1,720,991 research outputs found
Reduced chemical kinetics mechanism for syngas combustion and NOx formation
No full textChemical kinetics and computational fluid-dynamics (CFD) analysis were performed to evaluate the combustion of syngas derived from biomass solid feedstock in a micro-pilot ignited supercharged dual-fuel engine under lean conditions. For this analysis, a new reduced syngas chemical kinetics mechanism was developed and validated by comparing the ignition delay and laminar flame speed data with those obtained from experiments and other detail chemical kinetics mechanisms available in the literature. The reaction sensitivity analysis was conducted for ignition delay at elevated pressures in order to identify important chemical reactions that govern the combustion process. We found that H02+OH=H20+02 and H202+H=H2+H02 reactions showed very high sensitivity during high-pressure ignition delay times and had considerable uncertainty. The chemical kinetics of NOx formation was analysed for H2/CO/C02/CH4 syngas mixtures by using premixed laminar flame speed reactors. The new mechanism showed a very good agreement with experimental measurements and accurately reproduced the effect of the equivalence ratio on NOx formation. Finally, the new mechanism was used in a multidimensional CFD simulation to predict the combustion of syngas in a micro-pilot-ignited supercharged dual-fuel engine and results were compared with experiments. The mechanism showed the closest prediction of the in-cylinder pressure and the rate of heat release (ROHR)
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
Sustainable small-scale hydropower solutions in Central Asian countries for local and cross-border energy/water supply
Get PDFThe Central Asian area is confronted with a number of acute obstacles as it attempts to transition to a long-term electrical power supply. Small-scale hydropower systems may be a viable answer to these problems. Central Asian nations' hydropower resources are allocated unevenly. Regardless, it remains the most exploitable renewable energy source in the area, with both Kyrgyzstan and Tajikistan possessing some of the world's highest hydropower potential. Nonetheless, for fossil-fuel-rich nations like Uzbekistan, Turkmenistan, and Kazakhstan, hydropower will play a significant role in the future energy balance. Furthermore, because rivers often run across many boundaries, water security plays an important role in cross-border relations between Central Asian countries. To achieve effective exploitation of small hydropower potential, technological and financial expenditures are needed to improve the levelised cost of energy (LCOE) of diverse hydroelectric equipment by increasing lifetime, improving efficiency, and increasing yearly power output. Several of these issues can be resolved by installing small and micro hydropower plants in the many minor rivers and irrigation canals. A pumped hydro energy storage system should also be tested and certified for better usability. A hydrological digital twin of relevant river system and irrigation network should be constructed to increase the understanding for performance and enable system-level improvement. Furthermore, optimal performance necessitates constant monitoring of the network, necessitating the development of intelligent monitoring employing sensors in conjunction with control systems and smart grid interactions. This review focuses on the broad and efficient use of these existing resources, which are still underutilized
Diesel engine downsizing with application of biofuels
No full textIn this study, we have developed an optimization procedure for diesel engine downsizing with application of biofuels. The analysis was performed using the specialist thermodynamic software to simulate combustion and emission characteristics of an internal combustion engine. A JCB 165 kW Diesel Max commercial nonroad diesel engine has been selected for the project. The performance characteristics of this engine were set as reference. The results for the original engine and downsized engine were compared. The engine performance and emission characteristics with diesel fuel, different blends of soybean methyl ester (SME) and rapeseed methyl ester (RME) have been investigated. The obtained results showed that it was possible to achieve equal level of break power and torque for 50%-downsized engine as compared with those of the original engine. The results over different engine speeds and loads showed around 4-11% reduction range in fuel consumption, 4-11% reduction range in CO2 emissions and about 86-99% reduction range in PM emissions. However, the NOx emissions significantly increased. Further to decrease NOx emission level the exhaust gas recirculation (EGR) was applied
Feasibility study and design of an ocean wave power generation station integrated with a decommissioned offshore oil platform in UK waters
No full textWave energy exploits the movement of the wind across the surface of the sea to provide an inexhaustible, carbon-free energy source for electricity generation. This can potentially provide a significant contribution to electricity generation supply in the UK, meeting up to 20% of the UK’s electricity demand. This represents 30-50 MW capacity of electrical energy by 2020, and potentially 27 GW by 2050 as technology within the industry develops and matures. Studies show that developing marine energy resources in the UK can save 60 metric tons of carbon dioxide by 2025 and aid in the UK meeting 20-20-20 renewable energy objectives. In this paper the design of a wave power station integrated with a decommissioned offshore oil platform is proposed. This approach provides ideal conditions for the exploitation of wave energy for electricity generation. It not only saves the cost of decommissioning but also provides the offshore oil platform with new life, generating electrical energy from an inexhaustible source. The objective of this work was to conduct an extensive feasibility study to develop a proof of concept design for wave energy generation integrated with an offshore oil platform
CFD analysis of gas turbine combustor with vortex generator
Get PDFSwirl flows have been used lately for the modern gas turbine combustion to enhance the mixing and flame stabilization. Instabilities that occur due to such flow are often termed as precessing vortex core (PVC). This precessing vortex core has a greater effect on the flow characteristics and heat release and its interaction with the flame is important. The numerical analysis using Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) turbulence models were used to carry out simulations of gas turbine combustor to study the PVC and flame interaction in the flow fields. The boundary conditions were set as power output – 35 kW, Reynolds number - 52000 and the equivalence ratio - 0.65. The RANS results were more similar to the experimental one than the LES. The LES results were more useful in studying the PVC characteristics, PVC-flame interaction and instantaneous flow field. The RANS results were helpful in understanding the average flow fields. The grid requirement for both turbulence models and their importance was also studied
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
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