Large Eddy Simulation for high pressure flows: Model extension for compressible liquids

[EN] The present study gives a general outline for the fluid-dynamical calculation of flows at high pressure conditions. The main idea is to present a mathematical description of high pressure processes in liquids at compressible conditions, quantifying the effect of density variations on the flow pattern due to those pressure variations. The improved mathematical approach is coupled to a Large Eddy Simulation (LES) solver. The main code was developed by OpenSource Ltd. for OpenFOAM, and the authors have introduced the additional expressions in order to calculate particular variables. For validating the code improvement, the LES solver is applied to a modern common-rail nozzle injector used in diesel engines. Results have been compared against other calculations that assumed constant properties and simultaneously validated with experimental data. © 2010 Elsevier Ltd.This work has been funded by MINISTERIO DE CIENCIA E INNOVACION from Spain, in the framework of the project “ESTUDIO TEORICO EXPERIMENTAL DE LA INFLUENCIA DEL COMBUSTIBLE SOBRE LA CAVITACION Y EL DESARROLLO DEL CHORRO EVAPORATIVO”, Reference No. TRA2010-17564. The authors would like to thank Universidad de Valencia for the computer resources, technical expertise, the assistance provided and for allowing the use of the supercomputer Tirant.Payri, R.; Tormos, B.; Gimeno, J.; Bracho Leon, G. (2011). Large Eddy Simulation for high pressure flows: Model extension for compressible liquids. Mathematical and Computer Modelling. 54(7):1725-1731. https://doi.org/10.1016/j.mcm.2010.12.001S1725173154

Study of liquid and vapor phase behavior on Diesel sprays for heavy duty engine nozzles

A lot of effort has been put in the past years into the understanding of the delivery and development of diesel sprays in engine-like conditions as it has been proved to be a very important step for the design of better and cleaner commercial engines. Due to the bigger share of passenger cars engines over heavy duty engines, the research has been mainly focused on the investigation using small nozzles. This paper studies two nozzles with diameters representative of those that can be encountered in heavy duty engines, with the objective of corroborating the conclusions gathered for small nozzles representative of passenger car engines. The experimental data have been acquired by state-of-the-art techniques and equipment, and serves two purposes: further the understanding of the physics involved in the injection event and spray evaporation; and provide a dataset to CFD models that can accurately predict the behavior of the injection event. The tests were performed in a constant pressure flow vessel that allows to simulate engine-like conditions (1000 K and 15 Mpa) with continuous flow. The injection system tested is a novel, common-rail, solenoid-actuated injector for heavy duty applications which operates up to 220 Mpa. All experiments were performed in non-reacting conditions. The extended test matrix allowed to determine the influence of several parameters such as rail pressure, gas temperature, gas density, and nozzle geometry on the air-fuel mixing and evaporation process, by analyzing the spray penetration and spreading angle. Mie scattering and double-pass Schlieren optical configurations have been used to measure global liquid and vapor penetration, respectively. The data proves that spray penetration at low temperature can be up to 15% faster than spray penetration at high temperature conditions at the same density for the nozzles experi-mented, which limits the usability of low temperature experiments to infer the behavior of the injector at high temperature conditions. The data also shows that the nozzle with the biggest diameter provided the highest value of stabilized liquid length as expected. Also, when vapor phase is reached, the temperature has negligible effect on the global diesel spray morphology, and no influence on the tip penetration or on the spreading angle.This work was sponsored by "Ministerio de Economia y Competitividad" in the frame of the project "Estudio de la interaction chorro-pared en condiciones realistas de motor (SPRAY WALL)" reference TRA2015-67679-c2-1-R. Daniel Vaquerizo is partially supported through contract FPI-S2-2015-1069 of Programa de Apoyo para la Investigacion y Desarrollo (PAID) of Universitat Politecnica de Valencia.Payri, R.; Gimeno, J.; Bracho Leon, G.; Vaquerizo, D. (2016). Study of liquid and vapor phase behavior on Diesel sprays for heavy duty engine nozzles. Applied Thermal Engineering. 107:365-378. doi:10.1016/j.applthermaleng.2016.06.159S36537810

Experimental study of the injection conditions influence over n-dodecane and diesel sprays with two ECN single-hole nozzles. Part I: Inert atmosphere

In this research, two Engine Combustion Network (ECN) mono-orifice nozzles, referred to as Spray C and Spray D. respectively, were analyzed by performing visualization tests through Schlieren and Diffused Backlight Illumination (DBI) techniques under a wide range of ambient conditions in a non-reactive atmosphere. Spray C presents a straight nozzle designed with a sharp fillet in opposition to Spray D that has similar hydraulic properties, but with a convergent nozzle construction and a smoother corner. The experiments were carried out injecting two distinct fuels at different injection pressure ranges, from 50 MPa to 150 MPa with n-dodecane and to 200 MPa for diesel. The images were processed with Matlab home-built routines to calculate parameters as spray penetration, spreading angle, quasi steady liquid length, as well as the spray penetration derivative respect to the square root of time, presented in this document as R-parameter. The results showed a clear influence of nozzle geometry in all measured parameters, due mainly to the nature of Spray C to cavitation, which increase the spreading angle and consequently a reduction in vapor penetration. On the other hand, fuel properties also affected spray penetration due to its dependency on viscous forces expressed in terms of the Reynolds number and its volatility in case of liquid length. This last parameter was calculated employing two processing methodologies, finding a good general agreement between them.This work was supported by "Ministerio de Economia y Competitividad" of the Spanish Government in the frame of the projects "Estudio de la interaccion chorro-pared en condiciones realistas de motor", Ref. TRA2015-67679-c2-1-R. Moreover, the optical equipment employed in the project was purchased with investment from "Ministerio de Economia y Competitividad" FEDER-ICTS-2012-06.Gimeno, J.; Bracho Leon, G.; Marti-Aldaravi, P.; Peraza, JE. (2016). Experimental study of the injection conditions influence over n-dodecane and diesel sprays with two ECN single-hole nozzles. Part I: Inert atmosphere. Energy Conversion and Management. 126:1146-1156. https://doi.org/10.1016/j.enconman.2016.07.077S1146115612

Numerical Analysis of Urea to Ammonia Conversion in Automotive Selective Catalytic Reduction Realistic Conditions

[EN] The selective catalytic reduction (SCR) is a technology employed for NOx reduction purposes which is based on the injection of an Urea Water Solution (UWS) into the exhaust line. Conversion of this injected urea into ammonia is a key step to ensure high SCR efficiency. In order to study this phenomenon, a three-dimensional model of the urea-water injection process has been created to recreate realistic conditions. A Lagrangian-Eulerian approach has been followed to model liquid and gas phases, respectively. Droplet evaporation as well as relevant chemical processes have been included to recreate the thermolysis and hydrolysis phenomena, and the results have been validated against literature data. Then, the validated model has been applied to recreate an in-house experimental facility that measured spray macroscopic and microscopic characteristics by means of diffused back illumination (DBI) visualization. Probability density functions of the UWS droplet sizes as well as the velocity distributions have been obtained at three different regions of interest to be compared with the experimental data set. Contours of isocyanic acid and ammonia mass fractions have been included to show the chemical transformation from urea into its products. The model accurately replicates the experimental results, and it stands as a good methodology to predict the main spray characteristics as well as the chemical processes that take place in actual SCR systems.This research has been partially funded by Spanish Ministerio de Ciencia, Innovacion y Universidades through project RTI2018099706-B-100. Additionally, the experimental hardware was purchased through FEDER and Generalitat Valenciana under project IDIFEDER/2018/037. Additionally, the Ph.D. student J.M.-G. has been funded by a grant from the Government of Generalitat Valenciana with reference ACIF/2020/259 and financial support from The European Union.Payri, R.; Bracho Leon, G.; Marti-Aldaravi, P.; Marco-Gimeno, J. (2021). Numerical Analysis of Urea to Ammonia Conversion in Automotive Selective Catalytic Reduction Realistic Conditions. Industrial & Engineering Chemistry Research. 60(39):14329-14340. https://doi.org/10.1021/acs.iecr.1c02627S1432914340603

Computational Study of Urea-Water Solution Sprays for the Analysis of the Injection Process in SCR-like Conditions

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Industrial & Engineering Chemistry Research, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.iecr.0c02494.[EN] Exhaust after-treatment devices for NOx reduction have become mandatory for achieving the strict diesel emission standards. The selective catalytic reduction (SCR) method has proven to be efficient in this task. Nonetheless, in order to improve the efficiency of the system, the urea-water solution (UWS) injection process needs to be properly characterized due to the limited geometry of the exhaust line and its flow conditions. In combination with the experimental analysis into the system in a dedicated test rig, computational fluid dynamics studies provide better insights into the physical phenomena. Therefore, the main objective of this investigation is to achieve validated droplet size and velocity distributions in the simulation when compared to experiments. Three different positions along the spray are evaluated for that. The methodology adopted includes an Eulerian-Lagrangian approach to study the UWS spray. The results obtained with it show a proper experimental validation as well as the Sauter mean diameter distribution for the conditions tested. The proposed model accurately reproduces the main spray characteristics for different injection pressures and ambient conditions. Thus, the main conclusions obtained sum up in a good methodology for predicting UWS sprays in SCR-like conditions.This research has been partially funded by Spanish Ministerio de Ciencia, Innovacion y Universidades through project RTI2018-099706-B-100. Additionally, the experimental hardware was purchased through FEDER and Generalitat Valenciana under project IDIFEDER/2018/037.Payri, R.; Bracho Leon, G.; Marti-Aldaravi, P.; Marco-Gimeno, J. (2020). Computational Study of Urea-Water Solution Sprays for the Analysis of the Injection Process in SCR-like Conditions. Industrial & Engineering Chemistry Research. 59(41):18659-18673. https://doi.org/10.1021/acs.iecr.0c02494S18659186735941Han, L., Cai, S., Gao, M., Hasegawa, J., Wang, P., Zhang, J., … Zhang, D. (2019). Selective Catalytic Reduction of NOx with NH3 by Using Novel Catalysts: State of the Art and Future Prospects. Chemical Reviews, 119(19), 10916-10976. doi:10.1021/acs.chemrev.9b00202Reitz, R. D., Ogawa, H., Payri, R., Fansler, T., Kokjohn, S., Moriyoshi, Y., … Zhao, H. (2019). IJER editorial: The future of the internal combustion engine. International Journal of Engine Research, 21(1), 3-10. doi:10.1177/1468087419877990Dammalapati, S., Aghalayam, P., & Kaisare, N. (2019). Modeling the Effect of Nonuniformities from Urea Injection on SCR Performance Using CFD. Industrial & Engineering Chemistry Research, 58(44), 20247-20258. doi:10.1021/acs.iecr.9b04149Triantafyllopoulos, G., Katsaounis, D., Karamitros, D., Ntziachristos, L., & Samaras, Z. (2018). Experimental assessment of the potential to decrease diesel NOx emissions beyond minimum requirements for Euro 6 Real Drive Emissions (RDE) compliance. Science of The Total Environment, 618, 1400-1407. doi:10.1016/j.scitotenv.2017.09.274Inomata, Y., Hata, S., Mino, M., Kiyonaga, E., Morita, K., Hikino, K., … Murayama, T. (2019). Bulk Vanadium Oxide versus Conventional V2O5/TiO2: NH3–SCR Catalysts Working at a Low Temperature Below 150 °C. ACS Catalysis, 9(10), 9327-9331. doi:10.1021/acscatal.9b02695Xue, Z., Du, X., Rac, V., Rakic, V., Wang, X., Chen, Y., … Song, L. (2020). Partial Oxidation of NO by H2O2 and afterward Reduction by NH3-Selective Catalytic Reduction: An Efficient Method for NO Removal. Industrial & Engineering Chemistry Research, 59(20), 9393-9397. doi:10.1021/acs.iecr.9b06896Nuguid, R. J. G., Ferri, D., Marberger, A., Nachtegaal, M., & Kröcher, O. (2019). Modulated Excitation Raman Spectroscopy of V2O5/TiO2: Mechanistic Insights into the Selective Catalytic Reduction of NO with NH3. ACS Catalysis, 9(8), 6814-6820. doi:10.1021/acscatal.9b01514Yim, S. D., Kim, S. J., Baik, J. H., Nam, I., Mok, Y. S., Lee, J.-H., … Oh, S. H. (2004). Decomposition of Urea into NH3 for the SCR Process. Industrial & Engineering Chemistry Research, 43(16), 4856-4863. doi:10.1021/ie034052jZheng, G.; Fila, A.; Kotrba, A.; Floyd, R. Investigation of urea deposits in urea SCR systems for medium and heavy duty trucks. SAE Technical Papers, 2010, 2010-01-19.Strots, V. O., Santhanam, S., Adelman, B. J., Griffin, G. A., & Derybowski, E. M. (2009). Deposit Formation in Urea-SCR Systems. SAE International Journal of Fuels and Lubricants, 2(2), 283-289. doi:10.4271/2009-01-2780Abu-Ramadan, E.; Saha, K.; Li, X. Modeling of the injection and decomposition processes of urea-water-solution spray in automotive SCR systems. SAE 2011 World Congress and Exhibition, 2011, 2011-01-13.Sowman, J., Laila, D. S., Fussey, P., Truscott, A., & Cruden, A. J. (2019). Nonlinear model predictive control applied to multivariable thermal and chemical control of selective catalytic reduction aftertreatment. International Journal of Engine Research, 20(10), 1017-1024. doi:10.1177/1468087419859103Varna, A., Boulouchos, K., Spiteri, A., Dimopoulos Eggenschwiler, P., & Wright, Y. M. (2014). Numerical Modelling and Experimental Characterization of a Pressure-Assisted Multi-Stream Injector for SCR Exhaust Gas After-Treatment. SAE International Journal of Engines, 7(4), 2012-2021. doi:10.4271/2014-01-2822Varna, A., Spiteri, A. C., Wright, Y. M., Dimopoulos Eggenschwiler, P., & Boulouchos, K. (2015). Experimental and numerical assessment of impingement and mixing of urea–water sprays for nitric oxide reduction in diesel exhaust. Applied Energy, 157, 824-837. doi:10.1016/j.apenergy.2015.03.015Van Vuuren, N.; Brizi, G.; Buitoni, G.; Postrioti, L.; Ungaro, C. Experimental analysis of the urea-water solution temperature effect on the spray characteristics in SCR systems. SAE Technical Papers, 2015, 2015-24-25.van Vuuren, N.; Brizi, G.; Buitoni, G.; Postrioti, L.; Ungaro, C. AUS-32 Injector Spray Imaging on Hot Air Flow Bench. SAE Technical Papers, 2015, 2015-01-10.Kapusta, Ł. J., Sutkowski, M., Rogóż, R., Zommara, M., & Teodorczyk, A. (2019). Characteristics of Water and Urea–Water Solution Sprays. Catalysts, 9(9), 750. doi:10.3390/catal9090750Rogóż, R., Kapusta, Ł. J., Bachanek, J., Vankan, J., & Teodorczyk, A. (2020). Improved urea-water solution spray model for simulations of selective catalytic reduction systems. Renewable and Sustainable Energy Reviews, 120, 109616. doi:10.1016/j.rser.2019.109616Bebe, J. E.; Andersen, K. S. Validation of a CFD Spray Model Based on Spray Nozzle Characteristics. WCX 17: SAE World Congress Experience, 2017.Vojtíšek, M., & Kotek, M. (2014). Estimation of Engine Intake Air Mass Flow using a generic Speed-Density method. Journal of Middle European Construction and Design of Cars, 12(1), 7-15. doi:10.2478/mecdc-2014-0002Payri, R., Bracho, G., Gimeno, J., & Moreno, A. (2019). Investigation of the urea-water solution atomization process in engine exhaust-like conditions. Experimental Thermal and Fluid Science, 108, 75-84. doi:10.1016/j.expthermflusci.2019.05.019Payri, R.; Bracho, G.; Gimeno, J.; Moreno, A. Spray characterization of the urea-water solution (UWS) injected in a hot air stream analogous to SCR system operating conditions. SAE Technical Papers, 2019, 2019-01-07.Sechenyh, V., Duke, D. J., Swantek, A. B., Matusik, K. E., Kastengren, A. L., Powell, C. F., … Crua, C. (2019). Quantitative analysis of dribble volumes and rates using three-dimensional reconstruction of X-ray and diffused back-illumination images of diesel sprays. International Journal of Engine Research, 21(1), 43-54. doi:10.1177/1468087419860955BASF. AdBlueTechnical Leaflet. 2006, https://www.gabriels.be/sites/gabriels/files/pdf/technische_fiche_adblue-_engels.pdf (accessed October 8, 2019).Senecal, P. K.; Pomraning, E.; Richards, K. J.; Som, S. Grid-Convergent Spray Models for Internal Combustion Engine CFD Simulations. Internal Combustion Engine Division Fall Technical Conference; American Society of Mechanical Engineers, 2012.Patterson, M. A.; Reitz, R. D. Modeling the Effects of Fuel Spray Characteristics on Diesel Engine Combustion and Emission. SAE Technical Paper; JSTOR, 1998.Schmidt, D. P., & Rutland, C. J. (2000). A New Droplet Collision Algorithm. Journal of Computational Physics, 164(1), 62-80. doi:10.1006/jcph.2000.6568Chiang, C. H., Raju, M. S., & Sirignano, W. A. (1992). Numerical analysis of convecting, vaporizing fuel droplet with variable properties. International Journal of Heat and Mass Transfer, 35(5), 1307-1324. doi:10.1016/0017-9310(92)90186-vPayri, R., Gimeno, J., Martí-Aldaraví, P., & Viera, A. (2020). Measurements of the mass allocation for multiple injection strategies using the rate of injection and momentum flux signals. International Journal of Engine Research, 22(4), 1180-1195. doi:10.1177/1468087419894854Payri, R.; Salvador, F. J.; Gimeno, J.; Montiel, T. Aging of a Multi-Hole Diesel Injector and Its Effect on the Rate of Injection. SAE Technical Paper, 2020; pp 1–9Benjamin, S. F.; Roberts, C. A. Fuel Systems for IC Engines; IMechE; Woodhead Publishing: Cambridge, UK, 2012; pp 43–60.Gapin, A.; Demoulin, F.; Dumouchel, C.; Pajot, K.; Patte-Rouland, B.; Réveillon, J. 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Investigation of the urea-water solution atomization process in engine exhaust-like conditions

[EN] The injection process of the urea-water solution (UWS) determines the initial conditions for the mixing and evaporation of the fluid in the selective catalytic reduction system. In this study, the liquid atomization process of a UWS dosing system is investigated using optical diagnosis through back-light imaging. The droplet diameter distribution and the droplet velocity (in the axial and tangential components) of the liquid spray are quantified under different air flow and injection conditions. A new test facility was designed to study UWS spray under conditions that resemble those of the engine exhaust pipe, which is capable of reaching an air flow of 400 kg/h and air temperatures up to 400 degrees C. The test matrix consisted of variations in the air flow temperature, air mass flow and UWS injection pressure. A high speed camera was used for capturing the images of the liquid spray, comparing the atomized liquid behaviour in three different regions of the plume: the first one near the nozzle exit, and the other two in the developed region of the spray (one aligned with the injector axis and the other at the spray periphery). Increasing the injection pressure affected the atomization process producing smaller particles with higher velocities in the axial and tangential components, promoting wider global spray angles, that combined with high air flow temperatures could improve the evaporation and mixing process in the SCR system. The main contribution is the development of an alternative technique for the quantification of the droplet size and velocity.The equipment used for the experiments was financially supported by IDIFEDER2018 from Generalitat Valenciana. The author A. Moreno thanks the Universitat Politecnica de Valencia for his predoctoral contract (FPI-2018-S2-13), which is included within the framework of Programa de Apoyo para la Investigacien y Desarrollo (PAID).Payri, R.; Bracho Leon, G.; Gimeno, J.; Moreno-Gasparotto, AE. (2019). Investigation of the urea-water solution atomization process in engine exhaust-like conditions. Experimental Thermal and Fluid Science. 108:75-84. https://doi.org/10.1016/j.expthermflusci.2019.05.019758410

Development of an Oxy-Fuel Combustion System in a Compression-Ignition Engine for Ultra-Low Emissions Powerplants Using CFD and Evolutionary Algorithms

[EN] This study uses an optimization approach for developing a combustion system in a compression-ignition engine that is able to operate under oxy-fuel conditions, and produces mainly CO2 and H2O as exhaust gases. This is achieved because the combustion concept uses pure oxygen as an oxidizer, instead of air, avoiding the presence of nitrogen. The O-2 for the combustion system can be obtained by using a mixed ionic-electronic conducting membrane (MIEC), which separates the oxygen from the air onboard. The optimization method employed maximizes the energy conversion of the system, reducing pollutant emissions (CxHy, particulate matter, and carbon monoxides) to levels near zero. The methodology follows a novel approach that couples computational fluid dynamics (CFD) and particle swarm optimization (PSO) algorithms to optimize the complete combustion system in terms of engine performance and pollutant generation. The study involves the evaluation of several inputs that govern the combustion system design in order to fulfill the thermo-mechanical constraints. The parameters analyzed are the piston bowl geometry, fuel injector characteristics, air motion, and engine settings variables. Results evince the relevance of the optimization procedure, achieving very low levels of gaseous pollutants (CxHy and CO) in the optimum configuration. The emissions of CO were reduced by more than 10% while maintaining the maximum in-cylinder pressure within the limit imposed for the engine. However, indicated efficiency levels are compromised if they are compared with an equivalent condition operating under conventional diesel combustion.This research work has been supported by Grant PDC2021-120821-I00 funded by MCIN/AEI/10.13039/501100011033 and by EuropeanUnion NextGenerationEU/PRTR. This research was partially supported by Agencia Valenciana de la Innovacio (AVI) through the project "Demostrador de un motor de oxicombustion con captura de CO2" (INNVA1/2021/38).Serrano, J.; Bracho Leon, G.; Gómez-Soriano, J.; Spohr-Fernandes, C. (2022). Development of an Oxy-Fuel Combustion System in a Compression-Ignition Engine for Ultra-Low Emissions Powerplants Using CFD and Evolutionary Algorithms. Applied Sciences. 12(14):1-27. https://doi.org/10.3390/app12147104127121

Mixture Model Approach for the Study of the Inner Flow Dynamics of an AdBlue Dosing System and the Characterization of the Near-Field Spray

[EN] Selective Catalytic Reduction stands for an effective methodology for the reduction of NOx emissions from Diesel engines and meeting current and future EURO standards. For it, the injection of Urea Water Solution (UWS) plays a major role in the process of reducing the NOx emissions. A LES approach for turbulence modelling allows to have a description of the physics which is a very useful tool in situations where experiments cannot be performed. The main objective of this study is to predict characteristics of the flow of interest inside the injector as well as spray morphology in the near field of the spray. For it, the nozzle geometry has been reconstructed from X-Ray tomography data, and an Eulerian-Eulerian approach commonly known as Mixture Model has been applied to study the liquid phase of the UWS with a LES approach for turbulence modeling. The injector unit is subjected to typical low-pressure working conditions. The results extracted from it comprise parameters that characterize the hydraulic behavior as well as jet intact length. The conclusions drawn from the model depict differences in the flow behavior between the injector three orifices, with an under-prediction of nozzle and spray characteristics of LES formulation with respect to traditional RANS turbulence treatment.The presented work is funded by a grant of Generalitat Valenciana, with reference ACIF/2020/259 and of the European Union. Partial funding comes as well from Spanish Ministerio de Ciencia, Innovación y Universidades through project RTI2018-099706-B-100. Additionally, the experimental hard-ware was purchased through FEDER and Generalitat Valenciana under project IDIFEDER/2018/037.Payri, R.; Bracho Leon, G.; Marti-Aldaravi, P.; Marco-Gimeno, J. (2021). Mixture Model Approach for the Study of the Inner Flow Dynamics of an AdBlue Dosing System and the Characterization of the Near-Field Spray. SAE International. 1-12. https://doi.org/10.4271/2021-01-054811

Differences between single and double-pass schlieren imaging on diesel vapor spray characteristics

[EN] The use olschlieren imaging at high acquisition rate has been adopted as a standard optical technique for the analysis of vaporizing diesel sprays under engine-like conditions. A single-pass schlieren arrangement is typically used for the study of axially drilled single-orifice nozzles, as vessels with multiple optical accesses regularly allow line of sight visualization. Contrarily, for multi-spray nozzles, measurements are commonly performed through a single,optical access, in which case a double-pass arrangement is employed. As a consequence, the light beams pass through the test section twice, increasing the optical sensitivity of the schlieren setup. However, the influence this has on the macroscopic spray characteristics is still unclear. The scope of this study is to analyze the differences in vapor phase penetration and spreading angle measured for the same injection event, through high-speed imaging, for both single and double-pass schlieren configurations. Experiments were carried out with a three hole nozzle with a nominal orifice diameter of 90 mu m, named Spray B from the Engine Combustion Network, using commercially available diesel fuel and in non-reactive conditions. The impact of different injection pressures, chamber temperatures and densities on the spray captured by each setup was assessed. On the results, vapor. phase penetration and spreading angle followed the expected trend found in the literature, for the different boundary conditions tested. Comparing the optical setups, vapor phase penetration and spreading angle results obtained with the double-pass arrangement were marginally higher than those from the single-pass. The deviation was observed throughout all tested conditions. For spray tip penetration, although the discrepancy was approximately constant for different injection pressures and chamber temperature, it increased with increasing density. These results highlight the importance of a proper understanding regarding the limitations of optical diagnostics, in particular for results used in calibration of computational models. (C) 2017 Elsevier Ltd. All rights reserved.This research has been partially funded by FEDER and Spanish Ministerio de Economia y Competitividad through project TRA2015-67679-C2-1-R. Additionally, Alberto Viera is supported through the FPI contract 2016-S2-1361 of "Programa de Apoyo para la Investigacion y Desarrollo (PAID)" of Universitat Poltecnica de Valencia.Payri, R.; Salvador, FJ.; Bracho Leon, G.; Viera-Sotillo, AA. (2017). Differences between single and double-pass schlieren imaging on diesel vapor spray characteristics. Applied Thermal Engineering. 125:220-231. https://doi.org/10.1016/j.applthermaleng.2017.06.140S22023112

Near field visualization of diesel spray for different nozzle inclination angles in non-vaporizing conditions

[EN] Accurate experimental data are often needed to validate computational fluid dynamics models. These models regularly rely on experimental results from single-orifice axially drilled nozzles that do not fully represent real injectors, as the difference in inclination angles creates turbulent conditions at the nozzle outlet, consequences of which on the spray development are not yet fully understood. In this work, near-field visualization was done for two nozzle inclination angles in non-vaporizing conditions. Spray tip penetration, spreading angle, and axis angle fluctuations are reported. Three hypotheses are analyzed: liquid jet breakup mechanism, internal flow development, and cavitation. Experiments were carried out using n-Dodecane, testing a single orifice axially drilled and a three-orifice injector, from the Engine Combustion Network. The spray was observed with a diffused back-illumination technique and a long distance microscope, only visualizing the first 6 mm of spray tip penetration, for three injection pressures and four gas densities at ambient temperature. The multi-orifice injector produced a spray with wider spreading angle, which resulted in smaller penetration values. Additionally, higher spray axis angle fluctuations were observed for the multi-orifice injector, which increased for higher injection pressure and, to a lesser extent, with decreasing chamber density. Further analysis was performed with spreading angle fluctuations measurements, where results showed good agreement with spray axis angle fluctuations trends, implying that complex internal flow structures, and even incipient cavitation, could be present in the multi-orifice injector and be the cause of these spray axis angle fluctuations.This work was 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. Additionally, the optical equipment used for the project was purchased with funding from Ministerio de Economia y Competitividad FEDER-ICTS-2012-06.Payri, R.; Bracho Leon, G.; Marti-Aldaravi, P.; Viera-Sotillo, AA. (2017). Near field visualization of diesel spray for different nozzle inclination angles in non-vaporizing conditions. Atomization and Sprays. 27(3):251-267. https://doi.org/10.1615/AtomizSpr.2017017949S25126727