84 research outputs found

    Análisis computacional de la combustión de OMEx en condiciones de motores de encendido por compresión

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    [ES] El uso de combustibles líquidos de origen renovable en motores de combustión es un ámbito de gran actividad actual en el sector del transporte, especialmente en aplicaciones en las que la autonomía del vehículo juega un papel decisivo. Se trata de combustibles obtenidos por algún proceso de síntesis químico que utiliza como una de sus sustancias de partida el hidrógeno. Este último puede ser producido a partir de hidrólisis del agua utilizando electricidad de origen potencialmente renovable. En particular, el sector de los motores de encendido por compresión está llevando a cabo estudios detallados con OMEx (en inglés Oxymethylene diMethyl ethers), una familia de compuestos que pueden ser sintentizados con una eficiencia razonable y que tienen unas prestaciones adecuadas a este tipo de motores. El presente trabajo pretende comparar dos tipos de combustibles de esta familia mediante la aplicación de la dinámica de fluidos computaciona (CFD). Ambos combustibles son inyectados en una atmósfera con condiciones termodinámicas y de composición análogas a las que se dan en la cámara de combustión de un motor. Se comparan además una configuración de inyección de un motor de transporte pesado y uno de automoción mediante una modificación del diámetro de orificio. El alumno configurará y lanzará cálculos y realizará el post-procesado de una serie de casos con diferentes condiciones de funcionamiento, con el fin de comparar los cambios en el encendido y la estructura de llama al emplear los diferentes combustibles y diámetros de orificio. Los resultados del modelo se compararán con medidas experimentales, con el fin de analizar la capacidad predictiva del modelo.[EN] The use of liquid fuels of renewable origin in combustion engines is an area of great current activity in the transport sector, especially in applications in which vehicle autonomy plays a decisive role. These are fuels obtained by a chemical synthesis process that uses hydrogen as one of its starting substances. The latter can be produced by hydrolysis of water using electricity of potentially renewable origin. In particular, the compression ignition engine sector is carrying out detailed studies with OMEx (Oxymethylene diMethyl Ethers), a family of compounds that can be synthesized with reasonable efficiency and that have a performance suitable for this type of engine. The present work aims to compare two types of fuels from this family by applying computational fluid dynamics (CFD). Both fuels are injected into an atmosphere with thermodynamic and compositional conditions analogous to those found in the combustion chamber of an engine. An injection configuration of a heavy transport engine and an automotive engine is also compared by means of a modification of the orifice diameter. A number of cases have been setup, calculated and post-processed with different operating conditions, in order to compare the changes in ignition and flame structure when using different fuels and orifice diameters. The model results will be compared with experimental measurements in order to analyze the predictive capability of the model.Sanz Vila, A. (2022). Análisis computacional de la combustión de OMEx en condiciones de motores de encendido por compresión. Universitat Politècnica de València. http://hdl.handle.net/10251/181970TFG

    A Method to determine secondary codes and carrier phases of short snapshot signals

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    Recently, the Snapshot Real-Time Kinematic (SRTK) technique was demonstrated, which aims at achieving high accuracy navigation solutions with a very short signal collection. The main challenge in implementing SRTK is the generation of valid carrier-phase measurements, which relies on a data bit ambiguity (DBA) resolution process. For pilot signals, this step is equivalent to the correct selection of secondary code indexes (SCIs) from the ambiguous sets obtained from a multi-hypotheses (MH) acquisition process. Currently, SCI ambiguities are solved independently for each satellite. However, this method is ineffective when the snapshot signal is relatively short. In order to tackle this problem, this article proposes a new method that makes use of assistance data and processes information from all satellites to jointly solve the DBA issue. This new method is shown to be more effective in determining the correct SCI and enabling valid snapshot carrier-phase measurements, largely expanding the scope of high-accuracy snapshot positioning.This research was supported by the Albora Technologies and Universitat Politècnica de Catalunya with industrial PhD grant number DI 082 from the Generalitat de Catalunya and the project RTI2018-094295-B-I00 funded by the MCIN/AEI 10.13039/501100011033 which is co-funded by the FEDER programme. P.C. has been partially supported by the NSF under Awards CNS-1815349 and ECCS-1845833.Peer ReviewedPostprint (published version

    Prioritizing professionals? How the democratic and professionalized nature of interest groups shapes their degree of access to EU officials

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    Interest groups are key intermediary actors between civil society and public officials. The EU has long emphasized the importance of interacting with representative groups that involve their members. Additionally, there is an increasing trend toward the professionalization of groups that invest in organizational capacities to efficiently provide policy expertise. Both member involvement and organizational capacity are crucial features for groups to function as transmission belts that aggregate and transfer the preferences of their members to policymakers, thus reinforcing the legitimacy and efficiency of governance s

    Fast-PPP assessment in European and equatorial region near the solar cycle maximum

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    Oustanding Student Poster Award, European Geosciences Union General Assembly, 2014Award-winningPostprint (published version

    AATR an ionospheric activity indicator specifically based on GNSS measurements

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    This work reviews an ionospheric activity indicator useful for identifying disturbed periods affecting the performance of Global Navigation Satellite System (GNSS). This index is based in the Along Arc TEC Rate (AATR) and can be easily computed from dual-frequency GNSS measurements. The AATR indicator has been assessed over more than one Solar Cycle (2002–2017) involving about 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST or Ap), it is sensitive to the regional behaviour of the ionosphere and identifies specific effects on GNSS users. Moreover, from a devoted analysis of different Satellite Based Augmentation System (SBAS) performances in different ionospheric conditions, it follows that the AATR indicator is a very suitable mean to reveal whether SBAS service availability anomalies are linked to the ionosphere. On this account, the AATR indicator has been selected as the metric to characterise the ionosphere operational conditions in the frame of the European Space Agency activities on the European Geostationary Navigation Overlay System (EGNOS). The AATR index has been adopted as a standard tool by the International Civil Aviation Organization (ICAO) for joint ionospheric studies in SBAS. In this work we explain how the AATR is computed, paying special attention to the cycle-slip detection, which is one of the key issues in the AATR computation, not fully addressed in other indicators such as the Rate Of change of the TEC Index (ROTI). After this explanation we present some of the main conclusions about the ionospheric activity that can extracted from the AATR values during the above mentioned long-term study. These conclusions are: (a) the different spatial correlation related with the MOdified DIP (MODIP) which allows to clearly separate high, mid and low latitude regions, (b) the large spatial correlation in mid latitude regions which allows to define a planetary index, similar to the geomagnetic ones, (c) the seasonal dependency which is related with the longitude and (d) the variation of the AATR value at different time scales (hourly, daily, seasonal, among others) which confirms most of the well-known time dependences of the ionospheric events, and finally, (e) the relationship with the space weather events.Postprint (published version

    GPS differential code biases determination: methodology and analysis

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    The final publication is available at Springer via http://dx.doi.org/10.1007/s10291-017-0634-5We address two main problems related to the receiver and satellite differential code biases (DCBs) determination. The first issue concerns the drifts and jumps experienced by the DCB determinations of the International GNSS Service (IGS) due to satellite constellation changes. A new alignment algorithm is introduced to remove these nonphysical effects, which is applicable in real time. The full-time series of 18 years of Global Positioning System (GPS) satellite DCBs, computed by IGS, are realigned using the proposed algorithm. The second problem concerns the assessment of the DCBs accuracy. The short- and long-term receiver and satellite DCB performances for the different Ionospheric Associate Analysis Centers (IAACs) are discussed. The results are compared with the determinations computed with the two-layer Fast Precise Point Positioning (Fast-PPP) ionospheric model, to assess how the geometric description of the ionosphere affects the DCB determination and to illustrate how the errors in the ionospheric model are transferred to the DCB estimates. Two different determinations of DCBs are considered: the values provided by the different IAACs and the values estimated using their pre-computed Global Ionospheric Maps (GIMs). The second determination provides a better characterization of DCBs accuracy, as it is confirmed when analyzing the DCB variations associated with the GPS Block-IIA satellites under eclipse conditions, observed mainly in the Fast-PPP DCB determinations. This study concludes that the accuracy of the IGS IAACs receiver DCBs is approximately 0.3–0.5 and 0.2 ns for the Fast-PPP. In the case of the satellite DCBs, these values are about 0.12–0.20 ns for IAACs and 0.07 ns for Fast-PPP.Peer ReviewedPostprint (author's final draft

    Feasibility of snapshot GNSS carrier phase amendment based on LAMBDA ratio tests

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    This research was funded by Albora Technologies and Universitat Politècnica de Catalunya with industrial PhD grant number DI 082 from the Generalitat de Catalunya; This research was partially funded by the Spanish Ministry of Science and Innovation project RTI2018-094295-B-I00. P.C. has been partially supported by the NSF under Awards CNS-1815349 and ECCS-1845833.Peer ReviewedPostprint (author's final draft

    Fast precise point positioning: a system to provide corrections for single and multi-frequency navigation

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    Fast Precise Point Positioning (Fast-PPP) provides Global Navigation Satellite System corrections in real-time. Satellite orbits and clock corrections are shown to be accurate to a few centimeters and a few tenths of a nanosecond which, together with the determination of the fractional part of the ambiguities, enable global high-accuracy positioning with undifferenced Integer Ambiguity Resolution. The new global ionospheric model is shown to provide corrections accurate at the level of 1 Total Electron Content Unit over well-sounded areas and Differential Code Biases at the level of tenths of a nanosecond. These corrections are assessed with permanent receivers, treated as rovers, located at 100 to 800 kilometers from the reference stations of the ionospheric model. Fast-PPP achieves decimeter-level of accuracy after few minutes, several times faster than single- and dual-frequency ionospheric-free solutions, using a month of Global Positioning System data close to the last Solar Maximum and including equatorial rovers.Postprint (author's final draft

    Cloud-based single-frequency Snapshot RTK positioning

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    With great potential for being applied to Internet of Things (IoT) applications, the concept of cloud-based Snapshot Real Time Kinematics (SRTK) was proposed and its feasibility under zero-baseline configuration was confirmed recently by the authors. This article first introduces the general workflow of the SRTK engine, as well as a discussion on the challenges of achieving an SRTK fix using actual snapshot data. This work also describes a novel solution to ensure a nanosecond level absolute timing accuracy in order to compute highly precise satellite coordinates, which is required for SRTK. Parameters such as signal bandwidth, integration time and baseline distances have an impact on the SRTK performance. To characterize this impact, different combinations of these settings are analyzed through experimental tests. The results show that the use of higher signal bandwidths and longer integration times result in higher SRTK fix rates, while the more significant impact on the performance comes from the baseline distance. The results also show that the SRTK fix rate can reach more than 93% by using snapshots with a data size as small as 255 kB. The positioning accuracy is at centimeter level when phase ambiguities are resolved at a baseline distance less or equal to 15 km.This research was funded by Albora Technologies and Universitat Politècnica de Catalunya with industrial PhD grant number DI 082 from the Generalitat de Catalunya; This research was partially funded by the Spanish Ministry of Science and Innovation project RTI2018-094295-B-I00. P.C. has been partially supported by the NSF under Awards CNS-1815349 and ECCS-1845833Peer ReviewedPostprint (published version

    Feasibility of precise navigation in high and low latitude regions under scintillation conditions

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    Scintillation is one of the most challenging problems in Global Navigation Satellite Systems (GNSS) navigation. This phenomenon appears when the radio signal passes through ionospheric irregularities. These irregularities represent rapid changes on the refraction index and, depending on their size, they can produce also diffractive effects affecting the signal amplitude and, eventually producing cycle slips. In this work, we show that the scintillation effects on the GNSS signal are quite different in low and high latitudes. For low latitude receivers, the main effects, from the point of view of precise navigation, are the increase of the carrier phase noise (measured by s¿) and the fade on the signal intensity (measured by S4) that can produce cycle slips in the GNSS signal. With several examples, we show that the detection of these cycle slips is the most challenging problem for precise navigation, in such a way that, if these cycle slips are detected, precise navigation can be achieved in these regions under scintillation conditions. For high-latitude receivers the situation differs. In this region the size of the irregularities is typically larger than the Fresnel length, so the main effects are related with the fast change on the refractive index associated to the fast movement of the irregularities (which can reach velocities up to several km/s). Consequently, the main effect on the GNSS signals is a fast fluctuation of the carrier phase (large s¿), but with a moderate fade in the amplitude (moderate S4). Therefore, as shown through several examples, fluctuations at high-latitude usually do not produce cycle slips, being the effect quite limited on the ionosphere-free combination and, in general, precise navigation can be achieved also during strong scintillation conditions.Postprint (published version
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