1,720,956 research outputs found
Comprehensive assessment of hydrogen jet dynamics under split-injection conditions
No full textIn stratified charge combustion (SCC) approach, direct injection requires optimal air-fuel mixing to maximize engine performance. This study examined the potential of split injection strategy to enhance hydrogen mixing process through both experimental and computational approaches using direct injection hollow-cone injector. Quantitative hydrogen concentration was measured using Laser-induced breakdown spectroscopy (LIBS), while computational fluid dynamics (CFD) simulation was performed to investigate aerodynamics during injection process. The results showed that the first injection induces a pressure difference across hydrogen jet, boundary generating an upward-directed vortex. A shorter first injection duration intensifies the vortical structure in the jet, promoting stronger interaction between the first and second injections. This interaction enhances jet dispersion and improves mixture homogeneity.
CFD 모델을 이용한 정적 연소실 내 다단 분사 적용 수소 제트의 계산 및 검증
No full text학위논문(석사) - 한국과학기술원 : 기계공학과, 2025.2,[iii, 61 p. :]Hydrogen can serve as a carbon-neutral alternative energy carrier compared to conventional fossil fuels like gasoline and diesel, which emit CO2 upon combustion. This shift towards hydrogen significantly contributes to the goal of decarbonization. In this study, high-pressure (100 bar) direct injection (DI) of hydrogen using an outwardly opening hollow cone injector was performed in a constant volume chamber (CVC) with the aim of analyzing hydrogen jet behavior under varying ambient pressures (5, 10, and 15 bar). A 3D computational fluid dynamics (CFD) model based on the hollow cone injector geometry was created using CONVERGE (v.3.0.27) software to simulate the hydrogen jet flow dynamics. The CFD model employs the Reynolds-averaged Navier-Stokes (RANS) formulation. The model was validated by comparing the jet area against Schlieren images and the measured local equivalence ratio values obtained from the laser-induced breakdown spectroscopy (LIBS) experiment. Previous results revealed jet shrinkage (especially in the radial direction) at elevated ambient pressures for single injection experiments, observed through Schlieren imaging. This shrinkage led to potential non-flammable mixture formation near the spark plug, resulting in misfiring or no combustion. To address this issue, a double injection strategy was employed, splitting the injection into two sequences with a gap (dwell time) between them. This approach allows the jet to break into two parts, with the jet plume from the first injection interacting with the jet plume from the second injection. This interaction generates upward momentum, causing the jet area to expand in the radial direction. The total injection duration was fixed at 1 ms, with various split ratios (3:7, 5:5, and 7:3) and dwell times (0.2, 0.6, and 1.0 ms). The CFD model was utilized to determine the best approach for increasing radial penetration using double injection. The findings showed that a split ratio of 7:3 combined with a dwell time of 0.2 ms resulted in a wider jet width at the spark plug location. These results were further supported by measuring the local equivalence ratio at various locations throughout the jet.한국과학기술원 :기계공학과
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
Computational Modeling of Hydrogen Jet with Double Injection In a Constant Volume Chamber
No full textVariations 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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