- Bologna, Emilia-Romagna, Italy
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The aim of this work is to set up a methodology for simulating Common Rail high-pressure injectors based on coupling a lump-model with CFD two-phase multi-dimensional computations. The unit simulated is the Bosch injector. The injector... more
The aim of this work is to set up a methodology for simulating Common Rail high-pressure injectors based on coupling a lump-model with CFD two-phase multi-dimensional computations. The unit simulated is the Bosch injector. The injector lump-model resulted in the definition of the three sub-models for hydraulics, mechanics and electromagnetics. The second-order differential governing equations have been solved in Matlab/Simulink environment and are properly coupled together with the one-dimensional partial differential equations that describe the unsteady pipe flow. A detailed library of thermo-mechanical properties for ISO-4113 oil and diesel fuel is included. Cavitation effects on discharge coefficient in the main orifices were accounted for by using results from CFD steady two-phase flow simulations. The evaluation of the model capability was assessed by using detailed experiments carried out at different practical injector operating conditions. Instantaneous and integrated injected flow rate, and injector needle lift were measured and collected for comparison with simulation. CFD steady computations revealed to be unavoidable in driving the lump-model toward a high reliability of injector performances over the whole range of injection pressures and energizing times.
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In the next incoming future the necessity of reducing the raw emissions leads to the challenge of an increment of the thermal engine efficiency. In particular it is necessary to increase the engine efficiency not only at full load but... more
In the next incoming future the necessity of reducing the raw emissions leads to the challenge of an increment of the thermal engine efficiency. In particular it is necessary to increase the engine efficiency not only at full load but also at partial load condit ions. In the open literature very few technical papers are available on the partial load conditions analysis. In the present paper the analysis of the effect of the throttle valve rotational direction on the mixture formation is analyzed. The engine was a PFI 4-valves motorcycle engine. The throttle valve opening angle was 17.2', which lays between the very partial load and the partial load condition. The CFD code adopted for the analysis was the FIRE AVL code v. 2013.2. The exhaust, intake and compression phases till TDC were simulated: inlet/outlet boundary conditions from 1D simulations were imposed. The injection system operation was experimentally investigated in terms of spray shape and drop sizing and veloci ty for a proper tuning of the numerical model. The injection process was modelled and the final results in terms of mixture compositi on and turbulence level at the ignition time were investigated. The aim of the paper was to deeply analyze the dynamic effect of the throttle valve position on the engine behavior. The wallfilm effect on the effective mixture formation process was considered by means a new methodological approach. The wallfilm thickness and its dynamics affect the final mixture formation process and the level of the mixture index at the ignition time close to the spark plug. It is also necessary to consider that, even though the CFD simulations were RANS simulations, it could take some days for reaching the converged wallfilm thickness, even 20 or more engine cycles at full load conditions could be necessary. The research group proposed a new methodological approach for facing this problem within a computational time compatible with industrial applications too. \ua9 2015 SAE International
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Combustion process simulation based on CFD approach is a fundamental tool in order to assess the engine design. For Diesel engine applications a critical tool is the prediction of the boundary conditions of the combustion process, in... more
Combustion process simulation based on CFD approach is a fundamental tool in order to assess the engine design. For Diesel engine applications a critical tool is the prediction of the boundary conditions of the combustion process, in particular the injected fuel mass and the velocity profile of the injection itself. Usually for simulating the combustion process in HSDI engine the unique data about the injector geometry available are: a) Number of poppet holes; b) Geometrical area of the poppet holes; c) Electrical data from the ECU. By these inputs it is not possible to get satisfactory boundary conditions for the 3D model, while they can be used in a 1D model of the injector for obtaining results in terms of injected fuel mass and velocity profile. The idea at the basis of the paper is to simplify a complex model of the injector developed by the authors in order to get a model suitable for this kind of application. In particular this model is a black box in which it is possible to adjust some parameters based on the limited data available in order to get the results of interest
Research Interests:
Water injection is becoming a technology of increasing interest for SI engines development to comply with current and prospective regulations. To perform a rapid optimization of the main parameters involved by the water injection process,... more
Water injection is becoming a technology of increasing interest for SI engines development to comply with current and prospective regulations. To perform a rapid optimization of the main parameters involved by the water injection process, it is necessary to have reliable CFD methodologies capable of capturing the most important phenomena. In the present work, a methodology for the CFD simulation of combustion cycles of SI GDI turbocharged engines under water injection operation is proposed. The ECFM-3Z model adopted for combustion and knock simulations takes advantages by the adoption of correlations for the laminar flame speed, flame thickness and ignition delay times prediction obtained by a detailed chemistry calculation. The latter uses machine learning algorithms to reduce the time to generate the full database while still maintaining an even distribution along the variables of interest. The results demonstrate the applicability of the proposed methodology, capable of capturing not only the thermodynamic effects of water injection but also the chemical kinetics aspects related to the mixture water dilution whose prediction is mandatory for addressing the engine design according to different goals: complying with new emission directives and limits, turbine inlet temperature constraints, minimization of the BSFC and possibly engine power increase.
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The heat transfer phenomena in Internal Combustion Engines (ICEs) are one of the main research topics that need to be addressed to enhance the performance in terms of power, efficiency, emissions and reliability. The present study is... more
The heat transfer phenomena in Internal Combustion Engines (ICEs) are one of the main research topics that need to be addressed to enhance the performance in terms of power, efficiency, emissions and reliability. The present study is focused on the evaluation of the in-cylinder heat fluxes through the use of Computational Fluid Dynamic (CFD) simulations, with a wall function approach. In particular, the aim of this work is to present a new fully non-isothermal wall function obtained from the one-dimensional (1-D) energy balance equation for turbulent flows in the boundary layers, specifying all the steps and assumptions which have carried to the final fully compressible formulation. The new proposed wall function has been validated against experimental data of the General Motors (GM) Pancake Engine, representative of low Brake Mean Effective Pressure (bmep) operating point, comparing the results with other existing wall functions. With the objective of a mesh independency analysis, the wall functions considered have been tested with three different grids, varying the height of the first layer. Globally, it has been found that the new proposed wall function is less sensitive to the cell size: this feature could be exploited in a real modern engine for a better estimation of the heat fluxes in every part of the domain, where the cell sizes can vary due to the geometry complexity. Moreover, a hypothesis on how to make the new wall function suited also for an engine with much higher bmep is discussed. The simulations are performed by using Star-CD and the new proposed wall function has been implemented via subroutine
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ABSTRACT
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The modern spark ignition engines, due to the introduced strategies for limiting the consumption without reducing the power, are sensitive to both the detonation and the increase of the inlet turbine temperature. In order to reduce the... more
The modern spark ignition engines, due to the introduced strategies for limiting the consumption without reducing the power, are sensitive to both the detonation and the increase of the inlet turbine temperature. In order to reduce the risk of detonation, the use of dilution with the products of combustion (EGR) is an established practice that has recently improved with the use of water vapor obtained via direct or indirect injection. The application and optimization of these strategies cannot ignore the knowledge of physical quantities characterizing the combustion such as the laminar flame speed and the ignition delay, both are intrinsic property of the fuel and are function of the mixture composition (mixture fraction and dilution) and of its thermodynamic conditions. The experimental measurements of the laminar flame speed and the ignition delay available in literature, rarely report the effects of dilution by EGR or water vapor. To overcome the limitations of the experimentation is possible to predict the value of the ignition delay using numerical models based on chemical kinetics theory. The increased performance of computing systems makes possible the use of mechanism with a high number of species and reactions without an excessive temporal cost. In this work a methodology, based on a non-reduced kinetic scheme and an open-source solver (Cantera), is applied to the determination of the laminar flame speed and the ignition delay for a commercial gasoline surrogate, under the typical conditions of GDI engines with the addition of the effects of dilution with water and EGR
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ABSTRACT
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External gear pumps are widely used in many different applications because of their relatively low costs and high performances, especially in terms of volumetric and mechanical efficiency. The main weaknesses of external gear pumps can be... more
External gear pumps are widely used in many different applications because of their relatively low costs and high performances, especially in terms of volumetric and mechanical efficiency. The main weaknesses of external gear pumps can be summarized as follows: 1. Sudden increase or decrease of pressure inside volumes between teeth, which could lead respectively to noise emissions and to cavitation onset; 2. Necessity of limiting power losses and increasing volumetric efficiency, obtainable by reducing leakage flows between components; 3. Need of maintaining an ad-hoc minimum lubrication film thickness. In recent years many efforts, in terms of mathematical models and experimental tests, were done in order to limit energy losses and noise emissions. With the aim of deeply studying dynamic behaviour of external gear pumps and addressing their design, a 1D model was developed by means AMESim 2 code. In particular, a parametric model capable of simulating hydraulically balanced external gear pumps with unitary transmission ratio has been implemented. Geometrical parameters needed by the code were derived directly by ProE 2 code. The idea at the basis of the model was to use AMESim 2 icons as much as possible in order to fasten simulations: thus only some icons were developed by the authors in C++ code. In the current modeling approach the following items were taken into account: 1. Recovery of the clearance between bearing block and casing; 2. The actual position of the gears computing the displacement of the bearing center; 3. The actual wear profile. The model was then experimentally validated comparing simulated and experimental results for various delivering pressures, engine shaft speeds and gear teeth number (in particular pumps with ten and twelve teeth, characterized by single and double contact were considered). Moreover all models developed by the authors were customized in order to simplify the computational environment for users
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For increasing the thermal engine efficiency, faster combustion and low cycle-to-cycle variation are required. In PFI engines the organization of in-cylinder flow structure is thus mandatory for achieving increased efficiency. In... more
For increasing the thermal engine efficiency, faster combustion and low cycle-to-cycle variation are required. In PFI engines the organization of in-cylinder flow structure is thus mandatory for achieving increased efficiency. In particular the formation of a coherent tumble vortex with dimensions comparable to engine stroke largely promotes proper turbulence production extending the engine tolerance to dilute/lean mixture. For motorbike and scooter applications, tumble has been considered as an effective way to further improve combustion system efficiency and to achieve emission reduction since layout and weight constraints limit the adoption of more advanced concepts. In literature chamber geometry was found to have a significant influence on bulk motion and turbulence levels at ignition time, while intake system influences mainly the formation of tumble vortices during suction phase. The most common engine parameters believed to affect in-cylinder flow structure are: 1. Intake duct angle; 2. Inlet valve shape and lift; 3. Piston shape; 4. Pent-roof angle. The present paper deals with the computational analysis of three different head shapes equipping a scooter/motorcycle engine and their influence on the tumble flow formation and breakdown, up to the final turbulent kinetic energy distribution at spark plug. The engine in analysis is a 3-valves pent-roof motorcycle engine. The three dimensional CFD simulations were run at 6500 rpm with AVL FIRE code on the three engines characterised by the same piston, valve lift, pent-roof angle and compression ratio. They differ only in head shape and squish areas. The aim of the present paper is to demonstrate the influence of different head shapes on in-cylinder flow motion, with particular care to tumble motion and turbulence level at ignition time. Moreover, an analysis of the mutual influence between tumble motion and squish motion was carried out in order to assess the role of both these motions in promoting a proper level of turbulence at ignition time close to spark plug in small 3-valves engines.
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An ignition model based on Lagrangian approach was set-up. A lump model for the electrical circuit of the spark plug is used to compute breakdown and glow energy. At the end of shock wave and very first plasma expansion, a spherical... more
An ignition model based on Lagrangian approach was set-up. A lump model for the electrical circuit of the spark plug is used to compute breakdown and glow energy. At the end of shock wave and very first plasma expansion, a spherical kernel is deposited inside the gas flow at spark plug location. A simple model allows one to compute initial
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Upcoming Euro 4 and Euro 5 emission standards are increasing efforts on injection system developments in order to improve mixture quality and combustion efficiency. The target features of advanced injection systems are related to their... more
Upcoming Euro 4 and Euro 5 emission standards are increasing efforts on injection system developments in order to improve mixture quality and combustion efficiency. The target features of advanced injection systems are related to their capability of operating multiple injection with a precise control of the amount of injected fuel, low cycle-by-cycle variability and life drift, within flexible strategies. In order to accomplish this task, injector performance must be optimised by acting on: optimisation of electronic, driving circuit, detailed investigation of different nozzle hole diameter configurations, assessment of the influence of manufacturing errors on hole diameter and inlet rounding on injector performance.
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The paper investigates the variation of the mass of the fuel injected with respect to nominal conditions in Common Rail injection systems for Diesel automotive applications. Two possible operating conditions have been considered: the... more
The paper investigates the variation of the mass of the fuel injected with respect to nominal conditions in Common Rail injection systems for Diesel automotive applications. Two possible operating conditions have been considered: the consecutive injection of two injectors and the multiple shots of the same injector in the same engine cycle. An integrated experimental and numerical methodology has been used. Several experimental information were available in terms of instantaneous rail and pipe pressure and mass flow rate at different conditions. The 1D numerical model of the whole injection system was useful in addressing the questions remained unresolved in the post-experiments analysis. The experimental results show that injector performances are more related to pressure oscillations in injector connecting pipe rather than inside the common rail. The fuel mass is slightly depending on the mutual influence between two consecutive injectors while it is strongly affected by the dwell time (i.e., DTW) between consecutive shots of the same injector in the same engine cycle. The dwell time variation determines different pressure oscillation amplitudes in the injector connecting pipe at the electrical (nominal) start of the injection of the second pulse. As a consequence, different hydraulic (i.e., actual) start and duration of the injection of the second pulse occurs depending on dwell time. A parametric analysis showed that the injected fuel mass variation with dwell time can be reduced by using shorter and larger injector connecting pipes
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Shock absorbers and damper systems are important parts of automobiles and motorcycles because they have effects on safety, ride comfort, and handling. In particular, for vehicle safety, shock absorber system plays a fundamental role in... more
Shock absorbers and damper systems are important parts of automobiles and motorcycles because they have effects on safety, ride comfort, and handling. In particular, for vehicle safety, shock absorber system plays a fundamental role in maintaining the contact between tire and road. Generally, to assure the best trade-off between safety and ride comfort, a fine experimental tuning on all shock absorber components is necessary. Inside a common damper system the presence of several conjugated actions made by springs, oil and pressurized air requires a significant experimental support and a great number of prototypes and test. Aimed to reduce the design and tuning phases of a damper system, it is necessary to join these phases together with a numerical modelling phase. The aim of this paper is to present the development of a mono-dimensional (1D) model for simulating dynamic behaviour of damper system. In particular, a conventional telescopic fork produced by PAIOLI MECCANICA has been considered as testing bench. It is important to underline that the same approach could be used to simulate the dynamic behaviour of an automobile shock absorber system. Fork numerical modelling has to assure a faster design process and a performance optimisation, reducing at the same time, the design time between the product idea and its final assembly. PAIOLI MECCANICA had the necessity of modelling its forks in order to quickly test different solutions and to improve actual fork performances. The present research concerns only fore-carriage forks for road applications, i.e. forks used in motorcycle not dedicated to races. The fork model is developed in AMESim code using both hydraulic and pneumatic libraries. A sinusoidal displacement is directly impressed to the fork rod at different axial velocities (from 100 to 2000 mm/s) for simulating the axial excitation imposed to an actual fork by the road discontinuities. Numerical results are compared with experimental data recorded by PAIOLI MECCANICA. In particular, the fork numerical model demonstrates of being capable to reproduce the testing fields typically used as experimental test bench for motorcycle forks
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Research Interests: Computer Science and SAE
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ABSTRACT
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This work aims to provide an energy and critical analysis of the new “ecological scenario” that sees the world shift the transport sector from the classic fossil-fueled traction towards a purely electric traction. Is it a transition to a... more
This work aims to provide an energy and critical analysis of the new “ecological scenario” that sees the world shift the transport sector from the classic fossil-fueled traction towards a purely electric traction. Is it a transition to a cleaner and more environmentally friendly world? This is the central question we need to answer. In this context of forced electrification of passenger vehicles, the authors estimated the electricity surplus needed in Italy to face this transition with a projection up to 2050, considering the electricity demand of purely electric vehicles and for the production of green hydrogen for the fuel supply of fuel cell vehicles. Throughout this investigation, the authors discovered that, in 2050, the surplus of electricity to be produced compared to the current production in Italy (year 2021) is equal to +27.6% (1). This value increases if two limit scenarios are considered: it becomes +40.0% within a limit scenario in which the entire private car fleet is ...
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Combustion process simulation based on CFD approach is a fundamental tool in order to assess the engine design. For Diesel engine applications a critical tool is the prediction of the boundary conditions of the combustion process, in... more
Combustion process simulation based on CFD approach is a fundamental tool in order to assess the engine design. For Diesel engine applications a critical tool is the prediction of the boundary conditions of the combustion process, in particular the injected fuel mass and the velocity profile of the injection itself. Usually for simulating the combustion process in HSDI engine the unique data about the injector geometry available are: a) Number of poppet holes; b) Geometrical area of the poppet holes; c) Electrical data from the ECU. By these inputs it is not possible to get satisfactory boundary conditions for the 3D model, while they can be used in a 1D model of the injector for obtaining results in terms of injected fuel mass and velocity profile. The idea at the basis of the paper is to simplify a complex model of the injector developed by the authors in order to get a model suitable for this kind of application. In particular this model is a black box in which it is possible to adjust some parameters based on the limited data available in order to get the results of interest
Research Interests:
Many researchers in industry and academia are showing an increasing interest in the definition of fuel surrogates for Computational Fluid Dynamics simulation applications. This need is mainly driven by the necessity of the engine research... more
Many researchers in industry and academia are showing an increasing interest in the definition of fuel surrogates for Computational Fluid Dynamics simulation applications. This need is mainly driven by the necessity of the engine research community to anticipate the effects of new gasoline formulations and combustion modes (e.g., Homogeneous Charge Compression Ignition, Spark Assisted Compression Ignition) to meet future emission regulations. Since those solutions strongly rely on the tailored mixture distribution, the simulation and accurate prediction of the mixture formation will be mandatory. Focusing purely on the definition of surrogates to emulate liquid phase and liquid-vapor equilibrium of gasolines, the following target properties are considered in this work: density, Reid vapor pressure, chemical macro-composition and volatility. A set of robust algorithms has been developed for the prediction of volatility and Reid vapor pressure. A Bayesian optimization algorithm based ...
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Water injection is becoming a technology of increasing interest for SI engines development to comply with current and prospective regulations. To perform a rapid optimization of the main parameters involved by the water injection process,... more
Water injection is becoming a technology of increasing interest for SI engines development to comply with current and prospective regulations. To perform a rapid optimization of the main parameters involved by the water injection process, it is necessary to have reliable CFD methodologies capable of capturing the most important phenomena. In the present work, a methodology for the CFD simulation of combustion cycles of SI GDI turbocharged engines under water injection operation is proposed. The ECFM-3Z model adopted for combustion and knock simulations takes advantages by the adoption of correlations for the laminar flame speed, flame thickness and ignition delay times prediction obtained by a detailed chemistry calculation. The latter uses machine learning algorithms to reduce the time to generate the full database while still maintaining an even distribution along the variables of interest. The results demonstrate the applicability of the proposed methodology, capable of capturing...
Research Interests:
The heat transfer phenomena in Internal Combustion Engines (ICEs) are one of the main research topics that need to be addressed to enhance the performance in terms of power, efficiency, emissions and reliability. The present study is... more
The heat transfer phenomena in Internal Combustion Engines (ICEs) are one of the main research topics that need to be addressed to enhance the performance in terms of power, efficiency, emissions and reliability. The present study is focused on the evaluation of the in-cylinder heat fluxes through the use of Computational Fluid Dynamic (CFD) simulations, with a wall function approach. In particular, the aim of this work is to present a new fully non-isothermal wall function obtained from the one-dimensional (1-D) energy balance equation for turbulent flows in the boundary layers, specifying all the steps and assumptions which have carried to the final fully compressible formulation. The new proposed wall function has been validated against experimental data of the General Motors (GM) Pancake Engine, representative of low Brake Mean Effective Pressure (bmep) operating point, comparing the results with other existing wall functions. With the objective of a mesh independency analysis, the wall functions considered have been tested with three different grids, varying the height of the first layer. Globally, it has been found that the new proposed wall function is less sensitive to the cell size: this feature could be exploited in a real modern engine for a better estimation of the heat fluxes in every part of the domain, where the cell sizes can vary due to the geometry complexity. Moreover, a hypothesis on how to make the new wall function suited also for an engine with much higher bmep is discussed. The simulations are performed by using Star-CD and the new proposed wall function has been implemented via subroutine
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An ignition model based on Lagrangian approach was set-up. A lump model for the electrical circuit of the spark plug is used to compute breakdown and glow energy. At the end of shock wave and very first plasma expansion, a spherical... more
An ignition model based on Lagrangian approach was set-up. A lump model for the electrical circuit of the spark plug is used to compute breakdown and glow energy. At the end of shock wave and very first plasma expansion, a spherical kernel is deposited inside the gas flow at spark plug location. A simple model allows one to compute initial
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For increasing the thermal engine efficiency, faster combustion and low cycle-to-cycle variation are required. In PFI engines the organization of in-cylinder flow structure is thus mandatory for achieving increased efficiency. In... more
For increasing the thermal engine efficiency, faster combustion and low cycle-to-cycle variation are required. In PFI engines the organization of in-cylinder flow structure is thus mandatory for achieving increased efficiency. In particular the formation of a coherent tumble vortex with dimensions comparable to engine stroke largely promotes proper turbulence production extending the engine tolerance to dilute/lean mixture. For motorbike and scooter applications, tumble has been considered as an effective way to further improve combustion system efficiency and to achieve emission reduction since layout and weight constraints limit the adoption of more advanced concepts. In literature chamber geometry was found to have a significant influence on bulk motion and turbulence levels at ignition time, while intake system influences mainly the formation of tumble vortices during suction phase. The most common engine parameters believed to affect in-cylinder flow structure are: 1. Intake du...
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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... more
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' affidabilit\ue0, la ripetibilit\ue0 ed i limiti del modello numerico adottato.La generale attendibilit\ue0 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 velocit\ue0 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 \ue8 dedicata alla verifica del funzionamento dell'elettro-iniettore una volta inserito nel sistema di iniezione di un motore 4\ub7cilindri. 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 regolaz\uecone 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
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Upcoming Euro 4 and Euro 5 emission standards are increasing efforts on injection system developments in order to improve mixture quality and combustion efficiency. The target features of advanced injection systems are related to their... more
Upcoming Euro 4 and Euro 5 emission standards are increasing efforts on injection system developments in order to improve mixture quality and combustion efficiency. The target features of advanced injection systems are related to their capability of operating multiple injection with a precise control of the amount of injected fuel, low cycle-by-cycle variability and life drift, within flexible strategies. In order to accomplish this task, injector performance must be optimised by acting on: optimisation of electronic, driving circuit, detailed investigation of different nozzle hole diameter configurations, assessment of the influence of manufacturing errors on hole diameter and inlet rounding on injector performance.
Research Interests:
The paper investigates the variation of the mass of the fuel injected with respect to nominal conditions in Common Rail injection systems for Diesel automotive applications. Two possible operating conditions have been considered: the... more
The paper investigates the variation of the mass of the fuel injected with respect to nominal conditions in Common Rail injection systems for Diesel automotive applications. Two possible operating conditions have been considered: the consecutive injection of two injectors and the multiple shots of the same injector in the same engine cycle. An integrated experimental and numerical methodology has been used. Several experimental information were available in terms of instantaneous rail and pipe pressure and mass flow rate at different conditions. The 1D numerical model of the whole injection system was useful in addressing the questions remained unresolved in the post-experiments analysis. The experimental results show that injector performances are more related to pressure oscillations in injector connecting pipe rather than inside the common rail. The fuel mass is slightly depending on the mutual influence between two consecutive injectors while it is strongly affected by the dwell time (i.e., DTW) between consecutive shots of the same injector in the same engine cycle. The dwell time variation determines different pressure oscillation amplitudes in the injector connecting pipe at the electrical (nominal) start of the injection of the second pulse. As a consequence, different hydraulic (i.e., actual) start and duration of the injection of the second pulse occurs depending on dwell time. A parametric analysis showed that the injected fuel mass variation with dwell time can be reduced by using shorter and larger injector connecting pipes