Analysis of primary atomization in sprays using Direct Numerical Simulation

[ES] La comprensión de los fenómenos físicos que acontecen en la región densa (también conocida como campo cercano) durante la atomización de los sprays ha sido una de las mayores incógnitas a la hora de estudiar sus aplicaciones. En el sector industrial, el rango de interés abarca desde toberas en aplicaciones propulsivas a sprays en aplicaciones médicas, agrícolas o culinarias. Esta evidente falta de conocimiento obliga a realizar simplificaciones en la modelización, provocando resultados poco precisos y la necesidad de grandes caracterizaciones experimentales en la fase de diseño. De esta manera, los procesos de rotura del spray y atomización primaria se consideran problemas físicos fundamentales, cuya complejidad viene dada como resultado de un flujo multifásico en un régimen altamente turbulento, originando escenarios caóticos. El análisis de este problema es extremadamente complejo debido a la ausencia sustancial de teorías validadas referentes a los fenómenos físicos involucrados como son la turbulencia y la atomización. Además, la combinación de la naturaleza multifásica del flujo y su comportamiento turbulento resultan en una gran dificultad para afrontar el problema. Durante los últimos 10 años, las técnicas experimentales han sido finalmente capaces de visualizar la región densa, pero la confianza, análisis y efectividad de dichos experimentos en esta región del spray todavía requiere de mejoras sustanciales. En este contexto, esta tesis trata de contribuir al entendimiento de estos procesos físicos y de proporcionar herramientas de análisis para estos flujos tan complejos. Para ello, mediante Direct Numerical Simulations se ha afrontado el problema resolviendo las escalas de movimiento más pequeñas, y capturando todas las escalas de turbulencia y eventos de rotura. Uno de los objetivos de la tesis ha sido evaluar la influencia de las condiciones de contorno del flujo entrante en la atomización primaria y en el comportamiento turbulento del spray. Para ello, se han empleado dos condiciones de contorno diferentes. En primer lugar se ha empleado una condición de contorno sintética para producir turbulencia homogenea a la entrada, simulando el comporamiento de la tobera. Una de las características más interesantes de este método es la posibilidad de retocar los parámetros dentro del algoritmo. En particular, la escala de longitud integral se ha variado para evaluar la influencia de las estructuras mas grandes de la tobera en la atomización primaria. El análisis de la condición de contorno sintética también ha permitido el diseño óptimo de simulaciones de las cuales se han derivado estadísticas turbulentas significativas. En este escenario, se han llevado a cabo estudios más profundos sobre la influencia de propiedades de las estructuras turbulentas como la homogeneidad y la anisotropía tanto en el espectro de los flujos como en las estadísticas de las gotas. Para tal fin, se han desarrollado metodologías novedosas para computar el análisis espectral y la estadística de las gotas Entre los resultados de este análisis destaca la independencia de la condición de contorno de entrada en las estadísticas de las gotas, mientras que por otra parte, recalca que las características turbulentas desarrolladas en el interior de la tobera afectan a la cantidad total de masa atomizada. Estas consideraciones se encuentran respaldadas por el análisis espectral realizado, mediante el cuál se concluye que la turbulencia multifásica comparte el comportamiento universal descrito por las teorías de Kolmogorov.[CA] La comprensió dels fenòmens físics que succeïxen en la regió densa (també coneguda com a camp pròxim) durant l'atomització dels sprays ha sigut una de les majors incògnites a l'hora d'estudiar les seues aplicacions. En el sector industrial, el rang d'interés comprén des de toveres en aplicacions propulsives a sprays en aplicacions mèdiques, agrícoles o culinàries. Esta evident falta de coneixement obliga a realitzar simplificacions en la modelització, provocant resultats poc precisos i la necessitat de grans caracteritzacions experimentals en la fase de disseny. D'esta manera, els processos de ruptura del spray i atomització primària es consideren problemes físics fonamentals, la complexitat dels quals ve donada com resultat d'un flux multifàsic en un règim altament turbulent, originant escenaris caòtics. L'anàlisi d'este problema és extremadament complex a causa de l'absència substancial de teories validades dels fenòmens físics involucrats com són la turbulència i l'atomització. A més, la combinació de la naturalesa multifàsica del flux i el seu comportament turbulent resulten en una gran dificultat per a afrontar el problema. Durant els últims 10 anys les tècniques experimentals han sigut finalment capaces de visualitzar la regió densa, però la confiança, anàlisi i efectivitat dels experiments en esta regió del spray encara requerix de millores substancials. En este context, esta tesi tracta de contribuir en l'enteniment d'estos processos físics i de proporcionar ferramentes d'anàlisi per a estos fluxos tan complexos. Per a això, per mitjà de Direct Numerical Simulations s'ha afrontat el problema resolent les escales de moviment més menudes, al mateix temps que es capturen totes les escales de turbulència i esdeveniments de ruptura. Un dels objectius de la tesi ha sigut avaluar la influència que les condicions de contorn del flux entrant tenen en l'atomització primària i en el comportament turbulent del spray. Per a això, s'han empleat dos condicions de contorn diferents. En primer lloc s'ha empleat una condició de contorn sintètica per a produir turbulència homogènia a l'entrada, simulant el comportament de la tovera. Una de les característiques més interessants d'este mètod és la possibilitat de retocar els paràmetres dins de l'algoritme. En particular, l'escala de longitud integral s'ha variat per a avaluar la influència de les estructures mes grans de la tovera en l'atomització primària. L'anàlisi de la condició de contorn sintètica també ha permés el disseny òptim de simulacions de les quals s'han derivat estadístiques turbulentes significatives. En este escenari, s'han dut a terme estudis més profunds sobre la influència de propietats de les estructures turbulentes com l'homogeneïtat i l'anisotropia tant en l'espectre dels fluxos com en les estadístiques de les gotes. Per a tal fi, s'han desenrotllat metodologies noves per a computar l'anàlisi espectral i l'estadística de les gotes. Entre els resultats d'esta anàlisi destaca la independència de la condició de contorn d'entrada en les estadístiques de les gotes, mentres que d'altra banda, es recalca que les característiques turbulentes desenrotllades en l'interior de la tovera afecten a la quantitat total de massa atomitzada. Estes consideracions es troben recolzades per l'anàlisi espectral realitzat, per mitjà del qual es conclou que la turbulència multifásica compartix el comportament universal descrit per les teories de Kolmogorov.[EN] The understanding of the physical phenomena occurring in the dense region (also known as near field) of atomizing sprays has been long seen as one of the biggest unknown when studying sprays applications. The industrial range of interest goes from nozzles in combustion and propulsion applications to medical sprays, agricultural and food process applications. This substantial lack of knowledge is responsible for some important simplification in modeling, that often result to be inaccurate or simply partial, leading to the evident need of large experimental characterization during the design phase. In fact, the spray breakup and primary atomization processes are indeed fundamental problems of physics, which complexity results from the combination of a multiphase flow in a highly turbulent regime that leads to chaotic scenarios. The analysis of this problem is extremely problematic, due to a substantial lack of definitive theories about the physical phenomena involved, namely turbulence and atomization. Furthermore, the combination of the multiphase nature of the flow and its turbulent behavior makes substantially difficult to address the problem. Only within the last 10 years, experimental techniques have been capable of visualizing the dense region, but the experiments reliability, analysis and effectiveness in this region still requires vast improvements. In this scenario, this thesis aims to contribute in the understanding of these physical process and to provide analysis tools for these complex flows. In order to do so, Direct Numerical Simulations have been used for addressing the problem at its smallest scale of motion, while reliably capturing all turbulence scales and breakup events. The multiphase nature of the flow is accounted for by using the Volume of Fluid method. One of the goal of the thesis was to assess the influence of the inflow boundary conditions on the primary atomization and on the spray's turbulence behavior. In order to do so, two different boundary conditions were used. In a first place, a synthetic inflow boundary condition was used in order to produce a homogeneous turbulence inflow, simulating the nozzle behavior. One of the interesting features of this method was the possibility of tweaking the parameters within the algorithm. In particular, the integral length scale was varied in order to assess the influence of nozzle larger turbulent structures on the primary atomization. The analysis on the synthetic boundary condition also allowed to optimally design simulations from which derive meaningful turbulence statistics. On this framework, further studies were carried over on the influence of turbulent structures properties, namely homogeneity and anisotropy, on both the flows spectra and droplets statistics. In order to achieve this goal, novel procedures for both computing the flow spectra and analyzing droplets were developed and are carefully addressed in the thesis. The results of the analysis highlight the independence of droplets statistics from the inflow boundary condition, while, on the other hand, remarking how the total quantity of atomized mass is significantly affected by the turbulence features developed within the nozzle. This considerations are supported by the spectrum analysis performed, which also highlighted how multiphase turbulence shares the universal features described in Kolmogorov theories.Crialesi Esposito, M. (2019). Analysis of primary atomization in sprays using Direct Numerical Simulation [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/133975TESI

The interaction of droplet dynamics and turbulence cascade

The dynamics of droplet fragmentation in turbulence is described by the Kolmogorov-Hinze framework. Yet, a quantitative theory is lacking at higher concentrations when strong interactions between the phases and coalescence become relevant, which is common in most flows. Here, we address this issue through a fully-coupled numerical study of the droplet dynamics in a turbulent flow at R-lambda & AP; 140, the highest attained up to now. By means of time-space spectral statistics, not currently accessible to experiments, we demonstrate that the characteristic scale of the process, the Hinze scale, can be precisely identified as the scale at which the net energy exchange due to capillarity is zero. Droplets larger than this scale preferentially break up absorbing energy from the flow; smaller droplets, instead, undergo rapid oscillations and tend to coalesce releasing energy to the flow. Further, we link the droplet-size distribution with the probability distribution of the turbulent dissipation. This shows that key in the fragmentation process is the local flux of energy which dominates the process at large scales, vindicating its locality

Modulation of homogeneous and isotropic turbulence in emulsions

We present a numerical study of emulsions in homogeneous and isotropic turbulence at $Re_\lambda=137$. The problem is addressed via Direct Numerical Simulations (DNS), where the Volume of Fluid (VOF) is used to represent the complex features of the liquid-liquid interface. We consider a mixture of two iso-density fluids, where fluid properties are varied with the goal of understanding their role in turbulence modulation, in particular the volume fraction ($0.03<\alpha<0.5$), viscosity ratio ($0.01<\mu_d/\mu_c<100$) and large scale Weber number ($10.6<We_\mathcal{L}<106.5$). The analysis, performed by studying integral quantities and spectral scale-by-scale analysis, reveals that energy is consistently transported from large to small scales by the interface, and no inverse cascade is observed. Furthermore, the total surface is found to be directly proportional to the amount of energy transported, while viscosity and surface tension alter the dynamic that regulates energy transport. We also observe the $-10/3$ and $-3/2$ scaling on droplet size distributions, suggesting that the dimensional arguments which led to their derivation are verified in HIT conditions

Study of turbulence in atomizing liquid jets

[EN] Among the many unknowns in the study of atomizing sprays, defining an unambiguous way to analyze turbulence is, perhaps, one of the most limiting ones. The lack of proper tools for the analysis of the turbulence field (e.g. specific one/two-point statistics, spectrum, structure functions) limits the understanding of the overall phenomenon occurring, impeding the correct estimation of motion scales (from the Kolmogorov one to the integral one). The present work proposes a methodology to analyze the turbulence in atomizing jets using a pseudo-fluid method. The many challenges presented in these types of flows (such as temporal fluid properties uncertainties, strong anisotropy and lack of a priori chance of determining the motion scales) can be simplified by such a method, as it will be clearly shown by the smooth results obtained. Finally, the method is tested against the one-phase flows turbulent data available in the literature for the Kolmogorov scaling of the one-dimension energy spectra, showing how a pseudo-fluid method could provide a reliable tool to analyze multiphase turbulence, especially in spray's primary atomization.This research has been partially funded by Spanish Ministerio de Economia y Competitividad through project RTI2018-099706-B-100, "Estudio de la atomizacion primaria mediante simulaciones DNS y tecnicas opticas de muy alta resolucion". Additionally, the authors thankfully acknowledge the computer resources at MareNostrum 4 (Barcelona Supercomputing Center) and their technical support provided by FI-2017-2-0035 and TITAN (Oak Ridge Leadership Computing Facility) in the frame of the project TUR124.Torregrosa, AJ.; Payri, R.; Salvador, FJ.; Crialesi-Esposito, M. (2020). Study of turbulence in atomizing liquid jets. International Journal of Multiphase Flow. 129:1-12. https://doi.org/10.1016/j.ijmultiphaseflow.2020.103328S112129Agbaglah, G., Chiodi, R., & Desjardins, O. (2017). Numerical simulation of the initial destabilization of an air-blasted liquid layer. Journal of Fluid Mechanics, 812, 1024-1038. doi:10.1017/jfm.2016.835Aliseda, A., Hopfinger, E. J., Lasheras, J. C., Kremer, D. M., Berchielli, A., & Connolly, E. K. (2008). Atomization of viscous and non-newtonian liquids by a coaxial, high-speed gas jet. Experiments and droplet size modeling. International Journal of Multiphase Flow, 34(2), 161-175. doi:10.1016/j.ijmultiphaseflow.2007.09.003Antonia, R. A., Anselmet, F., & Chambers, A. J. (1986). Assessment of local isotropy using measurements in a turbulent plane jet. Journal of Fluid Mechanics, 163, 365-391. doi:10.1017/s0022112086002331Bassenne, M., Esmaily, M., Livescu, D., Moin, P., & Urzay, J. (2019). A dynamic spectrally enriched subgrid-scale model for preferential concentration in particle-laden turbulence. International Journal of Multiphase Flow, 116, 270-280. doi:10.1016/j.ijmultiphaseflow.2019.04.025Brändle de Motta, J. C., Costa, P., Derksen, J. J., Peng, C., Wang, L.-P., Breugem, W.-P., … Renon, N. (2019). Assessment of numerical methods for fully resolved simulations of particle-laden turbulent flows. Computers & Fluids, 179, 1-14. doi:10.1016/j.compfluid.2018.10.016Chorin, A. J. (1968). Numerical solution of the Navier-Stokes equations. Mathematics of Computation, 22(104), 745-762. doi:10.1090/s0025-5718-1968-0242392-2Comte-Bellot, G., & Corrsin, S. (1971). Simple Eulerian time correlation of full-and narrow-band velocity signals in grid-generated, ‘isotropic’ turbulence. Journal of Fluid Mechanics, 48(2), 273-337. doi:10.1017/s0022112071001599Desantes, 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/s00348-010-0919-8Pitsch, H., & Desjardins, O. (2010). DETAILED NUMERICAL INVESTIGATION OF TURBULENT ATOMIZATION OF LIQUID JETS. Atomization and Sprays, 20(4), 311-336. doi:10.1615/atomizspr.v20.i4.40Dodd, M. S., & Ferrante, A. (2016). On the interaction of Taylor length scale size droplets and isotropic turbulence. Journal of Fluid Mechanics, 806, 356-412. doi:10.1017/jfm.2016.550Duret, B., Luret, G., Reveillon, J., Menard, T., Berlemont, A., & Demoulin, F. X. (2012). DNS analysis of turbulent mixing in two-phase flows. International Journal of Multiphase Flow, 40, 93-105. doi:10.1016/j.ijmultiphaseflow.2011.11.014Elghobashi, S. (2019). Direct Numerical Simulation of Turbulent Flows Laden with Droplets or Bubbles. Annual Review of Fluid Mechanics, 51(1), 217-244. doi:10.1146/annurev-fluid-010518-040401Gauding, M., Danaila, L., & Varea, E. (2018). One-point and two-point statistics of homogeneous isotropic decaying turbulence with variable viscosity. International Journal of Heat and Fluid Flow, 72, 143-150. doi:10.1016/j.ijheatfluidflow.2018.05.013Gorokhovski, M., & Herrmann, M. (2008). Modeling Primary Atomization. Annual Review of Fluid Mechanics, 40(1), 343-366. doi:10.1146/annurev.fluid.40.111406.102200Gréa, B.-J., Griffond, J., & Burlot, A. (2014). The effects of variable viscosity on the decay of homogeneous isotropic turbulence. Physics of Fluids, 26(3), 035104. doi:10.1063/1.4867893Harris, V. G., Graham, J. A. H., & Corrsin, S. (1977). Further experiments in nearly homogeneous turbulent shear flow. Journal of Fluid Mechanics, 81(4), 657-687. doi:10.1017/s0022112077002286Hasslberger, J., Ketterl, S., Klein, M., & Chakraborty, N. (2018). Flow topologies in primary atomization of liquid jets: a direct numerical simulation analysis. Journal of Fluid Mechanics, 859, 819-838. doi:10.1017/jfm.2018.845Hinze, J. O. (1955). Fundamentals of the hydrodynamic mechanism of splitting in dispersion processes. AIChE Journal, 1(3), 289-295. doi:10.1002/aic.690010303Lasheras, J. C., & Hopfinger, E. J. (2000). Liquid Jet Instability and Atomization in a Coaxial Gas Stream. Annual Review of Fluid Mechanics, 32(1), 275-308. doi:10.1146/annurev.fluid.32.1.275Lebas, 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.2008.11.005Lee, K., Girimaji, S. S., & Kerimo, J. (2008). Validity of Taylor’s Dissipation-Viscosity Independence Postulate in Variable-Viscosity Turbulent Fluid Mixtures. Physical Review Letters, 101(7). doi:10.1103/physrevlett.101.074501Ling, Y., Fuster, D., Zaleski, S., & Tryggvason, G. (2017). Spray formation in a quasiplanar gas-liquid mixing layer at moderate density ratios: A numerical closeup. Physical Review Fluids, 2(1). doi:10.1103/physrevfluids.2.014005Ling, Y., Fuster, D., Tryggvason, G., & Zaleski, S. (2018). A two-phase mixing layer between parallel gas and liquid streams: multiphase turbulence statistics and influence of interfacial instability. Journal of Fluid Mechanics, 859, 268-307. doi:10.1017/jfm.2018.825LUCCI, F., FERRANTE, A., & ELGHOBASHI, S. (2010). Modulation of isotropic turbulence by particles of Taylor length-scale size. Journal of Fluid Mechanics, 650, 5-55. doi:10.1017/s0022112009994022Manin, J. (2018). NUMERICAL INVESTIGATION OF THE PRIMARY BREAKUP REGION OF HIGH-PRESSURE SPRAYS. Atomization and Sprays, 28(12), 1081-1100. doi:10.1615/atomizspr.2019026990MARMOTTANT, P., & VILLERMAUX, E. (2004). On spray formation. Journal of Fluid Mechanics, 498, 73-111. doi:10.1017/s0022112003006529Park, G. I., Bassenne, M., Urzay, J., & Moin, P. (2017). A simple dynamic subgrid-scale model for LES of particle-laden turbulence. Physical Review Fluids, 2(4). doi:10.1103/physrevfluids.2.044301Pope, S. B., 2001. Turbulent flows.Popinet, S. (2009). An accurate adaptive solver for surface-tension-driven interfacial flows. Journal of Computational Physics, 228(16), 5838-5866. doi:10.1016/j.jcp.2009.04.042Prakash, V. N., Martínez Mercado, J., van Wijngaarden, L., Mancilla, E., Tagawa, Y., Lohse, D., & Sun, C. (2016). Energy spectra in turbulent bubbly flows. Journal of Fluid Mechanics, 791, 174-190. doi:10.1017/jfm.2016.49Roghair, I., Mercado, J. M., Sint Annaland, M. V., Kuipers, H., Sun, C., & Lohse, D. (2011). Energy spectra and bubble velocity distributions in pseudo-turbulence: Numerical simulations vs. experiments. International Journal of Multiphase Flow, 37(9), 1093-1098. doi:10.1016/j.ijmultiphaseflow.2011.07.004Saddoughi, S. G., & Veeravalli, S. V. (1994). Local isotropy in turbulent boundary layers at high Reynolds number. Journal of Fluid Mechanics, 268, 333-372. doi:10.1017/s0022112094001370Salvador, F. J., S., R., Crialesi-Esposito, M., & Blanquer, I. (2018). Analysis on the effects of turbulent inflow conditions on spray primary atomization in the near-field by direct numerical simulation. International Journal of Multiphase Flow, 102, 49-63. doi:10.1016/j.ijmultiphaseflow.2018.01.019Scardovelli, R., & Zaleski, S. (2003). Interface reconstruction with least-square fit and split Eulerian-Lagrangian advection. International Journal for Numerical Methods in Fluids, 41(3), 251-274. doi:10.1002/fld.431Schmidt, O. T., Towne, A., Rigas, G., Colonius, T., & Brès, G. A. (2018). Spectral analysis of jet turbulence. Journal of Fluid Mechanics, 855, 953-982. doi:10.1017/jfm.2018.675Shinjo, 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.2010.03.008Uberoi, M. S. (1970). Turbulent Energy Balance and Spectra of the Axisymmetric Wake. Physics of Fluids, 13(9), 2205. doi:10.1063/1.1693225Villermaux, E. (2007). Fragmentation. Annual Review of Fluid Mechanics, 39(1), 419-446. doi:10.1146/annurev.fluid.39.050905.110214Wang, Y., & Bourouiba, L. (2018). Unsteady sheet fragmentation: droplet sizes and speeds. Journal of Fluid Mechanics, 848, 946-967. doi:10.1017/jfm.2018.359Zandian, A., Sirignano, W. A., & Hussain, F. (2018). Understanding liquid-jet atomization cascades via vortex dynamics. Journal of Fluid Mechanics, 843, 293-354. doi:10.1017/jfm.2018.11

Effects of isotropic and anisotropic turbulent structures over spray atomization in the near field

Sprays and atomization processes are extremely diffused both in nature and in industrial applications. In this paper we analyze the influence of the nozzle turbulence on primary atomization, focusing on the resulting turbulent field and atomization patterns in the Near Field (NF). In order to do so, a Synthetic Boundary Condition (SBC) and a Mapped Boundary Condition (MBC), producing respectively isotropic and anisotropic turbulent fields, have been generated as inflow conditions for the spray Direct Numerical Simulations (DNS). We present a specific methodology to ensure consistency on turbulence intensity and integral lengthscale between the two inflows. The analysis performed on the turbulent field (using one-point statistics and spectrum analysis) reveals a significantly stronger turbulent field generated by the inflow boundary conditions with anisotropic structures. While the increased turbulence field generated in the MBC case results in a higher number of droplets generated, the probability functions of both cases are extremely similar, leading to the non-obvious conclusion that the atomization patterns are only slightly affected by the inflow condition. These considerations are supported by the analysis of droplet size distributions, radial distribution functions, axial and radial distributions, highlighting extremely similar behaviors between the MBC and the SBC cases. Finally, these analyses and their computations are presented in detail, underlining how this type of point-process characterization shows interesting potential in future studies on sprays

Analysis on the efects of turbulent inflow conditions on spray primary atomization in the near-field by direct numerical simulation

[EN] It is widely acknowledged that the development of sprays in the near-field is of primary importance for the spray formation downstream, as it affects both the spray angle, as well as the intact core length. In this frame, the present work aims to study the effects of turbulence inlet boundary condition on the spray formation by means of Direct Numerical Simulations on a real condition at low Reynolds number. To this extent, the code Paris-Simulator has been used, while a digital filter-based algorithm was used in order to generate synthetic turbulence at the inlet boundary condition. The influence of turbulence intensity and lengthscale on the atomization process has been studied and analyzed through 3 simulation for which these parameters have been varied. The results clearly highlight how the atomization is heavily affected by the inlet turbulence configuration. An analysis of the different atomizing conditions has been conducted, aiming to understand how the variation introduced by the inlet boundary condition on the velocity field is affecting the local atomization dynamics.This work was partly sponsored by "Ministerio de Economia y Competitividad", of the Spanish Government, in the frame of the Project "Estudio de la interaccion chorro-pared en condiciones realistas de motor", Reference TRA2015-67679-c2-1-R. The author thankfully acknowledges the computer resources at MareNostrum (BSC) and the technical support provided by FI-2016-3-0031.Salvador, FJ.; Ruiz, S.; Crialesi Esposito, M.; Blanquer Espert, I. (2018). Analysis on the efects of turbulent inflow conditions on spray primary atomization in the near-field by direct numerical simulation. International Journal of Multiphase Flow. 102:49-63. https://doi.org/10.1016/j.ijmultiphaseflow.2018.01.019S496310

Fuel temperature influence on the performance of a last generation common-rail diesel ballistic injector. Part I: Experimental mass flow rate measurements and discussion

An experimental study is conducted in this paper in order to assess the influence of the fuel temperature on the performance of a last generation common-rail ballistic solenoid injector. Mass flow rate measurements are performed for a wide range of temperatures, extending from 253 to 373 K, representative of all the possible operating conditions of the injector in a real diesel engine, including cold start. The high pressure line and the injector holder were refrigerated, making it possible to carefully control the fuel temperature, whereas measurements at cold conditions were carried out with the help of a climatic chamber. Relevant features such as stationary mass flow, injection delay or the behaviour at the opening and closing stages are analysed together with parameters governing the flow, such as the injector discharge coefficient. Results show an important influence of the fuel temperature, especially at low injection pressure. A low injection temperature results in a lower stationary mass flow rate, whereas injection duration is also reduced. These results will be explained mainly through the fuel properties variation induced by temperature, together with the ballistic nature of the injector used for the study. A second part of the paper introduces a one-dimensional model that makes it possible to reproduce these results and further explain them through the analysis of other relevant variables, such as the needle lift.This work was partly sponsored by "Ministerio de Economia y Competitividad" (Spain) in the frame of the project "Comprension de la influencia de combustibles no convencionales en el proceso de inyeccion y combustion tipo diesel", reference TRA2012-36932. The equipment used in this work has been partially supported by FEDER project funds "Dotacion de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energetica y Medioambiental de Sistemas de Transporte (CiMeT), (FEDER-ICTS-2012-06)", in the frame of the operation program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain. This support is gratefully acknowledged by the authors.Salvador Rubio, FJ.; Gimeno, J.; Carreres Talens, M.; Crialesi Esposito, M. (2016). Fuel temperature influence on the performance of a last generation common-rail diesel ballistic injector. Part I: Experimental mass flow rate measurements and discussion. Energy Conversion and Management. 114:364-375. doi:10.1016/j.enconman.2016.02.042S36437511

Determination of critical operating and geometrical parameters in diesel injectors through one dimensional modelling, design of experiments and an analysis of variance

[EN] In this paper, a design of experiments and a statistical analysis of variance (ANOVA) are performed to determine the parameters that have more influence on the mass flow rate profile in diesel injectors. The study has been carried out using a one dimensional model previously implemented by the authors. The investigation is split into two different parts. First, the analysis is focused on functional parameters such as the injection and discharge pressures, the energizing time and the fuel temperature. In the second part, the influence of 37 geometrical parameters such as the diameters of hydraulic lines, calibrated orifices and internal volumes, among others, are analysed. The objective of the study is to quantify the impact of small variations in the nominal value of these parameters on the injection rate profile for a given injector operating condition. In the case of the functional parameters, these small variations may be attributed to possible undesired fluctuations in the conditions that the injector is submitted to. As far as the geometrical and flow parameters are concerned, the small variations studied are representative of manufacturing tolerances that could influence the injected mass flow rate. As a result, it has been noticed that the configuration of the inlet and outlet orifices of the control volume together with the discharge coefficient of the inlet orifice, among a few others, play a remarkable role in the injector performance. The reason resides in the fact that they are in charge of controlling the behaviour of the pressure in the control volume, which importantly influences injector dynamics and therefore the injection process. Variations of only 5% in the diameter of these orifices strongly modify the shape of the rate of injection curve, influencing both the injection delay and the duration of the injection process, consequently changing the total mass delivered.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research has been partially funded by FEDER and the Spanish ‘‘Ministerio de Economı´a y Competitividad’’ through the project TRA2015-67679- c2-1-R.Salvador, FJ.; Carreres, M.; Crialesi Esposito, M.; Plazas Torres, AH. (2018). Determination of critical operating and geometrical parameters in diesel injectors through one dimensional modelling, design of experiments and an analysis of variance. Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering. 232(13):1762-1781. https://doi.org/10.1177/0954407017735262S176217812321

Experimental investigation of the effect of orifices inclination angle in multihole diesel injector nozzles. Part-1-Hydraulic performance

[EN] Nozzle hydraulic performance has a significant impact on diesel spray development and combustion characteristics. Thus, it is important to understand the links between the nozzle geometry, the internal flow features and the spray formation. In this paper, a detailed analysis of the impact of the nozzle orifices inclination angle on its hydraulic performance is performed. For this purpose, three different nozzles with included angles of 90, 140 and 155 degrees are evaluated. Instantaneous injection rate and momentum flux are measured on a set of injector operating conditions (mainly injection pressure and discharge pressure). The results show that higher inclination angles lead to smaller mass flow and momentum flux at steady-state conditions, due to the higher losses at the orifice inlet. These losses are translated in lower both area and velocity coefficients. Nevertheless, the impact of this parameter is limited thanks to the counter-acting effect of the hydrogrinding process, which produces larger rounding radii at the orifice inlet as the included angle increases. Based on the experimental results, correlations of the discharge coefficient as a function of the Reynolds number are obtained and evaluated. (C) 2017 Elsevier Ltd. All rights reserved.This work was partly sponsored by "Ministerio de Economia y Competitividad", of the Spanish Government, in the frame of the Project "Estudio de la interaccion chorro-pared en condiciones realistas de motor", Reference TRA2015-67679-c2-1-R.Salvador, FJ.; López, JJ.; De La Morena, J.; Crialesi Esposito, M. (2018). Experimental investigation of the effect of orifices inclination angle in multihole diesel injector nozzles. Part-1-Hydraulic performance. Fuel. 213:207-214. https://doi.org/10.1016/j.fuel.2017.04.019S20721421