1,720,976 research outputs found
3D CFD Analysis of the Influence of Some Geometrical Engine Parameters on Small PFI Engine Performances – the Effects on the Tumble Motion and the Mean Turbulent Intensity Distribution
No full textAbstractIn scooter/motorbike engines coherent and stable tumble motion generation is still considered an effective mean in order to both reduce engine emissions and promote higher levels of combustion efficiency. The promotion of a stable and coherent tumble structure is largely believed in literature to enhance in-cylinder turbulence accelerating combustion process. In small PFI engine layout and weight constraints limit the adoption of more advanced concepts. In previous technical papers the authors demonstrated the influence of head shape and squish area on tumble vortex formation, development, breakdown and on final value of turbulence close to spark plug for small PFI engines. The main result of the this research was that the combustion chamber having the less squish area resulted to have the highest level of turbulence close to spark plug at ignition time. The geometry under analysis in the current paper is a 3-valves pent-roof motorcycle engine. 3D CFD simulations were ran at 6500rpm with AVL FIRE code. The chosen engine geometry was the geometry found to be the best set-up in terms of turbulence and combustion performances in the previous paper. In the present paper the head shape and the squish area were kept constant and the following engine parameters were varied: the intake duct angle (the angle of the intake duct entering the head was reduced of 6%, i.e. it was more directed toward the exhaust side of the chamber), the piston shape, and finally the compression ratio (it was reduced of 9%). The main goal of the current analysis is to understand which of these parameters is predominant in accelerating combustion for directing engine design toward the best set-up
Influence of the Diesel Injector Hole Geometry on the Flow Conditions Emerging from the Nozzle
No full textAbstractEngine performances are correlated to the overall fluid dynamic characteristics of the injection system that, in turns, are strictly correlated to the fluid dynamic performance of the injector geometry. It is particularly true for actual GDI and Diesel engines where micro-orifice configurations are associated to very high injection pressure.In relation to the Common Rail Diesel engines, over the last decade different injector hole shapes have been tested. Actually, the most used configurations are: cylindrical, k, and ks. In this paper, the performance of all these three injector hole shapes are evaluated in order to find out the influence of orifice conicity and hydro-grinding level on the main fluid dynamic characteristics like cavitation evolution inside the injector as well as the flow properties at nozzle exit. The fluid dynamic behavior of each considered hole is evaluated over the injection time by performing a fully transient CFD multiphase simulation (i.e. the needle motion is reproduced during the simulation). By the proposed simulation methodology, the evaluation of the cavitating flow evolution inside the injector is performed not only from the point of view of the overall spray characteristics emerging from the injector holes but also from the cavitation erosion risk over needle, nozzle, and hole internal surfaces
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
Sviluppo e validazione di un modello di film fluido per simulazioni CFD di motori a combustione interna
No full textA wall film model has been implemented in a customized version of KIVA code
developed at University of Bologna. Under the hypothesis of `thin laminar
ow'
the model simulates the dynamics of a liquid wall film generated by impinging
sprays. Particular care has been taken in numerical implementation of the
model.
The major phenomena taken into account in the present model are: wall film
formation by impinging spray; body forces, such as gravity or acceleration of the
wall; shear stress at the interface with the gas and no slip condition on the wall;
momentum contribution and dynamic pressure generated by the tangential and
normal component of the impinging drops; film evaporation by heat exchange
with wall and surrounding gas. The model doesn't consider the effect of the
wavy film motion and suppose that all the impinging droplets adhere to the
film. The governing equations have been integrated in space by using a finite
volume approach with a first order upwind differencing scheme and they have
been integrated in time with a fully explicit method.
The model is validated using two different test cases reproducing PFI gasoline and DI Diesel engine wall film conditions
The prediction of flash evaporation in superheated fuel injections for automotive applications
No full textIn gasoline Port Fuel Injection (PFI) and Direct Injection (GDI) internal combustion engines, the liquid fuel might be injected into a gaseous ambient in a superheated state, resulting in flash boiling of the fuel. The importance to investigate and predict such a process is due to the influence it has on the liquid fuel atomization and vaporization and thus on combustion, with direct implications on engine performances and exhaust gas emissions. The topic of the present PhD research involves the numerical analysis of the behaviour of the superheated fuel during the injection process, in high pressure injection systems like the ones equipping GDI engines. Particular emphasis is on the investigation of the effects of the fuel superheating degree on atomization dynamics and spray characteristics.
The present work is a look at the flash evaporation and flash boiling modeling, from an engineering point of view, addressed to keep the complex physics involved as simple as possible, however capturing the main characteristics of a superheated fuel injection
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