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Athens, Greece

The National Technical University of Athens , sometimes known as Athens Polytechnic, is among the oldest and most prestigious higher education institutions of Greece. It is named Metsovion in honor of its benefactors Nikolaos Stournaris, Eleni Tositsa, Michail Tositsas and Georgios Averoff, whose origin is from the town of Metsovo in Epirus.It was founded in 1837 as a part-time vocational school named Royal School of Arts which, as its role in the technical development of the fledgling state grew, developed into Greece's sole institution providing engineering degrees up until the 1950s, when polytechnics were established outside Athens. Its traditional campus, located in the center of the city of Athens on Patision Avenue, features a suite of magnificent neo-classical buildings by architect Lysandros Kaftantzoglou . A suburban campus, the Zografou Campus, was built in the 1980s.NTUA is divided into nine academic schools, eight being for the engineering disciplines, including architecture, and one for applied science . Undergraduate studies have a duration of five years. Admission to NTUA is highly selective and can only be accomplished through achieving exceptional grades in the annual Panhellenic Exams. It is a widely spread perception that the vast majority of each year's Panhellenic Exams top students interested in the science and technology opts to attend NTUA. The university comprises about 700 of academic staff, 140 scientific assistants and 260 administrative and technical staff. It also has about 8,500 undergraduates and about 1,500 postgraduate students. Eight of the NTUA's Schools are housed at the Zografou Campus, while the School of Architecture is based at the Patision Complex. Wikipedia.

The paper presents the results from the analysis of an experimental investigation with the aim to provide insight to the cyclic, instantaneous heat transfer phenomena occurring in both the cylinder head and exhaust manifold wall surfaces of a direct injection (DI), air-cooled diesel engine. The mechanism of cyclic heat transfer is investigated during engine transient events, viz. after a sudden change in engine speed and/or load, both for the combustion chamber and exhaust manifold surfaces. These results are then compared with relevant experimental data from steady state operation which in the present case are used as reference helping to reveal any potential influences of each transient event on cyclic heat transfer. The experimental installation allowed both long- and short-term signal types to be recorded on a common time reference base during the transient event. Processing of experimental data was accomplished using a modified version of one-dimensional heat conduction theory with Fourier analysis, capable to cater for the special characteristics of transient engine operation. Based on this model, the evolution of local surface heat flux during a transient event was calculated. Two engine transient events are examined, which present a key difference in the way the load and speed changes are imposed on each one of them. From the analysis of experimental results it is confirmed that each thermal transient event consists of two distinguished phases the " thermodynamic" and the " structural" one which are appropriately configured and analyzed. In the case of a severe variation, in the first 20 cycles after the beginning of the transient event, the wall surface temperature amplitude on cylinder head was almost three times higher than the one observed at the " normal" temperature oscillations occurring during the steady state operation. At the same time, peak pressure values in the same cycles are increased by almost 15% above their corresponding values at the final steady state. The same phenomena are valid for the exhaust manifold surfaces but on a moderated scale. © 2010 Elsevier Ltd.

Giakoumis E.G.,National Technical University of Athens
Renewable Energy | Year: 2013

In the present work, a detailed statistical investigation is conducted in order to a) assess the average values of all properties (incl. fatty acid composition) of the most investigated biodiesels and b) quantify the effects of feedstock unsaturation on the physical and chemical properties of the derived methyl ester. To this aim, the available literature on biodiesel properties and fatty acid composition was gathered (more than 750 papers published in International Journals and Conferences), and the reported measurements are statistically analyzed with respect to the feedstock and its chemical composition and structure; in total, 26 different biodiesel feedstocks are studied, comprising of twenty-two edible and non-edible vegetable oils and four animal fats. From the analysis, collective results and statistical data are derived for each property that are then compared with the European and American specifications. The effects of unsaturation are investigated with separate best-fit linear curves provided for each interesting property with respect to the average number of double bonds. The various trends observed are discussed and explained based on fundamental aspects of fuel chemistry and on the consequences they have on real engine operation. © 2012 Elsevier Ltd.

The present work evaluates the effects of using blends of diesel fuel with cottonseed or sunflower oils and their (methyl ester) bio-diesel in proportions of 10% and 20% (by vol.), on the combustion and emissions behavior of a fully instrumented, six-cylinder, turbocharged and after-cooled, heavy-duty, direct injection (DI), 'Mercedes-Benz' diesel engine. Combustion chamber and fuel injection pressure diagrams are obtained at two speeds and three loads. A heat release analysis of the experimentally obtained cylinder pressure diagrams is developed and used. Plots of histories in the combustion chamber of the heat release rate and temperatures, and the variation of interesting quantities such as maximum cylinder pressures and their rates, maximum cylinder temperatures and ignition delays reveal some interesting features, which shed light into the combustion mechanism and emissions formation when using these bio-fuels. The analysis results, together with the differing physical and chemical properties of these bio-fuels against those for the diesel fuel, which constitutes the 'baseline' fuel, aid the correct interpretation of the basic regulated emissions of smoke and nitrogen oxides measured at the engine exhaust. © 2012 Elsevier Ltd. All rights reserved.

This experimental investigation evaluates the combustion and exhaust emission characteristics of cottonseed oil and its (methyl ester) bio-diesel in blends with 20% by vol. of either n-butanol or diethyl ether (DEE), fueling a standard, experimental, single-cylinder, four-stroke, high-speed direct injection (HSDI), 'Hydra' diesel engine. The tests are conducted using each of the above fuel blends or neat cottonseed oil or its neat bio-diesel, with the engine operating at three different loads. Fuel consumption, exhaust smoke, nitrogen oxides (NOx), carbon monoxide (CO) and total unburned hydrocarbons (HCs) are measured. The differences in the performance and exhaust emissions of these fuel blends from the baseline operation of the diesel engine, i.e. when working with neat cottonseed oil or its neat bio-diesel, are compared. Fuel injection and combustion chamber pressure diagrams are obtained, and heat release rate analysis of the latter ones is performed revealing some interesting features of the combustion mechanisms. These results and the widely differing physical and chemical properties of n-butanol and DEE against those for the cottonseed oil and its bio-diesel are used to aid the correct interpretation of the observed engine behavior. It is revealed that n-butanol and DEE, which can be produced from biomass (bio-butanol and bio-DEE), when added to the vegetable oil or its bio-diesel improve the behavior of diesel engine. © 2012 Elsevier Ltd. All rights reserved.

Vamvatsikos D.,National Technical University of Athens
Earthquake Engineering and Structural Dynamics | Year: 2013

A novel set of SAC/FEMA-style closed-form expressions is presented to accurately assess structural safety under seismic action. Such solutions allow the practical evaluation of the risk integral convolving seismic hazard and structural response by using a number of idealizations to achieve a simple analytical form. The most heavily criticized approximation of the SAC/FEMA formats is the first-order power-law fit of the hazard curve. It results to unacceptable errors whenever the curvature of the hazard function becomes significant. Adopting a second-order fit, instead, allows capturing the hazard curvature at the cost of necessitating new analytic forms. The new set of equations is a complete replacement of the original, enabling (a) accurate estimation of the mean annual frequency of limit-state exceedance and (b) safety checking for specified performance objectives in a code-compatible format. More importantly, the flexibility of higher-order fitting guarantees a wider-range validity of the local hazard approximation. Thus, it enables the inversion of the formulas for practically estimating the allowable demand or the required capacity to fulfill any design objective.© 2012 John Wiley & Sons, Ltd..

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