1,720,962 research outputs found
Numerical study of hydrogen enrichment of lean methane/air turbulent premixed combustion
No full textL’enrichissement des hydrocarbures par l’hydrogène permet d’améliorer les performances de la combustion pauvre (augmentation de la réactivité, résistance à l’étirement, stabilité, réduction des polluants, …). Il est primordial de connaitre les caractéristiques de la combustion de ces combustibles hybrides dans différentes conditions, afin de pouvoir les utiliser d’une manière sûre et efficace dans les installations pratiques. L’approche expérimentale reste coûteuse et limitée à certaines conditions opératoires. Cependant, le calcul numérique peut constituer la solution la plus adaptée, compte tenu du progrès réalisé dans le domaine de l’informatique et de la modélisation. Dans ce contexte, ce travail que nous avons effectué à l’ICARE (Institut de Combustion, Aérothermique et Réactivité, CNRS Orléans) vise à compléter les résultats des essais expérimentaux. Les effets de la richesse du mélange et l’ajout de l’hydrogène sur la structure et la formation des polluants sont étudiés dans ce travail. L’augmentation de la richesse du combustible permet de stabiliser la flamme, mais augmente la température et produit plus de CO, CO2 et NOx. Par contre, l’addition de H2 augmente l’efficacité du mélange, stabilise la flamme avec une légère élévation de la température maximale et une diminution des fractions massiques de CO, CO2 et NOx. Le remplacement d’une fraction de 10% où même 20% du gaz principal par l’hydrogène améliore les performances des installations et ne nécessite aucune modification sur les systèmes de combustion.Fuel blending represents a promising approach for reducing harmful emissions from combustion systems. The addition of hydrogen to hydrocarbon fuels affects both chemical and physical combustion processes. These changes affect among others flame stability, combustor acoustics, pollutant emissions and combustor efficiency. Only a few of these issues are understood. Therefore, it is important to examine these characteristics to enable using blend fuels in practical energy systems productions. The experimental approach is restricted in general to specific operating conditions (temperature, pressure, H2 percentage in the mixture, etc.) due to its high costs. However, the numerical simulation can represent a suitable less costly alternative. The aim of this study done at ICARE is to complete the experiments. Equivalence ratio and hydrogen enrichment effects on lean methane/air flame structure were studied. The increase of the equivalence ratio, increases flame temperature and stability but produces more CO, CO2 and NOx. Hydrogen blending, increases flame stability and reduces emissions. The replacement of 10% or 20% of the fuel by hydrogen enhances installation efficiency with no modifications needed on the combustion system
Etude numérique de la combustion turbulente du prémélange pauvre méthane/air enrichi à l'hydrogène
No full textFuel blending represents a promising approach for reducing harmful emissions from combustion systems. The addition of hydrogen to hydrocarbon fuels affects both chemical and physical combustion processes. These changes affect among others flame stability, combustor acoustics, pollutant emissions and combustor efficiency. Only a few of these issues are understood. Therefore, it is important to examine these characteristics to enable using blend fuels in practical energy systems productions. The experimental approach is restricted in general to specific operating conditions (temperature, pressure, H2 percentage in the mixture, etc.) due to its high costs. However, the numerical simulation can represent a suitable less costly alternative. The aim of this study done at ICARE is to complete the experiments. Equivalence ratio and hydrogen enrichment effects on lean methane/air flame structure were studied. The increase of the equivalence ratio, increases flame temperature and stability but produces more CO, CO2 and NOx. Hydrogen blending, increases flame stability and reduces emissions. The replacement of 10% or 20% of the fuel by hydrogen enhances installation efficiency with no modifications needed on the combustion system.L’enrichissement des hydrocarbures par l’hydrogène permet d’améliorer les performances de la combustion pauvre (augmentation de la réactivité, résistance à l’étirement, stabilité, réduction des polluants, …). Il est primordial de connaitre les caractéristiques de la combustion de ces combustibles hybrides dans différentes conditions, afin de pouvoir les utiliser d’une manière sûre et efficace dans les installations pratiques. L’approche expérimentale reste coûteuse et limitée à certaines conditions opératoires. Cependant, le calcul numérique peut constituer la solution la plus adaptée, compte tenu du progrès réalisé dans le domaine de l’informatique et de la modélisation. Dans ce contexte, ce travail que nous avons effectué à l’ICARE (Institut de Combustion, Aérothermique et Réactivité, CNRS Orléans) vise à compléter les résultats des essais expérimentaux. Les effets de la richesse du mélange et l’ajout de l’hydrogène sur la structure et la formation des polluants sont étudiés dans ce travail. L’augmentation de la richesse du combustible permet de stabiliser la flamme, mais augmente la température et produit plus de CO, CO2 et NOx. Par contre, l’addition de H2 augmente l’efficacité du mélange, stabilise la flamme avec une légère élévation de la température maximale et une diminution des fractions massiques de CO, CO2 et NOx. Le remplacement d’une fraction de 10% où même 20% du gaz principal par l’hydrogène améliore les performances des installations et ne nécessite aucune modification sur les systèmes de combustion
Etude numérique de la combustion turbulente du prémélange pauvre méthane/air enrichi à l'hydrogène
No full textFuel blending represents a promising approach for reducing harmful emissions from combustion systems. The addition of hydrogen to hydrocarbon fuels affects both chemical and physical combustion processes. These changes affect among others flame stability, combustor acoustics, pollutant emissions and combustor efficiency. Only a few of these issues are understood. Therefore, it is important to examine these characteristics to enable using blend fuels in practical energy systems productions. The experimental approach is restricted in general to specific operating conditions (temperature, pressure, H2 percentage in the mixture, etc.) due to its high costs. However, the numerical simulation can represent a suitable less costly alternative. The aim of this study done at ICARE is to complete the experiments. Equivalence ratio and hydrogen enrichment effects on lean methane/air flame structure were studied. The increase of the equivalence ratio, increases flame temperature and stability but produces more CO, CO2 and NOx. Hydrogen blending, increases flame stability and reduces emissions. The replacement of 10% or 20% of the fuel by hydrogen enhances installation efficiency with no modifications needed on the combustion system.L’enrichissement des hydrocarbures par l’hydrogène permet d’améliorer les performances de la combustion pauvre (augmentation de la réactivité, résistance à l’étirement, stabilité, réduction des polluants, …). Il est primordial de connaitre les caractéristiques de la combustion de ces combustibles hybrides dans différentes conditions, afin de pouvoir les utiliser d’une manière sûre et efficace dans les installations pratiques. L’approche expérimentale reste coûteuse et limitée à certaines conditions opératoires. Cependant, le calcul numérique peut constituer la solution la plus adaptée, compte tenu du progrès réalisé dans le domaine de l’informatique et de la modélisation. Dans ce contexte, ce travail que nous avons effectué à l’ICARE (Institut de Combustion, Aérothermique et Réactivité, CNRS Orléans) vise à compléter les résultats des essais expérimentaux. Les effets de la richesse du mélange et l’ajout de l’hydrogène sur la structure et la formation des polluants sont étudiés dans ce travail. L’augmentation de la richesse du combustible permet de stabiliser la flamme, mais augmente la température et produit plus de CO, CO2 et NOx. Par contre, l’addition de H2 augmente l’efficacité du mélange, stabilise la flamme avec une légère élévation de la température maximale et une diminution des fractions massiques de CO, CO2 et NOx. Le remplacement d’une fraction de 10% où même 20% du gaz principal par l’hydrogène améliore les performances des installations et ne nécessite aucune modification sur les systèmes de combustion
Numerical investigation of counter-flow diffusion flame of biogas–hydrogen blends: Effects of biogas composition, hydrogen enrichment and scalar dissipation rate on flame structure and emissions
No full textThis study addresses numerically the influence of several operating conditions on the structure and NO emissions of a biogas diffusion flame. The analysis is conducted at atmospheric pressure in counter-flow configuration and mixture fraction space. CO2 volume in biogas is varied from 25% to 60%, H2 enrichment from 0% to 20% and the scalar dissipation rate from near equilibrium to near extinction. Particular attention is paid to CO2 chemical effect. CO2 contained in biogas can have chemical effects when it participates in chemical reactions and thermal effects when it acts like a pure diluent. Chemical effects of CO2 are elucidated by using the inert species technique. Flame structure is characterized by solving flamelet equations with the consideration of radiation and detailed chemistry.
It is observed that flame properties are very sensitive to biogas composition, hydrogen addition and scalar dissipation rate. CO2 increment decreases flame temperature, mass fraction of chain carrier radicals and NO emission index. Blending biogas with hydrogen increases the mixture heating value and makes the fuel more reactive. Hence, chain carrier radicals and NO index emission are all increased. The chemical effect of CO2 is found to be present overall scalar dissipation rate values where it reduces the maxima of temperature and OH mass fraction and increases the maxima of CO and NO mass fractions. H2 enrichment has a weak influence on CO2 chemical effect. Hydrogen-rich biogas flames produce less NO at high scalar dissipation rates
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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