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Massimo BORGHI

Professore Ordinario
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

2024 - Proposal and validation of a numerical framework for 3D-CFD in-cylinder simulations of hydrogen spark-ignition internal combustion engines [Articolo su rivista]
Sfriso, S.; Berni, F.; Fontanesi, S.; D'Adamo, A.; Frigo, S.; Antonelli, M.; Borghi, M.
abstract

2023 - An integrated 0D/1D/3D numerical framework to predict performance, emissions, knock and heat transfer in ICEs fueled with NH3–H2 mixtures: The conversion of a marine Diesel engine as case study [Articolo su rivista]
Berni, F.; Pessina, V.; Teodosio, L.; D'Adamo, A.; Borghi, M.; Fontanesi, S.
abstract

In the maritime transportation, e-fuels represent a valid alternative to fossil energy sour- ces, in order to accomplish the European Union goals in terms of climate neutrality. Among the e-fuels, the ammonia-hydrogen mixtures can play a leading role, as the combination of the two allows to exploit the advantages of each one, simultaneously compensating their gaps. The main goal of the present publication is the proposal of a robust numerical frame- work based on 0D, 1D and 3D tools for CFD analyses of internal combustion engines fueled with ammonia-hydrogen mixtures. The 1D engine model provides boundary conditions for the multi-dimensional in- vestigations and estimates the overall engine performance. 3D in-cylinder detailed ana- lyses are proficiently used to predict combustion efficiency (via the well-established G-equation model supported by laminar flame speed correlations for both ammonia and hydrogen) and emissions (with a detailed chemistry based approach). Heat transfer and knock tendency are evaluated as well, by in-house developed models. As for the 0D/1D chemical kinetics calculations, firstly they support 3D analyses (for example via the gen- eration of ignition delay time tables). Moreover, they allow insights on aspects such as NOx formation, to individuate mixture qualities able to strongly reduce the emissions.

2023 - Impact of fuel surrogate formulation on the prediction of knock statistics in a single cylinder GDI engine [Articolo su rivista]
Fontanesi, S.; Shamsudheen, F. A.; Gonzalez, E. G.; Sarathy, S. M.; Berni, F.; D'Adamo, A.; Borghi, M.; Breda, S.
abstract

The statistical tendency of an optically accessible single-cylinder direct-injection spark-ignition engine to undergo borderline/medium knocking combustion is investigated using 3D-CFD. Focus is made on the role of fuel surrogate formulation for the characterization of anti-knock quality and flame speed of the actual fuel. An in-house methodology is used to design surrogates able to emulate laminar flame speed and autoignition delay times of the injected fuel. Two different surrogates, characterized by increasing level of complexity, are compared. The most complex one (six components) improves the representation of the real fuel, highlighting the crucial role of accurate fuel kinetics to predict flame propagation and unburnt mixture reactivity. A devoted chemical mechanism including the oxidation pathways for all the species in the surrogate is also purposely developed for the current analysis. Knock is investigated using a proprietary statistical knock model (GruMo-UNIMORE Statistical Knock Model, GK-PDF), which can infer the probability of knocking events within a RANS formalism. Predicted statistical distributions are compared to measured counterparts. The proposed numerical/experimental comparison demonstrates the possibility to efficiently integrate complex-chemistry driven information in 3D-CFD combustion simulations without online solving chemical reactions: a combination of laminar flame speed correlations, ignition delay look-up tables, and a statistics-based knock model is adopted to estimate the percentage of knocking cycles in a GDI engine while limiting the computational cost of the simulations.

2023 - Modeling of gaseous emissions and soot in 3D-CFD in-cylinder simulations of spark-ignition engines: A methodology to correlate numerical results and experimental data [Articolo su rivista]
Berni, F.; Mortellaro, F.; Pessina, V.; Paltrinieri, S.; Pulvirenti, F.; Rossi, V.; Borghi, M.; Fontanesi, S.
abstract

2022 - A zonal secondary break-up model for 3D-CFD simulations of GDI sprays [Articolo su rivista]
Berni, F.; Sparacino, S.; Riccardi, M.; Cavicchi, A.; Postrioti, L.; Borghi, M.; Fontanesi, S.
abstract

In Gasoline Direct Injection (GDI) engines, the secondary break-up plays a significant role in air–fuel mixing. In fact, spray granulometry affects evaporation rate, liquid penetration and plume morphology. Operating pressures and temperatures of both liquid and gaseous phases strongly influence the droplet disruption mechanism in the combustion chamber. In 3D Computational Fluid Dynamics (CFD), several models can be adopted to simulate the secondary break-up process, among which the Reitz-Diwakar and the Kelvin-Helmholtz Rayleigh-Taylor (KHRT) are the most diffused ones in the engine community. However, application of such models in their original versions is limited to a reduced range of injection parameters and ambient conditions. As a matter of fact, large variations of them usually require ad-hoc calibrations of the model constants. To improve the predictive capabilities and reduce the need of case-by-case tuning, an alternative secondary break-up model is proposed in the present paper. It is based on the Reitz-Diwakar one but, compared to the latter, a zonalization of the break-up regimes is proposed. Specifically, it is assumed that only Stripping break-up can occur near the nozzle, while Bag break-up only takes place sufficiently far from it. Moreover, model parameters are now treated as functions of the operating conditions. In particular, the impact of the ambient density on the model parameters is analysed in the present work. The proposed model is calibrated via constant volume vessel simulations on a single-hole GDI research injector at vacuum-to-pressurized conditions (namely at 0.4, 1.0, and 3.0 bar(a) of back pressure), on equal temperature. Model parameters are found to be linear functions of the ambient density. Thereafter, model validation is carried out on two different GDI injectors. The first is again a single-hole (remarkably different compared to the previous one), while the second is a 5-hole prototype. Numerical results provided by the proposed model show a satisfactory agreement compared to the experiments in terms of liquid penetration, Phase Doppler Anemometry (PDA) data and imaging, without any dedicated tuning. Conversely, the Reitz-Diwakar and KHRT models, applied to simulate (with default calibration constants) the same injectors, provide results which remarkably deviate from the experiments.

2022 - An Alternative Solution for Microfluidic Chip Fabrication [Relazione in Atti di Convegno]
Ongaro, C.; Betti, A.; Zardin, B.; Siciliani, V.; Orazi, L.; Bertacchini, J.; Borghi, M.
abstract

2021 - CFD modelling of a hydrogen/air PEM fuel cell with a serpentine gas distributor [Articolo su rivista]
D'Adamo, A.; Riccardi, M.; Borghi, M.; Fontanesi, S.
abstract

Hydrogen-fueled fuel cells are considered one of the key strategies to tackle the achievement of fully-sustainable mobility. The transportation sector is paying significant attention to the development and industrialization of proton exchange membrane fuel cells (PEMFC) to be introduced alongside batteries, reaching the goal of complete de-carbonization. In this paper a multi-phase, multi-component, and non-isothermal 3D-CFD model is presented to simulate the fluid, heat, and charge transport processes developing inside a hydrogen/air PEMFC with a serpentine-type gas distributor. Model results are compared against experimental data in terms of polarization and power density curves, including an improved formulation of exchange current density at the cathode catalyst layer, improving the simulation results’ accuracy in the activation-dominated region. Then, 3D-CFD fields of reactants’ delivery to the active electrochemical surface, reaction rates, temperature distributions, and liquid water formation are analyzed, and critical aspects of the current design are commented, i.e., the inhomogeneous use of the active surface for reactions, limiting the produced current and inducing gradients in thermal and reaction rate distribution. The study shows how a complete multi-dimensional framework for physical and chemical processes of PEMFC can be used to understand limiting processes and to guide future development.

2021 - Lumped parameter model of vane pumps developed in OpenModelica environment [Relazione in Atti di Convegno]
Zardin, B.; Cillo, G.; Rizzoli, M.; Borghi, M.
abstract

In this paper, the authors present a 0D fluid dynamic model of a vane pump used to refill tanks with fuel. T he model is entirely developed in OpenModelica environment, where the authors have created specific libraries of elements suitable for the physical modelling of fluid power components and systems. Among the different approaches, the zero-dimension (0D) fluid-dynamic modelling of positive displacement machines is suitable to study many aspects as: the instantaneous flow rate, pressure and torque transients, the fluid borne noise related to the flow rate and pressure irregularity, the dynamic behaviour of the variable displacement control. Overall, this approach in modelling allows to link the geometrical features of the machine with its dynamic behaviour and for this reason is particularly useful in guiding the design. The model of the vane pump is described together with the main design features that can be analysed in terms of their influence on the pump behaviour. Besides the specific results obtained regarding the design of the pump, the paper also demonstr ates the use of OpenModelica language and environment, and its efficacy, into the applications of fluid power modelling and simulation.

2021 - On the use of tapered channels gas distributors to promote convection in PEM Fuel Cells [Relazione in Atti di Convegno]
D'Adamo, A.; Borghi, M.
abstract

Polymeric Exchange Membrane Fuel Cells (PEMFC) are promising power propulsion systems for the decarbonization of the transportation sector. Despite being a well-known method for the direct production of electric current from the reactants chemical energy, one of the major limitations to their large-scale industrial development are fluid dynamics and mass transport aspects, crucially limiting the electrochemistry rate under critical conditions. This is especially verified in PEMFC with serpentine-type gas distributors, for which such areas are identified in proximity of the gas channel bends where the dominant mechanism for species transport shifts from a convection-enhanced to a diffusion-limited one. An engineering method to enhance the convective transport in such deficient areas is the use of gas distributors with tapered channels, effectively forcing the flow in diffusive media and improving the reactants delivery rate and products removal. A numerical analysis is presented on a limited domain representing a section of a serpentine gas distributor. A multi-dimensional CFD study is carried out comparing conventional-type and tapered channel distributors, evaluating the combined effect of pressure losses, catalyst layers utilization, flow regime in anisotropic diffusion media and convection/diffusion balance via a non-dimensional analysis. The study covers various inlet Reynolds numbers and in-plane permeability of porous materials for two diffusion media thicknesses, with the aim to extend the generality of the study. Conclusions based on the simulation results outline channel tapering as a very effective way to improve the power density of PEMFC, although an energetic cost/benefit analysis indicates a reduced cell efficiency.

2021 - Towards grid-independent 3D-CFD wall-function-based heat transfer models for complex industrial flows with focus on in-cylinder simulations [Articolo su rivista]
Berni, F.; Cicalese, G.; Borghi, M.; Fontanesi, S.
abstract

Convective heat transfer heavily affects both efficiency and reliability in many industrial problems. For this reason, its proper estimation is mandatory since the early design stage. 3D-CFD simulations represent a powerful tool for the prediction of the heat fluxes. This is even more true considering that typical operating conditions of many applications prevent experimental characterization. As for 3D-CFD computations, the combination of Reynolds Averaged Navier Stokes (RANS) turbulence modeling and high-Reynolds wall treatment is still widely diffused in the industrial practice, to save both computational cost and time. The adoption of a high-Reynolds wall treatment based on wall functions, which permits the use of relatively coarse near-wall grids, implies specific restrictions for the height of the near-wall cell layer. In particular, the first cell-centroid must be placed in the fully turbulent (log-) region of the boundary layer. The main drawback of a cell-centroid falling into the viscous sub-layer consists in a huge overestimation of both wall shear stress and wall heat transfer. The lower the y+ is (i.e. the lower the wall distance is), the higher the predicted values are. As for many other industrial applications, Internal Combustion Engine (ICE) in-cylinder simulations remarkably suffer from the presence of low y+ values in the computational domain, mostly at part-loads and low-revving speeds. At specific operating points, such as idle conditions, it is nearly impossible to maintain y+ in the log-region, even during the compression stroke, when the velocity field should allow the dimensionless distance to reach the highest values in the engine cycle. To avoid such undesired overestimations of shear stress and heat transfer, a modified formulation of the thermal law of the wall (T+) to be used in the viscous sub-layer is proposed in the present paper. To further reduce the grid-dependency of the high-Reynolds wall treatment, a similar modification is applied to the velocity wall function (u+). Resulting wall heat flux and wall shear stress are shown to be grid-independent, at least for y+>3. The proposed alternative modeling for u+ inside the viscous sub-layer is validated in terms of flow field against experimental Laser-Doppler Anemometry (LDA) data and Direct Numerical Simulation (DNS) results. Despite the present analysis focuses on in-cylinder simulations, the alternative u+ and T+ formulations can be applied to any complex flow. Furthermore, the proposed modified laws of the wall can be adopted in conjunction with any wall-function-based heat transfer model.

2020 - A study on PVD coatings for reduction of friction and wear of swashplate axial piston pumps and motors [Relazione in Atti di Convegno]
Sola, R; Veronesi, P; Zardin, B; Borghi, M
abstract

Swashplate axial piston pumps and motors are widely used under severe conditions because of their capability to operate at high pressure values and various ranges of speeds, maintaining a good efficiency. In some operating conditions however, the machine efficiency may be relatively low because of insufficient lubrication and this causes rapid wear and high friction losses. PVD coatings may help in reducing the friction thus having a positive impact on the machine efficiency. For this reason, pin on disk testing were conducted to investigate the friction and wear behavior of different PVD coatings on various metallic substrates. A copper and tin alloy coated with PA-CVD DLC, a carburized 17NiCrMo7 with a PVD DLC coating and a nitrided 41CrAlMo7 PVD coated with TiCN were studied. Results of tribological testing, carried out at 0.2 and 0.5 m/s as sliding speed and 5000, 10000 and 20000 rounds as ending conditions, showed that wear and friction had been reduced; moreover, microstructure features were analyzed for understanding underlying mechanism and to allow selecting the most suitable coating for the application on the swashplate axial piston machine.

2020 - Analysis of the flow force compensation in relief valves with conical poppet [Relazione in Atti di Convegno]
Fornaciari, A.; Zardin, B.; Borghi, M.; Ceriola, M.
abstract

The paper deals with experimental tests and numerical simulations (3D and 0D fluid-dynamic modelling) of a conical poppet pressure relief valve with flow force compensation. The aim of the study was to realize a dynamic model of the valve, able to consider the effect of the pressure force, which arises downstream the metering edge and is determined by both the flow forces and the pressure recovery on the flow deflector. Starting from a 3D-CFD model, it was possible to study the interaction between the poppet opening and the pressure field, in order to evaluate the total pressure force as a function of the poppet displacement. The contribution of the pressure recovered on the deflector was separated from the traditional flow force and then parametrized as a function of some geometric features. It was then possible to develop a 0D fluid-dynamic model that is suitable not only for the considered valve but also for valves with similar geometries. Lastly, the model was validated using experimental data acquired on test bench for three different valves. The comparison of the predicted flow-pressure characteristics with the experimental ones indeed showed a good result matching. This model can also lead towards design considerations to study the behaviour of a larger number of valve geometries.

2020 - Application of the Sectional Method to Investigate Particle Number and Soot Mass in Ethanol and Gasoline Fueled Premixed Spark Ignition Engines [Relazione in Atti di Convegno]
Pessina, V.; Del Pecchia, M.; Breda, S.; Dalseno, L.; Borghi, M.
abstract

Emission modelling is still a timely topic in the engine research community. Soot emission reduction has gained its spotlight among the pollutants-related issues mainly due to the renewed interest in Gasoline Direct Injection. The conjunction of experimental measurements and numerical investigations provides an effective tool to cope with the constant evolution of the emission regulations. Thus, numerical models must be validated over a wide range of engine operating points and fuels. To this aim, the Sectional Method was applied to investigate Particulate Matter and Particle Number produced during combustion in a premixed spark ignition engine using 3D-CFD. Soot-related quantities were investigated for different values of equivalence ratio (from 1.0 up to 1.5) as well as for different fuels. Three different fuel types were examined: a commercial nonoxygenated American gasoline (TIER-2), a commercial Chinese gasoline (CHINA-6) with ethanol 10 %vol and pure Ethanol (E100). A detailed chemistry-based tabulated approach was exploited to compute a dedicated soot library, for each of the analyzed fuels, by means of 0D chemical kinetic simulations using a constant pressure reactor approach. Numerical results were compared to a database of experimental measurements collected from literature. The sooting tendency threshold dependency on equivalence ratio was also investigated and the results showed that the ethanol is the less sooting among the examined fuels, while the non-oxygenated gasoline exhibited the highest soot mass and Particle Number. This paper provides a CFD-based benchmark for soot mass and Particle Number for three fuel types with largely different chemical nature.

2020 - Experimental Validation of a 3D-CFD Model of a PEM Fuel Cell [Relazione in Atti di Convegno]
Riccardi, M.; D'Adamo, A.; Vaini, A.; Romagnoli, M.; Borghi, M.; Fontanesi, S.
abstract

The growing energy demand is inevitably accompanied by a strong increase in greenhouse gas emissions, primarily carbon dioxide. The adoption of new energy vectors is therefore seen as the most promising countermeasure. In this context, hydrogen is an extremely interesting energy carrier, since it can be used as a fuel in both conventional energy systems (internal combustion engines, turbines) and in Fuel Cells (FC). In particular, PEM (Polymeric Electrolyte Membrane) FC are given growing attention in the transportation sector as a Life-Cycle viable solution to sustainable mobility. The use of 3D CFD analysis of for the development of efficient FC architectures is extremely interesting since it can provide a fast development tool for design exploration and optimization. The designer can therefore take advantage of a robust and accurate modelling in order to define and develop fuel cell systems in a more time-efficient and cost-efficient way, to optimize their performance and to lower their production costs. So far, studies available in the scientific literature lack of quantitative validation of the CFD simulations of complete PEM fuel cells against experimental evidence. The proposed study presents a quantitative validation of a multi-physics model of a Clearpak PEM cell. The chemistry and physics implemented in the methodology allow the authors to obtain both thermal and electrical results, characterizing the performance of each component of the PEM. The results obtained, compared with the experimental polarization curve, show that the model is not only numerically stable and robust in terms of boundary conditions, but also capable to accurately characterize the performance of the PEM cell over almost its entire polarization range.

2020 - Modelling of hydraulic locking balancing circumferential grooves for servo-cylinders' piston [Relazione in Atti di Convegno]
Natali, E.; Zardin, B.; Cillo, G.; Borghi, M.
abstract

In the hydraulic servo-cylinders design, the circumferential grooves are used in order to reduce the effect of the locking force. This force arises as a consequence to the distribution of pressure around the piston, when both an eccentric position, caused by the load on the piston, and the manufacturing defects on the piston and cylinder surfaces are present. In this work an approach is presented for the calculation of the contribution of the grooves in the definition of the locking force and of the leakage flow rate. The mathematical model proposed is based on the Reynolds equation, properly combined with the continuity equation applied within the grooves. The results of the analysis are combined together with the ones coming from the analysis at the hydrostatic bearings at the rod ends, which have been analyzed on a previous step of the research. A numerical procedure is then created that, with the appropriate input, allows to study the different design configurations of the servo-cylinder. Results here shown are focused on exploring the effect of number, position, size of the grooves and manufacturing tolerances on the piston and cylinder. Simulations are also run under different operating conditions. For the real servo-cylinder configurations tested here, it is shown that five equally spaced grooves may be sufficient to decrease consistently the locking force while containing the flow losses. The procedure is also functional to investigate the bending and seizing of the piston during the different operating conditions, both in steady state and dynamic conditions.

2020 - The Hydraulic Power Generation and Transmission on Agricultural Tractors: Feasible architectures to reduce dissipation and fuel consumption-Part 2 [Relazione in Atti di Convegno]
Casoli, P.; Zardin, B.; Ardizio, S.; Borghi, M.; Pintore, F.; Mesturini, D.
abstract

Increasing interest in reducing pollutant emissions and fuel consumption of off-road vehicles has led to research alternative systems that aim to reduce the power dissipations of the hydraulic circuits. This work presents the advantages of few alternative solutions for a hydraulic high-pressure circuit of a medium-size tractor. The standard high-pressure circuit is a typical multiusers load sensing system that uses a single variable displacement pump to feed: steering, trailer brake, rear remotes, hitch and suspension. The alternative architectures have been simulated and compared in terms of mechanical energy consumption. In particular, the steering has been separated from the circuit, it has been actuated by means of a dedicated pump moved by an electric motor, in this way the priority valve could be removed and losses due the pressure compensators are reduced. A further architecture based on the insertion of the LS signal conditioner was studied. The results show that relevant energy saving can be achieved with the new alternative architectures; the physical prototyping of the most promising solutions will be realized as the next step of the project.

2020 - The Hydraulic Power Generation and Transmission on Agricultural Tractors: Feasible architectures to reduce dissipation and fuel consumption-Part i [Relazione in Atti di Convegno]
Gaiola, A.; Zardin, B.; Casoli, P.; Borghi, M.; Mazzali, F.; Pintore, F.; Fiorati, S.
abstract

This paper is aimed at investigating the benefits in terms of energy efficiency of new electro-hydraulic architectures for power distribution systems of a medium-size agricultural tractor, with a focus on the hydraulic high-pressure circuit. The work is part of a wider industrial research project called TASC (Smart and Clean Agricultural Tractors [1]). Traditional and alternative architectures have been modelled and energetically compared through simulation, using a lumped parameter approach. Experimental data previously acquired have been used to validate the models and to replicate real working conditions of the machine in the simulation environment. A typical on-field manoeuvre has been used as duty cycle, to perform an effective energetic analysis. The standard hydraulic circuit is a multi-users load sensing system that uses a single variable displacement pump to feed steering, trailer brake and auxiliary utilities in that order. The key idea of the proposed solutions is the separation of steering from the other implements, to optimize the entire energy management. In particular, the paper investigates new and flexible solutions for the auxiliary utilities, including an electro-hydraulic load sensing architecture with variable pump margin, an electronic flow matching and flow sharing architecture, and an electronic strategy for automatic pressure compensation. The simulation results show that good energy saving can be achieved with the alternative architectures, so that physical prototyping of the most promising solutions will be realized as next step of the project.

2019 - DESIGN AND MODELLING OF A CARTRIDGE PRESSURE AMPLIFIER [Relazione in Atti di Convegno]
Zardin, Barbara; Cillo, Giovanni; Zavadinka, Peter; Hanusovsky, Juraj; Borghi, Massimo
abstract

This works describes the modelling and simulation of a compact cartridge pressure amplifier for linear actuators, especially designed to fit within the rod of the piston. Hydraulic pressure amplifiers of the cylinder type are appreciated in hydraulic systems where high pressure work is needed, especially for a small part of the overall duty cycle. The use of these boosters allows the designer not to oversize the system, which will perform confining the high pressure operation only on the side of the hydraulic actuator. Starting from a previous research work on the same topic, this work proposes new designs for the cartridge amplifier to explore the influence of the control valve, which is the responsible for the delivering of the fluid to the amplifier. The new designs are discussed and then the results coming from the simulation performed with a lumped parameter model in a virtual test rig are shown. The operation of the amplifier is then applied to a more realistic duty cycle to illustrate and validate its operation.

2019 - Evaluation of the hydro - Mechanical efficiency of external gear pumps [Articolo su rivista]
Zardin, B.; Natali, Emiliano; Borghi, M.
abstract

This paper proposes and describes a model for evaluating the hydro-mechanical efficiency of external gear machines. The model is built considering and evaluating the main friction losses in the machines, including the viscous friction losses at the tooth tip gap, at the bearing blocks-gears gaps, at the journal bearings, and the meshing loss. To calculate the shear stress at each gap interface, the geometry of the gap has to be known. For this reason, the actual position of the gears inside the pump casing and consequent radial pressure distribution are numerically calculated to evaluate the gap height at the tooth tips. Moreover, the variation of the tilt and reference height of the lateral gaps between the gears and the pump bushings are considered. The shear stresses within the lateral gaps are estimated, for different lateral heights and tilt values. At the journal bearings gaps, the half Sommerfeld solution has been applied. The meshing loss has been calculated according to the suggestion of the International Standards. The hydro-mechanical efficiency results are then discussed with reference to commercial pumps experimentally characterized by the authors in a previous work. The average percentage deviation from experimental data was around 2%, without considering the most critical operating conditions (high delivery pressure, low rotational speed). The limits of this approach are also explained. Finally, the role of each source of loss is discussed, considering different operating conditions and two values of fluid viscosity. Lateral gap losses and meshing loss are much more relevant in determining the hydro-mechanical efficiency variation in the pump's operating range, especially at a low delivery pressure. Moreover, while lateral gap losses increase with the rotational speed, the meshing loss shows the opposite behavior. The tooth tip gap losses are never as relevant, but they increase at high pressure. The journal bearings losses become comparable with the lateral and meshing ones at high delivery pressure values. Considering the pumps analyzed and the operating range of delivery pressure values and rotational speed values, the meshing loss made the mechanical efficiency vary in a percentage range of ±7%, with lateral losses in the range of about the ±15%, when also considering the extreme operating points (low speed, high pressure; high speed, low pressure). The weight of the lateral losses slightly reduced when we analyzed the higher temperature results, while the meshing losses slightly increased.

2019 - Modelling of hydrostatic bearings for servo-cylinders [Relazione in Atti di Convegno]
Zardin, B.; Natali, E.; Cillo, G.; Borghi, M.
abstract

Hydraulic servo cylinders are widely used in versatile industrial applications such as machine tools, industrial robots, autonomous manufacturing systems and special applications in laboratories. To reduce friction and allow smooth and controllable displacement of the actuator, hydrostatic journal bearings are used at the ends of the rod. The design and manufacturing of this elements is challenging since the good operation relays on the very small tolerances required to bear the load on the cylinder and to reduce leakages. In this work, a virtual design and test tool for hydrostatic journal bearing with pockets, developed in OpenModelica environment, is presented. The influence of eccentricity and manufacturing tolerances is then studied and discussed. The model proposed has the aim to explore the extreme and critical operating conditions of the servo-cylinder and to help and/or improve the design phase.

2018 - Fluid-dynamic analysis of an in-line water piston pump [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Materi, Sergio; Argentino, Pierluigi
abstract

The paper focuses on the analysis of inline water piston pumps, by means of simulation of the fluid-dynamic behaviour and experimental characterization. These pumps are commonly used on the car wash systems, industrial washes systems and fire protection systems. They possess a robust architecture, made of a typical rod-crankshaft mechanism, which transforms the circular motion of the pump shaft in the reciprocating displacement of the piston. The pump analyzed in the paper, in particular, moves three pistons, shifted one another of 120°; each piston sucks from a tank and delivers water to a hydraulic line via automatic, spring loaded, poppet valves. The shaft, rod and other movable components are lubricated with mineral oil; the three ceramic pistons are isolated from this environment using opportune seals and work with water. This pump is robust and durable but suffers of some problems: the instantaneous pressure trend within each piston is ideally a square wave: the pressure is equal to the tank pressure during suction, while it is equal to the delivery pressure during the delivery phase. Instead, non –ideal behaviour of the poppet valves, leakages, fluid properties make the pressure trend more critical: during the pressure transient between the two high and low levels, pressure peaks and de-pressurization till aeration and cavitation occurrence may happen. These phenomena generate vibrations and noise and can damage the pump components. In order to study this, a lumped parameter fluid dynamic model of the pump has been realized, later compared with experimental results coming from the test rig to validate it. The model has been used to explore the dynamic pump behaviour in several operating conditions (various speed values and delivery pressure levels), calculating the flow irregularity, the pressure and forces instantaneous trends. The design characteristics of the poppet valves have been explored, in particular the spring characteristics, to discuss the trend of the previous variables.

2018 - Modelling and Simulation of a Cartridge Pressure Amplifier [Relazione in Atti di Convegno]
Zardin, Barbara; Cillo, Giovanni; Borghi, Massimo; Zavadinka, Peter; Hanusovsky, Juraj
abstract

Hydraulic pressure amplifiers of the cylinder type are much appreciated in hydraulic systems where high pressure work is needed only for a limited period of time, while during the remaining duty cycle the system operates at a standard level of pressure. The use of these elements allows the designer not to oversize the system, which will perform the work with a considerable power saving, confining the high pressure operation only on the side of the hydraulic cylinder. This works describes the modelling and simulation of a compact cartridge pressure amplifier for linear actuators. The cartridge amplifier is able to double or more the pressure in the system when needed and to not interfere during normal operation of the system. It has been designed to fit in the narrow space of the rod of normal hydraulic cylinder, being extremely compact and efficient. Designing such a component and the study of the main design parameters influence have required a strong work of modelling and simulation, performed with a lumped parameters approach to depict the dynamic behaviour of the amplifier. This work illustrates the building of the model and a first comparison between simulated and experimental data. Moreover, the simulation activity is enlarged to analysis of the influence of some operating and design parameters on the amplifier dynamic behavior

2018 - Modelling and Simulation of a Hydrostatic Steering System for Agricultural Tractors [Articolo su rivista]
Zardin, Barbara; Borghi, Massimo; Gherardini, Francesco; Zanasi, Nicholas
abstract

The steering system of a vehicle impacts on the vehicle performance, safety and on the driver’s comfort. Moreover, in off-road vehicles using hydrostatic steering systems, the energy dissipation also becomes a critical issue. These aspects push and motivate innovation, research and analysis in the field of agricultural tractors. This paper proposes the modelling and analysis of a hydrostatic steering system for an agricultural tractor to calculate the performance of the system and determine the influence of its main design parameters. The focus here is on the driver’s steering feel, which can improve the driver’s behavior reducing unnecessary steering corrections during the working conditions. The hydrostatic steering system is quite complex and involves a hydraulic circuit and a mechanical mechanism to transmit the steering to the vehicle tires. The detailed lumped parameters model here proposed allows to simulate the dynamic behavior of the steering system and to both enhance the understanding of the system and to improve the design through parameters sensitivity analysis.

2017 - Design Of Two-Stage On/Off Cartridge Valves For Mobile Applications [Relazione in Atti di Convegno]
Zardin, Barbara; Borghi, Massimo; Cillo, Giovanni; Rinaldini, Carlo Alberto; Mattarelli, Enrico
abstract

Cartridge valves are widely used in mobile applications, where they are screwed in manifolds, to realize opportune circuit layouts. These valves are quite simple in operation but require a sophisticated design in order to meet all the requirements needed in the mobile machines. Typically, the design process is developed realizing a first design concept and some prototypes and experimentally testing them; after this, the designer chases the optimal performances requested to the valve with a trial and error approach on the prototypes, involving high time and cost resources. In this paper an alternative design procedure is proposed, which involves dedicated simulations to analyze the main critical issues regarding the cartridge valve object of the study. Modelling and simulations here have been considered as steps into the design process of a new valve, which satisfies the requirements and well adapt to the necessities to operate at higher flow and pressure levels without compromising its performances. In that way, the number of prototypes, realized to validate the numerical results and verify the design process, has been considerably reduced, together with related time and costs.

2017 - Design and experimental development of a compact and efficient range extender engine [Articolo su rivista]
Borghi, Massimo; Mattarelli, Enrico; Muscoloni, Jarin; Rinaldini, Carlo Alberto; Savioli, Tommaso; Zardin, Barbara
abstract

The paper reviews the design and experimental development of an original range-extender single-cylinder two-stroke gasoline engine, rated at 30 kW (maximum engine speed: 4500 rpm). The goal of the project is to get most of the benefits of the two-stroke cycle (compactness, high power density, low cost), while addressing the typical issues affecting the conventional engines of this type. Among many recent similar propositions, the peculiarities of this engine, besides the cycle, are: external scavenging by means of an electric supercharger, piston controlled scavenge and exhaust ports (no poppet valves), gasoline direct injection (GDI), and a patented rotary valve for the optimization of the scavenging process, of the loop type. Lubrication is identical to a conventional four-stroke engine, and the rotary valve, connected to the crankshaft, helps to improve the balance of the piston reciprocating forces, yielding an excellent NVH behavior. It should be noted that, except the patented rotary valve, all the engine parts are standard automotive commercial components, that don’t require any specific expensive technology. In fact, the originality of the engine consists in the optimum combination of existing well assessed concepts. The scavenging and combustion systems of the engine are developed in the first phase of the project, including the construction and the experimental testing of a prototype. In the second phase, the air metering system of the prototype is completely modified: the piston pump is replaced by an electric supercharger, and engine load is now controlled by the supercharger speed, without throttle valve. The new engine is compared to a standard 4-stroke engine, developed in a previous project for the same application. The main advantages of the two-stroke engine may be summarized as follows: lower weight (−35%), higher brake efficiency (+6%, on average), less heat rejected (−18%), lower thermal and mechanical loads within the cylinder (−40%). The only concern, that will be addressed in a future phase of the study, is the compliance with very low NOx limits: in the worst scenario, the 2-stroke engine could be forced to adopt a well assessed but expensive after-treatment device.

2017 - Development of a 2-Stroke GDI Engine [Relazione in Atti di Convegno]
Savioli, Tommaso; Zardin, Barbara; Borghi, Massimo
abstract

Nowadays, high-pressure gasoline direct injection (GDI) can be considered a standard technology, due to the wide application on 4-stroke turbocharged engines. This technology - in combination with other specific solutions - has been successfully applied to a 500 cc, 30 kW 2-stroke engine, initially developed as a range extender. The engine is valve-less and cam-less, being the scavenge and exhaust ports controlled by the piston. An electric supercharger delivers the required airflow rate, without need of a throttle valve; the lubrication is identical to a 4-stroke. The current study reviews the development process, assisted by CFD simulation, that has brought to the construction of a prototype, tested at the dynamometer bed of the University of Modena and Reggio Emilia (Engineering Department "Enzo Ferrari"). An experimentally calibrated CFD-1d model is applied to predict full load engine performance. The results show an excellent fuel efficiency and a very low level of thermal and mechanical stress despite the high power density.

2017 - Development of a RANS-Based Knock Model to Infer the Knock Probability in a Research Spark-Ignition Engine [Articolo su rivista]
D'Adamo, Alessandro; Breda, Sebastiano; Iaccarino, Salvatore; Berni, Fabio; Fontanesi, Stefano; Zardin, Barbara; Borghi, Massimo; Irimescu, Adrian; Merola, Simona
abstract

Engine knock is one of the most limiting factors for modern Spark-Ignition (SI) engines to achieve high efficiency targets. The stochastic nature of knock in SI units hinders the predictive capability of RANS knock models, which are based on ensemble averaged quantities. To this aim, a knock model grounded in statistics was recently developed in the RANS formalism. The model is able to infer a presumed log-normal distribution of knocking cycles from a single RANS simulation by means of transport equations for variances and turbulence-derived probability density functions (PDFs) for physical quantities. As a main advantage, the model is able to estimate the earliest knock severity experienced when moving the operating condition into the knocking regime. In this paper, improvements are introduced in the model, which is then applied to simulate the knock signature of a single-cylinder 400cm3 direct-injection SI unit with optical access; the engine is operated with two spark timings, under knock-safe and knocking conditions respectively. The statistical prediction of knock resulting from the presented knock model is compared to the experimental evidence for both investigated conditions. The agreement between the predicted and the measured knock distributions validates the proposed knock model. Finally, limitations and some unprecedented possibilities given by the model are critically discussed, with particular emphasis on the meaning of RANS knock prediction.

2017 - Pressure Losses in Multiple-Elbow Paths and in V-Bends of Hydraulic Manifolds [Articolo su rivista]
Zardin, Barbara; Cillo, Giovanni; Borghi, Massimo; D'Adamo, Alessandro; Fontanesi, Stefano
abstract

Hydraulic manifolds are used to realize compact circuit layouts, but may introduce high pressure losses in the system because their design is usually oriented to achieving minimum size and weight more than reducing the pressure losses. The purpose of this work is to obtain the pressure losses when the internal connections within the manifold are creating complex paths for the fluid and the total loss cannot be calculated simply as the sum of the single losses. To perform the analysis both Computational Fluid Dynamic (CFD) analysis and experimental tests have been executed. After the comparison between numerical and experimental results, it was possible to assess that the numerical analysis developed in this work is able to depict the correct trends of the pressure losses also when complex fluid path are realized in the manifold. Successively, the numerical analysis was used to calculate the pressure loss for inclined connections of channels (or V-bends), a solution that is sometimes adopted in manifolds to meet the design requirements aimed towards the minimum room-minimum weight objective.

2017 - Pressure losses in hydraulic manifolds [Articolo su rivista]
Zardin, Barbara; Cillo, Giovanni; Rinaldini, Carlo Alberto; Mattarelli, Enrico; Borghi, Massimo
abstract

Hydraulic manifolds are used to realize compact circuit layout, but may introduce a high pressure drop in the system. Their design is in fact oriented more toward achieving minimum size and weight than to reducing pressure losses. This work studies the pressure losses in hydraulic manifolds using different methods: Computational Fluid Dynamic (CFD) analysis; semi-empirical formulation derived from the scientific literature, when available; and experimental characterization. The purpose is to obtain the pressure losses when the channels' connections within the manifold are not ascribable to the few classic cases studied in the literature, in particular for 90° bends (elbows) with expansion/contraction and offset intersection of channels. Moreover, since CFD analysis is used to predict pressure losses, general considerations of the manifold design may be outlined and this will help the design process in the optimization of flow passages. The main results obtained show how CFD analysis overestimates the experimental results; nevertheless, the numerical analysis represents the correct trends of the pressure losses.

2015 - Axial Balance of External Gear Pumps and Motors: Modelling and Discussing the Influence of Elastohydrodynamic Lubrication in the Axial Gap [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara
abstract

This paper focuses on the analysis of hydraulically balanced external gear pumps, in particular on the lubricating gap between the bushes and the gears. This topic is of key importance for the optimization of the machine efficiency because it both influences the mechanical-viscous friction and the volumetric losses. In this paper the intent is to investigate the role of the elastic deformation of the bushes surfaces, to compare the analysis done with rigid and elastic surfaces and finally to correlate the results with the design of the bushes balancing surfaces. A numerical procedure for the determination of the pressure distribution inside the gap bounded by gears sides and the bushes internal surfaces is presented and applied. With respect to past works of the authors, the procedure has been integrated taking into account the elastic deformation of the internal surfaces of the bushes and the variation of the dynamic viscosity of fluid, two well recognized phenomena that can play a key role on the determination of the bushes behaviour and lubricating gap pressure distribution. It is shown that, when the design of the bushes rear surfaces determines a strong balancing thrust, the bushes themselves need to tilt strongly with respect to the gears to generate an opportune widening thrust to avoiding contact with the gears. Useful suggestions for the bushes balancing surface design may be drawn from the analysis of the balancing maps reported in the paper, which illustrate the widening thrust magnitude and position in both the pure hydrodynamic and elasto-hydrodynamic cases, for different tilted positions and operating conditions.

2015 - Dynamic Modelling of an Off-Road Vehicle for the Design of a Semiactive, Hydropneumatic Spring-Damper System [Relazione in Atti di Convegno]
Panetta, Giuseppe; Mancarella, Francesco; Borghi, Massimo; Zardin, Barbara; Pintore, Francesco
abstract

In this paper a tool integrating a multibody full car model of a tractor and the hydraulic model of the suspension system is presented as a virtual tool able to help the designer and also the control tuning of the system. The full car approach is chosen in order to be able to describe all the vehicles movements (roll, yaw, pitch) while the detailed lumped parameters model of the hydraulic suspensions allows to consider the role of the electrohydraulic valves, accumulator, hydraulic actuator on the vehicle dynamic behaviour. The hydraulic model and the multibody model exchange forces and displacements at the joint points: one between actuator and sprung mass (chassis) and the other one between actuator and unsprung mass (front axle and wheels). Experimental test have been performed (suspension leveling maneuvers, tests on ISO 50008 track, bump tests) and the results of the numerical model have been compared with the experimental data, allowing the understanding of the influence of the numerous design and control parameters involved in the determination of the vehicle dynamic behaviour. The influence of mechanical and geometrical parameters on the damping force hysteresis measured during levelling test are shown and described. Finally, the dynamic behavior of the suspension is analyzed making reference to a dynamic test over a bump.

2015 - Energy Saving in the Hydraulic Circuit for Agricultural Tractors: Focus on the Power Supply Group [Articolo su rivista]
Borghi, Massimo; Zardin, Barbara; Pintore, Francesco
abstract

This work aims to analyze a complete hydraulic system of a medium size agricultural tractor, in order to perform an energy dissipation analysis and to suggest possibly alternative configurations and solutions. The fuel consumption and energy dissipation in off road vehicles have in fact become a key feature, given the great attention devoted to the need of reducing pollutant emissions, in order to satisfy the future emission limits. In this work the focus is on the fluid power supply group and the standard architecture of this unit has been compared with an alternative solution, called variable pump margin strategy and compared on the basis of the power consumption to perform the same duty cycle, showing that a relevant percentage of energy may be saved with simple modifications in the hydraulic power generator group.

2014 - Energy Savings in the Hydraulic Circuit of Agricultural Tractors [Relazione in Atti di Convegno]
BORGHI, Massimo; ZARDIN, Barbara; PINTORE, FRANCESCO; BELLUZZI, FRANCESCO
abstract

Increasing interest in reducing pollutant emissions and fuel consumption of off-road vehicles has led to research into alternative systems that aim to reduce the power dissipation of the hydraulic circuits equipping such vehicles. This work proposes alternative hydraulic architectures for agricultural tractors in comparison with traditional systems. The alternative circuit architecture uses independent metering valves and electronically controlled variable pump and involves different control strategies. The analysis is performed with reference to the hydraulic circuit and operating conditions of the remote utilities of a medium-sized tractor. A duty cycle for remote utilities is used for the analysis, obtained from experimental measurements on a tractor equipped with a front loader. Traditional and alternative architectures are modelled using a lumped parameter approach. In this way it is demonstrated that considerable energy savings can be achieved using the alternative architectures.

2014 - MODELLING AND SIMULATION OF THE HYDRAULIC CIRCUIT OF AN AGRICULTURAL TRACTOR [Relazione in Atti di Convegno]
Pintore, Francesco; Borghi, Massimo; Morselli, Riccardo; Benevelli, Alessandro; Zardin, Barbara; Belluzzi, Francesco
abstract

This work aims to analyse a complete hydraulic system of a medium size agricultural tractor, in order to perform an energy dissipation analysis and to test possible alternative configurations and solutions. The fuel consumption and energy dissipation in off-road vehicles have infact become a key feature, given the great attention devoted to the need of reducing pollutant emissions, in order to satisfy the future emission limits. Standard and alternative architecture configurations are modelled and compared on the basis of the power consumption to perform the same duty cycle. Among the results, it is worth highlighting that a relevant percentage of energy may be saved with simple modifications in the hydraulic power generation group.

2014 - Sperimentazione e simulazione nell'analisi del circuito idraulico di una trattrice agricola [Articolo su rivista]
Borghi, M.; Zardin, B.; Zanasi, N.; Pintore, F.; Belluzzi, F.
abstract

In questo lavoro si descrive la metodologia utilizzata per caratterizzare una parte del circuito idraulico di una trattrice agricola. Lo scopo dell’attività è stato quello di ricavare informazioni necessarie alla definizione delle caratteristiche di regolazione della parte di circuito analizzata da utilizzare successivamente in un modello di simulazione del circuito stesso con il quale replicare poi in un ambiente virtuale le effettive condizioni di lavoro incontrate dal veicolo durante le lavorazioni.

2013 - Banco prova per analisi e test di componenti oleodinamici [Articolo su rivista]
Borghi, Massimo; Zardin, Barbara; Pintore, Francesco; Benevelli, Alessandro
abstract

Presso il Dipartimento di Ingegneria “Enzo Ferrari” di Modena è installato un banco prova attrezzato sia per il test di componenti oleodinamici di piccole e medie dimensioni, sia per l’esecuzione di esercitazioni a scopo didattico. L’attrezzatura è stata sviluppata e messa insieme negli anni dal gruppo di ricerca che si occupa in particolare di sistemi e applicazioni oleodinamiche. In questi ultimi anni il gruppo ha concentrato i propri sforzi avendo come obiettivo principale l’ottimizzazione energetica di componenti e sistemi oleodinamici, in particolare relativamente al caso delle applicazioni mobili. Il Prof. M. Borghi ha coordinato come responsabile scientifico un progetto di ricerca di rilevante interesse nazionale PRIN07 [3] la cui tematica era volta all’analisi e ottimizzazione energetica del circuito idraulico di una trattrice agricola e le varie attività di ricerca che si sono sviluppate a partire dal progetto stanno tuttora progredendo anche verso una generalizzazione dei risultati verso altre tipologie di veicoli off-road. L’attrezzatura presente presso il Dipartimento di Ingegneria è stata potenziata proprio nell’ottica di fornire essa stessa un ausilio nella ricerca, oltre che nell’ambito dimostrativo puramente didattico; corredando l’unità di generazione della potenza idraulica con elementi esterni, si prevede di poter realizzare in futuro caratterizzazioni sperimentali mirate di componenti oleodinamici, avendo come obiettivo principale la valutazione delle caratteristiche dinamiche e delle prestazioni energetiche.

2012 - Fluid power supply unit for agricultural tractors: towards energy saving through simulation [Relazione in Atti di Convegno]
Pintore, Francesco; Zardin, Barbara; Borghi, Massimo
abstract

The final aim of the research is to test and verify the effectiveness of high efficiency hydraulic architectures in agriculture tractors. In this paper the attention has been focused on the fluid power delivery group of the vehicle in order to generate a model of the fluid power supply unit used to supply the high pressure circuit of an agricultural tractor able to replicate the performances and the dynamic behaviour of the actual system. The group is composed of a variable displacement axial piston pump equipped with pressure and flow compensators. Despite the evident advantages of the use of this system in the hydraulic applications for off-road vehicles, there are still some critical issues mainly due to instability in some operating onditions and to energy dissipation, that is a direct consequence of the use of dissipative elements to maintain control and avoid interference of loads. In this work an axial piston pump is modelled in detail and analysed in terms of dynamic behaviour of the swashplate, in particular two different versions of the displacement actuations are considered, the first realized using a single actuator that works against the pistons momentum and against a spring, the second that uses a bias and a control actuator to manage the displacement variation. A simple duty cycle is used to study the performance of the pressure and flow compensators. The dynamic behaviour of the two pumps isanalysed and compared allowing to evidence the main design parameters that play a relevant role in the pump performances; this is a key step for the future work, which aims at introducing electronic control for the pump displacement.

2012 - Hydraulic Circuit in Agricultural Tractors, a Step Forward for Energy Saving [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Pintore, Francesco; Belluzzi, Francesco
abstract

The increasing interest to reduce the pollutant emissions in off road vehicles drives the research to alternative solutions aimed to decrease power dissipation for the hydraulic circuit that equips these vehicles. In this work higher efficiency hydraulic architectures in agriculture tractors are proposed and compared with the traditional layout. The alternative circuit architecture uses independent metering valves and electronically controlled variable pump. The analysis is performed with reference to the hydraulic circuit and operating conditions typical of the remote utilities has been used, obtained through experimental measurement on a tractor equipped with a front loader. The traditional and alternative architectures have been modelled using a lumped parameter approach. In that way it has been possible to show that a considerable quantity of energy can be saved using the alternative architectures.

2012 - Independent metering architectures for agricultural tractors auxiliary utilities. [Relazione in Atti di Convegno]
Benevelli, Alessandro; Zardin, Barbara; Borghi, Massimo
abstract

The aim of this paper is to investigate the behaviour of an independent metering circuit architectures equipped with electro-hydraulic controlled multi-spools valves. The analysis is performed with reference to the hydraulic circuit and operating conditions usual of the auxiliary utilities of a mid-size power tractors. The increasing interest to reduce pollutant emissions drives the research to alternative solutions for the hydraulic circuit aimed to decrease power dissipation. From this point of view the independent metering architecture is a potentially energy saving system if compared with the traditional single spool valve architecture. This general feeling has however to be proved in the single application field because the amount of energy saved strongly depends on the kind of duty cycle involved in the analysis. For this work, a typical duty cycle for auxiliary utilities has been used, previously obtained through experimental measurement on a tractor equipped with a front loader. The duty cycle adopted involves two linear actuators, working togetherwith different loads and requiring different flows; this general condition cannot be considered favourable from the point of view of the energy saving potential of the new system but it highlights the fact that if there is an amount of energy saved in this condition, the investment need in time and costs is worth. The modelling is based on a lumped parameter approach and the independent metering valves are created developing a distributor block where any single metering element is modelled on the basis of the commercial EHPV Husco. Different control algorithms have been developed in C++ language to test different control strategy,evidencing the amount of energy saved with respect to the traditional architecture.

2012 - MISSION PROFILE FOR AGRICULTURAL TRACTORS: A FOCUS ON HYDRAULIC CIRCUIT [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Belluzzi, Francesco; Lanzoni, Luca
abstract

Mission profile for agricultural vehicles aims to define a picture of a typical working condition of the vehicle. The collection of these pictures gives information about the performance, the efficiency, and the eventual critical conditions with reference to the kind of operation and terrain. Unfortunately, to be at the same time quick, easy to be interpreted and effective, this analysis has to neglect the details and to take into consideration the whole situation. However, detailed considerations about the efficiency of the vehicle subsystems and of their components may derive only from a deeper analysis and it is from these information that designers and technicians can derive improvements of the system. A promising way to solve this discrepancy is to integrate experimental analysis with simulation: from experimental test on field is possible to define several duty cycles representing different working conditions on the vehicle. These data can then be used as input in a simulation model representing the system, able to replicate its dynamic behaviour. Finally, possible modifications of the system architecture or components, aimed at the improvement of the performance or efficiency, may be more easily tested on the virtual model. In this paper this methodology is presented with reference to the hydraulic circuit of an agricultural tractor, in particular the portion related to the managing of the auxiliary utilities, showing the capability to represent in detail the behaviour of the system and to explore the critical performances.

2011 - Analisi di macchine oleodinamiche a pistoni assiali a piatto inclinato [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Specchia, Emiliano; Pintore, Francesco
abstract

Questo articolo vuole presentare il compendio di diverse attività di analisi e modellazione sulle macchine oleodinamiche apistoni assiali a piatto inclinato, in corso di svolgimento presso il Dipartimento di Ingegneria Meccanica e Civile di Modena. Inparticolare si riferisce di un modello a parametri concentrati che è in grado di descrivere il comportamento in termini digrandezze istantanee (pressione nelle camere pompanti, portate, contributi di coppia all’albero e al piatto). Il modello integradiversi aspetti di interesse e rappresenta uno strumento particolarmente utile nella fase di progetto della macchina perché ingrado di mettere in luce, in modo qualitativo ma significativo, l’influenza dei principali parametri geometrici caratteristici,anche al variare delle condizioni di funzionamento; inoltre, il modello si presta allo studio dell’interazione tra la macchina ed ilcircuito in cui essa si trova inserita, indicando quindi strade per possibili ottimizzazioni dedicate all’applicazione specifica. Ilmodello integra anche lo studio del meccanismo di variazione della cilindrata, sottolineando i parametri di maggior influenzasul comportamento dinamico dello stesso. Dove è stato finora possibile, i risultati numerici ottenuti sono confrontati con quelliprovenienti dalla caratterizzazione sperimentale.

2011 - Displacement Control in Variable Displacement Axial Piston Swashplate Type Pumps [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Specchia, Emiliano; Pintore, Francesco; E., Corradini
abstract

This work deals in particular with variable displacement swashplate axial piston pumps which play a relevant role in feeding adjustable power for hydraulic mobile systems. In these machines the displacement changes with the inclination of the swashplate and to ensure a stable displacement setting is necessary to analyze the moments acting on the swashplate: the relevant contributions to this moment are due to the forces exerted by the pistons on the swashplate through the slipper bearings, which mainly depend on operating conditions, valve plate geometry, pistons angular positions, piston-slipper assembly inertia, viscous friction and on the force of the variable displacement actuator. The resistant moment is never equal to zero when speaking of actual machine and rises with delivery pressure up to consistent values which compromise the operation of the variable displacement mechanism. In the case of the machine studied the variable displacement mechanism is manually operated by the user, who has found significant difficulties in the displacement setting in some operating conditions.A lumped parameter model of the machine has been created which allows to determine the pressure transients within the pistons, taking into account the actual geometry of the valve plate and allowing to compute instantaneous and average moments acting on the swashplate. Comparison between the numerical average moment acting on the swashplate and experimental measurements on the machine has been done. At this point the influence of operating and design parameters has been analyzed and in particular it was found that the valve plate design together with the timing of the high and low pressure flow passages strongly influence the resistant moment arising on the swashplate. In particular, few modifications on the flow areas can lead to significant reduction of the resistant moment without compromising the machine operation.

2011 - Soluzioni innovative per la riduzione del consumo energetico di circuiti idraulici per trattrici agricole [Curatela]
Borghi, Massimo; Zardin, Barbara
abstract

I lavori raccolti in questa pubblicazione presentano i principali risultati ottenuti nell’ambito del Progetto di Rilevante Interesse Nazionale “Soluzioni innovative per la riduzione del consumo energetico di circuiti idraulici per trattrici agricole” (PRIN07 cod.2007Y3N8B7, coordinatore Prof. Massimo Borghi, Università di Modena e Reggio Emilia ), parzialmente finanziato dal MIUR, Ministero dell’Università e della Ricerca Scientifica, nell’arco del biennio 2008-2010.Il programma di ricerca ha perseguito l’obiettivo di investigare possibili strade per ottenere un incremento delle prestazioni energetiche dei sistemi idraulici presenti a bordo delle trattrici agricole di media potenza (90-150kW).Alcuni principali sottosistemi che costituiscono l’impianto idraulico di una trattrice agricola sono stati analizzati e modellati nell'intento di determinare un incremento dell'efficienza complessiva del sistema attraverso la riduzione della potenza e l'ottimizzazione del rendimento totale di conversione dell'energia.Particolarmente rilevante è l'approccio di ottimizzazione multi-obiettivo vincolata dato alla generazione dei sottosistemi parziali in vista della loro integrazione nel veicolo, dove la gestione ottimale delle caratteristiche di interfaccia con la sorgente di potenza vengano valutate alla luce della risposta all'interno di un modello virtuale della dinamica del veicolo.

2010 - Energy Comsumption of the Hydraulic Circuit of a Mid-Size Power Tractor [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Mancarella, Francesco; Specchia, Emiliano
abstract

This work focuses on the hydraulic circuit that feeds the remote actuators of a mid-size power agricultural tractor. First of all, the energy consumption of a traditional load sensing architecture, which uses a single electronically controlled spool valve, is analyzed. For this kind of circuit, the position of the spool generally determines, at the same time, pressure drops both at the inlet and at the outlet section. The consequence is that in the majority of the situations both the meter-in and the meter-out configuration is not optimized in terms of energy consumption.An alternative architecture, with an independent metering configuration, based on a pressure based control strategy is analyzed and modelled. Energy consumption comparisons of the two systems are made, using different duty cycles, involving resistant and overrunning loads.

2010 - Energy dissipation of the hydraulic circuit of remote auxiliary utilities of an agricultural tractor [Relazione in Atti di Convegno]
Borghi, Massimo; Mancarella, Francesco; Zardin, Barbara
abstract

The aim of this work is to analyze the energy dissipation related to the hydraulic circuit which controls the remote auxiliary utilities of an agricultural tractor. This circuit is a typical hydraulic load sensing multi actuators system. This kind of system provides a good control strategy but it is characterized by quite high energy dissipation, especially when several actuators are working together under different variable loads. In this paper, the traditional load sensing system is modelled using a lumped parameter approach, and theenergy dissipations are evaluated with reference to an actual duty measured on an agricultural tractor. Then, an alternative and more energy saving circuit architecture is introduced, based on an independent metering concept: in this architecture the single spool auxiliary valve is substituted with two electronically controlled proportional valves. The system has been also equipped with an electronically controlled variable pump; twostrategies to control both the pump and the proportional valves are introduced. The energetic analysis is performed also for the alternative architecture using the same duty cycle, with the aim to identify the advantages, disadvantages and the critical features of this system with respect to the original one. Significant energy saving percentage characterizes the independent metering architecture, which seems to be a promising alternative to the standard hydraulic load sensing system.

2010 - Numerical Analysis Of The Dynamic Behaviour Of Piston Journal Bearing In Axial Piston Pumps And Motors [Relazione in Atti di Convegno]
Specchia, Emiliano; Zardin, Barbara; Borghi, Massimo
abstract

This work presents a numerical analysis of the piston dynamic behaviour in axial piston swash plate type pumps and motors. The numerical method adopted is based on the solution of the piston motion equations which depend on the pressure distribution within the cylinder-piston gap. In order to determine this contribution, the Reynolds equation is applied in the lubricating fluid film between the piston and the cylinder. Besides the piston dynamic behaviour, the model permits to calculate the leakage flow through the gap and the friction forces acting on the piston and cylinder surface.After the presentation of the numerical procedure, the dynamic behaviour of the piston is firstly discussed, highlightingthe stability of the bearing. This work is part of a wider research activity focused on the study of positive displacement machines, with the aim to determine and maximize their global efficiency.

2010 - Remote actuation hydraulic circuit of agricultural tractors: alternative architectures for reducing energy consumption. [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Mancarella, Francesco
abstract

Nell’ambito di questo lavoro si analizza dal punto di vista energetico il circuito idraulico che alimenta le attrezzature ausiliarie di una trattrice agricola di media potenza. A tale scopo la tipica architettura circuitale del sistema, load sensing multi-attuatore, viene modellata in ambiente AMESim® al fine di individuare le criticità del sistema. Successivamente, viene analizzata un’architettura circuitale alternativa, basata sul concetto di metering indipendente e sull’utilizzo di una pompa a cilindrata variabile controllata elettronicamente, che mantiene le funzionalità del sistema standard e riduce allo stesso tempo il dispendio energetico. Il terreno comune per effettuare un confronto energetico fra le architetture è rappresentato da un ciclo di lavoro definito sperimentalmente utilizzando un caricatore frontale connesso ai distributori ausiliari di una trattrice agricola.Tale scelta è dovuta all’esigenza di utilizzare un termine di paragone per le diverse strategie che fosse verosimile e somigliante alle condizioni di lavoro tipiche della trattrice. I risultati raggiunti evidenziano un ampio margine di risparmio energetico caratterizzante l’architettura alternativa che dimostra così di essere promettente; nel seguito dell’attività di ricerca, un’analisi dettagliata del comportamento dinamico della pompa di alimentazione e delle valvole proporzionali che sostituiscono i distributori ausiliari permetterà di verificare la stabilità del sistema e valutare con maggior precisione il risparmio energetico.

2010 - The Critical Speed of Slipper Bearings in Axial Piston Swash Plate Type Pumps and Motors [Relazione in Atti di Convegno]
Borghi, Massimo; Specchia, Emiliano; Zardin, Barbara; E., Corradini
abstract

A stationary model is adopted to determine the criticalcondition for which the slipper moves away from the swashplatein an axial piston machine. The aim of the analysis is to find thecritical speed, i.e. the value of the machine speed for which theslipper moves away from the swashplate; usually this conditionmay determine bad operating behaviour of the machine, althougha retainer plate is used to maintain the slipper sufficiently near tothe swashplate.The influences of the pressure transition in the cylinder, theswashplate angle and the radial clearance between piston andcylinder on the critical speed are depicted. Successively, the roleof the position of the point of application of the resultant forcedue to the slipper-retaining plate contact is analyzed.

2009 - External Gear Pump Volumetric Efficiency: Numerical and Experimental Analysis [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Specchia, Emiliano
abstract

External gear pumps and motors are robust and low cost components and are widely used in industrial and mobile applications; nowadays however, optimal global efficiency represents a more crucial aspect to be considered when designing a hydraulic machine. For this reason, it becomes a primary necessity to investigate the phenomena which determine and affect the hydraulic machine total efficiency.In this work, the volumetric efficiency of external gear pumps is investigated by means of a mathematical model already presented in a previous paper and the results obtained are compared with experimental data.First of all, the mathematical model is briefly presented; then the predicted results are discussed considering the influence of the pump operating conditions. Moreover, the influence on the volumetric efficiency of the behaviour of the hydraulically balanced bearing blocks, and hence of the pump axial balance, is exposed. In particular, it is shown that the tilted position of the bearing blocks and the height of the lateral clearance can greatly affect the volumetric efficiency.The data coming from an experimental investigation carried out on commercial external gear pump units are then presented; both the volumetric and the mechanical efficiency have been measured.The comparison between the experimental data and the numerical results allows discussing the bearing blocks balancing behaviour during pump operation.

2009 - Numerical Analysis of the Dynamic Behaviour of Axial Piston Pumps and Motors Slipper Bearings [Articolo su rivista]
Borghi, Massimo; Specchia, Emiliano; Zardin, Barbara
abstract

This paper reports an analysis of the lubricationmechanism and the dynamic behaviour of axial pistonpumps and motors slipper bearings. A numericalprocedure is used to solve the Reynolds equation,written here with respect to the slipper-swash plate gap,whose height is considered variable in a twodimensional field and with time.The contributions of forces and moments acting on theslipper are illustrated and discussed, then the numericalmethod is presented to solve the Reynolds equation.Taking into consideration the slipper surface that isfacing the swash plate, different geometry profiles areconsidered and the subsequent dynamic behaviour ofthe slipper is investigated; in particular, it is shown that aflat profile cannot always guarantee the bearingcapability of the slipper and the lubrication in the gap iscompromised for some critical operating conditions.Successively, different non-flat profiles of the surface areconsidered and their impact on the slipper bearingdynamic behaviour is investigated in terms of tilt of theslipper α and central clearance height h0. Then, focusingon one of these non-flat profiles, the results arediscussed highlighting the influence of machineoperating conditions. These include rotational speed anda high pressure level and involve introducing a frictioncoefficient in order to evaluate the magnitude of frictionlosses determined by the slipper behaviour. Finally,some considerations are expressed about differencesbetween mode of operation of the pump and the motorrelated to slipper behaviour.

2009 - Numerical analysis of the dynamic behaviour of axial piston pumps and motors slipper bearings [Relazione in Atti di Convegno]
Borghi, M.; Specchia, E.; Zardin, B.
abstract

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. Successively, different non-flat profiles of the surface are considered and their impact on the slipper bearing dynamic behaviour is investigated in terms of tilt of the slipper α and central clearance height h0. Then, focusing on one of these non-flat profiles, the results are discussed highlighting the influence of machine operating conditions. These include rotational speed and a high pressure level and involve introducing a friction coefficient in order to evaluate the magnitude of friction losses determined by the slipper behaviour. Finally, some considerations are expressed about differences between mode of operation of the pump and the motor related to slipper behaviour. Copyright © 2009 SAE International.

2009 - Sviluppi nello studio di pompe e macchine volumetriche ad ingranaggi esterni [Articolo su rivista]
Borghi, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

L'articolo presenta un resoconto delle attività di ricerca, modellazione e simulazione relative alle macchine ad ingranaggi esterni, portate avanti dal gruppo di ricerca di Macchine e Sistemi Energetici presso il Dipartimento di Ingegneria Meccanica dell'Università di Modena e Reggio Emilia

2008 - External Gear Pumps and Motors Bearing Blocks Design: Influence on the Volumetric Efficiency [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

External gear pumps and motors, in their typical commercial design, are equipped with hydraulically balanced bearing blocks, which allow to maintain good volumetric efficiencies also when the pressure drop between the ports is high. The aim of this work is to analyze some geometrical aspects characterizing the bearing blocks design, evaluating their influence on the volumetric efficiency of the machine with the aid of a numerical model properly created. External gear pumps and motors operation behavior is strongly influenced by the volumetric efficiency; this parameter takes into account the leakages of fluid which typically affect the hydraulic machine operation and, together with the mechanical efficiency, determines its total efficiency and, consequently, has a great influence on power loss.

2008 - Modelling and Simulation of External Gear Pumps and Motors [Relazione in Atti di Convegno]
Zardin, Barbara; Borghi, Massimo
abstract

In this paper a lumped parameter model for the numerical simulation of the dynamic behaviour of external gear pumps and motors is presented. The model is developed in AMESim® environment, combining the use of AMESim® libraries of components and a self-made library developed in C++ code. The choice of a single modelling environment allows both the simulation of the machine dynamic behaviour and the analysis of the interaction between the external gear unit itself and the hydraulic circuit in which it is working. Particular attention is devoted in the model in order to consider the eccentric position of the gears inside the casing. Moreover, the relevance of an accurate definitions of the flow leakages involving the inter-teeth volumes, considering also the Couette flow contribution, is highlighted. Finally, a numerical analysis has been carried out by means of the model in order to determine the influence of load and rotational speed on the dynamic behaviour of the machine; results about the pressure ripple, flow rate at the outlet port, pressure transients on the inter-teeth volumes and gears position inside the casing are exposed and commented.

2007 - Tailoring Simplified Models for the Feeding Performances Prediction of CNG PWM Controlled Single Stage Injectors [Relazione in Atti di Convegno]
Borghi, Massimo; Franzoni, Federica; Milani, Massimo
abstract

In this paper, an orifice-based lumped parametermodel has been developed and tailored to predict thefeeding performances of a single stage, inwardlyopening, PWM controlled gas injector for automotiveapplications.In particular, simplifying the description of injectorrelevant sections, and adopting a “semi-perfect”approach to depict the gas properties dependency onpressure and temperature, the sub-sonic effluxthrough the injector metering section is studiedinvolving both an isentropic and a polytropicexpansion.Then, considering dry air as fluid medium, the injectorfeeding characteristics variations with the duty cycle,with the feeding pressure and with temperature arehighlighted.After, an experimental vs. numerical data comparisonextended to the injector whole operational field is usedto tailor the main corrective parameters of thesimplified numerical model: among others, particularattention is devoted to the efflux coefficient variationwith injector operating conditions.Successively, the parameters setting coming from theadoption of dry air is used to perform computationsinvolving other gases, such as the pure methane andthe Groningen gas (chosen as reference gas forCNG).Finally, through a numerical vs. experimentalcomparison about mass flow-rate, the reliability of thesimplified numerical model, and its design usefulnessto predict the injector feeding performances withdifferent gases of automotive interest, is highlighted.

2007 - The Preliminary Design of a Direct Actuation for CNG Pressure Regulator Low-Pressure Stage Control [Relazione in Atti di Convegno]
Franzoni, F.; Milani, M.; Montorsi, L.; Borghi, M.
abstract

This paper focuses on the preliminary design of aproportional solenoid aimed at controlling the lowpressure stage of a two stage pressure regulator forCNG applications.In particular, the dynamic performance of a two stagepressure regulator is firstly studied in the wholeoperational field of a four stroke, four cylinder sparkignition engine, equipped with a simplified lowpressureCommon Rail type collector serving fourPWM actuated single stage injectors.Then, with the aim of developing an electro-magneticdirect actuation, the dynamic performance of thesecond stage needle is adopted to drive the design ofa spires type, cylindrical coil proportional solenoid. Inparticular, both the steady and the transients stepsneeded to complete the preliminary design arehighlighted, and the influence of some relevant designparameters (such as the coil geometry and the air gap)on the actuation characteristics are evidenced.Finally, the proportional solenoid is introduced into astandard electro-magnetic control circuit, and itsdriving capabilities, its dynamic performance and itslimit of applications are determined for different actualoperating conditions of the second stage needle.

2006 - Numerical Characterization of Pipes And Hoses Dynamic Response [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

This paper deals with the study of pipes and hoses dynamic characteristics variation with the fluid-wall equivalent bulkmodulus description, with particular attention devoted to the analysis of the wall thickness, of the mechanical constraintsand of the internal pressure both on the fluid celerity, and on the pipe frequency response. In particular, consideringboth the case of plain stress and of plain strain, the pipe wall compliance and bulk modulus are firstly derived as afunction of the internal pressure and of the wall elastic and geometrical characteristics. Then, the influence of the pipegeometry and of the wall thickness on the pipe wall compliance and bulk modulus are highlighted for some materials ofinterest for industrial, automotive and aerospace applications (steel, aluminium, titanium and wired rubber), and thedependency of the equivalent bulk modulus on these parameters and on fluid physical characteristics is highlighted.Finally, the influence of mechanical constraints, of pipe geometry, of fluid physical properties, of wall material and offluid pressure on the global pipe dynamic response characteristics, and in particular on the fluid celerity, on the Machnumber and on the natural frequency, is evidenced.

2006 - The influence of aeration and cavitation on gear pumps and motors meshing volumes pressures [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

The paper describes the influence of the fluid modeling on cavitation and aeration detection in external gear pumps and motors inter-teeth volumes during the gears meshing process, in order to compare the results coming from the use of different physical models of air release/adsorption and cavitation. A simplified cavitation model is firstly involved, and pressure transients are calculated imposing a pressure cut when the fluid vapor pressure (or the dissolved air partial pressure) is reached. After, assuming an equivalent approach able to involve the vapor phase generation, the cavitation phenomena in the meshing volumes are deepened, and the influence of the fluid modeling enhancement on the cavitating machine behavior is highlighted. Then, the equivalent fluid approach is enhanced introducing the air release, and properly coupling the gaseous phases release/adsorption to the Henry's Law for not instantaneous processes. Finally, the influence of the air release/adsorption time constant on meshing volumes pressure transients are detailed, with particular attention devoted to the modification introduced by the cavitation detailing on the gaseous phase void fraction determination and on the angular extension of the cavitation phenomena detection.

2005 - Influence of Notch Shape and Number of Notches on the Metering Characteristics of Hydraulic Spool Valves [Articolo su rivista]
Borghi, Massimo; Milani, Massimo; R., Paoluzzi
abstract

The paper presents theoretical and experimental results of studies on the influence of shape and number of spool notches on the discharge characteristics (discharge coefficient, velocity coefficient and flow angle) of a hydraulic distributor metering edge. The flow rate vs. pressure drop and the steady state axial flow-force vs. pressure drop diagrams are determined for spools with different configurations of multiple notched metering edges. Various combinations of the shape and number of the notches modulating the metering area of the passage between supply and drain ports were investigated and correlated with flow rate, axial flow force and pressure drop, in order to get estimates of discharge coefficient and flow angle. The procedure is applied to all the data collected during the experimental activity, and shows the behaviour of the flow characteristics in both fully turbulent and transitional region of motion. The influence of notch shape and number on the metering edge flow characteristics is evaluated as well.

2005 - Mechanical Cushion Design Influence on Cylinder Dynamics [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; F., Conrad
abstract

The paper deals with the simulation and theexperimental verification of the dynamic behaviour of alinear actuator equipped with different configurations ofmechanical cushion. A numerical model, developedand tailored to describe the influence of differentmodulation of the discharged flow-rate (and of thecorrespondent discharging orifice design) on thecushioning characteristics variation is firstlyintroduced. Then, with respect to the case of thecylindrical cushioning engagement, both the reliabilityand the limits of the numerical approach arehighlighted through a numerical vs. experimentalcomparison, involving the piston velocity and thecylinder chambers pressure. After, with the aim ofhighlighting the effect of mechanical cushions designon a two effect linear actuator dynamic performances,the characteristics modulation of four alternativecushioning systems are determined and deeplyanalyzed. Finally, a sensitivity analysis about theinfluence of the variation of the main geometricalparameters is introduced and, thanks to theintroduction of some dimensional and non-dimensionalparameters of engineering interest, some usefulguidelines in selecting the most effective cushionshape are highlighted.

2005 - Pressure Transients in External Gear Pumps and Motors Meshing Volumes [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

In this paper a lumped parameters numerical model isreviewed to study the meshing process of external gearpumps and motors, with the aim of highlighting theinfluence of some geometrical design parameters andoperating conditions on inter-teeth volumes pressures.The inter-teeth space is modeled adopting a two-volumeapproach, properly tailored both for the pump and for themotor units behavior description. In both cases, thecommunications between the interconnected inter-teethvolumes and the high and low pressure ports aresketched as variable equivalent turbulent restrictors; flowareas have been determined as functions of the gearsand of the meshing grooves main design parameters.The inter-teeth pressures, and the leakage flows, arecalculated solving the incompressible and isothermalcontinuity equation, contemporarily applied to bothvolumes and properly combined with the classicalturbulent orifice equation. Successively, for a referenceoperating condition, properly chosen for underlining theinter-teeth meshing cycle and corresponding to a verylow pressure load, the meshing processes of an externalgear pump and of an external gear motor are compared.Among others, the attention is focused on the behaviorof those hydraulic variables more conditioning themeshing cycle, and the differences rising up in interteethpressure peaks and in cavitation interval amplitudeand angular positioning are evidenced. Then, themeshing process analysis is expanded to cover theexternal gear units common operating field, both interms of rotational speed (from 500 to 3000 rpm) and interms of the high pressure port value (from 10 to 250bar). In all cases, the general trend shows that cavitationhas a deeper influence on external gear pumpsoperation, while external gear motors are subjected tomore significant pressure peaks, particularly markedduring the low pressure part of the meshing cycle.Attention is also focused on the influence of gears interaxialdistance and axial width on the meshing processcharacteristics, in order to assess how the volumedimensions could differently affect pressure peaks andcavitation phenomena in pumps and motors.Finally, the role of the balancing plates grooves inconditioning pressure peaks and cavitation is highlightedand, with particular care devoted to external gearmotors, some useful guidelines for their design areoutlined.

2005 - Studying the Axial Balance of External Gear Pumps [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

In this paper some design aspects related to externalgear pumps balancing surfaces are studied, and someuseful guidelines for designing bearing blocksbalancing surfaces are suggested. In order to studybearing blocks axial balance, a numerical procedurefor the determination of the pressure distribution insidethe clearance bounded by gears sides and bearingblocks internal surfaces is firstly presented andapplied. After, the influence of bearing blocksgeometry and pump operating conditions on thewidening thrust is highlighted, considering bothconstant and variable lateral clearance heights. Then,the computations are performed to evaluate thewidening thrust variation as a function of bearingblocks relative tilt with respect to gears lateral sides,and both positive and negative bearing blocks tilts areevidenced and discussed. Finally, the numericalprocedure is validated through a comprehensivecomparison of its results with experimental data(coming from some bibliographic sources), and someuseful guidelines in designing external gear pumpsbalancing surfaces are defined.

2005 - Studying the Efficiency of a Compact Excavator Primary Workgroup Hydraulic Control System [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

This paper studies the proportional directional controlvalves design influence on the energetic behavior of amid-power compact excavator.In particular, with reference to the hydraulic circuitactuating the primary workgroup, in the paper thehydraulic power metering performed with the boomcylinder proportional control valve is studied, and somedesign solution useful in reducing both the hydraulicpower dissipation, and the power absorption from themachinery prime mover are highlighted.The analysis, experimentally performed for differentoperating conditions, is carried out highlighting theinfluence of a metering configuration both on the supplypressure modulation and on the flow-rate supplied tothe actuator.The hydraulic power metering and the boom actuationhydraulic efficiency are defined for two alternativeproportional control valve metering configurations and,within the limits implicitly implied on the actuation circuitarchitecture, a possible design solution in determiningthe improvement of the boom actuation systemperformances is investigated.

2005 - The Influence of the Notch Shape and Number on Proportional Directional Control Valve Metering Characteristics [Articolo su rivista]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio
abstract

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.After, a quantitative analysis of the metering characteristics is introduced, with the aim of determining the influence of the metering configuration, of the spool position and of the operating conditions on the efflux characteristics (the discharge coefficient and the jet angle).

2004 - About the Prediction of Pressure Variation in the Inter-Teeth Volumes of External Gear Pumps [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

The paper deals with the analysis of the inter-teeth pressure transients during gears meshing cycle of external gear pumps. A lumped parameter model, tailored for the prediction of pressures in the meshing zone, is firstly presented. The numerical model, based on the integration of the continuity equation, is applied to the inter-teeth volumes, communicating with the neighbouring ambient through geometry dependent orifices. A comparison between numerical results, obtained considering both constant and variable discharge coefficients, is illustrated. Successively, the dependency of pressure transients on gear pump operating conditions, mainly in terms of delivery pressure and rotational speed, is investigated. The effect of some geometric parameters is also discussed, mainly considering different gears widths and interaxial distances, and high-pressure recess positioning. Finally, in order to highlight the influence of the cavitation modelling on low pressure transition, the results coming from the application of two simplified approaches are shown and compared.

2004 - Optimization of the Intake System on Diesel Engines Featuring a High Pressure Injection System [Capitolo/Saggio]
Borghi, Massimo; Cantore, Giuseppe; Mattarelli, Enrico; Milani, Massimo; Fontanesi, Stefano; Montorsi, Luca; D., Balestrazzi
abstract

Combustion in Diesel engines is controlled by the interaction between fuel jet and mean and turbulent flow field. Therefore, the use of novel fuel injection strategies should be always integrated with the optimisation of the mean and turbulent flow field within the cylinder. While in the last years injection system technology has evolved at an impressive rate, establishing new standards, the development of design criteria for intake ports, ducts and plenums is not keeping the same pace. The authors believe that a substantial work should be carried out in this field. For this purpose numerical simulation should play a fundamental role to cut development time, as well as to gain a better understanding of the complex thermo-fluid-dynamics phenomena occurring within the engines.This paper reviews the fundamentals of the experimental and theoretical work carried out at DIMEC-University of Modena and Reggio for supporting the development of more efficient HSDI Diesel engines.

2004 - Stydying the Flow Field Inside Lateral Clearances of External Gear Pumps [Relazione in Atti di Convegno]
Paltrinieri, Fabrizio; Borghi, Massimo; Milani, Massimo
abstract

In this paper the flow field in the clearances bounded by gears lateral sides and bearing blocks internal surfaces of external gear pumps is studied. Firstly, the pressure distribution is determined applying the Laplace equation to the domain limited by two successive teeth profiles, the middle lines of the first and of the last space and the drain circle, and the main leakage paths inside the clearance are evaluated. Then, the leakage flows between the spaces, and between each space and the drain ambient, are calculated considering different boundary conditions and teeth shapes, and the streamlines are highlighted in order to evidence the main leakage paths. The information gathered through this flow field analysis are used to define equivalent conductance for leakage paths, useful to be adopted in simple lumped parameters models, usually applied with the aim to determine the pressure distribution inside pump casing or, for example, gear pumps volumetric efficiency.

2004 - The Effect of Flow Forces Compensating Profile on the Metering Characteristics of a Conical Seat Valve [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio
abstract

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.

2004 - The Influence of the Notch Shape and Number on Proportional Directional Control Valve Metering Characteristics [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio
abstract

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 asymmetrical 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. After, a quantitative analysis of the metering characteristics is introduced, with the aim of determining the influence of the metering configuration, of the spool position and of the operating conditions on the efflux characteristics (the discharge coefficient and the jet angle).

2004 - The influence of Swirl Control Strategies on the Intake Flow in Four Valve HSDI Diesel Engines [Relazione in Atti di Convegno]
Mattarelli, Enrico; Borghi, Massimo; D., Balestrazzi; Fontanesi, Stefano
abstract

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 computer 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 (fist 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.While the steady flow tests (both numerical and experimental) indicate that the first and the third strategy massively enhance the swirl intensity in comparison to the baseline (+75 %, according to experiments), intake stroke calculations show an almost null advantage. Furthermore, the actual in-cylinder flow field presents complex patterns that cannot be described in terms of Swirl Ratio.

2003 - A Conservative High Resolution Scheme for the Study of Gases and Liquids Homentropic Flows [Relazione in Atti di Convegno]
Borghi, Massimo; C., Bussi; Milani, Massimo; Paltrinieri, Fabrizio
abstract

In this paper a high-resolution explicit integration scheme is introduced and adopted to study the one-dimensional homentropic flow of a generic fluid, applicable to gaseous and liquid phase. The generally valid governing equations for one-dimensional homentropic flows are firstly introduced and, without forcing any assumption in relation to the nature of the fluid, an investigation of mathematical properties of the system of equations is given in order to derive the characteristic matrix and the system eigenvalue. Then, the Maxwell differential formulation of the fluid constitutive equations is introduced, with the purpose of providing a general state equation which retains its validity for both gases and liquids, and with the aim of expressing and explicitly calculating pressure, pressure derivative with respect to density and sound speed as functions of fluid bulk modulus. Starting from the differential formulation of the state equation, a high-resolution explicit integration scheme, based on conservative formulation of the governing equations for fluid flows, is then introduced and discussed. Finally, the well-known shock tube test is employed to study both liquid and gaseous flows, and the forthcoming numerical vs. analytical results comparison is used to assess the accuracy and the stability of the integration scheme.

2003 - A Numerical Approach to the Hydraulic Fluid Properties Prediction [Relazione in Atti di Convegno]
Borghi, Massimo; Bussi, Carlo; Milani, Massimo; Paltrinieri, Fabrizio
abstract

This paper presents a numerica! approach tailored for the prediction ofhydraulic fluids physical and thennodynarnic properties, starting from a limited number of information about fluid viscosity and fluid density. Firstly, the review of some experimental based prediction models available in literature for the fluid viscosity variations is presented, and the more accurate ones for the analysis ofindustrial and automotive hydraulic fluids (mineral oils, lubricants and fuels) are selected. Then, the paper highlights the step of a possible procedure able to defme thevariations both of other physical fluid praperties (such as the isothermal or the isentropic bulk modulus, the constant pressure or the constant volume specific heat, the constant pressure, orthe constant volume, volume expansion coefficient), and of the main thermodynamic fluid properties (such as the specific entropy, the specific enthalpy and the specific internal energy).Finally, the resu1ts coming from the numerical approach previously outlined are compared with experimental data, found in literature for different mineral oils, in a range of temperature from O to 160°C and of pressure from O to 600 bar.

2003 - Studio del Campo di Moto nei Meati Laterali di Macchine Volumetriche ad Ingranaggi Esterni [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio
abstract

Viene presentato lo studio del campo di moto nel meato, supposto ad altezza costante, esistente tra i fianchi delle ruote dentate e le superfici delle fiancate di bilanciamento di macchine volumetriche ad ingranaggi esterni. A partire dalla determinazione della distribuzione di pressione nel meato vengono determinati, al variare della geometria e delle condizioni al contorno, le portate e le linee di corrente. La valutazione delle portate scambiate dal generico vano con i vani contigui e con l’ambiente di drenaggio viene poi utilizzata per mettere a punto un modello di meato a parametri concentrati che si mostra essere più accurato di quello utilizzato in precedenti lavori per il calcolo della distribuzione di pressione nei vani tra i denti affinando la determinazione delle conduttanze caratteristiche degli strozzatori in esso considerati. I risultati, relativi a diverse geometrie di ruote dentate di corrente impiego, vengono poi confrontati tra loro al fine di evidenziare l’influenza dei parametri geometrici caratteristici delle dentature sulla distribuzione di pressione nel meato, sulla ripartizione delle principali portate di fuga e sulle dimensioni caratteristiche degli strozzatori equivalenti considerati nei modelli a parametri concentrati. I risultati ottenuti mostrano altresì come il modello proposto risulti adeguato per le geometrie di dentatura considerate e pare particolarmente promettente per essere utilizzato nella previsione e calcolo del rendimento volumetrico.

2003 - Un modello numerico per l’analisi termodinamica di motori Stirling–Beale [Relazione in Atti di Convegno]
Borghi, Massimo; M., Bonnici; Cavazzuti, Marco; Barozzi, Giovanni Sebastiano
abstract

Si presenta un modello simulativo applicabile ai motori lineari a pistoni liberi a ciclo Stirling, secondo lo schema proposto da Beale. Il modello si basa sulla discretizzazione temporale delle equazioni del moto dei pistoni e delle equazioni di bilancio di massa e di energia per il volume di lavoro della macchina. Il modello è destinato all’esecuzione di analisi di stabilità e di efficienza di soluzioni progettuali alternative, in sede di dimensionamento dei dispositivi

2002 - Analysis of a F1 Car Hydraulic Circuit Dynamic Behaviour [Articolo su rivista]
Borghi, Massimo; Milani, Massimo; M., Piraccini; M., Flandoli
abstract

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 versus 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.Finally, the paper reports the analysis of those hydraulic variables not controlled by the on-board diagnostic, with the aim to analyze the behavior of the power unit and of the pipes when submitted to the sudden hydraulic power request correspondent to a gear shift.

2002 - CFD Analysis of the In-Cylinder Flow in DI Diesel Engines [Capitolo/Saggio]
Borghi, Massimo; Cantore, Giuseppe; Mattarelli, Enrico; Milani, Massimo; Fontanesi, Stefano; Montorsi, Luca
abstract

Non disponibile

2002 - Modelling and Simulating Hydraulically Balanced External Gear Pumps [Relazione in Atti di Convegno]
Borghi, Massimo; Paltrinieri, Fabrizio; Milani, Massimo
abstract

The paper presents some developments of a research activity regarding hydraulically balanced external gear pumps.Numerical models are introduced in order to study gears radial equilibrium and axial bearing blocks balance. A numericalapproach useful for determining the eccentric positions assumed by gears inside the pump casing and to assess the radialthrusts acting on gears is proposed. The effect of the running in process on the casing internal surface and on the pressure distribution in sealed spaces between teeth is also shown and discussed. At the end a numerical model useful in designing bearing blocks balancing surfaces is outlined. Comparisons of numerical and experimental results seem to encourage the development of the study.

2001 - Analisi funzionale di un elettro-iniettore per sistema di iniezione common-rail [Relazione in Atti di Convegno]
D., Baccolini; Borghi, Massimo; Milani, Massimo; S., Falfari; A., Mazza
abstract

In questo lavoro vengono presentati alcuni dei risultati ottenuti durante lo studio del comportamento dinamico di un elettro-iniettore per applicazioni Common Rail, facente parte del sistema di iniezione presente a bordo di un motore Diesel 4 cilindri di elevata potenza specifica. Nella sua prima parte, il lavoro presenta il modello numerico adottato per lo studio del comportamento dinamico di un elettro-iniettore di corrente impiego industriale (BOSCH), realizzato utilizzando un codice di calcolo specificatamente sviluppato per lo studio di sistemi idraulici sottoposti a veloci transitori di comando.Successivamente, vengono proposti i risultati ottenuti applicando allo stadio di comando elettroidraulico dell'iniettore alcune delle strategie di comando e controllo disponibili nella mappatura standard della centralina elettronica presente a motore. L'analisi dell'influenza del ciclo di comando sulle caratteristiche di funzionamento dell'elettro-iniettore viene, eseguita con riferimento al comportamento temporale di alcune delle variabili di maggior interesse progettuale, quali gli spostamenti dell'ancora dello stadio di comando e dello spillo di iniezione, la pressione nella camera di controllo e nelpozzetto di iniezione, la portata ela massa iniettate per ciclo.Questa prima parte dello studio viene conclusa da una verifica numerico/sperimentale della massa iniettata per ciclo al variare del regime di rotazione e della pressione media nel rail,con lo scopo di determinare l' affidabilità, la ripetibilità ed i limiti del modello numerico adottato.La generale attendibilità delle previsioni numeriche, soprattutto in termini di massa iniettata per ciclo, permette di utilizzare le informazioni precedentemente introdotte per .determinare le caratteristiche di efflusso del combustibile dai fori di iniezione, quali ad esempio il coefficiente di efflusso, la velocità media del fluido e l'area effettiva nella sezione di uscita dall'iniettore. Nel lavoro vengono presentati e discussi i risultati ottenibili applicando tre modelli di efflusso disponibili in bibliografia.La seconda parte del lavoro è dedicata alla verifica del funzionamento dell'elettro-iniettore una volta inserito nel sistema di iniezione di un motore 4·cilindri. il modello numerico-precedentemente adottato per lo studio del comportamento dell'elettro-iniettore viene inserito in un modello sviluppato persimulare I'intero sistema di iniezione di un motore ad accensione spontanea soggetto a condizioni di funzionamento "reali", coinvolgente sia il ciclo di comando applicato alla valvola di regolazione della pressione nel Rail (presente sulla linea di mandata della pompa di iniezione di alta pressione), siaun'opportuna fasatura dei comandi imposti ai quattro elettro-iniettori coinvolti. Il funzionamento del sistema di iniezione viene poi analizzato con 'lo_scopo di evidenziare come, all'intemodi un ciclo di iniezione, il duty cycle imposto dalla entralina elettronica alla valvola di regolazìone della pressione 'nel rail possa, imporre ai quattro iniettori un comportamento differente, e come la poitatae la massa iniettate per ciclo risultino variabili da iniettore ad iniettore.

2001 - Analysis of a f1 car hydraulic circuit dynamic behavior [Relazione in Atti di Convegno]
Borghi, M.; Milani, M.; Piraccini, M.; Flandoli, M.
abstract

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. Finally, the paper reports the analysis of those hydraulic variables not controlled by the on board diagnostic, with the aim to analyze the behavior of the power unit and of the pipes when submitted to the sudden hydraulic power request correspondent to a gear shift. Copyright © 2001 Society of Automotive Engineers, Inc.

2001 - Dynamic Analysis of Diesel Engine Common Rail Injection System. Part I: Injector Dynamics [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Piraccini, Matteo
abstract

The aim of the paper is to analyze the dynamic behavior of an actual electro-hydraulic injector, included into a high-pressure accumulator injection system (Common Rail).Firstly, a brief introduction of the hypotheses adopted for a lumped parameter description of each part of an industrial version of the injector (BOSCH) is outlined, together with the definition of the hypotheses assumed to treat the fuel efflux through the injection holes, through the internal mechanical couplings and the damping orifices, or to descript of the cavitations.Then, the dynamic behavior of the injector is analyzed adopting some of the command signals imposed to the pilot stage by the Electronic Central Unit (ECU), as actually implemented into the standard map of an on board ECU of a industrial diesel engine. Among others, the paper presents the results coming from the injector handling for medium values of the crank-shaft regime (1800 and 2400 rpm), for different pressure levels in the Rail and involving also the pilot injection.The reliability of the numerical results is stated through a wide numerical vs. experimental comparison, made up on the basis of the fuel mass injected for each cycle.Finally, the discharge characteristics characterizing the injection are determined, such as the effective mean velocity and the effective area of the liquid core at the holes exit, or injection holes discharge coefficient.

2001 - Dynamic Analysis of Diesel Engine Common Rail Injection System. Part II: Four-Cylinder Injection System [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Piraccini, Matteo
abstract

The paper is aimed at studying the overall dynamic behavior of the Common Rail Injection System actually used on a 4 cylinder industrial Diesel engine.Firstly, the paper introduces the main characteristics of a lumped and distributed parameters model of the high pressure branch of an actual Common Rail System, and the main hypotheses assumed to model it using a multi-port approach code for the analysis of the dynamic response of hydraulic systems submitted to fast transients.The model of the Common Rail System is then used to study its dynamic behavior when involved in the handling of the engine injection cycle for medium values of the crankshaft regime and for different pressure levels in the Rail. The analysis is performed applying to the injectors, to the pressure control valve and to the high-pressure pump the control strategies imposed by the Electronic Central Unit (ECU), as actually implemented into an industrial ECU for Diesel engine management.The model reliability and accuracy are evidenced through a numerical vs. experimental data comparison, mainly in term of rail pressure dynamic behavior.The analysis successively outlined in the paper allows to state how the hydraulic behavior of the Common Rail System interact with the electro-hydraulic injectors dynamics, and to determine the influence of this interaction on the total injected mass per cycle.

2001 - Dynamic analysis of diesel engine common rail injection system. Part I: Injector dynamics [Relazione in Atti di Convegno]
Borghi, M.; Milani, M.; Piraccini, M.
abstract

The aim of the paper is to analyze the dynamic behavior of an actual electro-hydraulic injector, included into a high-pressure accumulator injection system (Common Rail). Firstly, a brief introduction of the hypotheses adopted for a lumped parameter description of each part of an industrial version of the injector (BOSCH) is outlined, together with the definition of the hypotheses assumed to treat the fuel efflux through the injection holes, through the internal mechanical couplings and the damping orifices, or to descript of the cavitations. Then, the dynamic behavior of the injector is analyzed adopting some of the command signals imposed to the pilot stage by the Electronic Central Unit (ECU), as actually implemented into the standard map of an on board ECU of a industrial diesel engine. Among others, the paper presents the results coming from the injector handling for medium values of the crank-shaft regime (1800 and 2400 rpm), for different pressure levels in the Rail and involving also the pilot injection. The reliability of the numerical results is stated through a wide numerical vs. experimental comparison, made up on the basis of the fuel mass injected for each cycle. Finally, the discharge characteristics characterizing the injection are determined, such as the effective mean velocity and the effective area of the liquid core at the holes exit, or injection holes discharge coefficient.

2001 - Dynamic analysis of diesel engine common rail injection system. Part II: Four-cylinder injection system [Relazione in Atti di Convegno]
Borghi, M.; Milani, M.; Piraccini, M.
abstract

The paper is aimed at studying the overall dynamic behavior of the Common Rail Injection System actually used on a 4 cylinder industrial Diesel engine.Firstly, the paper introduces the main characteristics of a lumped and distributed parameters model of the high pressure branch of an actual Common Rail System, and the main hypotheses assumed to model it using a multi-port approach code for the analysis of the dynamic response of hydraulic systems submitted to fast transients.The model of the Common Rail System is then used to study its dynamic behavior when involved in the handling of the engine injection cycle for medium values of the crankshaft regime and for different pressure levels in the Rail. The analysis is performed applying to the injectors, to the pressure control valve and to the high-pressure pump the control strategies imposed by the Electronic Central Unit (ECU), as actually implemented into an industrial ECU for Diesel engine management.The model reliability and accuracy are evidenced through a numerical vs. experimental data comparison, mainly in term of rail pressure dynamic behavior.The analysis successively outlined in the paper allows to state how the hydraulic behavior of the Common Rail System interact with the electro-hydraulic injectors dynamics, and to determine the influence of this interaction on the total injected mass per cycle.

2001 - Hydraulic Locking In Spool-Type Valves. Tapered Clearances Analysis [Articolo su rivista]
Borghi, Massimo
abstract

The paper deals with the analysis on the influence of geometrical characteristics on the locking force acting on spools in tapered clearances exposed to decentralizing pressure drops. An estimation is presented of the different results in locking force prediction deriving from the comparison of the "classical" one-dimensional approach of flow and a more complex description represented by the Reynolds equation. A sensitivity analysis on the influence of clearance geometrical parameters is performed, showing the limits of application of the one-dimensional approach. Two non-dimensional geometric variables are identified, which can be adopted to define some polynomial corrective functions correlating one-dimensional results with more reliable two-dimensional solutions. The determination of the locking force can therefore be performed by an analytical process, involving the "classical" one-dimensional solution and a polynomial correction which is a simple two-variable function of the clearance geometry. In comparison with results coming from the direct solution of the Reynolds equation, the process leads to errors confined within the range of a few per cent, considering clearances in a wide dimensional range representing a large amount of couplings actually encountered in hydraulic spool valves.

2001 - Influenza del Rodaggio sulle Condizioni di Funzionamento di Macchine Volumetriche ad Ingranaggi Esterni [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; M., Guidetti
abstract

Si illustrano gli ultimi sviluppi di un modello, descritto in (Bonacini e Borghi, 1990) ed in (Borghi et al., 1997), per il calcolo dell’andamento della pressione nei vani compresi tra due denti consecutivi, le fiancate ed il corpo di macchine volumetriche ad ingranaggi esterni. Nella prima parte del lavoro viene presentato un modello per la determinazione della posizione assunta dalle ruote, durante il funzionamento, all’interno del corpo della macchina. In particolare, la posizione di lavoro delle ruote è determinata valutando separatamente due contributi: il primo dovuto al recupero del gioco esistente tra le fiancate ed il corpo; il secondo legato alla capacità di sostentamento del carico della coppia rotoidale lubrificata costituita dall’albero della ruota e dalle boccole alloggiate nelle fiancate. In questo modo è possibile evidenziare, da un lato le condizioni di funzionamento che portano le ruote ad interferire con la superficie interna del corpo, dall’altro l’entità dell’asportazione di materiale dal corpo stesso. I profili della superficie interna del corpo così ottenibili vengono poi confrontati, per macchine operatrici di corrente produzione industriale di diverse caratteristiche geometriche, con i corrispondenti rilevati al termine di processi di rodaggio appositamente predisposti. I confronti effettuati mostrano la sostanziale validità del modello presentato, la sua generale attendibilità e l’applicabilità industriale.

2001 - Integration of 3D-CFD and Engine Cycle Simulations: Application to An Intake Plenum [Relazione in Atti di Convegno]
Borghi, Massimo; Mattarelli, Enrico; Montorsi, Luca
abstract

The purpose of this paper is to compare defferent 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 bbench support the theoretical study.The most promisig simulation technique presented in the paper is the integrated 1D and 3D-CFDsimulation. This numerical approach showed itself to be particularly suitable for analysing complex engine components where the flow patterns are fully transient.

2001 - Reliability of fluid cavitation analysis by means of an equivalent fluid characteristics modelling [Relazione in Atti di Convegno]
Borghi, Massimo; C., Bussi; Milani, Massimo; R., Paoluzzi
abstract

The modelling of two-phase flows, and in particular the modelling of cavitating flows, represents a remarkable field of interest for fluid power machines and components analysis. Even if the cavitation is a phenomenon physically well known and experimentally well detectable, it is very difficult to introduce its development and effects into numerical models built up for machines and components behaviour analysis. The aim of this paper is to analyse the alternate approach to the two-phase flow description, based on the definition of an “equivalent fluid”, having physical-chemical characteristics defined by a proper combination of a given mixture of different fluids (liquid-gas included). In deeper detail, the correctness of an “equivalent fluid” approach, which is made with the aim to reduce the number of differential equations to be solved in presence of two-phase flows, has to be thoroughly investigated. This is achieved by the simulation of an adiabatic cylinder filled with a water-air mixture, which expand isentropically from atmospheric pressure towards the vapour tension. This simple test case is investigated applying both the “equivalent fluid” model and a homogeneous pressure zero-dimensional two-zone model, which is solved by direct integration. The final scope of the paper is to determine to which extent the “equivalent fluid” approach is able to reproduce the actual behaviour of a cavitating flow, with particular attention paid to the correct representation of heat transfer phenomena. Some of the examples are referred to water, but no major limitation exists to the application of the approach to mineral oil.

2000 - Analisi del comportamento dinamico del circuito idraulico di selezione marcia di una vettura di Formula 1 [Relazione in Atti di Convegno]
Cantore, Giuseppe; Borghi, Massimo; Piraccini, M.; Baccolini, D.; Flandoli, M.
abstract

n.d.

2000 - Computational Fluid Dynamics in Solid Particle Estimation in Hydraulic Poppet Valves [Articolo su rivista]
Borghi, Massimo; Milani, Massimo; R., Paoluzzi
abstract

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, axisymmetric 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 sizes.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.

2000 - Flow-Forces Effect on the Behavior of an Open Center Hydraulic Distributor [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; E., Sedoni
abstract

The effect of steady-state axial flow-forces on the motion of an open center hydraulic distributor notched spool is considered. More in details, the spring driven spool centering is considered, in which undesired axial flow-forces could overcome the spring action. A steady-state analysis of the forces influencing the spool motion is reported, calculating the axial flow-force for different positions of the spool. Different notched shapes of the metering edge are considered, and an optimized solution for the notched edge of the spool is proposed at last.

2000 - Flow-forces effect on the behavior of an open center hydraulic distributor [Relazione in Atti di Convegno]
Borghi, M.; Milani, M.; Sedoni, E.
abstract

The effect of steady-state axial flow-forces on the motion of an open center hydraulic distributor notched spool is considered. More in details, the spring driven spool centering is considered, in which undesired axial flow-forces could overcome the spring action. A steady-state analysis of the forces influencing the spool motion is reported, calculating the axial flow-force for different positions of the spool. Different notched shapes of the metering edge are considered, and an optimized solution for the notched edge of the spool is proposed at last.

2000 - Stationary Axial Flow Forces Analysis on Compensated Spool Valves [Articolo su rivista]
Borghi, Massimo; Milani, Massimo; R., Paoluzzi
abstract

The paper deals with the application of a simplified numerical analysis, based on Computational Fluid Dynamics (CFD), of the flow field inside the compensated port connections of a reference spool valve. The aim of the study was the evaluation of the proposed analysis procedure, to put in evidence the major effects related to the presence of steady state flow forces affecting the spool equilibrium. Starting from an initial summary of the dimensional analysis proposed by the authors to approach the application of CFD to hydraulic components, the paper presents the results of three commonly used compensating profiles for two reference spool positions. In order to validate the simulation, the curves obtained for one of the three geometries are compared with the experimental data obtained on an equivalent port connection of a commercial distributor.

1999 - CFD as a Design Tool for Fluid Power Components [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; R., Paoluzzi
abstract

The paper collects some examples of CFD application to hydraulic components design, aimed at showing how a complex tool can be used both for the internal flow characterisation and the macroscopic analysis of component behaviour.In its first part, the paper deals with the steady-state characterisation of a commercial 4/3 on Zoff distributor, and focuses the attention on CFD strategies used in order to obtain an accurate description of steady-state axial flow-forces, acting on the spool of the component. The solution of simplified models (axis-symmetric) and the development of an extended and novel non-dimensionalization technique are the key to the use of a limited number of distributor configurations and a minimum number of operational conditions to obtain a full characterisation of the component.The second part of the paper is devoted to hydraulic locking analysis, where CFD is applied to tapered 3D geometry in order to validate the results of specific design assumptions and to verify the results obtained by a simplified, though two-dimensional, approach to radial forces estimation in spool valves. As a final example, the last part of the paper is dedicated to particle tracking analysis and collisioni erosion prediction, using a simplified approach based on the hypothesis of uncoupled motion of fluid and particles. In this last case, the CFD computed flow field, is used in arder to allow the solution of the lagrangian equations of motion for solid particles dragged by the fluid according to a given law. The aim of the examples collected is not the solution of the problems dealt with (to this purpose the reader is referred to the bibliography), but rather the identification of areas and methods where the application of a complex and expensive design toollike CFD analysis can reach the breakeven point of a convenient application in the design phase of a hydrauliccomponent.

1999 - Computational Fluid Dynamics in Solid Particles Effect Estimation in Hydraulic Poppet Valves [Relazione in Atti di Convegno]
R., Paoluzzi; Borghi, Massimo; Milani, Massimo
abstract

This paper deals with the analysis of the interaction between solid contamination and internai 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.

1999 - Erosion Estimation in a Pressure Relief Valve by Means of Particles Tracking Analysis [Relazione in Atti di Convegno]
Borghi, Massimo; R., Paoluzzi; Milani, Massimo
abstract

One of the effects of solid contaminant in hydraulic circuits is the erosion of internal parts. This is particularly important when the eroded parts are in the metering edge of valves, because this modifies the area function with unpredictable effects not only on efficiency, but also on functionality of the entire system.The aim of this paper is to investigate a possible alternative to long time-lasting and expensive experiments on erosion, using a lagrangian approach to particle tracking in a flow field whose variables are known. Two gaussian distributions of particles with mass are tracked for two metering edge openings, and are qualitatively compared with the results of an experimental investigation.The final part of the paper describes a first tentative approach to the use of data to estimate the amount of material eroded by impacting particles, presenting some details on flow velocity and angle in different sections of the valve related to data on the yeld characteristic of the impact. The last part is mainly qualitative, and only referable to massless particles. It is however a necessary preliminary step toward the solution of the complete problem, presently under development.

1999 - Le forze Radiali in Valvole a Cassetto [Articolo su rivista]
Borghi, Massimo; Cantore, Giuseppe; Milani, Massimo; R., Paoluzzi
abstract

A partire dal calcolo della spinta radiale agente sulle porzioni di cursore in ricoprimento, la memoria illustra le linee guida principali per un corretto dimensionamento e posizionamento delle scanalature circonferenziali di bilanciamento.

1999 - Pompe a Palette: Sperimentazione e Calcolo [Articolo su rivista]
Borghi, Massimo; Milani, Massimo; A., Valentini
abstract

L'articolo presenta i principali risultati ottenuti, con l'ausilio di modelli numerici a parametri concentrati, nell'ottimizzazione funzionale di macchine volumetriche operatrici a palette, sia a cilindrata fissa che variabile.

1999 - Pompe a Pistoni Assiali a Cilindrata Variabile: Verifica Sperimentale del Rendimento [Articolo su rivista]
Borghi, Massimo; Milani, Massimo; A., Valentini; M., Guidetti
abstract

La memoria illustra i principali risultati ottenuti durante la caratterizzazione sperimentale di macchine volumetriche operatrici a cilindrata variabile, del tipo a pistoni a piastra inclinata (swash plate), dotate di sistemi di regolazione della cilindrata idraulici ed elettro-idraulici.

1999 - Pompe a Pistoni Assiali a Cilindrata Variabile: il Rendimento Volumetrico [Articolo su rivista]
Borghi, Massimo; Milani, Massimo; A., Valentini
abstract

La memoria illustra le potenzialità applicative di strumenti di progettaione assistita da calcolatore a parametri concnetrati nel campo del dimensionamento e dell'ottimizzazione funzionale di pompe a pistoni assiali a piastra inclinata.

1999 - Stationary and Dynamic Analysis of a Water Relief Valve [Relazione in Atti di Convegno]
R., Paoluzzi; Borghi, Massimo; Milani, Massimo
abstract

The use of water as a working fluid in hydraulic circuits is being receiving an increasing attention by both manufacturers and users, due to its environmental characteristics. Although the use of water is neither new nor innovative (more than one hundred years ago it was widely used to transfer power, and many pump and valve manufacturers have commerciai product Iines for water hydraulics) its introduction in the product line of a manufacturers brings many problems to the attention of the designers, from technology adaptation to material compatibility, from erosion to cavitation.The purpose of this paper, based on a joint activity by Cemoter, University of Modena, Aron SpA and Cermet, is to show how the use of a combined approach to valve analysis can provide useful information to shorten the time to market of a valve using tap water as working fluido Starting from an initial reminder of the basic differences between mineraI oil and water in hydraulic circuits, the paper shows the results of some CFD computations on a relief valve, to evaluate the qualitative form of the pressure and velocity field, and to assess the influence of the increased turbulence on the field of motion.In the final part, the results of a comprehensive experimental characterization of the component are presented and considered in view of the indication provided by CFD analysis, both in term of steady state characteristic curves, and dynamic response.

1999 - Variable Displacement Axial Piston Pump Volumetric Efficiency Analysis [Relazione in Atti di Convegno]
Cantore, Giuseppe; Borghi, Massimo; Milani, Massimo
abstract

This paper describes a study of the volumetric efficiency of a variable displacement axial piston pump. A theoretical model, based on the continuity equation and properly combined with a simplified analytical treatment of leakage flows, is first presented and used to characterise the stationary behaviour of a 9 piston pump for different operating conditions and different configurations. In this study attention is focused on pump volumetric efficiency dependency on overall operational conditions as supply pressure, pump speed, leakage clearance heights, swash plate angle and port plate timing. Successively, a numerical vs. experimental comparison of steady-state pump characteristics is presented; this last part of the paper has been developed with the aim of showing the validity limits of the assumptions made to build up the numerical model. Results confirm the applicability of the simplified hypotheses introduced and validates the analysis of volumetric efficiency previously performed.

1998 - Analisi della Risposta Dinamica del Circuito di Comando degli Attuatori di un Escavatore [Relazione in Atti di Convegno]
Borghi, Massimo; Cantore, Giuseppe; Milani, Massimo; A., Valentini
abstract

Vengono presentati i risultati ottenuti dallo studio del comportamento dinamico del circuito idraulico di comando degli attuatori di un escavatore. Più nel dettaglio, utilizzando il codice commerciale AMESim è stato messo a punto un modello di simulazione numerica a parametri concentrati dei circuito idraulico di comando della benna posteriore di un escavatore, per studiare la risposta di uno degli attuatori lineari (il boom cylinder) nella condizione di carico trascinante. L'analisi della risposta dinamica dei sistema idraulico ha permesso di evidenziare come, nella particolare condizione operativa imposta, la discesa dei carico non risulti facilmente controllabile dall'operatore, e venga ad essere completata in un tempo particolarmente breve. L'inserimento di una valvola di bilanciamento (o di overcenter) di corrente produzione industriale, come componente di controllo e di sicurezza, tra il martinetto di comando della benna e il circuito idraulico, ha permesso di verificare come tale componente possa esercitare la sua funzione in presenza di un comando a pressione costante applicato al suo stadio di pilotaggio. Allo scopo è stato previsto l'utilizzo di un accumulatore a precarica sulla linea di pilotaggio della valvola di bilanciamento, in grado, inoltre, di assorbire le eventuali pulsazioni di pressione nella camera lato pistone del boom cylinder, indotte dall'elasticità della struttura meccanica. L'ultima parte del lavoro è dedicata alla scelta della pressione di precarica e dei volume dell'accumulatore, ai fini del raggiungimento della configurazione necessaria ad assicurare il completo controllo della fase di discesa dei carico.

1998 - Analysis of hydraulic components using computational fluid dynamics models [Articolo su rivista]
Borghi, Massimo; Cantore, Giuseppe; Milani, Massimo; R., Paoluzzi
abstract

This paper presents some results obtained during the computational fluid dynamics (CFD) analysis of internal flows inside a hydraulic component, using a scaling technique applied to numerical pre- and post-processing. The main aim of the work is to demonstrate the reduction of computational work needed for a complete analysis of component behaviour over a wide range of operating conditions. This result is achieved through the adoption of a methodology aimed at giving the highest level of generality to a non-dimensional solution, thereby overcoming the two major limitations encountered in the use of CFD in fluid power design: computer resources and time. In the case study, the technique was applied to a hydraulic distributor and computations were performed with a commercial computational fluid dynamics code. The key factor of this technique is the evaluation, for a given distributor opening, of the Reynolds number of the flow in the metering region. Provided that this number is high enough to ensure that the discharge coefficient has reached its asymptotic value, the characterization of the flow by a single non-dimensional numerical run can be shown. The theoretical contents of the analysis of the re-scaling technique, which focuses on the engineering information necessary in component design, are described in detail. The bases for its subsequent application to actual cases are then outlined. Finally, a fairly close correlation between numerical results and experimental data is presented.

1998 - NUMERICAL ANALYSIS OF THE LATERAL FORCES ACTING ON SPOOLS OF HYDRAULIC COMPONENTS [Relazione in Atti di Convegno]
Borghi, M.; Cantore, G.; Milani, M.; Paoluzzi, R.
abstract

This paper deals with the analysis of pressure distribution within the fluid film in the clearance between spool and sleeve of hydraulic components, in order to predict the value of the locking force induced by unbalanced pressure acting on tapered geometries. Particular care is devoted to the investigation of the lateral force dependency on clearance and eccentricity of the spool. Some theoretical results are presented, obtained solving (by the finite difference method) the two dimensional Reynolds equation for the fluid film. These results are then compared to those deriving from a generally adopted predictive formula. Results show remarkable differences, up to 70 %, in presence of high values of eccentricity. Moreover, an analogous Reynolds’ based solution is performed for a tapered geometry of the spool with one balancing groove, with particular attention to the influence of its length and position on resulting locking force and leakage flow. Also the locking force reducing effect of a balancing groove is characterized, and a saturated behavior when the groove is placed very close to the high pressure spool side has been found.

1998 - Numerical analysis of the lateral forces acting on spools of hydraulic components. [Relazione in Atti di Convegno]
Borghi, Massimo; Cantore, Giuseppe; Milani, Massimo; Paoluzzi, Roberto
abstract

This paper deals with the analysis of pressure distribution within the fluid film in the clearance between spool and sleeve of hydraulic components, in order to predict the value of the locking force induced by unbalanced pressure acting on tapered geometries. Particular care is devoted to the investigation of the lateral force dependency on clearance and eccentricity of the spool. Some theoretical results are presented, obtained solving (by the finite difference method) the two dimensional Reynolds equation for the fluid film. These results are then compared to those deriving from a generally adopted predictive formula. Results show remarkable differences, up to 70 %, in presence of high values of eccentricity. Moreover, an analogous Reynolds' based solution is performed for a tapered geometry of the spool with one balancing groove, with particular attention to the influence of its length and position on resulting locking force and leakage flow. Also the locking force reducing effect of a balancing groove is characterized, and a saturated behavior when the groove is placed very close to the high pressure spool side has been found.

1998 - TRANSIENT FLOW FORCE ESTIMATION ON THE PILOT STAGE OF A HYDRAULIC VALVE [Relazione in Atti di Convegno]
Borghi, M.; Milani, M.; Paoluzzi, R.
abstract

The effect of flow forces on the spool equilibrium of hydraulic components is well known, and a number of methods have been developed in order to estimate their effect. They span from analytical expression, to experimental evaluation, to CFD analysis. This last approach is usually considered too demanding to the purpose of hydraulic component design, however a careful approach to the problem statement can lead to the collection of a complete set of data, starting from a limited number of numerical runs. A further extension to transient flow is made possible by the acceptance of further approximations on the effect of fluid compressibility, leading to a computational technique able to extend the amount of information extracted from a single model.

1998 - Transient flow force estimation on the pilot stage of a hydraulic valve. [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paoluzzi, Roberto
abstract

The effect of flow forces on the spool equilibrium of hydraulic components is well known, and a number of methods have been developed in order to estimate their effect. They span from analytical expression, to experimental evaluation, to CFD analysis. This last approach is usually considered too demanding to the purpose of hydraulic component design, however a careful approach to the problem statement can lead to the collection of a complete set of data, starting from a limited number of numerical runs. A further extension to transient flow is made possible by the acceptance of further approximations on the effect of fluid compressibility, leading to a computational technique able to extend the amount of information extracted from a single model.

1997 - Bilanciamento delle Macchine Oleodinamiche ad Ingranaggi Esterni [Relazione in Atti di Convegno]
Cantore, Giuseppe; Borghi, Massimo; Milani, Massimo
abstract

n.d.

1997 - Distribuzione della pressione nei vani di una pompa a palette [Relazione in Atti di Convegno]
Borghi, Massimo; Cantore, Giuseppe; Milani, Massimo
abstract

In questo lavoro sono presentati e discussi i risultati ottenuti da una serie di rilievi sperimentali volti alla misura della pressione nei vani di una pompa a palette di produzione industriale.Le prove, effettuate in diverse condizioni di funzionamento della macchina, evidenziano alcune singolarita' originate probabilmente dal recupero dei giochi da parte delle palette; tali fenomeni si manifestano in prossimita' delle zone di commutazione, laddove la pressione inizia ad aumentare o a diminuire.Vengono inoltre presentati i risultati di un modello di calcolo semplificato, basato sull'applicazione dell'equazione di continuita' ai vani della macchina.Il confronto fra i risultati forniti dal calcolo e quelli sperimentali si mostra incoraggiante nelle sue linee generali, nonostante la semplicita' del modello. Vengono fornite indicazioni per l'ulteriore miglioramento della modellizzazione.

1997 - Experimental and Numerical Analysis of Forces on a Hydraulic Distributor [Relazione in Atti di Convegno]
Borghi, Massimo; Cantore, Giuseppe; Milani, Massimo; R., Paoluzzi
abstract

The paper relates about experiments and Computational Fluid Dynamics (CFD) analysis on forces acting on a commerci al 4/3 distributor. Experimental results are reported, together with a detailed discussion to asses their reliability. The same results are then used to drive the approach to numerical simulation, in order to minimise the number of runs needed to gather the required informations in term of pressure drop and spool forces.A description of the benefits achievable with an extensive use of dimensional analysis is presented, showing how, within the validity limits of the same set of equations (turbulent or laminar), non-dimensional results of a numerical computation can be consistently extended to various flow conditions. Some final considerations are then reserved to a few indications useful for valve geometry improvement; furthermore a discussion is reported about some controversial numerical and experimental results.

1997 - L'impiego dei coefficienti di efflusso nelle simulazioni del ciclo dei motori alternativi a combustione interna (The use of discharge coefficients in thermo-fluid-dynamic numerical simulation of reciprocating internal combustion engines) [Relazione in Atti di Convegno]
Cantore, Giuseppe; Mattarelli, Enrico; Borghi, Massimo; A. A., Boretti; G., Guerrini
abstract

II progetto e lo sviluppo di motori ad alte prestazioni trova un valido supporto nelle simulazioni termofluidodinamiche del ciclo. Tali simulazioni consentono sia di studiare l'evoluzione temporale delle principali grandezze termodinarniche e di flusso nel motore, sia di prevedere le caratteristiche prestazionali del motore stesso. L'accuratezza dei risultati di queste simulazioni è estremamente importante ai fini di una loro applicazione sistematica in ambito industriale. In questo lavoro vengono discussi alcuni aspetti inerenti la modellizzazione del flusso attraverso i condotti e le valvole dei motori, allo scopo di migliorare le capacità predittivedella simulazione numerica, mediante un uso critico dei dati sperimentali. Si è osservato che, per le consuete modalità con cui si effettuano le prove di flussaggio stazionario delle valvole, è talvolta necessario correggere il valore dei coefficienti di efilusso da introdurre nella simulazione. Vengono allo scopo proposte alcune relazioni dedotte per via teorica, da integrarsi con i risultati di un'analisi numerica tridimensionale, o di ulteriori provesperimentali.L'influenza delle correzioni proposte, e le relative conseguenze sui risultati della simulazione di ciclo, sono state valutate con riferimento al caso di un motore Ferrari per laFormula 1. E' risultato che le entità delle correzioni al coefficiente di efilusso sono in alcuni casi significative, raggiungendo anche il 25%. Sensibili, anche se decisamente meno rilevanti, sono le differenze che si riscontrano per i risultati della simulazione in termini di prestazioni globali del motore.

1997 - Pressure balancing in external gear pumps and motors [Articolo su rivista]
Cantore, G.; Milani, M.; Borghi, M.
abstract

The paper relates on a numerical method for designing balancing bearing block areas for external gear pumps and motors. At first, a way is presented for obtaining pressure distribution inside spaces between teeth, bearing blocks and casing; the procedure, based on integration of the continuity equation for sealed spaces, permits also the evaluation of some interesting aspects dealing with the influence of rotational speed, dynamic viscosity and gears eccentricity. Then, a method is presented for calculating pressure distribution in the layer bounded by gears sides and bearing blocks. The method, starting from pressure distribution in spaces, is based on the integration of the laspace equation over the whole layer. Axial thrust on bearing blocks and its point of application are then calculated. Finally, the same problem is analysed with a simplified numerical approach, as well based on the integration of the laplace equation, but on the small portion of the layer corresponding to one tooth, with only one boundary condition. At the end, calculations are made for a commercial pump, obtaining balancing aeras very close to the ones designed by the manufacturer.

1997 - Pressure balancing in external gear pumps and motors[Bilanciamento delle macchine oleodinamiche a ingranaggi esterni] [Articolo su rivista]
Cantore, Giuseppe; Milani, Massimo; Borghi, Massimo
abstract

The paper relates on a numerical method for designing balancing bearing block areas for external gear pumps and motors. At first, a way is presented for obtaining pressure distribution inside spaces between teeth, bearing blocks and casing; the procedure, based on integration of the continuity equation for sealed spaces, permits also the evaluation of some interesting aspects dealing with the influence of rotational speed, dynamic viscosity and gears eccentricity. Then, a method is presented for calculating pressure distribution in the layer bounded by gears sides and bearing blocks. The method, starting from pressure distribution in spaces, is based on the integration of the laspace equation over the whole layer. Axial thrust on bearing blocks and its point of application are then calculated. Finally, the same problem is analysed with a simplified numerical approach, as well based on the integration of the laplace equation, but on the small portion of the layer corresponding to one tooth, with only one boundary condition. At the end, calculations are made for a commercial pump, obtaining balancing aeras very close to the ones designed by the manufacturer.

1997 - Sperimentazione con Fluidodinamica Computazionale di un Distributore Oleodinamico [Articolo su rivista]
Borghi, Massimo; Cantore, Giuseppe; Milani, Massimo; R., Paoluzzi
abstract

La memoria si occupa della riprogettazione di un distributore oleodinamico di tipo on-off mediante l'utilizzo di strumenti di progettazione assistita da calcolatore, sottolineando quali aspetti progettuali debbano essere considerati per ridurre l'effetto delle forze di flusso assiali.

1996 - A theoretical model for the calculation of the drug distribution profile in matrices of different shape to achieve the desired drug release kinetics [Articolo su rivista]
Forni, Flavio; Vandelli, Maria Angela; Borghi, Massimo
abstract

The drug release kinetics from a matrix is often affected by the matrix geometry. To compensate for the influence of the matrix geometry on the drug release, a nonhomogeneous drug distribution has been suggested. Keeping in mind this approach, a theoretical mathematical model to calculate the drug distribution profile according to The matrix geometry is proposed. This approach could be useful in achieving the desired drug release kinetics without varying the matrix geometry.

1996 - Computational Methods for the Fluid Dynamic Optimization of High-Performance Engines [Relazione in Atti di Convegno]
Cantore, Giuseppe; A. A., Boretti; Mattarelli, Enrico; Borghi, Massimo
abstract

n.d.

1996 - Fluido contaminato? No grazie! [Articolo su rivista]
Cantore, Giuseppe; Borghi, Massimo; Milani, Massimo; M., Bianchi
abstract

n.d.

1996 - Numerical optimization of a racing engine with variable intake and exhaust geometry and valve actuation [Relazione in Atti di Convegno]
A. A., Boretti; Borghi, Massimo; Cantore, Giuseppe; Mattarelli, Enrico
abstract

This paper presents a numerical study on a racing engine with variable intake and exhaust geometry and valve actuation. The study is carried out by using dynamic engine simulations. Aim of the analysis is the evaluation of the benefits these devices have on engine performance. Results show clear advantages over the full range of engine speed.

1996 - Riduzione delle oscillazioni di pressione e del rumore in una pompa ad ingranaggi [Relazione in Atti di Convegno]
P., Pelloni; Borghi, Massimo; P., Casoli; G., Toderi; S., Negrini
abstract

Al fine di ridurre le oscillazioni di pressione alla mandata di una pompa ad ingranaggi ed il rumore, si è realizzato uno studio sperimentale per poter valutare il comportamento della pompa stessa dopo la applicazione di un risonatore di Helmholtz. Sono State provate tre diverse configurazioni di risonatore: due realizzate a puro scopo di indagine di laboratorio; ed una che risulta assemblata al corpo stesso della pompa, ed è, quindi, adatta alla produzione in serie.

1996 - Sul calcolo della spinta sulle fiancate nelle macchine oleodinamiche ad ingranaggi esterni [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; G., Toderi
abstract

In un precedente lavoro è stato presentato un metodo approssimato ·per il calcolo delle pressioni sulle fiancate delle ruote dentate di macchine oleodinamìche ad- ingranaggi esterni, calcolo effettuato sulla base delle pressioni agenti nei vani compresi fra i denti. I risultati allora ottenuti integrando l'equazione di Laplace nella porzione di meato delimitato dai piani di mezzeria di due vani adiacenti, vengono ora confrontati con quelli ottenuti dall'integrazione della stessa equazione di Laplace sull'intero meato posto tra la fiancata e la ruota dentata.Quest'ultimo calcolo, a fronte di una minor semplicità, consente di prescindere da qualunque ipotesi sull'andamento della pressione tra il fondo dei vani e la camera di drenaggio; inoltre esso fornisce direttamente i risultati anche per il dente sul quale si ha ilcontatto di ingranamento cui è affidata la tenuta tra gli ambienti di alta e di bassa pressione. TI confronto, effettuato per una famiglia di pompe geometricamente simili, porta ad affermare che, per la maggior parte dei denti, i risultati ottenuti con il procedimento messo a punto in questo lavoro sono in pieno accordo con quelli ottenuti sulla base del procedimento approssimato, le cui ipotesi di base risultano così ben verificate.Vengono poi calcolati, per la famiglia di macchine considerata, la spinta complessiva sulle fiancate ed il relativo punto di applicazione in diverse posizioni angolari delle ruote.

1995 - Experimental and Computational Methods for Swirl Port Design in Internal Combustion Engines [Relazione in Atti di Convegno]
A. A., Boretti; Cantore, Giuseppe; Borghi, Massimo; Mattarelli, Enrico
abstract

The paper reviews the minimum losses and intake flow conditioning criteria typically adopted for the design of swirl ports in two valve Direct Injection (DI) Diesel engines, as well as in some two valve Spark Ignition (SI) engines. The standard experimental practice, based on the use of steady flow discharge and swirl coefficients as a measure of port design quality is first presented. The analogous computational methodology, where the steady flow is simulated, is then introduced. The computational methodology is extensively validated against a data set for a series of ports, of the direct, hybrid and helical type. The computational methodology is finally applied to simulate the transient flow within the engine during the intake stroke. The computed Intake Valve Closure (IVC) flow field provides a more rational basis for port optimization than steady flow coefficients, even if these latter simulations have still to be properly validated.

1995 - Influence of Intake Port Design on Permeability and Rate of Combustion in a Four Valve High Performance Engine [Relazione in Atti di Convegno]
A. A., Boretti; Mattarelli, Enrico; Borghi, Massimo; A., Dominici; G., Guerrini
abstract

The paper presents some improvements to the design of the intake port and valve assembly of a new Ferrari 5.5 liter engine, in order to increase both permeability and rate of combustion. Design has been supported by CFD-3D simulations and experiments.

1995 - Numerical Simulation of Turbulent Combustion in a Four Valve Spark Ignition Engine with CRI/Turbokiva 2.0 Code [Relazione in Atti di Convegno]
Cantore, Giuseppe; Borghi, Massimo; Mattarelli, Enrico; G. M., Bianchi; A. A., Boretti; L., Chinni
abstract

An enhanced engineering version of the Los Alamos National Laboratory's Kiva 3 code, called CRI/Turbokiva 2.0, was applied to the study of the mean and turbulent flow field evolution during compression and combustion in a spark ignition engine. A kinetically influenced turbulent combustion model was formulated to overcome the limitations of the standard turbulent combustion model. Mean velocity, turbulence intensity and turbulent length scale results are presented and compared with experimental data, providing satisfactory agreement. These comparisons provide a proper validation work for the fluid dynamic and combustion parts of the code.

1994 - Cogenerative combined cycle power plants fueled by coal and biomass gas [Relazione in Atti di Convegno]
Borghi, Massimo; Cantore, Giuseppe; A., Peretto; P. R., Spina
abstract

This paper proposes a system made-up by a Lurgi fixed-bed gasifier fed with coal or biomass and by a dual pressure level gas-steam combined cycle power plant in cogenerative application. Some comparisons among different configuration plants with single or double intercooled compression gas turbine are carried-out. In this analysis gas turbine off-design operating conditions, due to the use of low-medium Lower Heating Value coal or biomass gas fuel, are pointed-out. A constrained minimization algorithm is used for solving simultaneously all equations describing the system (included the ones representing energy balances and chemical equilibrium in the gasifier) to calculate the integrated plant performance. Results show that the proposed plant can work with energy conversion efficiency not much lower than the one obtainable when the gas turbine is fed with methane, that is the fuel for which the gas turbine itself was designed. Nevertheless, increases up to 15% in both electrical and thermal power are evaluated.

1994 - Computational analysis with Turbokiva code on multivalves spark ignition engine performance [Relazione in Atti di Convegno]
Cantore, Giuseppe; Borghi, Massimo; L., Chinni; Mattarelli, Enrico; A., Dominici; L., Marmorini; P., Martinelli
abstract

n.d.

1994 - Numerical Study of Volumetric Efficiencies in a High Speed, Four Valve, Four Cylinder, Spark Ignition Engine [Relazione in Atti di Convegno]
A. A., Boretti; Borghi, Massimo; Cantore, Giuseppe
abstract

High power output, four stroke, motorcycle engines are characterised by specific power levels well beyond 150 HPllitre also in production engines. These power levels are obtained through extremely high values of volumetric efficiencies in tbe 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-artcomputational methods. These computational metbods include stati c three dimensional computations as well as dynamic one and three dimensional computations. The engine geornetric 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.

1993 - Prestazioni di pompe ad ingranaggi per motori a carter secco in presenza di miscele olio-aria [Relazione in Atti di Convegno]
Borghi, Massimo; Cantore, Giuseppe; L., Mosele
abstract

Si riferisce sui risultati di una prima serie di rilievi sperimentali volti a determinare le prestazioni di pompe ad ingranaggi per la lubrificazione di motori automobilistici ad elevate prestazioni a carter secco. In particolare viene evidenziata l'influenza della presenza di aria nella miscela con l'olio sulla portata destinata alla lubrificazione del motore. In questa prima fase della ricerca è stato appositamente studiato e realizzato un banco prova nel quale si vuole simulare il funzionamento del gruppo di lubrificazione nel motore, utilizzando i reali componenti del circuito. Si è anche studiata l'influenza del serbatoio-separatore e del posizionamento del radiatore olio sulle prestazioni di queste pompe.

1993 - Sulla simulazione del ciclo di piccoli motori diesel funzionanti con miscele gassose artificiali [Relazione in Atti di Convegno]
Borghi, Massimo; A., Brighenti; Cantore, Giuseppe; P., Osti
abstract

In questo lavoro viene rielaborato un modello di simulazione del ciclo di motori Diesel ad iniezione diretta, precedentemente studiato dagli autori. Cio' e' stato possibile grazie alla disponibilita' di una serie di dati sperimentali relativi a piu' motori appartenenti ad una stessa famiglia e funzionanti con aria. Il modello e' stato modificato rispetto alla versione precedente e calibrato in maniera piu' accurata per renderlo adatto a prevedere le prestazioni dell'intera famiglia di motori considerata in un piu' ampio campo di condizioni operative. Viene riportato inoltre un confronto fra i risultati ottenuti utilizzando per la simulazione due diversi modelli fenomenologici di combustione a singola zona. Lo scopo di questa fase della ricerca e' quello di utilizzare il modello per confrontare le prestazioni di motori costruiti per funzionare in aria, quando, con o senza modifiche, siano alimentati con miscele gassose artificiali come per esempio ossigeno ed anidride carbonica, con o senza argon. In questo lavoro si presenta l'influenza della concentrazione di argon, a percentuale di ossigeno costante, nella parte inerte della suddetta miscela ternaria, senza modificare la geometria del motore. In particolare si e' evidenziato che una percentuale di circa il 60% del gas inerte deve contenere un gas monoatomico come l'argon, essendo la restante parte costituita da anidride carbonica, se si vogliono ottenere diagrammi pressione - angolo di manovella e lavori indicati vicini a quelli trovati con il modello applicato al motore funzionante ad aria.

1991 - Calcolo delle pressioni sui fianchi degli ingranaggi di macchine oleodinamiche ad ingranaggi esterni [Articolo su rivista]
Borghi, Massimo; C., Bonacini
abstract

Il lavoro riguarda la determinazione della distribuzione della pressione nei meati tra le fiancate ed ifianchi delle ruote dentate delle macchine oleodinamiche ad ingranaggi esterni. La distribuzione della pressione nel meato può essere ricavata in maniera semplice e con buona approssimazione integrando l'equazione di Laplace nel dominio geometrico delimitato dal profilo della dentaiura, dai segmenti radiali di mezzeria di duevani adiacenti e dalla circonferenza che delimita la gola di drenaggio. Grazie alla linearità del problema, alla simmetria geometrica del dominio considerato ed in virtù delle particolari condizioni al contorno assunte, è sufficiente determinare la distribuzione delle pressioni per una sola condizione al contorno, essendo possibile dedurre da questa quelle relative a qualsiasi altra condizione. Dalle determinazioni effettuate con questoprocedimento su numerose macchine commerciali, diverse per disegno e numero di denti, è risultato che, a parità di condizionial contorno, la pressione media nel dominio di calcolo assume valori che differiscono soltanto di poche unità percentuali. Ciò consente di stimare in maniera semplicissima, ma con approsslmazione in generale accettabile, la spinta totale agentesull' intera fiancata.

1990 - Calcolo delle pressioni nei vani fra i denti di una macchina oleodinamica ad ingranaggi esterni [Articolo su rivista]
C., Bonacini; Borghi, Massimo
abstract

Viene esposto un procedimento per il calcolo delle pressioni nei vani delimitati da due denti contigui di un ingranaggio e dalle superfici interne del corpo di una macchina oleodinamica ad ingranaggi esterni. Più esattamente il procedimento porta ad individuare l'andamento della pressione in un vano genericonell'intervallo, temporale o angolare, durante il quale il vano stesso è «isolato» dagli ambienti di bassa e di alta pressione. Dai risultati è possibile risalire ai carichi medi agenti sui vari organi della macchina e, in particolare, alle spinte sulle fiancate. Nellemacchine con fiancate mobili assialmente la conoscenza di queste spinte è necessaria per determinare l'area e la forma delle superfici di equilibramento idraulico.

1989 - Comparative study on the ways of converting steam power plants to steam-gas combined cycle power plants [Relazione in Atti di Convegno]
Negri Di Montenegro, Giorgio; Bettocchi, Roberto; Cantore, Giuseppe; Borghi, Massimo; Naldi, Giovanni
abstract

The authors consider gas-steam combined cycle power plants derived from existing steam power plants by inserting a Brayton cycle gas turbine as a topper. The conversion of superheated, superheated-reheated and regenerative steam cycle power plants is examined. Two methods of conversion are studied: replacing the original steam generator with a recovery boiler either with afterburning at the gas turbine exhaust or not, and keeping the steam generator of the working steam plant in operation and burning fuel inside the gas turbine exhaust gases. In the latter instance the possibility of adding external air, through the steam generator air preheater, to the gas turbine exhaust gases is considered too. The combined overall power plant efficiency and the gas-to-steam-power ratio are evaluated and a comparison is made between the values obtained for the two methods. The overall efficiency is also compared with that of the original working steam plant. The study shows that maximum overall efficiencies are attained when adopting a recovery boiler and that the afterburning at the gas-turbine exhaust is not always advantageous.

1989 - Criteri per la indivuazione delle caratteristiche di impianti di prova per modelli di micro-turbine idrauliche a reazione [Relazione in Atti di Convegno]
Borghi, Massimo; G., Naldi; C., Bonacini
abstract

In questo lavoro viene proposto un metodo semplice per individuare quali caratteristiche di portata e prevalenza debba avere un impianto di prova a circuito chiuso per modelli di turbine idrauliche a reazione con indice caratteristico nq compreso fra 20 e 300. Vengono ricavate le relazioni che legano, in questo campo, la portata al salto ed alle caratteristiche geometriche e funzionali del modello: dimensione, indice caratteristico e velocità di rotazione. Queste relazioni sono dedotte dai criteri usuali di dimensionamento delle turbine a reazione e in particolare dalla dipendenza del coefficiente di velocità periferica dall'indice caratteristico.

1988 - A comparative study on the ways of converting steam power plants to steam-gas combined cycle power plants [Relazione in Atti di Convegno]
G., Negri Di Montenegro; R., Bettocchi; Cantore, Giuseppe; Borghi, Massimo; G., Naldi
abstract

The authors consider gas-steam combined cycle power plants derived from existing steam power plants by inserting a Brayton cycle gas turbine as a topper. The conversion of superheated, superheated-reheated and regenerative steam cycle power plants is examined. Two methods of conversion are studied: replacing the original steam generator with a recovery boiler either with afterburning at the gas turbine exhaust or not, and keeping the steam generator of the working steam plant in operation and burning fuel inside the gas turbine exhaust gases. In the latter instance the possibility of adding external air, through the steam generator air preheater, to the gas turbine exhaust gases is considered too. The combined overall power plant efficiency and the gas-to-steam-power ratio are evaluated and a comparison is made between the values obtained for the two methods. The overall efficiency is also compared with that of the original working steam plant. The study shows that maximum overall efficiencies are attained when adopting a recovery boiler and that the afterburning at the gas-turbine exhaust is not always advantageous.

1988 - Le prestazioni di gruppi combinati gas-vapore con sezioni a vapore a due pressioni [Relazione in Atti di Convegno]
Borghi, Massimo; G., Naldi; A., Dal Passo
abstract

In questo studio si presenta un criterio per la determinazione della pressione intermedia e della ripartizione delle portate ottimali nel caso di gruppi combinati gas-vapore con sezìcne a vapore avente caldaia a recupero a due livelli di pressione, a vapore surriscaldato il circuito di alta pressione e a vapore saturo secco quella di bassa. Vengono qui in particolare esaminati il rendimento del gruppo combinato ed il rapporto tra le potenze delle due sezioni, per la determinazione dei quali giocano un ruolo fondamentale i vincoli esìstenti sul valore minimo del titolo del vapore nell'espansione in turbina, nonché la temperatura di scarico dei fumi e quindi l'efficienza di scambio termico.Lo studio svolto, valido per qualunque turbogas assegnato, è stato qui riferito al caso di gruppo a gas operante secondo un ciclo di Brayton, che risulta la soluzione più diffusa nelle attuali applicazioni.

1988 - Modello interpretativo del comportamento di valvole di sicurezza [Articolo su rivista]
Cantore, Giuseppe; G., Minelli; R., Bettocchi; Borghi, Massimo; G., Naldi
abstract

Le prestazioni operative di una valvola di sicurezza sono tanto più brillanti quanto minori sono, per una data portata effluente, la sovrapressione di apertura e lo scarto di chiusura. A tal scopo, lo studio qui presentato consente di individuare la configurazione più opportuna di dette valvole.

1987 - CONVERSION OF STEAM AND GAS POWER PLANTS TO COMBINED CYCLES [Relazione in Atti di Convegno]
G., Negri di Montenegro; R., Bettocchi; Cantore, Giuseppe; Borghi, Massimo; G., Naldi
abstract

This paper studies the repowering of already operating steam or turbogas plants through the fitting of a turbogas unit as topper in the first case, and a steam unit as bottomer in the second, thus obtaining steam-gas combined plants. As to steam plants, a methodology has been defined which permits evaluation of both the overall efficiency and gas to steam power ratio of the derived combined plant obtained by superposing a turbogas unit on any assigned steam plant so as to permit integral utilization or minimum modification of the steam section.

1987 - Forecastings the performance of safety valves [Articolo su rivista]
Minelli, G.; Borghi, M.; Carra, R.
abstract

The experimental profiles of the thrust from the fluid on the valve shutter and of the gate outlet flow volume on variation in the shutter height can be generalized to geometrically similar valves. Three sets of experiments confirm the viability of the numerical method for forecasting the practical performance of safety valves. But the profile experimental diagram has to be supplemented by the pressure flow volume diagram based on the spring rigidity and prestress, the nature of the fluid, the upstream temperature and the downstream pressure. Then the calculation procedure can be extremely rapid, and the functional parameters influencing the behaviour of a valve can undergo controlled variation to determine the performance data.

1987 - Steam-Gas Combined Units with Multiple Expansion, Re-heating Gas Section[GRUPPI COMBINATI GAS-VAPORE CON SEZIONE A GAS AD ESPANSIONE FRAZIONATA INTERRISCALDATA.] [Articolo su rivista]
R., Bettocchi; Borghi, Massimo
abstract

The paper covers the study of steam-gas combined units fitted with a gas section that realizes multiple expansion with only one intermediate pressure to which re-heating is effected. The aim of the study is to point out the choice of the particular type of gas cycles considered on the overall efficiency of the unit and the ratio between the power of the gas and steam sections. The investigation methodology adopted, which keeps account of the irreversibilities of the transformations in the turbomachines by means of polytropic efficiency, assumed constant, essentially consists in evaluation the variations in the performance of the units being examined compared to those of simply combined units. The expansion ratio and the input temperature of the low-pressure turbine have been assumed as variables.

1986 - A STEAM-GAS COMBINED PLANTS OPTIMIZATION [Relazione in Atti di Convegno]
G., Negri di Montenegro; R., Bettocchi; Cantore, Giuseppe; Borghi, Massimo; G., Naldi
abstract

An optimum-design general criterion for steam-gas combined plants is illustrated by which the characteristics of the gas and steam sections can be established to obtain maximum overall efficiency of the plant. The methodology is based on the choice, as an independent variable of the temperature, of the exhaust gases at the recovery boiler inlet. Consideration is given to gas units operating according to a Brayton cycle, with and without afterburning and in accordance with reheat-gas-turbine cycles, and to steam units realized with superheat, superheat reheat, and extraction- heater steam cycles. It is concluded that in order to obtain high-performance combined plants it is not advisable to adopt particularly complicated steam sections, that is, fitted with regeneration and superheat reheating; it is, on the other hand, desirable to match turbo-gas plants operating according to a multiple expansion with reheating cycles, and steam plants with simple superheating.

1986 - Numerical determination of safety valve efficiencies [Articolo su rivista]
Minelli, G.; Borghi, M.; Carra, R.
abstract

Based on observed thrust and flow volume profiles as a function of the lift in closure and nozzle assemblies of known geometry, the flow volume can easily be determined for variation in pressure for a safety valve with a geometrically similar closure and nozzle of any size, combined with a spring of any prestress and rigidity. The outflow conditions and the spring capacity are considered, starting with a non-dimensional evaluation in order to generalize the problem. The resulting program permits calculation of the operating characteristics of a safety valve of specific properties under set operating conditions, in only a few minutes, even using a medium capacity computer. (R.H.)