1,720,971 research outputs found
Virtual GDI Engine as a Tool for Model-Based Calibration
No full textRecent and forthcoming fuel consumption reduction
requirements and exhaust emissions regulations are forcing
the development of innovative and particularly complex
intake-engine-exhaust layouts. In the case of Spark Ignition
(SI) engines, the necessity to further reduce fuel consumption
has led to the adoption of direct injection systems,
displacement downsizing, and challenging intake-exhaust
configurations, such as multi-stage turbocharging or turboassist
solutions. Further, the most recent turbo-GDI engines
may be equipped with other fuel-reduction oriented
technologies, such as Variable Valve Timing (VVT) systems,
devices for actively control tumble/swirl in-cylinder flow
components, and Exhaust Gas Recirculation (EGR) systems.
Such degree of flexibility has a main drawback: the
exponentially increasing effort required for optimal engine
control calibration. Even if extremely efficient and
statistically-based experiments have recently been introduced
as standard protocols during test-cell calibration activity, the
time and the instrumentation required for a fully-validated
test-cell calibration dataset has been steeply increasing during
the last few years.
The methodology proposed in this paper is based on
computing technologies, and deeper understanding of
physical phenomena, which have been accessible only in very
recent times. If the availability of dimensional models fast
enough to be used in an iterative loop (aimed at the
optimization of pre-designed cost or goal functions) allows
the introduction of virtual-engine based calibration
techniques, the challenge is to identify the best way to take
advantage of them.
One necessary step is the reduction of fully 1-D engine
models to simpler (and faster to resolve) but still-dimensional
engine thermo-fluid-dynamics representations. One of the
outcomes of this work is the demonstration that fullyautomatic
geometry simplifications (to reduce the
computational effort) may still not guarantee model
consistency, the main reasons being the assignment of
inadequate boundary parameters (such as imposed wall
temperatures) resulting after merging various elements, in an
effort to reduce model complexity.
The second and most important phase is the definition of the
calibration scheme. As it always happens with model-based
design, the goals of the overall activity should be closely
related to the accuracy of the simulation tool. The present
project demonstrates the possibility of using simulation tools
in a new environment, which is somehow in-between desktop
design-oriented simulation (1-D and 3-D models) and realtime
model-based control (0-D). The model reliability, and
therefore the geometry reduction consistency, has been
carefully checked to limit significant accuracy loss, especially
for the variables being used for virtual calibration. Also, in
the paper the limits of the model are introduced and taken
into account, and the definition of cost functions and
constraints (related to emissions limitation, fuel consumption
reduction, and components protection criteria) is discussed.
Finally, the paper shows the application of the overall virtualengine
based calibration methodology to a Gasoline Direct
Injection (GDI) turbocharged engine, equipped with tumbleflaps
and Variable Valve Timing (VVT) systems. Simulation
(and corresponding look-up-tables calibration) results are
compared to experimentally measured ones (with similar sets
of calibration parameters), demonstrating the potential of adopting the proposed methodology as an intermediate step
between engine development and calibration-related test cell
(and on-board) activities
Adolescenti adottati e relazioni familiari e sociali
No full textGli adolescenti adottati costituiscono un gruppo con peculiarità proprie: sono italiani a tutti gli effetti, inseriti nel nostro tessuto sociale (scuola, lavoro ecc.), ma sono nati in luoghi lontani e in età più o meno precoce hanno dovuto lasciare la loro terra per essere introdotti in una nuova famiglia e in un nuovo paese con un background etnico e culturale assai diverso. Certamente il nostro contesto socioculturale vede una presenza sempre più numerosa di persone appartenenti a diversi gruppi etnici, ma ciò non costituisce necessariamente un elemento di facilitazione per l’inserimento dei ragazzi adottati: anzi, spesso è un elemento confusivo, in quanto non di rado essi vengono etichettati come “immigrati” e riportano di essere oggetto di discriminazione. Dunque la questione dell’identità etnica è davvero rilevante. In questo lavoro abbiamo voluto approfondire questo aspetto e abbiamo cercato di dare risposta ad alcune domande quali: gli adolescenti adottati come vivono l’appartenenza al proprio gruppo etnico? Che significato ha nella loro vita? Come vengono visti dagli altri? Sono vittime di episodi di discriminazione? Qual è il punto di vista dei genitori e cosa fanno concretamente per trasmettere loro la cultura del paese di origine
Evaluation of hole-specific injection rate based on momentum flux measurement in GDI systems
No full textA novel methodology for the estimation of the mass flow rate delivered by each hole of a multi-hole GDI nozzle is presented and discussed in this paper. The proposed method is based on the measurement of the impact force of each jet and it is able to evaluate the individual hole injection rate and injected mass using the relationship between the spray momentum flux and the mass flow rate. Three different nozzles are tested, one featuring equal hole diameters and two with differentiated hole-to-hole dimensions. Firstly, results are validated in terms of total injection rate, comparing the sum of the individual hole flow rates with the signal from a Zeuch-based flow meter. Secondly, outcomes are compared with the direct measurement of the injected quantity by means of a special device able to collect and weight the fuel delivered from each hole. Results evidence an excellent agreement in terms of mass flow rate dynamic profile as the proposed method is able to detect both opening and closure transients and the static flow rate. The proposed method proved to be able to capture the dynamic mass flow rate in transient conditions, i.e. very short injections, overcoming a limitation of the methodology proposed in a previous study. Moreover, in terms of injected mass, the results show a percentage error lower than 5% for medium and long energizing times and a maximum error of 9.5% for short injections in ballistic operating conditions
Adverse reaction to specific immunotherapy for house-dust mite in a patient with Anisakis allergy
No full textThe 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
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