Search Results

Direct Injection (DI) is believed to be one of the key strategies for maximizing the thermal efficiency of Spark Ignition (SI) engines and meet the ever-tightening emissions regulations. This paper explores the use of Liquefied Petroleum Gas (LPG) liquid phase fuel in a 1.5 liter SI four cylinder gasoline engine with double over head camshafts, four valves per cylinder, and centrally located DI injector. The DI injector is a high pressure, fast actuating injector enabling precise multiple injections of the finely atomized fuel sprays. With DI technology, the injection timing can be set to avoid fuel bypassing the engine during valve overlap into the exhaust system prior to combustion. The fuel vaporization associated with DI reduces combustion chamber and charge temperatures, thereby reducing the tendency for knocking. Fuel atomization quality supports an efficient combustion process.

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.

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 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.

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.

Direct Injection (DI) is believed to be one of the key strategies for maximizing the thermal efficiency of Spark Ignition (SI) engines and meeting the ever-tightening emissions regulations. This paper explores the use of propane and methane gas fuels in a 1.5 liter SI four cylinder gasoline engine with double over head camshafts, four valves per cylinder, and a centrally located DI injector. With DI technology, the injection timing can be set to avoid fuel bypassing the engine during valve overlap into the exhaust system prior to combustion. DI of fuel reduces the embedded air displacement effects of gaseous fuels and lowers the charge temperature. Injection timings and compression ratio are optimized for best performances at Wide Open Throttle (WOT) conditions when configured to achieve homogeneous charge at stoichiometry or run lean jet controlled stratified.

Standard design practice usually adopts steady flow tests for addressing optimisation of the intake valve-port assembly. Recently, with more user-friendly CFD tools and with increased computing power, intake stroke simulations, handling both piston and valves motion, have become practical. The purpose of this paper is to compare the design guidelines provided by the standard steady flow tests (both experimental and numerical) and the information coming from a CFD-3D intake stroke analysis. Reference is made to a four valve HSDI Diesel engine. Three swirl control strategies are investigated. It is supposed that one intake valve is kept closed, while the other one operates normally (first strategy). The second strategy consists in a 50% reduction of the lift of both valves. Finally, the third possibility is the blockage of one intake port by means of a simple butterfly valve.

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 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.

High power output, four stroke, motorcycle engines are characterised by specific power levels well beyond 150 HP/litre also in production engines. These power levels are obtained through extremely high values of volumetric efficiencies in the range of high engine speed, resulting from highly optimised gas exchange processes. In the present paper, a four cylinder, four valve per cylinder engine with a four-in-one exhaust is optimised for volumetric efficiencies by using state-of-the-art computational methods. These computational methods include static three dimensional computations as well as dynamic one and three dimensional computations. The engine geometric and operating parameters optimised by using these computations agree fairly well with those optimised by using experiments, thus demonstrating the effectiveness of the proposed computational practice.

High power output, four stroke, motorcycle engines are characterised by a complex combustion evolution strongly influenced by the properties of the averaged and turbulent flow field. In the present paper, state-of-the-art detailed computational methods are used to investigate the combustion evolution in a four cylinder, four valve per cylinder engine with a four-in-one exhaust where volumetric efficiencies and mixture compositions have been previously computed. Three dimensional unsteady computations of intake, compression, combustion and expansion strokes are performed. The method proves to be effective in qualitatively predicting heat release rate variations with engine speed and volumetric efficiency, while the simple modelling of the turbulent combustion does not allow to precisely define the magnitude of these variations.

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.

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.

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.

The paper presents experimental and theoretical results obtained for a mechanical Diesel fuel injection system, made up of a distributor-type pump, four delivery pipes and four four-hole injectors. Pressure in the pumping chamber, in two locations along the fuel line and within the injector is measured directly, as well as the injector needle lift. The flow rate is evaluated through the measure of pressure in the injection chamber. Experimental results are sustained by theoretical results. The numerical model considers systems of ordinary differential equations representing the operation of injector, pump, delivery valve and line volume elements. Only a few model details are presented. Similar approaches are in use by many years, and the accuracy they provide is generally accepted to be fairly good. Theoretical and experimental results are presented vs. the time at different pump speeds, showing a very satisfactory accuracy.

This paper presents experimental and computational results obtained on an in line, six cylinder, naturally aspirated, gasoline engine. Steady state measurements were first collected for a wide range of cam and spark timings versus throttle position and engine speed at part and full load. Simulations were performed by using an engine thermo-fluid model. The model was validated with measured steady state air and fuel flow rates and indicated and brake mean effective pressures. The model provides satisfactory accuracy and demonstrates the ability of the approach to produce fairly accurate steady state maps of BMEP and BSFC. However, results show that three major areas still need development especially at low loads, namely combustion, heat transfer and friction modeling, impacting respectively on IMEP and FMEP computations. Satisfactory measurement of small IMEP and derivation of FMEP at low loads is also a major issue.

This paper reports an analysis of the lubrication mechanism and the dynamic behaviour of axial piston pumps and motors slipper bearings. A numerical procedure is used to solve the Reynolds equation, written here with respect to the slipper-swash plate gap, whose height is considered variable in a two dimensional field and with time. The contributions of forces and moments acting on the slipper are illustrated and discussed, then the numerical method is presented to solve the Reynolds equation. Taking into consideration the slipper surface that is facing the swash plate, different geometry profiles are considered and the subsequent dynamic behaviour of the slipper is investigated; in particular, it is shown that a flat profile cannot always guarantee the bearing capability of the slipper and the lubrication in the gap is compromised for some critical operating conditions.