1,720,996 research outputs found
Optical Characterization of Biodiesel and Diesel Fuel Sprays from a CR Injection Apparatus
No full textThe fuels from renewable resources have obtained an increasing interest for transport application in the last decade because of their biodegradability, potential improvements on exhaust emissions and benefits on the virtuous CO2 cycle of the earth.
The different physic-chemical characteristics of the biofuel, respect to diesel fuel, affect the combustion phenomenon in diesel engines being different the droplets distribution in the combustion chamber and, consequently, the air-fuel mixture preparation in the ignition delay ready to be burned. The recent trend to enhance the spray atomisation, increasing the injection pressure and the hole number in the nozzle to better distribute the fuel, imposes a deep understatement of the spray characteristics in terms of tip penetration, cone-angle, droplet velocity, fragmentation and vaporization.
The modern Common Rail (CR) injection apparatus enable a management of injection strategy both in terms of injection pressure and injection number and timing per cycle. They allow to exploit all the potentiality of modulated combustion in engine for NOx and noise reduction, acting on pilot and pre-injections, and matter particulate using post and late injections.
In this paper a study of overall behaviour of spray from rapeseed methylester (RME) biofuel and diesel fuel has been carried out in an optically accessible vessel filled with inert gas (N2) with pressure ranging between 0.1 to 5.0 MPa. The injections were obtained by a CR apparatus driven by a Programmable Electronic Control Unit (PECU) enabling different strategies performances.
The injector mounted an axially disposed cylindrical single hole nozzle (0.18 mm in diameter and 1.0 mm in thickness) and the investigated injection pressures have been 60, 90 and 120 MPa.
The sprays have been lightened by a pulsed sheet (100 μm in thickness and 10 ns in duration) generated by the second harmonic of a Nd-YAG laser and matched at different instant from the start of injection. The jet images have been captured by a CCD camera collecting the light scattered at right angle and synchronized with the light sheet. A digital pulser/delayer has allowed finely investigating the entire spray duration (1.0 ms). The spray characteristics have been extracted by a digital image processing software. Tip penetration and spray cone-angle have been strictly measured while droplet velocities and nozzle discharge coefficient have been derived
from the data.
The diverse characteristics of the investigated fuels have produced quite differences in sprays global performances in terms of penetrations and cone-angles. These differences have shown a no-monotonic behaviour during the spray duration and their relationships with the injection pressure have been observed
Modelling of primary breakup process of a multi-hole spray for Gasoline Direct Engine applications
No full textThe paper proposes a numerical methodology for the simulation of a gasoline spray generated by a multi-hole injector of a current production wall-guided Gasoline Direct Injection engine. Particular care is dedicated to the accurate representation of the spray primary breakup by means of an atomization model. The model is purposely implemented to take into account cavitation phenomena and turbulent effects induced by the nozzle geometry through a simplified approach. Since a high primary breakup rate is expected, an initial distribution of atomized droplets is predicted at the nozzle hole exit by the numerical approach. The spray is at first experimentally investigated in a test vessel at non-evaporative ambient conditions and under quiescent conditions, injecting commercial gasoline at two different injection pressures (10.0 and 20.0 MPa). The spray is characterised in terms of both instantaneous mass flow rate and morphology. Numerical simulations are performed and then compared against experiments in order to evaluate their capability to correctly predict liquid spray penetration, droplet size distribution and spray morphology. The new approach is a fairly simple yet reliable solution able to predict the influence of the nozzle hole (in terms of discharge coefficient, diameter and length) and neglecting geometrical details usually far from being easily accessed by engine developers
Biofuel Spray Behaviour from Diesel Engine CR Injection Apparatus at Different Operative Conditions
No full textGDI Sprays for S.I. Engines: Evolution and Wall Impingement at Different Operative Conditions
No full textGoing 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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