1,720,998 research outputs found
Four Stroke Engine Geometry for Stratified Charge Combustion
No full textIn four-stroke engines direct injection increases power and fuel economy, which is further improved by charge stratification, due to pumping loss reduction and better combustion efficiency at partial loads. Charge stratification can be obtained by different techniques and injector designs. In every case late injection is necessary for stratification, which however is impaired by fuel dilution and spreading in consequence of burnt gas expansion, leading to incomplete combustion at very light loads. A numerical study has been carried out modifying KIVA code to handle new piston shapes. An innovative combustion chamber that is split in two volumes and allows fuel confinement during combustion has been conceived. CFD comparison has been made between a conventional combustion chamber and the proposed new one in term of combustion efficiency. Combustion is enhanced by the new design and unburnt emissions are reduced
Early stages of the mechanical alloying of TiC-TiN powder mixtures
No full textThe present work focuses on the alloying behavior of TiC-TiN powder mixtures submitted to mechanical processing by ball milling. Accurate X-ray diffraction analyses indicate a progressive modification of the unit cell parameters of the TiC and TiN phases, suggesting the formation of TiC- and TiN-rich solid solutions with an increasingly larger content of solutes. Once the discrete character of the mechanical treatment is taken into due account, the smooth change of the unit cell parameters can be explained by a sequence of mutual dissolution stages related to individual collisions. At each collision, the average chemical composition of small amounts of TiC- and TiN-rich phases changes discontinuously. The discontinuous changes can be tentatively ascribed to local mass transport processes activated by the mechanical deformation of powders at collisions
XEBIC at the Dual Beam
No full textAfter its golden age during the decades of the development of Silicon IC technology, nowadays Electron Beam Induced Current (EBIC) technique comes back to importance mostly on photonic and high speed electron devices based on compound semiconductors. A new approach for recording a fast EBIC embedded in a Dual Beam system is presented. The combined use of multi-slicing FIB, SEM and EBIC enables 3D tomography of P-N junctions and drives TEM preparation in failure analysis studies of leaky junctions. (C) 2013 Published by Elsevier Ltd
Formation of metastable solid solutions by mechanical alloying of immiscible Ag and Bi
No full textThis work investigates the effects of the Vickers micro-hardness of Ag powders on the alloying process undergone by Ag90Bi10 powder mixtures submitted to ball milling. The transformation kinetics has been studied by quantitative X-ray diffraction. The experimental findings indicate that Bi gradually dissolves into Ag, finally forming a crystalline solid solution in which thermodynamic solubility limits are largely exceeded. It is shown that the rate of Bi dissolution, and the solubility degree, decrease as the Vickers micro-hardness of Ag powders increase
Environmental impact of the Furtei gold mine: implications for the geoenvironmental model of epithermal “high sulfidation” deposits
No full text
The reaction of enargite with alkaline NaClO solutions: an AFM and flow-through study
No full textThe reaction of enargite, Cu3AsS4, with alkaline NaClO solutions is of interest for hydrometallurgical applications. In this
study, the surface of cleavage fragments was observed ex situ by atomic force microscopy (AFM), X-ray photoelectron spectroscopy
(XPS) and scanning electron microscopy (SEM) after sequential interaction (up to 240 min) with a 0.27 M NaClO/0.03 M NaOH
solution (pH 12.2) at room temperature (295 ± 2 K). Likewise, the evolution of the reaction of enargite powder (25 < size
fraction
Variations and controls on the copper/arsenic ratios in waters at the Furtei gold mine, Sardinia, italy
No full textMotore HCPC per applicazioni pesanti
No full textLa presente memoria riguarda un concetto innovativo per controllare la combustione HCCI (Homogeneous Charge
Compression Ignition) in motori ad Accensione Spontanea, denominato Homogeneuous Charge Progressive Combustion
(HCPC) e che è basato sul principio dello split-cycle. In precedenti lavori è stata dimostrata la validità del concetto per motori
per applicazioni leggere. Questo articolo riporta uno studio numerico con tecniche di fluidodinamica computazionale (CFD) di
una versione del motore HCPC per applicazioni pesanti. Il motore ha una cilindrata di 13 litri ed eroga una potenza di 700 kW
a 2200 giri/min con un rendimento indicato massimo del 49%, mantenendo una combustione con basse emissioni
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