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HDDI in Mild combustion
No full textMild combustion is an emerging technology in several fields of practical applications, from material treatment to energy conversion as well as to pollutant abatement [1]. In a survey of potential keys for the mitigation of environmental problem, it represents a flexible and clean process that is the result of a trade-off in the optimization of fuel conversion with respect to efficiency (in term of energy saving and pollutant abatement) while not requiring drastic changes in the configuration of traditional plants. In this chapter the attention will be focused on non-premixed combustion processes, thus on configurations where the fuel and the oxidant flows are fed separately, then mix and react. A combination of both heating and dilution of oxidant and/or fuel yields a not premixed combustion process which is named Hot Diluted Diffusion Ignition (HDDI) [2, 4] when
• heating contributes significantly to the creation of an oxidative structure in the sense that no combustion process occurs without it;
• dilution is so intense that the maximum temperature attainable inside this structure is so low that, in turn, it affects significantly its placement in the mixture fraction domain, the structure itself and the physical and chemical kinetics when compared to a diffusion flame process
Numerical Study of Mild Combustion in Hot Diluted Diffusion Ignition (HDDI) regime
No full textMild Combustion is a process defined on the ground of well-identified external parameters, namely the temperature of reactants and the maximum allowable temperature increase. Although the definition is rigorous, it is necessary to identify unique, intrinsic structural properties of processes evolving in such conditions in the different, basic configurations that make Mild Combustion relevant from practical point of view.
In this paper the configuration of opposed jets of hot air versus cold fuel/diluent mixture, here referred as Hot Diluted Diffusion Ignition (HDDI), has been considered. Distributions of temperature and heat release rate as a function of the mixture fraction are evaluated for different values of the external parameters, i.e. pre-heating temperature of the air, fuel dilution, pressure and strain rate. They have been used in order to identify combustion regimes on the ground of their location and broadness. In particular, it has been shown that a significant broadening of heat release distribution is associated to oxidant temperatures higher than the auto-ignition temperature of homogeneous charge for a characteristic time comparable to the convective characteristic time of the system, supporting the conceptual model of “distributed oxidation”. In the asymptotic condition with very diluted fuel where the pyrolysis region, typical of standard diffusion flames, is no longer present in the heat release profiles, the sub-domain Mild-HDDI Combustion is identified. In this regime the position of the maximum heat release is completely uncorrelated with the stoichiometric mixture fraction. In this case the oxidation takes place only where the autoignition can develop inside constrain of the residence time of the fuel in the system
MIXING EFFICIENCY OF JET IN CROSS-FLOW CONFIGURATION IN A TUBULAR REACTOR FOR MILD COMBUSTION STUDIES
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DYNAMIC BEHAVIOUR OF METHANE OXIDATION IN PREMIXED FLOW REACTOR
No full textThermokinetic temperature oscillations related to oxidation of small hydrocarbons have not been extensively studied yet, because they occur in a temperature and pressure range not relevant for practical applications. Exploitation of new combustion methodologies such as Mild Combustion also indicated such a phenomenology in small-hydrocarbons oxidation. In this paper, experimental characterization of dynamic behavior occurring in methane mild combustion in premixed flow conditions reported in a previous work was extended and a comparative analysis with data obtained by means of numerical studies was performed. The experimental study was carried out in an atmospheric jet-stirred flow reactor at different inlet temperature and mixture compositions. Several typologies of temperature oscillations were identified whose amplitudes and frequencies strongly depend on the temperature and carbon/oxygen ratio considered. These dynamic behaviors were tentatively explained by means of a rate of production analysis performed by using different methane oxidation kinetic models available in the literature. It was shown that the CH 3 recombination path present in the methane oxidation mechanism plays a key role in modulation of temperature oscillations
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
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