1,720,961 research outputs found
Global uncertainty and sensitivity analysis of a reduced chemical kinetic mechanism of a gasoline, n-butanol blend in a high pressure rapid compression machine
No full textA detailed evaluation of a recently developed combined n-butanol/toluene reference fuel (TRF) reduced chemical kinetic mechanism (Agbro, 2017) describing the low temperature oxidation of n-butanol, gasoline and a gasoline/n-butanol blend was performed using both global uncertainty and sensitivity methods with ignition delays as the predicted output for the temperature range 678 - 858 K, and an equivalence ratio of 1 at 20 bar. A global sampling technique was applied in the simulations in order to quantify the uncertainties of the predicted ignition delays when incorporating the effects of uncertainties in forward rate constants in the simulations. In addition, a variance-based global sensitivity analysis using a high dimensional model representation (HDMR) method was carried out to understand and rank the parameters responsible for the predicted uncertainties. The results showed that uncertainties in predicting key target quantities for the various fuels studied are currently large but driven by few reactions. Global sensitivity analysis of the mechanism based on predicted ignition delays of stoichiometric TRF mixtures, showed the toluene + OH route = phenol + CH3 to be among the most dominant pathways in terms of the predicted output uncertainties but an update on the mechanism based on recent data from the study of Seta led to the toluene + OH hydrogen abstraction reaction becoming the most dominant reaction as expected. For the TRF/n-butanol blend, hydrogen abstraction reactions by OH from n-butanol appear to be key in predicting the effect of blending. Uncertainties in the temperature dependence of relative abstraction rates from the ? and ? sites may still be present within current mechanisms, and in particular may affect the ability of the mechanisms to capture the low temperature delay times for n-butanol. Further studies of the product channels for n-butanol + OH for temperatures of relevance to combustion applications could help to improve current mechanisms. At higher temperatures, the reactions of HO2 and that of formaldehyde with OH also became critical and attempts to reduce uncertainties in the temperature dependent rates of these reactions would be useful
Global uncertainty and sensitivity analysis of a reduced chemical kinetic mechanism of a gasoline, n-butanol blend in a high pressure rapid compression machine.
Get PDFA detailed evaluation of a recently developed combined n-butanol/toluene reference fuel (TRF) reduced chemical kinetic mechanism describing the low temperature oxidation of n-butanol, gasoline and a gasoline/n-butanol blend was performed using both global uncertainty and sensitivity methods with ignition delays as the predicted output for the temperature range 678 - 858 K, and an equivalence ratio of 1 at 20 bar. The results obtained when incorporating the effects of uncertainties in forward rate constants in the simulations, showed that uncertainties in predicting key target quantities for the various fuels studied are currently large but driven by few reactions. Global sensitivity analysis of the mechanism based on predicted ignition delays of stoichiometric TRF mixtures, showed the toluene + OH route = phenol + CH3 to be among the most dominant pathways in terms of the predicted output uncertainties but an update on the mechanism based on data from a recent study led to the toluene + OH hydrogen abstraction reaction becoming the most dominant reaction as expected. For the TRF/n-butanol blend, hydrogen abstraction reactions by OH from n-butanol appear to be key in predicting the effect of blending. Uncertainties in the temperature dependence of relative abstraction rates from the α and γ sites may still be present within current mechanisms, and in particular may affect the ability of the mechanisms to capture the low temperature delay times for n-butanol. Further studies of the product channels for n-butanol + OH for temperatures of relevance to combustion applications could help to improve current mechanisms. At higher temperatures, the reactions of HO2 and that of formaldehyde with OH also became critical and attempts to reduce uncertainties in the temperature dependent rates of these reactions would be useful
Experimental and Chemical Kinetic Modelling Study on the Combustion of Alternative Fuels in Fundamental Systems and Practical Engines
Get PDFIn this work, experimental data of ignition delay times of n-butanol, gasoline, toluene reference fuel (TRF), a gasoline/n-butanol blend and a TRF/n-butanol blend were obtained using the Leeds University Rapid Compression Machine (RCM) while autoignition (knock) onsets and knock intensities of gasoline, TRF, gasoline/n-butanol and TRF/n-butanol blends were measured using the Leeds University Optical Engine (LUPOE). The work showed that within the RCM, the 3-component TRF surrogate captures the trend of gasoline data well across the temperature range. However, based on results obtained in the engine, it appears that the chosen TRF may not be an excellent representation of gasoline under engine conditions as the knock boundary of TRF as well as the measured knock onsets are significantly lower than those of gasoline. The ignition delay times measured in the RCM for the blend, lay between those of gasoline and n-butanol under stoichiometric conditions across the temperature range studied and at lower temperatures, n-butanol acts as an octane enhancer over and above what might be expected from a simple linear blending law. In the engine, the measured knock onsets for the blend were higher than those of gasoline at the more retarded spark timing of 6 CA bTDC but the effect disappears at higher spark advances. Future studies exploring the blending effect of n-butanol across a range of blending ratios is required since it is difficult to conclude on the overall effect of n-butanol blending on gasoline based on the single blend that has been considered in this study.
The chemical kinetic modelling of the fuels investigated has also been evaluated by comparing results from simulations employing the relevant reaction mechanisms with the experimental data sourced from either the open literature or measured in-house. Local as well as global uncertainty/sensitivity methods accounting for the impact of uncertainties in the input parameters, were also employed within the framework of ignition delay time modelling in an RCM and species concentration prediction in a JSR, for analysis of the chemical kinetic modelling of DME, n-butanol, TRF and TRF/n-butanol oxidation in order to advance the understanding of the key reactions rates that are crucial for the accurate prediction of the combustion of alternative fuels in internal combustion engines. The results showed that uncertainties in predicting key target quantities for the various fuels studied are currently large but driven by few reactions. Further studies of the key reaction channels identified in this work at the P-T conditions of relevance to combustion applications could help to improve current mechanisms.
Moreover, the chemical kinetic modelling of the autoignition and species concentration of TRF, TRF/n-butanol and n-butanol fuels was carried out using the adopted TRF/n-butanol mechanism as input in the engine simulations of a recently developed commercial engine software known as LOGEengine. Similar to the results obtained in the RCM modelling work, the knock onsets predicted for TRF and TRF/n-butanol blend under engine conditions were consistently higher than the measured data. Overall, the work demonstrated that accurate representation of the low temperature chemistry in current chemical kinetic models of alternative fuels is very crucial for the accurate description of the chemical processes and autoignition of the end gas in the engine
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
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
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