1,720,959 research outputs found
A universally applicable 0D turbulence model based on the physical analysis of fundamental tumble behaviors in spark-ignition engines
No full textPredicting turbulence in a zero-dimensional (0D) simulation is an undeniably challenging task due to the complexity of in-cylinder charge motion. In that respect, a physics-based understanding of in-cylinder flow phenomena is of vital importance for establishing high-fidelity 0D turbulence models under diverse engine conditions. The proposed 0D model is hence built upon the kinetic energy analyses of tumble, evidenced by three-dimensional computational fluid dynamics. Specifically, the overall 0D turbulence model consists of an intake model, a spinning up model, and a turbulence production model. The major difference between this model and the existing 0D turbulence models is that this model is grounded on a kinetic energy perspective of tumble, as opposed to an angular momentum perspective of tumble. That is, the behaviors of tumble, such as spinning up and vortex breakdown, are interpreted and modeled based on the changes in the kinetic energy of tumble. This enables the proposed model to secure wider applicability at various engine conditions, which were otherwise difficult to achieve. Therefore, the 0D simulation in this study was able to predict turbulent intensities at the conditions, differing in valve strategy, engine geometry, and engine operation, without changing any validation constants. Furthermore, along with the validation points used in this study, better predictions of turbulent intensity were achieved using the proposed model compared to the existing state-of-the-art model.N
Solid oxide fuel cell-internal combustion engine hybrid system utilizing an internal combustion engine for anode off-gas recirculation, external reforming, and additional power generation
No full textA solid oxide fuel cell (SOFC)-internal combustion engine (ICE) hybrid system is proposed and analyzed. Although the existing SOFC-ICE hybrid system improves the efficiency of the SOFC stand-alone system by deriving additional power from the anode off-gas in the ICE, the proposed hybrid system further increases the system efficiency by utilizing the ICE for anode off-gas recirculation, external reforming, and additional power generation. Accordingly, we developed models for the SOFC and ICE and performed simulations to understand the operational characteristics of the hybrid system. Through simulation, the influence of each control parameter was analyzed, and the system operable ranges were determined according to the rate of system heat loss. When the heat loss considered is the least, a gross system efficiency of 66.9% is achieved at the optimum point. Thus, this study developed a high-efficiency SOFC-ICE hybrid system by combining methods that utilize the ICE as a recirculation blower, reformer, and power generator.N
Assessment of hydrocarbons for gasoline surrogate: An optimization study
No full textA fuel surrogate is a model fuel that replicates combustion phenomena of real transportation fuels within computational framework. Successful surrogate formulation would be emulating multiple physical and chemical properties that are most influential to combustion characteristics using a minimum number of surrogate com-ponents. To achieve this goal, utilization of hydrocarbons with proper representation of actual constituents of real fuels is one of the most critical requirements. The major goal of this paper is to identify hydrocarbons that have a great potential to advance the current gasoline surrogates in terms of emulations in hydrocarbon class composition and combustion related properties, and to promote further experimental and computational in-vestigations for those hydrocarbons. In this paper, 19 hydrocarbons including the ones that have not been used for gasoline surrogate applications are assessed through an optimization approach. Surrogate mixtures are formulated for petroleum-derived gasoline fuels using new hydrocarbons along with conventional gasoline surrogate components (n-heptane, iso-octane, toluene, 1-hexene), and potential improvements in target property emulations by addition of the new surrogate components are evaluated. Among four hydrocarbon classes investigated in this study which are iso-alkane, cycloalkane, aromatic, and olefin, optimized results indicate that expanding iso-alkane representation by using multiple iso-alkane components with different molecular size is the most effective approach to emulate various target properties of typical gasoline batches. Also, among 19 new hydrocarbons tested, 2-methylbutane appears to be a favorable option for a small iso-alkane, 2,2,3,3-tetramethyl-hexane for a large iso-alkane, cyclopentane for a cycloalkane, and 1,2,4-trimethylbenzene for a large aromatic. With a new surrogate palette that includes these promising hydrocarbons, surrogate mixtures are formulated for 5 different batches of gasoline, which shows capabilities to emulate composition characteristics and target properties tested, including knock resistance and distillation curve.N
Development of a Hybrid System of Molten Carbonate Fuel Cell and Homogeneous Charge Compression Ignition Engine for Distributed Power Generation
No full textA new hybrid system of molten carbonate fuel cell (MCFC) and homogenous charge compression ignition (HCCI) engine is suggested to improve the overall system efficiency and performance. In the proposed system, the catalytic burner in a standalone MCFC system is replaced with the HCCI engine. The HCCI engine is chosen over conventional spark-ignition or compression-ignition engines since it has been demonstrated to operate with highly diluted reactant mixture, which is suitable to run directly with the MCFC anode off-gas. A nonisothermal numerical model that incorporates major fuel cell losses is developed to predict the fuel cell performance. The fuel cell model assumes parallel anode and cathode flow configuration with LiNaCO3 as an electrolyte. It is integrated with an in-house HCCI engine model to investigate the hybrid system performance. At the selected design point operation around 300 kW power output, the maximum hybrid system efficiency is 21.2% (relative) higher than that of a standalone fuel cell system and, thus, achieving around 60% overall, which demonstrates the potential of the suggested hybrid system as a highly-efficient distributed power generation source in the near future.N
Optimization of molten carbonate fuel cell (MCFC) and homogeneous charge compression ignition (HCCI) engine hybrid system for distributed power generation
No full textAbstractIn a previous study, a new hybrid system of molten carbonate fuel cell (MCFC) and homogeneous charge compression ignition (HCCI) engine was developed, where the HCCI engine replaces the catalytic burner and produces additional power by using the left-over heating values from the fuel cell stack. In the present study, to reduce the additional cost and footprint of the engine system in a hybrid configuration, the possibility of engine downsizing is investigated by using two strategies, i.e. the use of a turbocharger and the use of high geometric compression ratio for the engine design, both of which are to increase the density of the intake charge and thus the volumetric efficiency of the engine. Combining these two strategies, we suggest a new engine design with ∼60% of displacement volume of the original engine. In addition, operating strategies are developed to run the new hybrid system under part load conditions. It is successfully demonstrated that the system can operate down to 65% of the power level of the design point, while the system efficiency remains almost unchanged near 63%
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
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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