1,720,957 research outputs found
Advanced Modeling of Common Rail Injector Dynamics and Comparison with Experiments
No full textThe aim of this work is to set up a
methodology for simulating Common Rail highpressure
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 submodels
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
The role of simulation in the development of a fast-actuation solenoid C.R. Injection System
No full textUpcoming 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 fuel injected, low cycle-by-cycle variability and life drift, within flexible strategies. In order to accomplish this task, performance must be optimised since injection system concept development by acting on. The extensive use of numerical approach has been identified as a necessary integration to experiments in order to put on the market high quality injection systems accomplishing strict engine control strategies. The modelling approach allows focusing the experimental campaign only on critical issues saving time and costs, furthermore it is possible to deeply understand inner phenomena that cannot be measured. The lump/1D model of the whole system built into the AMESimÒ code was presented in previous works: particular attention was devoted in the simulation of the electromagnetic circuits, actual fluid-dynamic forces acting on needle surfaces and discharge coefficients, evaluated by means 3D-CFD simulations.
In order to assess new injection system dynamic response under multiple injection strategies reproducing actual engine operating conditions it is necessary to find the proper model settings. In this work the integration between the injector and the system model, which comprehends the pump, the pressure regulator, the rail and the connecting-pipes, will be presented. For reproducing the dynamic response of the whole system will be followed a step-by-step approach in order to prevent modelling inaccuracies. Firstly will be presented the linear analysis results performed in order to find injection system own natural frequencies. Secondly based on linear analysis results will be found proper injection system model settings for predicting dynamic response to external excitations, such as pump perturbations, pressure regulator dynamics and injection pulses. Thirdly experimental results in terms of instantaneous flow rate and integrated injected volume for different operating conditions will be presented in order to highlight the capability of the modelling methodology in addressing the new injection system design
Analisi e progettazione di un “Urea Delivery Module” per sistemi catalitici SCR
No full textNell’ambito del continuo processo di sviluppo dei motori Diesel riveste sempre maggiore importanza la problematica
dell’abbattimento delle emissioni di ossidi di azoto. La tecnologia della riduzione catalitica selettiva (SCR) per mezzo
dell’ammoniaca sta trovando sempre maggior impiego. L’efficienza dimostrata nella conversione dei NOx supera il 95%. Da
molti anni è stata applicata nel campo dei motori stazionari di grossa taglia e successivamente nel settore dei veicoli heavyduty.
Oggi si sta ampiamente diffondendo anche nel trasporto light-duty e nelle autovetture di alta gamma.
La presente memoria descrive il processo di progettazione di un sistema di alimentazione di urea che si va ad integrare in un
sistema SCR completo. Le funzioni dell’Urea Delivery Module – UDM – sono quelle di aspirare il fluido AdBlue dal
serbatoio, filtrarlo, pomparlo regolandone la pressione di mandata all’iniettore, provvedere allo sghiacciamento nel caso di
partenze a freddo sino a -20°C grazie ad un opportuno heater elettrico, ospitare sensori di pressione, temperatura, qualità urea e
livello urea nel serbatoio.
L’attività, svolta in collaborazione con Magneti Marelli Powertrain ha portato allo sviluppo di un prototipo avanzato su cui
sono in corso i primi test sperimentali. Le sfide principali che sono state affrontate nella progettazione sono state la
compattazione del layout, l’integrazione con il serbatoio, l’analisi termo-fluidodinamica dedicata al problema dello
scongelamento e non ultimo il contenimento di pesi e costi del prodotto.
Lo sviluppo ha visto una prima fase di modellazione idraulica del sistema al fine di definire le performance e le specifiche
del sistema, cui è seguita una fase di modellazione solida dei componenti e una analisi tridimensionale del problema dello
scongelamento. Per quest’ultimo problema è stato realizzato un apposito modello CFD-3D multi-fase (liquido-solido) in grado
di simulare il passaggio di stato (scongelamento). Nel dominio solido si risolve la conduzione descritta dall’equazione di
Fourier, mentre nel dominio liquido viene risolta la dinamica di un liquido pesante descritto dalle equazioni di Navier-Stokes.
Il calcolo è non stazionario e l’obiettivo è la determinazione del fronte di scongelamento nel tempo. Il modello ha permesso
un’ottimizzazione della distribuzione delle sorgenti di potenza elettrica sin dalle prime fasi della progettazione, permettendo di
impostare il design di tutto il sistema in maniera armonica con le esigenze termiche
Numerical Investigation of Critical Issues in Multiple-Injection Strategy Operated by a New C.R. Fast-Actuation Solenoid Injector
No full textAdvanced Modelling of a New Diesel Fast Solenoid Injector and Comparison with Experiments
No full textUpcoming 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.
The paper will focus on the use of an integrated lump-1D/3D methodology for the design of advanced new fast solenoid Common Rail (C.R.) injector for high speed diesel engines. A lump-model built up in AMESimâ environment was used to address the injector design. Particular attention has been devoted in the simulation of the electromagnetic circuit. The functional relation between current and electromagnetic force at different air-gap values, as well as of fluid dynamics parameters was obtained by running an axial-symmetric model built into a finite-element code. Sub-models were introduced in order to account for the contribution of squish motion and actual fluid-dynamics force acting upward on needle surfaces. Multidimensional CFD simulations were extensively used in order to feed the model with the discharge coefficient of the orifices as a function of flow regimes and geometrical details.
Preliminary experimental results in terms of instantaneous flow rate and integrated injected volume for different operating conditions will be presented in order to validate the modelling methodology and to highlight new injector performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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