1,720,982 research outputs found
A CFD Investigation of Syngas Spark Ignition Engines
No full textIn the last two decades, specific interest has been addressed towards Internal Combustion
Engines (ICEs) powered by bio-fuels. The growing interest for bio-fuels is related to constantly
increasing stringent exhaust gases regulations and to a remarkable request of reduction of CO2-
emissions. In the same direction (CO2-emissions reduction) and, additionally with the aim to
minimize the dependence from crude oil, several alternative fuels have gained attention in the
automotive industry. The fuels of bio-origin can provide a feasible solution to worldwide
petroleum crisis by promising a sustainable development, energy conservation and
environmental preservation. Gasoline and diesel-driven engines are the major sources of Green-
House Gases (GHG) emissions [1-3]. Scientists around the world have been explored several
alternative energy sources including biomass derived fuels, biogas, primary alcohol, vegetable
oils, biodiesel, etc. These alternative energy sources are largely environmental-friendly but their
use needs further investigations in relation to the specific applications. Some of them can be
used directly while others need to be formulated to bring their relevant properties closer to
those of conventional fuels.
This work deals with some features of spark ignition engines powered by syngas. The ENEA
GRID Cresco resources have been used to perform accurate simulations using an advanced
parallel CFD code
A CFD Analysis of the Air Flow through the Matrix Regenerator of Stirling Engines
No full textIn this paper, a thermo-fluid dynamic 3-D numerical model of the air flow through the stacked woven matrix of Stirling engines regenerators has been used to characterize the pressure drop and heat transfer through the regenerator. Firstly, an isothermal flow, at 293 K, through the porous media has been analyzed. Four different matrices have been considered, two aligned and two misaligned and the simulations have been carried out over a range of Reynolds numbers from 5 to 2000. Two friction factor correlations have been obtained for the aligned and the misaligned matrices, respectively, and the results are compared with experimental data in the literature. Following this, heat transfer between the air flow and the matrix has been considered by varying the inlet gas temperature, i.e. 500-750 K, and keeping the wall temperature of the regenerator at 300 K. In this case, the simulations have been carried out over a Reynolds number ranging from 8 to 1700 by using the misaligned matrix. The regenerator efficiency and the Nusselt number as function of Re are given. A correlation equation for Nusselt number is given and compared with experimental results in the literature
Influence of piston shape and injector geometry on combustion and emission characteristics of syngas in direct-injection spark-ignition engine
No full textThis paper presents a numerical study of the influence of piston shape and injector geometry on combustion and emissions characteristics of a direct-injection spark-ignition engine fueled by syngas (50% by volume of hydrogen, 50% by volume of carbon monoxide) under low/medium load conditions. Three different piston cup geometries namely: High-clearance Combustion Cup (HCC), Low-clearance Combustion Cup (LCC) and Omega Combustion Cup (OCC) have been considered with a compression ratio of 14. An axial full-cone gas jet injector has been considered together with a hollow-cone gas jet injector with several included half-angles, i.e. 30°, 45°, 52.5° and 60°. Computational fluid dynamics modelling has been performed to simulate the combustion process. The results indicate that, in terms of performance, OCC shape is favorable, even if OCC generates relatively higher NOx than the other two configurations. A further analysis has been performed by simulating an engine with OCC piston shape and an included half-angle of injection of 30°, by varying the Start Of Injection (SOI). The results show that the flame propagation velocity reduces as the SOI advances, since the fuel distribution becomes more homogeneous approaching to a premixed case. However, the flame speed reduction is partially balanced by the disappearance of very lean regions thanks to fuel convection and diffusion
A Thermodynamic Analysis of Low-temperature Heat Recovery for ORC Power Plants
No full textIn the last years, increasing interest has been addressed towards Organic Rankine Cycle (ORC) power plants as a consequence of their potential integration with low¬grade heat sources. Available thermal heat sources are solar energy, geothermal energy, biomass, and waste heat from various thermal processes such as heat from exhaust gases of internal combustion engines. In this work, a low-temperature geothermal source (below 100 °C) has been considered, and an accurate thermodynamic analysis has been performed in order to assess the capability of this source in the heat recovery process, by considering several power plant configurations and different working fluids. In addition, the integration of this low¬grade heat source with a higher temperature thermal source (i.e. solar thermal and biomass combustion) has been investigated to improve the thermal efficiency. Very promising results are obtained by this integration. Specifically, a noticeable reduction of solar collector surfaces in one case and of biomass consumption in the other case has been observed respect to the configurations wherein only solar thermal source and biomass combustion were considered, respectively
An Optimization Algorithm of Stirling Engine Performance for Low-Grade Heat Recovery
No full textThis paper deals with the optimization of the performance of Stirling engines for power generation by recovering low-enthalpy sources. A thermodynamic model, together with a Single Objective Genetic Algorithm (SOGA) to optimize the engine performance in terms of efficiency and specific power output, has been employed. The second order Simple Analysis model has been improved by including both heat transfer through the cylinder walls and mechanical losses. The new Improved Simple Analysis (ISA) model has been validated by considering the performance of the GPU-3 engine. The overall accuracy of the simulations is satisfactory with respect to measurements available in the literature. Two cases have been studied with a temperature gap between thermal sources of 80 and 60 K, respectively. The results show that the Gamma configuration is the best choice for the recovery of low-enthalpy energy sources, since it provides, for both cases, a higher specific power output than the other configurations, with a comparable efficiency. The geometry details of the optimal engines are given, thus providing guidance for the engine design. Finally, the engine performance has been analysed by varying the hot source temperature and engine mean pressure
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
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