A computational methodology to account for the liquid film thickness evolution in Direct Numerical Simulation of prefilming airblast atomization

Prefilming airblast atomization is widely used in aero engines. Fundamental studies on the annular configuration of airblast atomizers are difficult to realize. For this reason, researchers focused on planar configurations. In this regard, the Karlsruhe Institute of Technology (KIT) developed a test rig to conduct experimental activities, conforming a large database with results for different conditions. Such data allow validation of two-phase flow calculations concerning primary atomization on these devices. The present investigation proposes a Direct Numerical Simulation (DNS) on the KIT planar configuration through the Volume of Fluid (VOF) method within the PARIS code. The novelty compared to DNS reported in the literature resides in the use of a boundary condition that accounts not only for the gas inflow turbulence but also for the spatio-temporal evolution of the liquid film thickness at the DNS inlet and its effect on turbulence. The proposed methodology requires computing precursor single-phase and two-phase flow Large-Eddy Simulations. Results are compared to DNS that only account for a constant (both timewise and spanwise) liquid film thickness at the domain inlet, validating the workflow. The proposed methodology improves the qualitative description of the breakup mechanism, as its different stages (liquid accumulation behind the prefilmer edge, bag formation, bag breakup, ligament formation and ligament breakup) coexist spanwise for a given temporal snapshot. This implies more continuous atomization than the one predicted by the constant film thickness case, which showed the same breakup stage to be present along the prefilmer span for a given instant and led to a more discretized set of atomization events. The proposed workflow allows quantifying the influence of the liquid film flow evolution above the prefilmer on primary breakup frequency and atomization features.Comment: Preprint submitted to International Journal of Multiphase Flo

On the relation between the external structure and the internal characteristics in the near-nozzle field of diesel sprays

[EN] In this paper, a high-resolution visualization technique has been used in combination with an extensively validated 0D model in order to relate the external structure of a diesel spray to the internal properties in the vicinity of the nozzle. For this purpose, three single-hole convergent nozzles with different diameters have been tested for several pressure conditions. The analysis of the obtained images shows that the spray width significantly changes along the very first millimeters of the spray. From the high resolution images captured, two parameters have been evaluated. The first one is the external non-perturbed length, where droplet detachment has not been observed. The second one is a transitional length, defined as the axial position where the spray width increases linearly after a transient behavior, making it possible to establish a spray cone angle definition. Furthermore, the internal liquid core length has been estimated for these nozzles using an extensively validated zero-dimensional model. The intact liquid core length has proved to be correlated with both the transitional length and the non-perturbed length with a very high degree of reliability. In the case of the transitional length, a quadratic correlation has been observed, whereas a linear relationship has been confirmed between the intact core length and the non-perturbed length. The results presented here may help to shed light on better understanding of such a complex process as atomization.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Ministerio de Economia y Competitividad, Spanish Government, under the project 'Comprension de la influencia de combustibles no convencionales en el proceso de injeccion y combustion tipo diesel' (project number TRA2012-36932) The PhD studies of D. Jaramillo have been funded by "Conselleria d'Educacio'Cultura i Esports'' of "Generalitat Valenciana'', Spain, by means of ''Programa Vali+ d per a personal investigador en formacio''. Reference ACIF/2015/040.Benajes, J.; Salvador, FJ.; Carreres, M.; Jaramillo-Císcar, D. (2017). On the relation between the external structure and the internal characteristics in the near-nozzle field of diesel sprays. Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering. 231(3):360-371. https://doi.org/10.1177/0954407016639464S3603712313Desantes, J. M., Payri, R., Salvador, F. J., & Gil, A. (2006). Development and validation of a theoretical model for diesel spray penetration. Fuel, 85(7-8), 910-917. doi:10.1016/j.fuel.2005.10.023Kim, H. J., Park, S. H., & Lee, C. S. (2010). A study on the macroscopic spray behavior and atomization characteristics of biodiesel and dimethyl ether sprays under increased ambient pressure. Fuel Processing Technology, 91(3), 354-363. doi:10.1016/j.fuproc.2009.11.007Klein-Douwel, R. J. H., Frijters, P. J. M., Seykens, X. L. J., Somers, L. M. T., & Baert, R. S. G. (2009). Gas Density and Rail Pressure Effects on Diesel Spray Growth from a Heavy-Duty Common Rail Injector†. Energy & Fuels, 23(4), 1832-1842. doi:10.1021/ef8003569Lee, C. S., Lee, K. H., Reitz, R. D., & Park, S. W. (2006). EFFECT OF SPLIT INJECTION ON THE MACROSCOPIC DEVELOPMENT AND ATOMIZATION CHARACTERISTICS OF A DIESEL SPRAY INJECTED THROUGH A COMMON-RAIL SYSTEM. Atomization and Sprays, 16(5), 543-562. doi:10.1615/atomizspr.v16.i5.50Desantes, J. M., Payri, R., Salvador, F. J., & De la Morena, J. (2010). Influence of cavitation phenomenon on primary break-up and spray behavior at stationary conditions. Fuel, 89(10), 3033-3041. doi:10.1016/j.fuel.2010.06.004Payri, R., Salvador, F. J., Gimeno, J., & Soare, V. (2005). Determination of diesel sprays characteristics in real engine in-cylinder air density and pressure conditions. Journal of Mechanical Science and Technology, 19(11), 2040-2052. doi:10.1007/bf02916497Desantes, J. M., Salvador, F. J., López, J. J., & De la Morena, J. (2010). Study of mass and momentum transfer in diesel sprays based on X-ray mass distribution measurements and on a theoretical derivation. Experiments in Fluids, 50(2), 233-246. doi:10.1007/s00348-010-0919-8Salvador, F. J., Ruiz, S., Gimeno, J., & De la Morena, J. (2011). Estimation of a suitable Schmidt number range in diesel sprays at high injection pressure. International Journal of Thermal Sciences, 50(9), 1790-1798. doi:10.1016/j.ijthermalsci.2011.03.030Linne, M. A., Paciaroni, M., Berrocal, E., & Sedarsky, D. (2009). Ballistic imaging of liquid breakup processes in dense sprays. Proceedings of the Combustion Institute, 32(2), 2147-2161. doi:10.1016/j.proci.2008.07.040Kastengren, A. L., Tilocco, F. Z., Duke, D. J., Powell, C. F., Zhang, X., & Moon, S. (2014). TIME-RESOLVED X-RAY RADIOGRAPHY OF SPRAYS FROM ENGINE COMBUSTION NETWORK SPRAY A DIESEL INJECTORS. Atomization and Sprays, 24(3), 251-272. doi:10.1615/atomizspr.2013008642Kastengren, A., & Powell, C. F. (2014). Synchrotron X-ray techniques for fluid dynamics. Experiments in Fluids, 55(3). doi:10.1007/s00348-014-1686-8Som, S., & Aggarwal, S. K. (2010). Effects of primary breakup modeling on spray and combustion characteristics of compression ignition engines. Combustion and Flame, 157(6), 1179-1193. doi:10.1016/j.combustflame.2010.02.018Lebas, R., Menard, T., Beau, P. A., Berlemont, A., & Demoulin, F. X. (2009). Numerical simulation of primary break-up and atomization: DNS and modelling study. International Journal of Multiphase Flow, 35(3), 247-260. doi:10.1016/j.ijmultiphaseflow.2008.11.005Shinjo, J., & Umemura, A. (2010). Simulation of liquid jet primary breakup: Dynamics of ligament and droplet formation. International Journal of Multiphase Flow, 36(7), 513-532. doi:10.1016/j.ijmultiphaseflow.2010.03.008Shinjo, J., & Umemura, A. (2011). Detailed simulation of primary atomization mechanisms in Diesel jet sprays (isolated identification of liquid jet tip effects). Proceedings of the Combustion Institute, 33(2), 2089-2097. doi:10.1016/j.proci.2010.07.006Ménard, T., Tanguy, S., & Berlemont, A. (2007). Coupling level set/VOF/ghost fluid methods: Validation and application to 3D simulation of the primary break-up of a liquid jet. International Journal of Multiphase Flow, 33(5), 510-524. doi:10.1016/j.ijmultiphaseflow.2006.11.001Bermúdez, V., Payri, R., Salvador, F. J., & Plazas, A. H. (2005). Study of the influence of nozzle seat type on injection rate and spray behaviour. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 219(5), 677-689. doi:10.1243/095440705x28303Payri, F., Bermúdez, V., Payri, R., & Salvador, F. J. (2004). The influence of cavitation on the internal flow and the spray characteristics in diesel injection nozzles. Fuel, 83(4-5), 419-431. doi:10.1016/j.fuel.2003.09.010Payri, R., Molina, S., Salvador, F. J., & Gimeno, J. (2004). A study of the relation between nozzle geometry, internal flow and sprays characteristics in diesel fuel injection systems. KSME International Journal, 18(7), 1222-1235. doi:10.1007/bf02983297Salvador, F. J., Ruiz, S., Salavert, J., & De la Morena, J. (2012). Consequences of using biodiesel on the injection and air–fuel mixing processes in diesel engines. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 227(8), 1130-1141. doi:10.1177/0954407012463667Basak, N., & Das, D. (2009). Photofermentative hydrogen production using purple non-sulfur bacteria Rhodobacter sphaeroides O.U.001 in an annular photobioreactor: A case study. Biomass and Bioenergy, 33(6-7), 911-919. doi:10.1016/j.biombioe.2009.02.007Salvador, F. J., Romero, J.-V., Roselló, M.-D., & Martínez-López, J. (2010). Validation of a code for modeling cavitation phenomena in Diesel injector nozzles. Mathematical and Computer Modelling, 52(7-8), 1123-1132. doi:10.1016/j.mcm.2010.02.027Andriotis, A., & Gavaises, M. (2009). INFLUENCE OF VORTEX FLOW AND CAVITATION ON NEAR-NOZZLE DIESEL SPRAY DISPERSION ANGLE. Atomization and Sprays, 19(3), 247-261. doi:10.1615/atomizspr.v19.i3.30Salvador, F. J., Hoyas, S., Novella, R., & Martínez-López, J. (2011). Numerical simulation and extended validation of two-phase compressible flow in diesel injector nozzles. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 225(4), 545-563. doi:10.1177/09544070jauto1569Salvador, F. J., Martínez-López, J., Caballer, M., & De Alfonso, C. (2013). Study of the influence of the needle lift on the internal flow and cavitation phenomenon in diesel injector nozzles by CFD using RANS methods. Energy Conversion and Management, 66, 246-256. doi:10.1016/j.enconman.2012.10.011Hiroyasu, H. (2000). SPRAY BREAKUP MECHANISM FROM THE HOLE-TYPE NOZZLE AND ITS APPLICATIONS. Atomization and Sprays, 10(3-5), 511-527. doi:10.1615/atomizspr.v10.i3-5.130Sou, A., Hosokawa, S., & Tomiyama, A. (2007). Effects of cavitation in a nozzle on liquid jet atomization. International Journal of Heat and Mass Transfer, 50(17-18), 3575-3582. doi:10.1016/j.ijheatmasstransfer.2006.12.033Macian, V., Bermudez, V., Payri, R., & Gimeno, J. (2003). NEW TECHNIQUE FOR DETERMINATION OF INTERNAL GEOMETRY OF A DIESEL NOZZLE WITH THE USE OF SILICONE METHODOLOGY. Experimental Techniques, 27(2), 39-43. doi:10.1111/j.1747-1567.2003.tb00107.xOtsu, N. (1979). A Threshold Selection Method from Gray-Level Histograms. IEEE Transactions on Systems, Man, and Cybernetics, 9(1), 62-66. doi:10.1109/tsmc.1979.4310076Payri, R., Tormos, B., Salvador, F. J., & Araneo, L. (2008). Spray droplet velocity characterization for convergent nozzles with three different diameters. Fuel, 87(15-16), 3176-3182. doi:10.1016/j.fuel.2008.05.028DELACOURT, E., DESMET, B., & BESSON, B. (2005). Characterisation of very high pressure diesel sprays using digital imaging techniques. Fuel, 84(7-8), 859-867. doi:10.1016/j.fuel.2004.12.003Yue, Y., Powell, C. F., Poola, R., Wang, J., & Schaller, J. K. (2001). QUANTITATIVE MEASUREMENTS OF DIESEL FUEL SPRAY CHARACTERISTICS IN THE NEAR-NOZZLE REGION USING X-RAY ABSORPTION. Atomization and Sprays, 11(4), 471-490. doi:10.1615/atomizspr.v11.i4.100Desantes, J. M., Payri, R., Garcia, J. M., & Salvador, F. J. (2007). A contribution to the understanding of isothermal diesel spray dynamics. Fuel, 86(7-8), 1093-1101. doi:10.1016/j.fuel.2006.10.011Desantes, J. M., Arregle, J., Lopez, J. J., & Cronhjort, A. (2006). SCALING LAWS FOR FREE TURBULENT GAS JETS AND DIESEL-LIKE SPRAYS. Atomization and Sprays, 16(4), 443-474. doi:10.1615/atomizspr.v16.i4.6

Numerical analysis of flow characteristics in diesel injectors nozzles with convergent-divergent orifices

[EN] The geometry of diesel injector nozzles is known to significantly affect the characteristic spray behavior and emissions formation. In this paper, a novel nozzle concept, consisting of orifices with a convergent-divergent shape, is investigated through Computational Fluid Dynamics techniques. Three of these nozzles, characterized by different degrees of conicity, are compared to a nozzle with cylindrical orifices, which acts as a baseline. A homogeneous equilibrium model, validated against experimental data in previous works by the authors, is used to calculate the eventual cavitation formation inside these orifices. Additionally, the characteristics of the flow at the orifice outlet are analyzed for the four aforementioned nozzles in terms of their steady-state mass flow, effective outlet velocity and area coefficient. The results show that convergent-divergent nozzles exhibit a high cavitation intensity, located in the transition between the convergent and the divergent sections. This high cavitation intensity tends to compensate for the expected velocity decrease induced by the divergent shape, producing effective velocity values similar to those achieved by the cylindrical nozzle in many of the simulated conditions. The characteristics of the flow, together with the higher spray opening angles expected due to the divergent section of the nozzle, may improve atomization and fuel-air mixing processes.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Ministerio de Economia y Competitividad, of the Spanish Government, Project 'Estudio de la interaccion chorro-pared en condiciones realistas de motor' (Grant Number TRA2015-67679-c2-1-R). The PhD studies of David Jaramillo have been funded by "Conselleria d'Educacio Cultura i Esports" of "Generalitat Valenciana", Spain, by means of "Programa Vali+d per a personal investigador en formacio" (reference ACIF/2015/040).Salvador, FJ.; De La Morena, J.; Carreres, M.; Jaramillo-Císcar, D. (2017). Numerical analysis of flow characteristics in diesel injectors nozzles with convergent-divergent orifices. Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering. 231(14):1935-1944. https://doi.org/10.1177/0954407017692220S193519442311

Effects of a Teaching Personal and Social Responsibility Model Intervention in Competitive Youth Sport

The aim of this study was to implement the teaching personal and social responsibility (TPSR) model in a competitive context analyzing the differences between the intervention and the control group on personal and social responsibility, prosocial behaviors, and self-efficacy in youth soccer players. Participants were 34 youth soccer players between the ages of 14 and 16 years old (15.18 ± 0.72) divided into two different soccer teams of 17 members, corresponding to the control and intervention groups. The implementation of the TPSR model took place during 9 months, including initial and ongoing coach training (3 months), program implementation (three sessions per week lasting 90 min during 6 months), and a series of expert-led seminars for athletes (one session per week lasting 90 min during 4 months). The questionnaires used to collect data were the Personal and Social Responsibility Questionnaire, Prosocial Behavior Scale, and two Children’s Self-efficacy Scales. Results indicated that the TPSR intervention group obtained an increase in post-test levels of personal and social responsibility, prosocial behavior, and self-efficacy due to the application of the TPSR model compared with control group that used a conventional sport teaching methodology. The conclusion is that the TPSR model has the potential to be adapted and implemented with flexibility in youth sport competition contexts in order to improve personal and social responsibility, prosocial behavior, and self-efficacy

Modeling gaseous non-reactive flow in a lean direct injection gas turbine combustor through an advanced mesh control strategy

[EN] Fuel efficiency improvement and harmful emissions reduction are the main motivations for the development of gas turbine combustors. Numerical computational fluid dynamics (CFD) simulations of these devices are usually computationally expensive since they imply a multi-scale problem. In this work, gaseous non-reactive unsteady Reynolds-Averaged Navier-Stokes and large eddy simulations of a gaseous-fueled radial-swirled lean direct injection combustor have been carried out through CONVERGE (TM) CFD code by solving the complete inlet flow path through the swirl vanes and the combustor. The geometry considered is the gaseous configuration of the CORIA lean direct injection combustor, for which detailed measurements are available. The emphasis of the work is placed on the demonstration of the CONVERGE (TM) applicability to the multi-scale gas turbine engines field and the determination of an optimal mesh strategy through several grid control tools (i.e., local refinement, adaptive mesh refinement) allowing the exploitation of its automatic mesh generation against traditional fixed mesh approaches. For this purpose, the normalized mean square error has been adopted to quantify the accuracy of turbulent numerical statistics regarding the agreement with the experimental database. Furthermore, the focus of the work is to study the behavior when coupling several large eddy simulation sub-grid scale models (i.e., Smagorinsky, Dynamic Smagorinsky, and Dynamic Structure) with the adaptive mesh refinement algorithm through the evaluation of its specific performances and predictive capabilities in resolving the spatial-temporal scales and the intrinsically unsteady flow structures generated within the combustor. This investigation on the main non-reacting swirling flow characteristics inside the combustor provides a suitable background for further studies on combustion instability mechanisms.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was partly sponsored by the program "Ayuda a Primeros Proyectos de Investigacion (PAID-06-18), Vicerrectorado de Investigacion, Innovacion y Transferencia de la Universitat Politecnica de Valencia (UPV), Spain.'' The support given to Mr. Mario Belmar by Universitat Politecnica de Valencia through the "FPI-Subprograma 2'' grant within the "Programa de Apoyo para la Investigacion y Desarrollo (PAID-01-18)'' is gratefully acknowledged.Payri, R.; Novella Rosa, R.; Carreres, M.; Belmar-Gil, M. (2020). Modeling gaseous non-reactive flow in a lean direct injection gas turbine combustor through an advanced mesh control strategy. Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering. 234(11):1788-1810. https://doi.org/10.1177/0954410020919619S1788181023411Patel, N., Kırtaş, M., Sankaran, V., & Menon, S. (2007). Simulation of spray combustion in a lean-direct injection combustor. Proceedings of the Combustion Institute, 31(2), 2327-2334. doi:10.1016/j.proci.2006.07.232Luo, K., Pitsch, H., Pai, M. G., & Desjardins, O. (2011). Direct numerical simulations and analysis of three-dimensional n-heptane spray flames in a model swirl combustor. Proceedings of the Combustion Institute, 33(2), 2143-2152. doi:10.1016/j.proci.2010.06.077Masri, A. R., Pope, S. B., & Dally, B. B. (2000). Probability density function computations of a strongly swirling nonpremixed flame stabilized on a new burner. Proceedings of the Combustion Institute, 28(1), 123-131. doi:10.1016/s0082-0784(00)80203-9Johnson, M. R., Littlejohn, D., Nazeer, W. A., Smith, K. O., & Cheng, R. K. (2005). A comparison of the flowfields and emissions of high-swirl injectors and low-swirl injectors for lean premixed gas turbines. Proceedings of the Combustion Institute, 30(2), 2867-2874. doi:10.1016/j.proci.2004.07.040Sankaran, V., & Menon †, S. (2002). LES of spray combustion in swirling flows. Journal of Turbulence, 3, N11. doi:10.1088/1468-5248/3/1/011Jones, W. P., Marquis, A. J., & Vogiatzaki, K. (2014). Large-eddy simulation of spray combustion in a gas turbine combustor. Combustion and Flame, 161(1), 222-239. doi:10.1016/j.combustflame.2013.07.016Ding, G., He, X., Xue, C., Zhao, Z., & Jin, Y. (2015). Preliminary design and experimental verification of a triple swirler combustor. Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 229(12), 2258-2271. doi:10.1177/0954410015573555Menon, S., & Patel, N. (2006). Subgrid Modeling for Simulation of Spray Combustion in Large-Scale Combustors. 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Ballistic imaging of the near field in a diesel spray. Experiments in Fluids, 40(6), 836-846. doi:10.1007/s00348-006-0122-0Desantes, J. M., Salvador, F. J., López, J. J., & De la Morena, J. (2010). Study of mass and momentum transfer in diesel sprays based on X-ray mass distribution measurements and on a theoretical derivation. Experiments in Fluids, 50(2), 233-246. doi:10.1007/s00348-010-0919-8Reddemann, M. A., Mathieu, F., & Kneer, R. (2013). Transmitted light microscopy for visualizing the turbulent primary breakup of a microscale liquid jet. Experiments in Fluids, 54(11). doi:10.1007/s00348-013-1607-2Chen, R.-H., & Driscoll, J. F. (1989). The role of the recirculation vortex in improving fuel-air mixing within swirling flames. Symposium (International) on Combustion, 22(1), 531-540. doi:10.1016/s0082-0784(89)80060-8Presser, C., Gupta, A. K., & Semerjian, H. G. (1993). Aerodynamic characteristics of swirling spray flames: Pressure-jet atomizer. 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Vorticity-scalar alignments and small-scale structures in swirling spray combustion. Proceedings of the Combustion Institute, 29(1), 577-584. doi:10.1016/s1540-7489(02)80074-8Lebas, R., Menard, T., Beau, P. A., Berlemont, A., & Demoulin, F. X. (2009). Numerical simulation of primary break-up and atomization: DNS and modelling study. International Journal of Multiphase Flow, 35(3), 247-260. doi:10.1016/j.ijmultiphaseflow.2008.11.005Zhou, Y., Huang, Y., & Mu, Z. (2017). Large eddy simulation of the influence of synthetic inlet turbulence on a practical aeroengine combustor with counter-rotating swirler. Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 233(3), 978-990. doi:10.1177/0954410017745900Torregrosa, A. J., Broatch, A., García-Tíscar, J., & Gomez-Soriano, J. (2018). Modal decomposition of the unsteady flow field in compression-ignited combustion chambers. 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Experimental assessment of ignition characteristics of lubricating oil sprays related to low-speed pre-ignition (LSPI)

This is the author's version of a work that was accepted for publication in International Journal of Engine Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published as https://doi.org/10.1177/14680874211013268[EN] Low-speed pre-ignition (LSPI) remains one of the challenges of Direct Injection (DI) Spark Ignition (SI) engines due to its potential to induce a heavy knock. Several mechanisms have been identified in the literature as plausible causes for LSPI. The physical and chemical properties of lubricant oils play a role on some of these causes. The present work aims at getting an independent procedure to determine the proneness of lubricant oils to ignite. To this end, the ignition delay (ID) of different oil formulations is experimentally determined in a constant-pressure flow facility through two different optical techniques: Schlieren and OH* chemiluminescence imaging. The investigation explores the effect of base-stock formulation, oil specification quality level, different additive types content, aging, and oxidation on oil reactivity for several thermodynamic conditions. Differences in ignition delay were found among base stocks, correlating with the American Petroleum Institute (API) group classification. However, no significant differences were found among additive packages previously reported to yield different LSPI occurrences. Hence, differences in reactivity among lubricating oil formulations are not the determining factor explaining their different LSPI occurrences in an engine. Similarly, specific lubricant additive content, aging, and oxidation do not importantly modify the measured ignition delay.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Part of the experimental hardware used in this work was purchased through funds obtained from IDIFEDER/2018/037 ``Diagnostico optico a alta velocidad para el estudio de procesos termo-fluidodinamicos en sistemas de inyeccion.''Tormos, B.; García-Oliver, JM.; Carreres, M.; Moreno-Montagud, C.; Domínguez, B.; Cárdenas, MD.; Oliva, F. (2022). Experimental assessment of ignition characteristics of lubricating oil sprays related to low-speed pre-ignition (LSPI). International Journal of Engine Research. 23(8):1327-1338. https://doi.org/10.1177/146808742110132681327133823

An Open-set Recognition and Few-Shot Learning Dataset for Audio Event Classification in Domestic Environments

The problem of training a deep neural network with a small set of positive samples is known as few-shot learning (FSL). It is widely known that traditional deep learning (DL) algorithms usually show very good performance when trained with large datasets. However, in many applications, it is not possible to obtain such a high number of samples. In the image domain, typical FSL applications are those related to face recognition. In the audio domain, music fraud or speaker recognition can be clearly benefited from FSL methods. This paper deals with the application of FSL to the detection of specific and intentional acoustic events given by different types of sound alarms, such as door bells or fire alarms, using a limited number of samples. These sounds typically occur in domestic environments where many events corresponding to a wide variety of sound classes take place. Therefore, the detection of such alarms in a practical scenario can be considered an open-set recognition (OSR) problem. To address the lack of a dedicated public dataset for audio FSL, researchers usually make modifications on other available datasets. This paper is aimed at providing the audio recognition community with a carefully annotated dataset for FSL and OSR comprised of 1360 clips from 34 classes divided into pattern sounds and unwanted sounds. To facilitate and promote research in this area, results with two baseline systems (one trained from scratch and another based on transfer learning), are presented.Comment: To be submitted to Expert System with Application

Evaluation of diurnal responses of Tetradesmus obliquus under nitrogen limitation

Tetradesmus obliquus is an oleaginous microalga with high potential for triacylglycerol production. We characterized the biochemical composition and the transcriptional landscape of T. obliquus wild-type and the starchless mutant (slm1), adapted to 16:8 h light dark (LD) cycles under nitrogen limitation. In comparison to the nitrogen replete conditions, the diurnal RNA samples from both strains also displayed a cyclic pattern, but with much less variation which could be related to a reduced transcription activity in at least the usually highly active processes. During nitrogen limitation, the wild-type continued to use starch as the preferred storage compound to store energy and carbon. Starch was accumulated to an average content of 0.25 g·gDW−1, which is higher than the maximum observed under nitrogen replete conditions. Small oscillations were observed, indicating that starch was being used as a diurnal energy storage compound, but to a lesser extent than under nitrogen replete conditions. For the slm1 mutant, TAG content was higher than for the wild-type (average steady state value was 0.26 g·gDW−1 for slm1 compared to 0.06 g·gDW−1 for the wild-type). Despite the higher TAG content in the slm1, the conversion efficiency of photons into biomass components for the slm1 was only half of the one obtained for the wild-type. This is related to the observed decrease in biomass productivity (from 1.29 gDW·L−1·day−1 for the wild-type to 0.52 gDW·L−1·day−1 for the slm1). While the transcriptome of slm1 displayed clear signs of energy generation by degrading TAG and amino-acids during the dark period, no significant variation of these metabolites could be measured. When looking through the diurnal cycle, the photosynthetic efficiency was lower for the slm1 mutant compared to the wild-type especially during the second half of the light period, where starch accumulation occurred in the wild-type.publishedVersionPaid Open Acces