Aeronáutica

URI permanente para esta comunidadhttps://inta.metricsalad.com/handle/123456789/37

Muchas de las líneas de investigación del INTA se centran en el ámbito aeronáutico. Estas líneas van encaminadas a reforzar las competencias en nuevas tecnologías, haciendo especial hincapié a las relacionadas con caracterización de emisiones producidas por turborreactores, investigación en tecnologías del hidrógeno y otras energías renovables, motores cohete con propulsante líquido y sólido, estudio de materiales funcionales, diseño y fabricación de superficies hielofóbicas, recubrimientos protectores para la corrosión por biomasa, estructuras activas avanzadas y robótica, generación avanzada de trayectorias sobre UAVs, aprendizaje automático e inteligencia artificial sobre minería de datos aerodinámicos y actuadores de plasma y sus aplicaciones.

La investigación de la Aeronáutica se materializa en proyectos financiados con fondos propios, como por ejemplo GERD, que trata del estudio de las condiciones y las tipologías de formación de hielo en superficies. Actualmente se están finalizando las tareas de implementación del nuevo de viento de engelamiento, único en el país, duplicando la capacidad de realización de ensayos en condiciones de formación de hielo.

En el sector aeronáutico del INTA cabe destaca el CIAR, un centro de ensayos en vuelo innovador, que proporciona apoyo técnico y logístico en la experimentación de sistemas de vuelo no tripulados en el ámbito de operación civil o dual y el CEDEA, un centro de ensayos para caracterización de aeronaves y sus componentes tanto tripuladas como no tripuladas, experimentación de misiles, cohetes e I+D de proyectos aeronáuticos de energía y estudio de la atmósfera.

Otros campos de investigación relacionados con la Aeronáutica son la tecnología del vuelo, la aerodinámica teórica y experimental, materiales y estructuras, desarrollo de pinturas, estudio de nuevas fuentes de energía, con programas de I+D dentro del campo de la propulsión y de su aplicación aeroespacial, estudio del impacto medioambiental de los propulsantes y trabajos relacionados con los combustibles y lubricantes en el ámbito aeroespacial y de la Defensa Nacional.

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A chamber for studying planetary environments and its applications to astrobiology
(IOP Science Publishing, 2006-07-13) Mateo Martí, Eva; Prieto Ballesteros, O.; Sobrado, J. M.; Gómez Elvira, J.; Martín Gago, J. A.; Instituto Nacional de Técnica Aeroespacial (INTA); Comunidad de Madrid
We have built a versatile environmental simulation chamber capable of reproducing atmospheric compositions and surface temperatures for most of the planetary objects. It has been especially developed to make feasible in situ irradiation and characterization of the sample under study. The total pressure in the chamber can range from 5 to 5 × 10−9 mbar. The required atmospheric composition is regulated via a residual gas analyser with ca ppm precision. Temperatures can be set from 4 K to 325 K. The sample under study can be irradiated with ion and electron sources, a deuterium ultraviolet (UV) lamp and a noble-gas discharge UV lamp. One of the main technological challenges of this device is to provide the user the possibility of performing ion and electron irradiation at a total pressure of 0.5 mbar. This is attained by means of an efficient differential pumping system. The in situ analysis techniques implemented are UV spectroscopy and infrared spectroscopy (IR). This machine is especially suitable for following the chemical changes induced in a particular sample by irradiation in a controlled environment. Therefore, it can be used in different disciplines such as planetary geology, astrobiology, environmental chemistry, materials science and for instrumentation testing.
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Silicon Surface Nanostructuring for Covalent Immobilization of Biomolecules
(ACS Publications, 2008-06-03) Rogero, Celia; Chaffey, Benjamin T.; Mateo Martí, Eva; Sobrado, J. M.; Horrocks, Benjamin R.; Houlton, Andrew; Lakey, Jeremy H.; Briones, C.; Martín Gago, J. A.; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Ciencia e Innovación (MICINN)
We present a straightforward strategy to control the average distance of immobilized biomolecules on silicon surfaces. We exploit the reaction taking place between the amino residues within the biomolecules (lysine groups of proteins or the N-terminus of oligomers of peptide nucleic acid, PNA) and the aldehyde-terminated groups presented in a mixed aldehyde/alkyl organic monolayer on a silicon surface. The mixed monolayers were prepared by a thermal reaction of hydrogen-terminated Si(111) with a mixture of undecene and undecenyl-aldehyde. We quantitatively evaluate the surface concentration of aldehyde in the monolayer by atomic force microscopy and an intensity analysis of core level X-ray photoemission spectroscopy peaks. These complementary techniques show that the surface density of the reactive terminal groups reflects the mole fraction of aldehyde in the reactive solution used to modify the silicon surface. The further immobilization of proteins or peptide nucleic acids on the monolayer shows that the density of biomolecules reproduces the aldehyde surface density, which indicates a specific covalent attachment and a negligible nonspecific adsorption. The proposed procedure makes possible to control the average distance of the immobilized active biomolecules on the silicon surface, which could be of great relevance for applications in the interdisciplinary field of biosensors.
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Kinetic and chemorheological modelling of the polymerization of 2,4- Toluenediisocyanate and ferrocene-functionalized hydroxyl-terminated polybutadiene
(Elsevier, 2018-02-26) Lucio, B.; De la Fuente, J. L.; Ministerio de Economía y Competitividad (MINECO)
The reaction of 2,4-toluenediisocyanate (2,4-TDI) and a metallocenic-prepolymer derived from hydroxyl-terminated polybutadiene (HTPB) was studied in bulk and under isothermal conditions (50–80 °C) by rheological methods. Two regions distinguished and limited by the gel point, identified as the crossover of loss tangent (tan δ) at different frequencies, were analysed from different rheological properties during the curing process of this novel metallo-polyurethane (PU). The initial part of this polymerization, dominated by the viscous behaviour (from η0 ≈ 5 Pa s to η = 250 Pa s), was modelled through the Arrhenius isothermal model, in which the presence of two rheokinetic stages, due to different isocyanate groups in the 2 and 4 positions for this asymmetric monomer, was found until the gelation is reached. The contributions of the main reactions for the region analysed, before the gel point of this polyaddition, are discussed. The gel transition was identified, and the viscoelastic behaviour of the gelation process was studied in depth. In addition, from the evolution of the storage modulus (G′) recorded, the overall polymerization reaction was described by a Kamal-Sourour kinetic expression for the reaction rate. The different kinetic parameters obtained for the autocatalytic model used yielded predictions that agree very well with the experimental data, finding a significant autocatalytic effect. An isoconversional method allowed the determination of the dependence of the activation energy on the conversion degree during the network formation of this advanced functional ferrocene-PU, which is of great interest in rocket technology research for the development of the aerospace industry.
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Droplet breakup criterion in airfoils leading edge vicinity
(Aerospace Research Central, 2018-05-07) García Magariño, A.; Velázquez, Ángel; Sor, Suthyvann; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Economía y Competitividad (MINECO)
A new breakup criterion is proposed in this paper for droplets subject to the flowfield generated by an incoming airfoil (that is, the criterion should be applied only to this type of aerodynamics flow). This criterion is based on the study of the characteristic times involved in the problem. These are the characteristic external flowfield variation time and the characteristic droplet deformation time. The criterion takes the shape of an empirical correlation that relates the Weber number at the onset of the breakup to the external flowfield and droplet characteristics. Experimental data on the droplet deformation and breakup tests conducted in a rotating arm facility are used to generate the data used to develop the correlation. Droplets, with diameters in the range of 0.3–3.6 mm, are allowed to fall in the path of an incoming airfoil attached to the end of a rotating arm. Airfoil velocities vary between 50 and 90 m∕s. The airfoil leading-edge radius varies from 0.030 to 0.103 m. Experiments are recorded with a high-speed camera using the shadowgraph illumination technique. The empirical breakup correlation applies to droplets that break in the bag and stamen mode. Some additional limited data on droplets that break in the bag and the shear mode are analyzed to see how they fit into the correlation.
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Entropy production by implicit Runge–Kutta schemes
(Springer Link, 2019-01-23) Lozano, Carlos; Instituto Nacional de Técnica Aeroespacial (INTA)
This paper follows up on the author’s recent paper “Entropy Production by Explicit Runge–Kutta schemes” (Lozano in J Sci Comput 76(1):521–564, 2018. https://doi.org/10.1007/s10915-017-0627-0), where a formula for the production of entropy by fully discrete schemes with explicit Runge–Kutta time integrators was presented. In this paper, the focus is on implicit Runge–Kutta schemes, for which the fully discrete numerical entropy evolution scheme is derived and tested.
Acceso Abierto
Development and characterization of a low-cost wind tunnel balance for aerodynamic drag measurements
(IOP Science Publishing, 2019-06-17) Bardera, Rafael; García Magariño, A.; Matías García, J. C.; Donoso, Eduardo; Sor, Suthyvann; Instituto Nacional de Técnica Aeroespacial (INTA)
Drag force measurement is one of the most important data that can be obtained in wind tunnel tests. Drag force is directly related to the energy that a vehicle needs to move, and, therefore, to the fuel costs associated with it. For vehicles, drag forces are usually measured in wind tunnels. The typical instruments for drag measurement are the force balances, which are usually complex and expensive instruments. The aim of this investigation is to study the development of a low-cost in-house balance for drag measurements in a wind tunnel. Based on a commercial available load cell XFTC300 Series in combination with simple elements designed and manufactured at INTA, a balance capable of measuring the drag force to models in a considerably wide adjustable range has been developed and characterized. The balance has been calibrated and used in a wind tunnel. Tests were carried out on a truck model, a simplified frigate shape and an Ahmed Body to obtain the resistance coefficient and evaluate the operation of the balance.
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A Comparative Study on HCN Polymers Synthesized by Polymerization of NH4CN or Diaminomaleonitrile in Aqueous Media: New Perspectives for Prebiotic Chemistry and Materials Science
(Chemistry Europe: European Chemical Societies Publishing, 2019-08-02) Ruiz Bermejo, Marta; De la Fuente, J. L.; Carretero González, J.; García Fernández, L.; Rosa Aguilar, M.; Agencia Estatal de Investigación (AEI); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
HCN polymers are a group of complex and heterogeneous substances that are widely known in the fields of astrobiology and prebiotic chemistry. In addition, they have recently received considerable attention as potential functional material coatings. However, the real nature and pathways of formation of HCN polymers remain open questions. It is well established that the tuning of macromolecular structures determines the properties and practical applications of a polymeric material. Herein, different synthetic conditions were explored for the production of HCN polymers from NHCN or diaminomaleonitrile in aqueous media with different concentrations of the starting reactants and several reaction times. By using a systematic methodology, both series of polymers were shown to exhibit similar, but not identical, spectroscopic and thermal fingerprints, which resulted in a clear differentiation of their morphological and electrochemical properties. New macrostructures are proposed for HCN polymers, and promising insights are discussed for prebiotic chemistry and materials science on the basis of the experimental results.
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Watch your adjoints! Lack of mesh convergence in inviscid adjoint solutions
(Aerospace Research Central, 2019-08-05) Lozano, Carlos; Instituto Nacional de Técnica Aeroespacial (INTA)
It has been long known that 2D and 3D inviscid adjoint solutions are generically singular at sharp trailing edges. In this paper, a concurrent effect is described by which wall boundary values of 2D and 3D inviscid continuous and discrete adjoint solutions based on lift and drag are strongly mesh dependent and do not converge as the mesh is refined. Various numerical tests are performed to characterize the problem. Lift-based adjoint solutions are found to be affected for any flow condition, whereas drag-based adjoint solutions are affected for transonic lifting flows. A (laminar) viscous case is examined as well, but no comparable behavior is found, which suggests that the issue is exclusive to inviscid flows. It is argued that this behavior is caused by the trailing edge adjoint singularity.
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Characterization of an electrostatic filter prototype for bioaerosol flowmetering for INTA Investigation Aerial Platforms
(Elsevier, 2019-08-20) Bardera, Rafael; García Magariño, A.; González, Elena; Aguilera, Á.; Sor, Suthyvann; Instituto Nacional de Técnica Aeroespacial (INTA)
The characterization of the airborne microorganisms at different altitudes of the atmosphere is usually conducted by means of aerial platforms. It is very interesting to know the biological processes in the atmosphere. However, there are problems associated to the fact that sampling systems are embarked on an aircraft and the low presence of microorganisms at high altitude. A prototype of a new electrostatic filter for bioaersol flowmetering dedicated to biology investigations has been developed. This prototype was designed to be installed on board in aerial platforms of INTA. The experimental characterization of the aerodynamic flow was performed in order to investigate the behaviour of the filter when different air intake widths and different mechanical deflectors are employed. A combination of these impactor with the filters based on industrial electrostatic precipitator technology have been studied. Non-intrusive Particle Image Velocimetry technique has been used to measure the flow field inside the filter when it was running under controlled conditions in laboratory. This study is a first investigation on the flow field of filter for bioaerosol flowmetering to be embarked on an aircraft. The results show the influence of each parameter in the flow field that could be used for further investigations and designs.
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Entropy and adjoint methods
(Springer Link, 2019-11-11) Lozano, Carlos; Instituto Nacional de Técnica Aeroespacial (INTA)
Aerodynamic drag can be partially approximated by the entropy flux across fluid domain boundaries with a formula due to Oswatitsch. In this paper, we build the adjoint solution that corresponds to this representation of the drag and investigate its relation to the entropy variables, which are linked to the integrated residual of the entropy transport equation. For inviscid isentropic flows, the resulting adjoint variables are identical to the entropy variables, an observation originally due to Fidkowski and Roe, while for non-isentropic flows there is a significant difference that is explicitly demonstrated with analytic solutions in the shocked quasi-1D case. Both approaches are also investigated for viscous and inviscid flows in two and three dimensions, where the adjoint equations and boundary conditions are derived. The application of both approaches to mesh adaptation is investigated, with especial emphasis on inviscid flows with shocks.
Acceso Abierto
ISOTOPICALLY LABELLED MATERIALS FOR DEGRADATION DETECTION
(2020-01-02) MORA NOGUÉS, Julio; BENEDITO BORRÁS, Adolfo; GARCÍA SANCHO, Amador; ALONSO RUIZ, Rafael
The invention relates to an isotopically marked material comprising a functional synthetic polymer and optionally a functional additive and to its use in the detection of material contamination or degradation or wear, preferably when said material is an industrial material, a space material or a prosthetic material.
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Differential iron management in monocotyledon and dicotyledon plants from the Río Tinto basin.
(Springer Link, 2020-01-06) De la Fuente, V.; Rufo, L.; Ramírez, E.; Sánchez Gavilán, I.; Amils, R.; Rodríguez Rivas, Noé; Ministerio de Economia Industria y Competitividad (MINECO); 0000-0002-2239-6523
The study of plants adapted to an extreme environment with a high concentration of iron such as Río Tinto allowed the study of important elements for the development and control of plant growth including their localization, management, and storage. The absorption, transport, and accumulation of iron were studied in different species of dicotyledons (Sarcocornia pruinosa, Salicornia patula, Arthrocnemum macrostachyum, and Halogeton sativus of the Chenopodiaceae family) and monocotyledons (Imperata cylindrica, Cynodon dactylon, and Panicum repens from the Poaceae family), all obtained from the Río Tinto banks in different sample collection campaigns. The results clearly show that phytoferritin is not observed in the chloroplast of monocotyledons, an important difference from what is observed in dicotyledons. The presence of plastids with a high concentration of iron in the sieve tubes of monocotyledons strongly suggests their possible role in the transport and accumulation of iron in these plants.
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Breakup criterion for droplets exposed to the unsteady flow generated by an incoming aerodynamic surface
(Elsevier, 2020-03-15) López Gavilan, Pablo; Velázquez, Ángel; García Magariño, A.; Sor, Suthyvann; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Economía y Competitividad (MINECO)
An experimental and theoretical study is presented on the problem of droplet breakup exposed to a continuously accelerating flow generated by an incoming aerodynamics surface. Droplet breakup experiments were carried out in a rotating arm facility. Droplet diameters were of the order of 1 mm. The maximum velocity of the airfoils located at the end of the rotating arm was 90 m/s. Droplet deformation was computed using a phenomenological model developed previously by the authors. The dynamics of this deformation was coupled to an instability model based on the growth of Rayleigh-Taylor waves at the droplet surface. It was found that, within the experimental uncertainty, breakup occurs when the instability wavelength approaches the droplet hydraulic diameter assuming that it flattens and deforms as an oblate spheroid. This fact allowed for the generation of a theoretical closed-form droplet deformation and breakup model that predicts the onset of breakup with discrepancies of about ±10 % when compared to the experimental results. Finally, as an application case, this closed-form model is used to simulate an actual situation in which the objective is to investigate whether a series of droplets that are approached by an airfoil either impact on its surface, or break prior to collision, or break without colliding, or pass through undamaged.
Acceso Abierto
Droplet deformation and trajectory without interferences in the incoming airfoil shoulder region
(Aerospace Research Central, 2020-05-22) García Magariño, A.; Sor, Suthyvann; Velázquez, Ángel; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Economía y Competitividad (MINECO)
A new experimental campaign has been conducted in the shoulder region of an incoming airfoil of chord 1050 mm, where droplets are separated enough to neglect interferences between them. Droplets of three sizes (500, 950, and 1250 μmof radius) were allowed to fall in the path of an incoming airfoil while shadowgraph images were recorded by a high-speed video camera at 40,000 fps. The airfoil model was placed at the end of a rotating arm and moved at four velocities (30, 40, 50, and 60 m∕s). Three different regions of the shoulder were tested. Droplet deformation and trajectories are presented. Droplets evolve as a conjunction of two half-oblate spheroids that tilt as the model approaches. The tilting is larger in the higher regions of the shoulder. The trajectory model derived for droplet in the stagnation line of a moving airfoil has been formally derived for the shoulder region and applied to the experimental data, showing very good agreement being the mean discrepancy less than 4% for the trajectory and 10% for the deformation.
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Temperature effect on aqueous NH4CN polymerization: Relationship between kinetic behaviour and structural properties
(Elsevier BV, 2020-06-05) Mas, I.; De la Fuente, J. L.; Ruiz Bermejo, Marta; Agencia Estatal de Investigación (AEI); De la Fuente, J. L. [https://orcid.org/0000-0002-1855-0153]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Herein, a kinetic analysis for aqueous NH4CN polymerizations is presented, which is consistent with an autocatalytic model when polymerizations are performed at relatively high temperatures, 80–90 °C. Further experiments at lower polymerization temperatures, approximately 50 °C, have demonstrated that this relevant prebiotic reaction follows nth-order kinetics rather than an autocatalytic mechanism. In addition, the sol fractions of these precipitation polymerizations have been evaluated by UV–Vis measurements, which also show a mechanistic shift with the reaction temperature. This change in the kinetic behaviour led to the proposal of a simple empirical methodology to describe both chemical- and diffusion-controlled regions. Despite the simplicity of the approach based on the Hill equation, fundamental kinetic parameters, such as the activation energy, can be determined in the diffusion-free zone. These results motivated a systematic structural characterization study of the respective insoluble polymers by means of elemental analysis, FT-IR and NMR spectroscopies and XRD. All these kinetic and structural analyses confirmed that the temperature has a significant effect on the polymerization kinetic of the system, on the macrostructural features and properties of the HCN-based polymers, and presumably also on the polymerization pathways. These data increase our knowledge about the chemistry of this particular family of HCN polymers, which is currently of interest both in the field of materials science and in prebiotic chemistry and astrobiology.
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Droplet ratio deformation model in combination with droplet breakup onset modeling
(Aerospace Research Central, 2020-08-25) García Magariño, A.; Velázquez, Ángel; Sor, Suthyvann; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Economía y Competitividad (MINECO)
Droplet deformation and breakup in the continuously accelerated flowfield generated by an incoming airfoil have been studied. The upper limit of droplet deformation and the minimum distance to the airfoil model at which the breakup onset takes place have been modeled. Three analytical equations have been developed based on the combination of two models: a droplet deformation and trajectory model for droplets in a continuously accelerated flowfield, and a breakup model for droplets in the vicinity of a leading edge of an airfoil model. The verification was made using experimental data obtained for water droplets whose diameters were in the range from 400 to 1800 μm impinging on airfoils of three different chord sizes moving at velocities from 50 to 90 m/s90 m/s. The rotating arm facility at National Institute of Aerospace Technology was used for this purpose. The analytical equations of the model were in good agreement with the experimental data. The upper limit of droplet deformation was verified by 95.40% of the tested experimental cases, and the minimum distance to the airfoil was verified in 99.65% of the cases.
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Aerodynamic investigation of a morphing wing for micro air vehicle by means of PIV
(MDPI, 2020-10) Bardera, Rafael; Rodríguez Sevillano, A.; García Magariño, A.; Ministerio de Defensa; García Magariño, A. [0000-0002-6039-8407]
A wind tunnel tests campaign has been conducted to investigate the aerodynamic flow around a wing morphing to be used in a micro air vehicle. Non-intrusive whole field measurements were obtained by using PIV, in order to compare the velocity and turbulence intensity maps for the modified and the original version of an adaptive wing designed to be used in a micro air vehicle. Four sections and six angles of attack have been tested. Due to the low aspect ratio of the wing and the low Reynold number tested of 6.4 × 104, the influence of the 3D effects has been proved to be important. At high angles of attack, the modified model prevented the detachment of the stream, increased the lift of the wing and reduced the turbulence intensity level on the upper surface of the airfoil and in the wake.
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Particle-bound PAH emissions from a waste glycerine-derived fuel blend in a typical automotive diesel engine
(Elsevier, 2020-10) Ballesteros, R.; Ramos, A.; Sánchez - Valdepeñas García - Moreno, Jesús; Sánchez Valdepeñas, J. [0000-0002-9594-8894]
Polynuclear or polycyclic aromatic hydrocarbons (PAH) are known to be one of the most dangerous types of compounds of their class due to their carcinogenic potential. Some atmospheric PAH are measured and regulated to quantify the air quality. However, in order to better understand the presence of these compounds in the atmosphere it is crucial to study the PAH emissions sources. In this work, we analyze the particulate-bound PAH emissions, as well as their carcinogenic potential, from a typical baseline diesel engine using a promising alternative fuel obtained from the glycerol surplus in the biodiesel production industry. This advanced biofuel (Mo.bio) is a ternary mixture of residual glycerine-derived fuel (FAGE), a conventional fatty acid methyl ester (FAME) and a diesel fuel. Two operating conditions representative of the conflicting scenarios when studying polluting emissions (speeds of 50 km/h and 70 km/h typical of urban and extra-urban driving conditions) are used. In addition, with the purpose of deepening the understanding of the behavior of this new fuel, tests are carried out modifying the Exhaust Gas Recirculation (EGR) ratio. The PAH samples are collected before the aftertreatment systems in order to assess the possible formation of PAH with this type of fuel and to evaluate the options of the aftertreatment devices. Sampling is carried out using fiber-glass filters, extracting the trapped PAH using Soxhlet method. The analytical procedure (liquid chromatography with fluorescence detection) allows to appreciate differences between the different fuels and modes of operation, observing higher emissions of benzo[a]pyrene (BaP) and dibenz[a,h]anthracene (DahA) for the diesel fuel than for the mixture containing residual glycerine-derived fuel. Therefore, it is concluded that the fossil fuel has a larger carcinogenic potential in these conditions, and that the Mo.Bio fuel may possibly expand the EGR ratio range without increasing the requirement of the particle filter.
Acceso Abierto
10,000 h molten salt corrosion testing on IN617, uncoated and aluminide ferritic steels at 580 ºC
(Richter C., 2020-12) Agüero, A.; Audigié, P.; Rodríguez, Sergio; European Commission (EC)
Long term testing of two ferritic-martensitic steels (P91 and VM12-SHC) with and without slurry deposited aluminide coatings containing 20 wt.% of Al at the surface was carried out by exposing these materials to the Solar Salt, a eutectic mixture composed of 60 % NaNO3 - 40 % KNO3 at 580ºC. This salt is currently used in operating thermal solar power plants as heat transfer and storage fluid. Tubes made of expensive Ni based alloys are employed to mitigate corrosion. The tested uncoated ferritic materials exhibited very high corrosion rates developing thick, easily detached scales. IN617 was also tested as a reference and experienced very low corrosion up to 5,000 h, but after 10,000 h a 50 ȝm thick, mostly NiO scale had developed with Na0.6CoO2 crystals deposited on top. There was also evidence of significant Cr depletion at the alloy surface. Carcinogenic CrVI was found in the Solar Salt melt in which the three uncoated alloys were immersed. In contrast, the two coated ferritic steels did not show evidence of degradation after 10,000 h and the most significant microstructural change was the development of a very thin protective NaAlO2 layer on their surface. An industrial process to deposit these coatings on the inner surfaces of pipes has already been developed.
Acceso Abierto
Robust anti-icing superhydrophobic aluminum alloy surfaces by grafting fluorocarbon molecular chains
(Elsevier, 2020-12) Rico, V.; Mora, J.; García Gallego, Paloma; Agüero, A.; Borrás, A.; González Elipe, A.R.; López-Santos, C.; Universidad de Sevilla; European Comission (EC); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Infusion of low surface tension liquids in nanostructured surfaces is currently used to promote an anti-icing response, although the long term stability of these systems is often jeopardized by losses of the infused liquid. In this work, we propose an alternative to the infusion procedure to induce a more effective and long lasting anti-icing capacity. The method consists of a combination of surface nanostructuration with the chemical grafting of fluorocarbon molecules. Al6061 substrates have been subjected to laser roughening and further modified with a nanostructured Al2O3 thin film to achieve a dual roughness and porous surface state. These surfaces have been subjected to a grafting treatment with perfluorooctyltriethoxysilane (PFOTES) vapor or, for comparative purposes, infused with a low surface tension liquid. A comparative analysis of the wetting, water condensation and anti-icing properties of these two systems showed an outstandingly better performance for the grafted surfaces with respect to the infused ones. Grafted surfaces were markedly superhydrophobic and required higher water vapor pressures to induce condensation. When looking for their anti-icing capacity, they presented quite long freezing delay times for supercooled water droplets (i.e. almost four hours) and exhibited a notably low ice accretion in a wind tunnel test. The high aging resistance and durability of these grafted surfaces and the reproducibility of the results obtained when subjected to successive ice accretion cycles show that molecular grafting is an efficient anti-icing methodology that, in aggressive media, may outperform the classical infusion procedures. The role of the fluorocarbon chains anchored on the surface in inducing an anti-icing functionality is discussed.

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