1,720,981 research outputs found
Wasted spark duration measurement as a method for firing TDC identification in small engines
No full textDistributed generation represents a valid option for reducing
transmission losses and overall power system complexity.
Back-up power is another option that can ensure valuable
safety margins in the scenario of extensive penetration of
renewables, and can also act as balancing sources. Spark
ignition (SI) engines are often the prime choice for such
applications with sizes ranging from single cylinder
configurations to large bore units. Augmenting control
margins without increasing the number of sensors is an
essential aspect for small size engines. Common practice for
such power units is to employ fixed ignition timing with so
called wasted spark systems, i.e. two events per cycle one
during compression and one during the exhaust stroke.
Nonetheless, application of more complex control systems
such as fuel injection are becoming more and more
widespread even for this engine category. Within this
context, a method was developed for identifying TDC
phasing based on current measurements in the secondary
ignition circuit for engines that feature wasted spark
systems. The method was applied on a 50 cc SI unit
connected to a 1 kW power generator. The only
modification to the ignition system was to substitute the coil
with an automotive type piece; this was required because the
original component featured common ground wiring for the
primary and secondary side, thus rendering current
measurements much more difficult to implement. Duration
of the actual spark event was found to be a good parameter
for distinguishing between ignition occurring during the
compression stroke or during exhaust. Statistical distribution
during sequences of 200 cycles recorded at three different
levels of load was used for testing the identification
algorithm. The developed method was verified with pressure
measurements to distinguish between the two events, i.e.
compression and exhaust. Limitations of the method are
discussed and the possible ways of improving its application
were identified
0D/1D Modeling of Lean-Burn Conditions in a Hydrogen SI Engine for Closer Correlation of In-Cylinder Chemical Species with Optical Data
No full textDesign of an Optically Accessible Intake Manifold for Characterization of Liquid and Gaseous Jets in PFI Operating Conditions
Full text linkThe intake manifold and its components play a key role in the proper formation of air–fuel mixtures suitable for correct engine operation. In this article, starting from the original intake manifold design fitted to an optically accessible spark-ignited engine, a new solution was developed so as to allow the application of high-speed imaging of the fuel jet located between the runner and intake valves (Port Fuel Injection). To compare the two designs in terms of overall engine performance parameters such as volumetric efficiency, 0D/1D simulations were performed in motored conditions. Measurements at different crankshaft speed values were used for calibrating the intake line parameters and providing boundary conditions. Finite Element Analysis (FEM) was performed in SolidWorks to verify the structural strength of the new design when operating in the most critical conditions, i.e., boosted operation. As an overall conclusion, the results show that the new design guarantees a wider range of intake pressure values during the intake stroke, thus expanding the possible operative points. This can be obtained without compromising structural integrity, given that predicted safety factors were well above acceptable limits even for relatively high boost levels
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
Valorization of n-butanol as Gasoline Replacement in a DISI Engine and the Effect of Injection Phasing
No full textEste artículo presenta la valorización del n-butanol en motores de encendido por chispa e inyección directa y su efecto durante el proceso de inyección.Alcohols represent a viable replacement for gasoline, with the advantages of providing improved energy security as well as reduced environmental impact. Compared to ethanol, which holds the majority of the alternative fuels market share in transportation, butanol features higher energy density and better compatibility with existing fuel systems designed for gasoline. Given this background, the present study investigated the use of pure n-butanol fueling of a wall guided direct injection spark ignition (DISI) engine with optical accessibility through the piston crown. Different start of injection points were considered, and variations of soot emissions were evaluated based on smoke measurements. Besides thermodynamic investigations through the analysis in-cylinder pressure traces, flame chemiluminescence was applied for a more detailed view of the chemical processes during combustion. All conditions were benchmarked to gasoline fueling, thus giving comprehensive information on the effect of fuel properties. It was found that the change in injection timing, even by a relatively reduced crank angle, had a significant effect on the smoke at the exhaust, for both fuel types. Early fuel delivery resulted in high soot emissions, while late injection had the opposite effect. No soot-nitrogen oxides trade-off point, specific for diesel power units, could be identified, but the optimum injection strategy resulted in high engine output and low particulate emissions. The alcohol featured increased sensitivity to changes in the start of injection, but also showed the potential for very low smoke. The investigations further emphasize the importance of air-fuel mixture formation and also identified ways to minimize the environmental impact of DISI engines through the development of optimized control strategies.1. Introduction 2. Methodology 2.1. Experimental setup 2.2. Thermodynamic analysis 3. Results and discussion 4. Conclusions. [email protected]@[email protected]@[email protected]
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
- …
