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Modeling of Aqueous Urea Solution injection with characterization of spray-wall cooling effect and risk of onset of wall wetting
Get PDFAbstractThe definition of a sufficiently resolved heat transfer model with spray cooling effect as a function of each droplet kinetic and thermal parameters is a key factor in the numerical simulation of aqueous urea (AUS) based Selective Catalytic Reduction (SCR) exhaust after-treatment systems.A consolidated spray-wall interaction model [1] has been implemented on the open source 3D finite volume software OpenFOAM and a critical investigation of its behaviour in engine representative conditions is reported.A simplified test case is used to highlight the influence of the chosen model on the numerical simulation of the system, reducing the importance of the other spray sub-models in the Lagrangian-Eulerian computational framework. The coupling between the droplet evaporation heat flux and the gas-solid interface thermal boundary condition has been studied, pointing out the significance of each contribution.The main focus of this work is to present reference conditions to simulate the spray-dry wall spray impingement behavior to determine the ‘onset of wall wetting’ thermal conditions
1D-3D Coupled Simulation of the Fuel Spray Propagation Inside the Air-Box of a Moto3 Motorbike: Analysis of Spray Targeting and Injection Timing
No full textIn this work an integration between a 1D code (Gasdyn) with a CFD code (OpenFOAM®) has been applied to improve the performance of a Moto3 engine. The four-stroke, single cylinder S.I. engine was modeled, in order to predict the wave motion in the intake and exhaust systems and to study how it affects the cylinder gas exchange process. The engine considered was characterized by having an air induction system with integrated filter cartridge, air-box and intake runner, including two fuel injectors, resulting in a complex air-path from the intake mouth to the intake valves, which presents critical aspects when a 1D modeling is addressed. The exhaust and intake systems have been optimized form the point of view of the wave action. However, due to the high revolution speed reached by this type of engine, the interaction between the gas stream and the fuel spray becomes a key aspect to be addressed in order to achieve the best performance at the desired operating condition. In particular, the evaporation of the fuel injection causes an increase of charge density due to the cooling of the fuel droplets, resulting in a supercharging effect. Moreover, a precise targeting and injection timing of the spray is important in order to avoid liquid film formation in undesired zone, which usually lead to irregular power output. This work proposes an analysis, by means of coupled 1D-3D simulation, of the fuel spray propagation inside the air-box. Spray-wall interaction is considered as well as liquid film formation and evaporation. The final target of the study is the analysis of the fuel injection strategy both on the point of view of targeting and timing, finalized to the optimization of the injection system for the engine which will be used in the next championship
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
CFD modeling and experimental characterization of urea/water solution injection inside SCR systems of diesel engines
No full textIl lavoro proposto pone l'attenzione sulla caratterizzazione dell'iniezione a bassa pressione utilizzata nella sezione pre-catalitica di un sistema per la riduzione di ossidi d'azoto (Selective Catalytic Reduction) applicato a veicoli. La Phase Doppler Anemometry rappresenta il principale strumento per la valutazione delle proprietà cinematiche di uno spray in condizioni operative realistiche. La dimensione e la velocità delle gocce iniettate da due diversi iniettori è misurata principalmente attraverso l'uso di un banco prova in grado di riprodurre le condizioni termo-fluidodinamiche di un sistema di rimozione inquinanti. I dati sono utilizzati, in accoppiamento con la visualizzazione della morfologia dello spray attraverso Shadow Imaging, per inizializzare i modelli di iniezione da inserire in simulazioni CFD con approccio Lagrangiano-Euleriano realizzate con il software open-source OpenFOAM. I risultati numerici sono validati sulla base di dati raccolti rispettivamente nella regione d'iniezione e vicino alla superficie solida di impatto dello spray. La cospicua frazione di massa liquida che interagisce con le pareti del sistema è quantificata attraverso un patternator meccanico in grado di produrne una distribuzione spaziale. Le misure mostrano che più' della metà del liquido iniettato impatta con la parete solida del sistema, in qualsiasi condizione di flusso gassoso. Le simulazioni fluidodinamiche sono usate per valutare l'intrusività dello strumento nel sistema e successivamente sono comparate ai risultati di flusso di massa liquida, sottolineando come l'assegnazione di un numero costante di gocce ad ogni parcel computazionale migliori la rappresentazione dello spray. Un modello di interazione spray-parete basato su dati di letteratura è stato implementato nel codice, introducendo una soglia termica nell'identificazione del regime di impatto e risolvendo lo scambio termico con le superfici del sistema. L'interazione termica diretta tra gocce e solido è identificata come il termine principale nel bilancio termico delle pareti solide, ed è rappresentata con mappe di impatto che sintetizzano il fenomeno. Dal punto di vista dello spray, l'interazione con le pareti rappresenta l'unica sorgente di break-up delle gocce primarie, che non riescono a essere deviate dal flusso gassoso.The present work focuses on the characterization of the low-pressure driven injection applied to the pre-catalytic section of a Selective Catalytic Reduction system for vehicle applications. Phase Doppler Anemometry represents the main technique to assess the spray kinematic features in cross-flow conditions in a very confined environment. The experiments are mostly carried out in a test bench able to reproduce Diesel engine exhaust after-treatment operating conditions, providing size and velocity distributions of the droplets generated by two different commercially available injectors. The data are used, coupled with qualitative Shadow Imaging visualizations of the sprays, to initialize a numerical injection model for each nozzle, to be included in a Lagrangian-Eulerian framework handled with the open-source platform OpenFOAM. The CFD simulation is validated on the near-nozzle behavior in quiescent air and on the data collected close to the primary impingement surface in cross-flow conditions. A conspicuous fraction of the liquid mass impacts the surface and its quantification is carried out with a mechanical patternator, producing spatially resolved mass distributions and showing that the entrainment in cross-flow is always less than the 50% of the injected mass. The simulation is used to estimate the intrusiveness of the instrument in the system, and then it is compared to the mass flux data, highlighting the improvement produced by the fixed number of droplets per parcel approach in the definition of the dispersed phase. A literature based spray-wall interaction model is implemented in the CFD code, introducing a thermal threshold on the interaction regime identification and the conductive heat transfer between spray and walls, which are solved in their thermal transients. The direct interaction of the droplets with the solid surfaces is identified as the paramount term in the walls energy balance, and is represented with synthetic impingement maps. On the other hand the impact on the walls is found to be the only source of break-up for the primary droplets, which are not deflected by the flow.DIPARTIMENTO DI ENERGIA29ONORATI, ANGELOBOTTANI, CARLO ENRIC
Diesel exhaust fluid injection at low pressure for SCR DeNOx after treatment systems : CFD modeling and validation
No full textLAUREA MAGISTRALEIl presente lavoro si vuole inserire nel contesto dell’abbattimento degli inquinanti
dei motori a combustione interna e, più precisamente, nello sviluppo di
sistemi SCR (Selective Catalytic Reduction). Lo scopo del presente lavoro è
dunque la validazione di uno spray di acqua e di soluzione Urea-acqua (UWS)
in OpenFOAMR", e la valutazione di tutti i modelli CFD che entrano in gioco
nella descrizione dei fenomeni fisici che si verificano durante l’iniezione.
Su questo argomento non molti studi sono stati svolti e, avendo a disposizione
poca letteratura a riguardo, molti aspetti non sono stati indagati a
fondo. Tuttavia sono presenti in letteratura gi`a numerosi modelli che tentano
di descrivere quello che rappresenta il problema cruciale dei sistemi SCR:
la formazione di deposito che causa l’otturazione delle tubature di scarico.
Si intuisce dunque l’importanza e la necessità effettiva di avere a disposizione
uno strumento che permetta di descrivere al meglio la propagazione
dello spray in differenti condizioni di flusso dei gas di scarico. Infatti, con
tale strumento, si possono valutare tutte quelle situazioni che portano a un
malfunzionamento di tutto il sistema SCR con notevole risparmio in termini
economici e tempistici.
Il corpo principale di questo lavoro di tesi quindi sarà dedicato allo studio
dell’evoluzione di uno spray caratterizzato da una bassa pressione di iniezione
nel software OpenFOAM. Per testare la bontà dei risultati delle simulazioni,
questi sono paragonati a dati ottenuti con tecniche ottiche e pubblicati in
articoli scientifici.
Di fronte a delle incongruenze prettamente fisiche, si è presentata la necessità
di implementare tre modelli di drag, che sono stati inseriti nella libreria del
software e sono stati valutati. Infine, avendo raggiunto la validazione dello spray in differenti regimi di flusso
dei gas di scarico, ulteriori analisi sono state svolte, col fine di comprendere
l’effettiva evoluzione dello spray nelle simulazioni e paragonarlo alla realta.Within the context of reducing the pollutant emissions of internal combustion
engines and, in particular, in the development of Selective Catalytic
Reduction systems, this research project aims to the validation of a low pressure
spray of both water and Urea-water solution in OpenFOAM and to
evaluate the CFD models that describe the physical phenomena occurring in
injections.
On this topic, not many studies are present in literature and many aspects
have not been investigated yet, even though there are already many studies
that aim to describe the main SCR problem: the wall impingement that
causes deposit formations. The actual need of a correct spray is therefore
fundamental to guarantee the correct CFD analysis of SCR systems.
The present work is focused on the propagation and evolution of a low pressure
spray in the open-source finite volume code OpenFOAM, in order to
clarify the behaviour of these sprays. The results of the simulations are compared
to data obtained by optical techniques. As some controversies rose up,
three drag models were implemented in the OpenFOAM library and then
tested. Finally, once reached the validation of the spray in different environmental
conditions, further analysis were done in order to comprehend the
evolution of this spray and compare it to reality
Modello numerico di un canale per l'adsorbimento di anidride carbonica da gas combusti
No full textLAUREA MAGISTRALEL'oggetto della tesi è la presentazione e validazione di un modello di un canale adsorbente per la separazione dell'anidride carbonica dai gas combusti provenienti da centrali di generazione energetica. Il modello è l'elemento basilare per simulare il funzionamento di una tecnologia innovativa di cattura post-combustione di anidride carbonica (CCS). L'idea di base per questa tecnologia è l'adsorbimento dell'anidride carbonica contenuta nei gas combusti su carbone attivo in un reattore monolitico con struttura a nido d'ape. La rigenerazione dell'adsorbente è ottenuta attraverso l'impiego di un flusso di vapore spillato dalla sezione a bassa pressione del ciclo di potenza, secondo uno schema TSA (Thermal Swing Adsorption). Il monolito è montato in un dispositivo rotante con architettura di tipo Ljungstrom attraversato alternativativamente da gas combusti in un settore, e da vapore, aria o altri flussi negli restanti settori (così da alternare fasi di adsorbimento, scarico e rigenerazione). Il modello del singolo canale adsorbente è il punto di partenza per un futuro studio di fattibilità tecnico-economica. Questa Tesi presenta i principi dell'adsorbimento su carbone attivo per differenti specie, tratta le più rilevanti peculiarità del processo proposto e descrive un modello matematico per l'adsorbimento, lo scambio termico e di massa ed il trasporto di quantità di moto ed energia per il canale e per il reticolo macro- e micro- poroso della matrice. Il modello matematico è quindi tradotto in un modello numerico, con l'implementazione dello schema di Lax-Wendroff a due passi (Richtmyer) per la risoluzione di un problema differenziale non stazionario 1D + 1D (canale + macro-pori). Infine il modello è validato attraverso dati di letteratura e vengono formulate alcune riflessioni, mostrando possibili semplificazioni per rendere più efficiente lo strumento di simulazione mantenendo la necessaria accuratezza.This dissertation presents and validates a model of an absorbent channel for the separation of carbon dioxide from the flue gas of power plants. This model is the basic element to simulate an innovative technology for post-combustion Carbon Capture and Sequestration (CCS). The basic idea of this technology is the absorption of carbon dioxide from flue gas onto a honeycomb monolithic reactor made of activated carbon. The regeneration of such a sorbent is carried out by steam bled from the low pressure section of the power cycle, according to a Thermal Swing Adsorption (TSA) scheme. The monolith is mounted in a rotating Ljungstrom-like device alternatively crossed by flue gas in a sector, and by steam/air or other flows in the other sectors (thus alternating phases of absorption, flushing and regeneration). The model of the single absorbent channel is the starting point for a future techno-economic feasibility study. This Thesis presents the basics of absorption onto activated carbon for different species; it discusses the main peculiarities of the proposed process; it defines a mathematical model of the absorption, mass and heat transfer, as well as momentum and energy transport along the channel, in the macro- and micro- pores of the absorbent matrix. The mathematical model is then translated into a numerical model, with the implementation of the two-step Lax-Wendroff (Richtmyer) scheme for the solution of the unsteady 1D + 1D (channel + macro-pores) differential problem. Finally, the model is validated against literature data and some consideration are drawn, showing possible simplifications to make the simulation tool more efficient, while preserving the due accuracy
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