1,721,008 research outputs found
Sources of CO emissions in an HCCI engine: A numerical analysis
No full textIn this paper, we investigate the factors influencinga reliable prediction of CO emissions in a homogeneouscharge compression ignition (HCCI) engineusing an improved probability density function(PDF)-based engine cycle model. The PDF-based stochasticreactor model (SRM) as validated in our previouswork [1] is utilized to identify critical sourcesof CO emissions numerically. The full cycle modelincludes detailed chemical kinetics, accounts for theinhomogeneities in temperature and composition, andhas been demonstrated to provide sufficiently reliablepredictions of the combustion and engine parametersand emissions [1–3].The single-zone, multizone, and CFD-based enginecycle models have been widely used to gaininsight into HCCI combustion; however, in general,the predictions of CO emissions have been poor [4].The underprediction of CO emissions using a singlezone-based model results from its inability to accountfor the inhomogeneities. A closed volume, 10-zonemodel faced intrinsic difficulty in predicting the COemissions, underpredicting the measurements by anorder of magnitude [5]. Studies involving a sequentialmultizone model [6] and the segregated solver [7]approaches also showed an error of around 70% inpredicting the CO emissions. Such underpredictionwas attributed to the lack of mass and energy trans-fer between the zones while emphasizing the need formore detailed description of the in-cylinder temperaturedistribution [8]. A 9-zone-based full cycle modelwith mass exchange between zones required modificationof rate constants for the CO oxidation reactionto obtain a good agreement against measurements [9].A CFD-coupled cycle model located the cylinder linerwall as a major source of CO emissions, but the COemissions were underpredicted by 80% [10]. In anotherstudy, the segregated multizone-based modelwas improved by incorporating heat transfer and mixingduring the post-main heat release part of theengine cycle and the CO emissions were predictedas 50% of the measurements for a specific operatingpoint [11]. It has been pointed out that implementinga certain inhomogeneity in the perfectly stirred individualzones of the multizone model could improvethe prediction capability [9].In our previous works, the integrated SRM-basedengine cycle model was demonstrated to predict COemissions at 70–80% of the measurements. Here, weemploy the model to investigate the factors responsiblefor the calculation of CO emissions in such aPDF-based modeling approach
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Investigating the significance of octane number in controlling HCCI engines
No full textThe role of octane number in controlling homogeneous charge compression ignition (HCCI) combustion and emissions, in a multi-cylinder engine was studied. An improved probability density function based stochastic reactor model coupled with a commercial engine cycle simulator was presented. A convective heat loss sub-model (based on a stochastic jump process) and a coalescence-dispersion approach was employed to account for inhomogeneities due to turbulent mixing, fluid-wall interactions, and fluctuations. The base case comparison of the model predictions with the measurements demonstrated the robustness of the integrated full cycle model in reliably predicting the auto-ignition timing, peak pressure as well as CO, HC, and NOx emissions. The improved PDF-based engine cycle simulator outperformed the widely used single-zone based cycle models and provided a significant insight into CO emissions prediction. The auto-ignition timing and the in-cylinder pressure and emissions were sensitive to octane number variation. The magnitudes as well as the trends for the combustion parameters and the emissions (CO, HC, and NOx) were predicted reasonably well by the model. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004)
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Analysis of the HCCI combustion of a turbocharged truck engine using a stochastic reactor model
No full textHomogeneous Charge Compression Ignition (HCCI) engines arouse great interest due to their high thermal efficiency and very low emissions of nitrogen oxides (NOx) and particulates. Critical issue of the HCCI combustion is the control of the engine since the combustion process is mostly dominated by chemical kinetics. Therefore the accurate assessment of the chemical kinetic is fundamental in numerical simulation of this kind of engines. Experimentally It has been demonstrated that even in HCCI engine the charge within the cylinder is not fully homogeneous, but many quantities, such as temperature, density and equivalence ratio, vary along the combustion chamber. These inhomogeneities influence the combustion process and yield the homogeneous reactor model to be not completely adequate to simulate HCCI combustion. This paper focuses on the use of a stochastic rector model in order to account for temperature inhomogeneities in the numerical simulation of the HCCI combustion. Moreover, the chemical kinetic code has been coupled to GT - Power Code, a 1-D fluid dynamics code, in order to accurately simulate the operation of a turbocharged truck engine
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