Documents disponibles écrits par cet auteur

Hydraulic circuit design rules to remove the dependence of the injected fuel amount on dwell time in multijet CR systems / Baratta, Mirko in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 13 p Titre : Hydraulic circuit design rules to remove the dependence of the injected fuel amount on dwell time in multijet CR systems Type de document : texte imprimé Auteurs : Baratta, Mirko, Auteur ; Andrea Emilio Catania, Auteur ; Alessandro Ferrari, Auteur Année de publication : 2009 Article en page(s) : 13 p Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Oscillations;  pressure;  fuels;  waves;  ejectors;  pipes;  rails;  design Résumé : In multijet common rail (CR) systems, the capability to manage multiple injections with full flexibility in the choice of the dwell time (DT) between consecutive solenoid current pulses is one of the most relevant design targets. Pressure oscillations triggered by the nozzle closure after each injection event induce disturbances in the amount of fuel injected during subsequent injections. This causes a remarkable dispersion in the mass of fuel injected when DT is varied. The effects of the hydraulic circuit layout of CR systems were investigated with the objective to provide design rules for reducing the dependence of the injected fuel amount on DT. A multijet CR of the latest solenoid-type generation was experimentally analyzed at different operating conditions on a high performance test bench. The considerable influence that the injector-supplying pipe dimensions can exert on the frequency and amplitude of the injection-induced pressure oscillations was widely investigated and a physical explanation of cause-effect relationships was found by energetics considerations, starting from experimental tests. A parametric study was performed to identify the best geometrical configurations of the injector-supplying pipe so as to minimize pressure oscillations. The analysis was carried out with the aid of a previously developed simple zero-dimensional model, allowing the evaluation of pressure-wave frequencies as functions of main system geometric data. Pipes of innovative aspect ratio and capable of halving the amplitude of injected-volume fluctuations versus DT were proposed. Purposely designed orifices were introduced into the rail-pipe connectors of a commercial automotive injection system, so as to damp pressure oscillations. Their effects on multiple-injection performance were experimentally determined as being sensible. The resulting reduction in the injector fueling capacity was quantified. It increased by lowering the orifice diameter. The application of the orifice to the injector inlet-pipe with innovative aspect ratio led to a hydraulic circuit solution, which coupled active and passive damping of the pressure waves and minimized the disturbances in injected fuel volumes. Finally, the influence of the rail capacity on pressure-wave dynamics was studied and the possibility of severely reducing the rail volume (up to one-fourth) was assessed. This can lead to a system not only with reduced overall sizes but also with a prompter dynamic response during engine transients. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Hydraulic circuit design rules to remove the dependence of the injected fuel amount on dwell time in multijet CR systems [texte imprimé] / Baratta, Mirko, Auteur ; Andrea Emilio Catania, Auteur ; Alessandro Ferrari, Auteur . - 2009 . - 13 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 13 p Mots-clés : Oscillations;  pressure;  fuels;  waves;  ejectors;  pipes;  rails;  design Résumé : In multijet common rail (CR) systems, the capability to manage multiple injections with full flexibility in the choice of the dwell time (DT) between consecutive solenoid current pulses is one of the most relevant design targets. Pressure oscillations triggered by the nozzle closure after each injection event induce disturbances in the amount of fuel injected during subsequent injections. This causes a remarkable dispersion in the mass of fuel injected when DT is varied. The effects of the hydraulic circuit layout of CR systems were investigated with the objective to provide design rules for reducing the dependence of the injected fuel amount on DT. A multijet CR of the latest solenoid-type generation was experimentally analyzed at different operating conditions on a high performance test bench. The considerable influence that the injector-supplying pipe dimensions can exert on the frequency and amplitude of the injection-induced pressure oscillations was widely investigated and a physical explanation of cause-effect relationships was found by energetics considerations, starting from experimental tests. A parametric study was performed to identify the best geometrical configurations of the injector-supplying pipe so as to minimize pressure oscillations. The analysis was carried out with the aid of a previously developed simple zero-dimensional model, allowing the evaluation of pressure-wave frequencies as functions of main system geometric data. Pipes of innovative aspect ratio and capable of halving the amplitude of injected-volume fluctuations versus DT were proposed. Purposely designed orifices were introduced into the rail-pipe connectors of a commercial automotive injection system, so as to damp pressure oscillations. Their effects on multiple-injection performance were experimentally determined as being sensible. The resulting reduction in the injector fueling capacity was quantified. It increased by lowering the orifice diameter. The application of the orifice to the injector inlet-pipe with innovative aspect ratio led to a hydraulic circuit solution, which coupled active and passive damping of the pressure waves and minimized the disturbances in injected fuel volumes. Finally, the influence of the rail capacity on pressure-wave dynamics was studied and the possibility of severely reducing the rail volume (up to one-fourth) was assessed. This can lead to a system not only with reduced overall sizes but also with a prompter dynamic response during engine transients. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

Multidimensional modeling of natural gas jet and mixture formation in direct injection spark ignition engines—development and validation of a virtual injector model / Baratta, Mirko in Transactions of the ASME . Journal of fluids engineering, Vol. 133 N° 4 (Avril 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 133 N° 4 (Avril 2011) . - 14 p. Titre : Multidimensional modeling of natural gas jet and mixture formation in direct injection spark ignition engines—development and validation of a virtual injector model Type de document : texte imprimé Auteurs : Baratta, Mirko, Auteur ; Andrea E. Catania, Auteur ; Pesce, Francesco C., Auteur Année de publication : 2011 Article en page(s) : 14 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : compressible  flow,  computational  fluid  dynamics,  fuel  systems,  internal  combustion  engines,  jets,  nozzles,  numerical  analysis,  pistons,  schlieren  systems,  shock  waves,  turbulence Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : During the last few years, the integration of CFD tools in the internal combustion (IC) engine design process has continually increased, allowing time and cost savings as the need for experimental prototypes has diminished. Numerical analyses of IC engine flows are rather complex from both the conceptual and operational sides. In fact, these flows involve a variety of unsteady phenomena and the right balance between numerical solution accuracy and computational cost should always be reached. The present paper is focused on computational modeling of natural gas (NG) direct injection (DI) processes from a poppet-valve injector into a bowl-shaped combustion chamber. At high injection pressures, the gas efflux from the injector and the mixture formation processes include turbulent and compressible flow features, such as rarefaction waves and shock formation, which are difficult to accurately capture with numerical simulations, particularly when the combustion chamber geometry is complex and the piston and intake/exhaust valve grids are moving. In this paper, a three-dimensional moving grid model of the combustion engine chamber, originally developed by the authors to include simulation of the actual needle lift, has been enhanced by increasing the accuracy in the proximity of the sonic section of the critical valve-seat nozzle, in order to precisely capture the expansion dynamics the methane undergoes inside the injector and immediately downstream from it. The enhanced numerical model was then validated by comparing the numerical results to Schlieren experimental images for gas injection into a constant-volume bomb. Numerical studies were carried out in order to characterize the fuel-jet properties and the evolution of mixture formation for a centrally mounted injector configuration in the case of a pancake-shaped test chamber and the real engine chamber. Finally, the fluid properties calculated by the model in the throat section of the critical nozzle were taken as reference data for developing a new effective virtual injector model, which allows the designer to remove the whole computational domain upstream from the sonic section of the nozzle, keeping the flow properties virtually unchanged there. The virtual injector model outcomes were shown to be in very good agreement with the results of the enhanced complete injector model, substantiating the reliability of the proposed novel approach. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA400013 [...] [article] Multidimensional modeling of natural gas jet and mixture formation in direct injection spark ignition engines—development and validation of a virtual injector model [texte imprimé] / Baratta, Mirko, Auteur ; Andrea E. Catania, Auteur ; Pesce, Francesco C., Auteur . - 2011 . - 14 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 133 N° 4 (Avril 2011) . - 14 p. Mots-clés : compressible  flow,  computational  fluid  dynamics,  fuel  systems,  internal  combustion  engines,  jets,  nozzles,  numerical  analysis,  pistons,  schlieren  systems,  shock  waves,  turbulence Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : During the last few years, the integration of CFD tools in the internal combustion (IC) engine design process has continually increased, allowing time and cost savings as the need for experimental prototypes has diminished. Numerical analyses of IC engine flows are rather complex from both the conceptual and operational sides. In fact, these flows involve a variety of unsteady phenomena and the right balance between numerical solution accuracy and computational cost should always be reached. The present paper is focused on computational modeling of natural gas (NG) direct injection (DI) processes from a poppet-valve injector into a bowl-shaped combustion chamber. At high injection pressures, the gas efflux from the injector and the mixture formation processes include turbulent and compressible flow features, such as rarefaction waves and shock formation, which are difficult to accurately capture with numerical simulations, particularly when the combustion chamber geometry is complex and the piston and intake/exhaust valve grids are moving. In this paper, a three-dimensional moving grid model of the combustion engine chamber, originally developed by the authors to include simulation of the actual needle lift, has been enhanced by increasing the accuracy in the proximity of the sonic section of the critical valve-seat nozzle, in order to precisely capture the expansion dynamics the methane undergoes inside the injector and immediately downstream from it. The enhanced numerical model was then validated by comparing the numerical results to Schlieren experimental images for gas injection into a constant-volume bomb. Numerical studies were carried out in order to characterize the fuel-jet properties and the evolution of mixture formation for a centrally mounted injector configuration in the case of a pancake-shaped test chamber and the real engine chamber. Finally, the fluid properties calculated by the model in the throat section of the critical nozzle were taken as reference data for developing a new effective virtual injector model, which allows the designer to remove the whole computational domain upstream from the sonic section of the nozzle, keeping the flow properties virtually unchanged there. The virtual injector model outcomes were shown to be in very good agreement with the results of the enhanced complete injector model, substantiating the reliability of the proposed novel approach. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA400013 [...]

Premixed-diffusive multizone model for combustion diagnostics in conventional and PCCI diesel engines / Baratta, Mirko in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 133 N° 10 (Octobre 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 10 (Octobre 2011) . - 13 p. Titre : Premixed-diffusive multizone model for combustion diagnostics in conventional and PCCI diesel engines Type de document : texte imprimé Auteurs : Baratta, Mirko, Auteur ; Andrea E. Catania, Auteur ; Alessandro Ferrari, Auteur Année de publication : 2011 Article en page(s) : 13 p. Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Combustion  Diesel  engines  Ignition Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A new multizone premixed-diffusive combustion model has been developed, assessed, and applied to diagnose the burning process and emission formation in a conventional and in a premixed charge compression ignition (PCCI) diesel engine. The model is based on the Dec conceptual scheme, which considers combustion as a two-stage quasi-steady process: All fuel particles undergo a first rich premixed combustion phase, and the products complete their oxidation in close-to-stoichiometric conditions at the jet periphery through a diffusion flame. The combustion chamber contents have been divided into several homogeneous zones to which the energy and mass conservation principles were applied. The computed thermodynamic and thermochemical properties in the burned gas zones allowed a post-processing analysis to be made of the nitric oxides (NO), particulate matter (PM), and carbon monoxide (CO) formation. The model requires the in-cylinder pressure trace and other experimental engine quantities as input data and calculates the premixed and diffusive heat release rates along with the temperature and mass evolutions of the different zones. Thus, the model is not predictive but diagnostic: The objective is to interpret measured engine data in order to obtain insight into the in-chamber combustion and pollutant formation processes. The model has been tested on EGR-sweeps and under full-load conditions on the conventional engine and under a high EGR operating condition on the PCCI engine. With reference to NO emissions, the model results showed an excellent agreement with the experimental data for all the tests even when the main model parameters were kept constant for different test conditions. Good results were also obtained for the prediction of the CO and PM emission levels. Finally, for the premixed combustion zone, it was ascertained that higher local A/F ratios were required in the PCCI combustion mode than in the conventional mode as a consequence of the increase in the degree of premixing. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013300 [...] [article] Premixed-diffusive multizone model for combustion diagnostics in conventional and PCCI diesel engines [texte imprimé] / Baratta, Mirko, Auteur ; Andrea E. Catania, Auteur ; Alessandro Ferrari, Auteur . - 2011 . - 13 p. Génie mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 10 (Octobre 2011) . - 13 p. Mots-clés : Combustion  Diesel  engines  Ignition Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A new multizone premixed-diffusive combustion model has been developed, assessed, and applied to diagnose the burning process and emission formation in a conventional and in a premixed charge compression ignition (PCCI) diesel engine. The model is based on the Dec conceptual scheme, which considers combustion as a two-stage quasi-steady process: All fuel particles undergo a first rich premixed combustion phase, and the products complete their oxidation in close-to-stoichiometric conditions at the jet periphery through a diffusion flame. The combustion chamber contents have been divided into several homogeneous zones to which the energy and mass conservation principles were applied. The computed thermodynamic and thermochemical properties in the burned gas zones allowed a post-processing analysis to be made of the nitric oxides (NO), particulate matter (PM), and carbon monoxide (CO) formation. The model requires the in-cylinder pressure trace and other experimental engine quantities as input data and calculates the premixed and diffusive heat release rates along with the temperature and mass evolutions of the different zones. Thus, the model is not predictive but diagnostic: The objective is to interpret measured engine data in order to obtain insight into the in-chamber combustion and pollutant formation processes. The model has been tested on EGR-sweeps and under full-load conditions on the conventional engine and under a high EGR operating condition on the PCCI engine. With reference to NO emissions, the model results showed an excellent agreement with the experimental data for all the tests even when the main model parameters were kept constant for different test conditions. Good results were also obtained for the prediction of the CO and PM emission levels. Finally, for the premixed combustion zone, it was ascertained that higher local A/F ratios were required in the PCCI combustion mode than in the conventional mode as a consequence of the increase in the degree of premixing. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013300 [...]