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Dimitriu S.,Polytechnic University of Bucharest | Manoliu V.,National Institute of Aerospace Research Elie Carafoli INCAS | Alexandrescu E.,Romanian Research and Development Institute for Gas Turbines COMOTI | Ionescu G.,National Institute of Aerospace Research Elie Carafoli INCAS | And 2 more authors.
Metalurgia International

The thermal barrier coatings (TBC) multilayer ceramic structures represent the protection solution widely accepted for the "hot parts" of turbo engines, co-generative systems for the power industry or of some benchmarks strongly thermal tested in syderurgy (iron and steel industry). From the whole assembly of wear factors that act simultaneously at high values, the most disturbing on layers reliability is the thermal shock. This paper presents the behavior at thermal stresses of some new duplex and triplex compositional gradient ceramic structures in order to reduce the effect of phasic changes at high temperatures. The set-up conditions of the thermal experiment shows similarities with turbo engines functioning under extreme conditions (take-off, stop engine, etc.). Electron microscopy investigations will highlight the multilayer microstructure obtained by techniques such as APS - air plasma spray and HVOF - high velocity oxygen fuel, associated to the ceramic, composite materials used. The thermal shock in extreme conditions produces large changes within interfacial and intrafacial TBCs structure. In this paper one presents the formation mechanism of the nanoscale TGO layers - thermal grown oxide, which can initiate depreciation of the structure at the interface bond coat - ceramic layer. Some considerations on ceramic layers delamination mechanism will be taken into account by analyzing the structural changes induced by extreme thermal conditions. Source

Banu A.,Polytechnic University of Bucharest | Marcu M.,Institute of Physical Chemistry Ilie Murgulescu | Alexandrescu E.,Romanian Research and Development Institute for Gas Turbines COMOTI | Anghel E.M.,Institute of Physical Chemistry Ilie Murgulescu
Journal of Solid State Electrochemistry

Electrochemical depositions of hybrid polypyrrole/nickel cobalt oxide (PPy/NiCoO) coatings onto ferritic stainless steel surface were carried out with different electrochemical techniques from 0.1 M pyrrole (Py) in 0.2-M oxalic acid (OA) solution and less than 150-nanometer-sized NiCoO particles. The structural properties of the composite were investigated by using different methods such as transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometer (EDS) and Raman spectroscopy. The embedded NiCoO particles, uniformly distributed onto the surface of the PPy film, have similar oxide ratios corresponding to a mixed oxide structure. The electrochemical characterization was done using polarization curves and linear sweep voltammetry (LSV) related to oxygen reduction reaction (ORR) in alkaline solution and hydrogen peroxide as an oxygen source. Concerning the exchange current densities for ORR, the obtained values (between 1.06 and 1.45 × 10−3 mA cm−2 for a total amount of NiCoO of 0.1 mg cm−2) are comparable with other polymer films with Pt. © 2014, Springer-Verlag Berlin Heidelberg. Source

Alexandrescu E.,Romanian Research and Development Institute for Gas Turbines COMOTI | Banu A.,Polytechnic University of Bucharest | Trifanescu M.,Polytechnic University of Bucharest | Paraschiv A.,Romanian Research and Development Institute for Gas Turbines COMOTI
Applied Mechanics and Materials

Today conventional titanium-based alloys represent one third of the weight of modern aircraft engines and, are the second most used engine material following Ni-based superalloys. [1] Titanium aluminide alloys based on intermetallic phases γ (TiAl) and α2 (Ti3Al) and the most recent – orthorhombic titanium aluminide, are widely recognized as having the potential to meet the design requirements for high temperature applications. The outstanding thermo-physical and mechanical properties of these materials rely mainly on the strongly ordered nature and the directional bonding of the compounds. These involve: high melting point, above 14600C, low density of 3,9-5 g/cm3, according the alloying degree, high elastic modulus (high stiffness), high yield strength and good creep resistance at high temperature, low diffusion coefficient, good structural stability at high temperature. The main objective of our paper are focussed on the shortterm mechanical properties if Titanium niobium aluminide at 850°C. High temperatures mechanical properties evaluation was performed by tensile testing at temperature of 850°C on universal static and dynamic testing machine Instron 8802, equipped with high temperature system, for maximum 1000°C, and extensometer with a measuring basis of 40 mm. The mechanical tensile test was performed according the ASTM E8, with control of deformation and a testing rate of 10-4 mmsec.-1. Short-term behavior request of the support uncovered alloys, at 850°C has proved to be modest and it seems obvious that the alloys based on titanium aluminides cannot be used without protective coatings. © (2014) Trans Tech Publications, Switzerland. Source

Petcu A.C.,Romanian Research and Development Institute for Gas Turbines COMOTI | Plesu V.,Polytechnic University of Bucharest | Berbente C.,Polytechnic University of Bucharest
UPB Scientific Bulletin, Series B: Chemistry and Materials Science

Camelina is one of the most promising sources of renewable fuels. The crude oil obtained from this plant can be chemically treated and converted into bio-diesel or bio-kerosene. To study straight camelina oil combustion process is very important to know as many of its properties as possible. In this article, estimation methods of several thermophysical properties, such as: critical properties, density, thermal conductivity, and specific heat are presented. Where it was possible, the estimated values have been compared with experimental measurements, thus validating the used method. Source

Gherman B.G.,Romanian Research and Development Institute for Gas Turbines COMOTI | Malael I.,Romanian Research and Development Institute for Gas Turbines COMOTI | Mihaescu M.,KTH Royal Institute of Technology | Porumbel I.,Romanian Research and Development Institute for Gas Turbines COMOTI
22nd AIAA Computational Fluid Dynamics Conference

The paper presents the aerodynamic analysis of an air jet pump by means of Reynolds Averaged Navier-Stokes (RANS) simulations. A baseline configuration, reproducing an existing jet pump is first analysed from the perspective of overall mean compressible flow behaviour, turbulence production and mixing, and efficiency performance. Several constructive solutions are proposed in order to achieve enhanced mixing and efficiency performance. All the cases are investigated for the same operating condition of interest. As a result of the numerical analysis, two solutions are selected as potential improved constructive solutions in terms of mixing and efficiency performance. It is intended to complement the study by further experimental measurements for the baseline set-up and for the two selected configurations, in order to assess their actual performance and to validate the numerical data. © 2015, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Source

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