with respect to the case of the cylindrical cushioning engagement, both the reliability and the limits of the numerical approach are highlighted through a numerical vs. experimental comparison, involving the piston velocity and the cylinder chambers pressure. After, with the aim of highlighting the effect of mechanical cushions design on a two effect linear actuator dynamic performances, the characteristics modulation of four alternative cushioning systems are determined and deeply analyzed.
Technical Paper

Pressure Transients in External Gear Pumps and Motors Meshing Volumes

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.
Technical Paper

Studying the Axial Balance of External Gear Pumps

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.
Technical Paper

Tailoring Simplified Models for the Feeding Performances Prediction of CNG PWM Controlled Single Stage Injectors

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.
Technical Paper

The Effect of Flow Forces Compensating Profile on the Metering Characteristics of a Conical Seat Valve

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.
Journal Article

Cavitating Flows in Hydraulic Multidimensional CFD Analysis

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.