1,720,976 research outputs found
Characterization of Hydrotreated Vegetable Oil (HVO) in a Euro 6 Diesel Engine as a Drop-In Fuel and With a Dedicated Calibration
Full text linkRenewable fuels can play an important role in achieving future goals of energy
sustainability and CO2 reduction. In particular, hydrotreated vegetable oil (HVO) represents one
of the most promising alternatives to petroleum-derived diesel fuels. Several studies have shown
that conventional diesel engines can run on 100% HVO without significant modifications to the
hardware and control strategies. The current activity has experimentally evaluated the potential
of HVO as a “drop-in” fuel, i.e., without changes to the original baseline calibration, comparing
it to conventional diesel fuel on a 2.3-litre Euro 6 compression ignition engine.
Tests revealed that HVO can significantly reduce engine-out soot (by more than 60%), HC and
CO emissions (by about 40%), compared to diesel, while NOx levels and fuel conversion
efficiency remain relatively unchanged under steady-state warmed-up conditions. The
advantages of HVO proved to be further enhanced when the engine has not yet warmed up.
Using statistical techniques of design of experiments (DoE) at three warmed-up steady-state
operating points, the main engine control parameters were recalibrated to demonstrate that
engine-out emissions can be further optimized with a dedicated calibration
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
Experimental analysis on the effects of multiple injection strategies on pollutant emissions, combustion noise, and fuel consumption in a premixed charge compression ignition engine
No full textEarly single-injection premixed charge compression ignition (PCCI) strategies in compression ignition engines have been widely studied as a promising solution to meet the ever-increasing stringent emissions regulations. Although their application to diesel engines may provide several upsides (such as a massive and simultaneous reduction of NOx and soot engine-out emissions), especially at low to medium loads, several drawbacks, including an excessive amount of engine-out carbon monoxide (CO) and unburned hydrocarbons (HC) as well as intense combustion noise (CN), usually reveal to be major constraints. As a matter of fact, PCCI combustion systems are not yet consolidated enough for practical applications, although intensive research has been carried out to overcome its common limitations. Indeed, further research is still required. In this work, an experimental analysis has been carried out to highlight the potential benefits derived from the introduction of multiple (i.e., double and triple) fuel injection PCCI strategies on a 3.0-liter diesel engine, purposely designed to be operated with PCCI combustion concepts at low to medium engine loads. The experimental tests include the application of several fuel injection strategies: double- and triple-pulse PCCI schemes, featuring various fuel injection timing sweeps, and different fuel quantity distributions among each fuel shot were compared with a baseline single-pulse PCCI and a triple-injection conventional diesel combustion (CDC) pattern. The results are presented in terms of exhaust pollutant emissions, CN, and fuel consumption at two different engine operating points within a low to medium speed and load area of the engine map. Splitting the fuel injection into a double-stage pattern turned out ensuring appreciable drops of both engine-out HC and CO emissions, up to 50% lower than the single-injection PCCI levels, but still significantly worse than CDC outcomes, with penalties above +120%. Engine-out soot and nitrogen oxides (NOx) emissions retained considerably smaller than typical CDC values (with abatement ranging between −50% and −99%), while double-pulse PCCI calibrations featuring delayed second injection timings allowed to effectively dampen excessive CN intensity (of up to 7 dBA below the CN of the reference single-stage PCCI schedule), while slightly improving fuel economy. Finally, the introduction of a triple-stage pattern in PCCI revealed to have the potential to further reduce the emissions of incomplete combustion species and fuel consumption, when compared with single- and double-injection patterns (especially at low load), as well as to further deadening CN. However, besides being still ineffective in reaching the CDC performance even at low load (bsfc slightly over +4%, HC no better than +100%), when increasing the engine load, these benefits become milder to the point that the soaring calibration complexity required by a triple-stage PCCI pattern might not render it worthwhile
Effects of Rate-Shaped and Multiple Injection Strategies on Pollutant Emissions, Combustion Noise and Fuel Consumption in a Low Compression Ratio Diesel Engine
Full text linkAn experimental investigation has been carried out to highlight the effects of different injection strategies on the performance and emissions of a low compression ratio Euro 5 diesel engine operated with high EGR rates. Rate-shaped main injections, achieved with piezoelectric and solenoid injectors by means of boot and injection fusion, respectively, as well as optimized multiple injection patterns have been compared. The results of the comparisons, performed with reference to a state-of-the-art double pilot-Main (pM) strategy, are presented in terms of engine-out exhaust emissions, combustion noise (CN) and fuel consumption. Rate-shaped main injections, when included in delayed multiple injection patterns, have shown a minor influence on reducing NOx, while a slight deterioration in soot has been found. Both a double pilot and a boot injection schedule have been able to reduce CN at low loads. A higher reduction in CN has been obtained with an injection fusion event. Finally, DoE optimized triple and quadruple injection strategies have led to improved soot-NOx trade-offs, with respect to the pM calibration. In fact, splitting the injection helps to entrain air inside the fuel plumes, thus creating locally leaner mixture (less prone to forming soot) and allowing increasing the EGR rates (reducing NOx formation)
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
Effect of the application of an uncooled high-pressure EGR strategy in low-load diesel PCCI operation
Full text linkThe exploitation of new advanced combustion concepts referred to as low-temperature combustion (LTC) strategies gives the possibility to reduce the typical NOx and PM emissions from conventional diesel combustion. These strategies are implemented using high quantity of exhaust gas recirculated at the intake manifold, which allows to lower the peak combustion temperatures, thus reducing NOx, and advancing the fuel injection timing, thus keeping the PM emission under control. Cooling the EGR can be beneficial, as the increment in density of the burned gases downstream the EGR cooler reflects in a further decrement of NOx and PM emissions. On the other hand, the lower EGR temperatures may enhance higher in-cylinder formation of unburned hydrocarbon (HC) and carbon monoxide as well as negatively affect the exhaust gas temperature upstream the after-treatment line. This latter effect can be particularly detrimental especially at low engine speeds and loads and/or during engine warm-up. In these cases, in fact, the after-treatment system is not able to convert the incomplete combustion species because the light-off temperature of the catalyst is not reached. This work tries to present a comparison between cold and hot EGR strategies in the case of a short EGR route configuration. The results highlight a reduction in terms of tailpipe HC and CO emissions for low-torque engine working points, when using hot EGR strategies, especially due to the enhancement of the DOC working temperature. On the other hand, the area of the map where PCCI combustion is achievable with uncooled EGR shows to be reduced with respect to the regular cold EGR strategy
CCL20-CCR6 interaction modulates primary cultures epithelial breast cancer cell migration and metalloproteinase expression
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