ESTUDIO DE LA INFLUENCIA DE LAS CARACTERÍSTICAS DEL FLUJO INTERNO EN TOBERAS SOBRE EL PROCESO DE INYECCIÓN DIÉSEL EN CAMPO PRÓXIMO

La formación de la mezcla aire-combustible es uno de los procesos que tienen un efecto de mayor importancia en las prestaciones y las emisiones de contaminantes de los motores Diesel. Con el objetivo de incrementar el conocimiento respecto a este fenómeno numerosos estudios, tanto teóricos como experimentales, así como de modelado fluidodinámico, han sido desarrollados a lo largo de las últimas décadas. Sin embargo, el estudio del flujo en el interior de las toberas de inyección, así como su efecto sobre la atomización del combustible y el desarrollo del chorro en sus primeras etapas, muestra aún incertidumbres significativas, constituyendo un reto importante para la investigación en este campo. En esta tesis se desarrolla una técnica de visualización a alta resolución para la caracterización del chorro Diesel en campo próximo. De esta forma se puede establecer de forma más directa la relación entre las características del flujo en el interior de los orificios de descarga y la formación del chorro. Además, la obtención de imágenes con una gran resolución espacial permite caracterizar la estructura del chorro de forma más exhaustiva de lo que es habitual con otras técnicas. En este sentido, se ha analizado en primer lugar la influencia que tiene la aparición de cavitación en el interior de los orificios de descarga de las toberas sobre la formación del chorro. Para ello se han utilizado una serie de modelos simplificados de tobera consistentes en láminas de acero taladradas, así como una tobera mono-orificio cilíndrica. Como resultado de este estudio se puede ver que la cavitación aumenta de forma significativa tanto el ángulo de apertura del chorro como las irregularidades del contorno del mismo, favoreciendo el proceso de atomización. Una vez estudiada la influencia de la cavitación se han utilizado tres toberas de geometría cónica, con el fin de realizar un estudio similar en condiciones no cavitantes.De La Morena Borja, J. (2011). ESTUDIO DE LA INFLUENCIA DE LAS CARACTERÍSTICAS DEL FLUJO INTERNO EN TOBERAS SOBRE EL PROCESO DE INYECCIÓN DIÉSEL EN CAMPO PRÓXIMO [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/11098Palanci

Using a one-dimensional spray model to improve liquid length and ignition delay estimations for diesel flames

[EN] In the current paper, a methodology based on the combination of a one-dimensional spray model and experimental correlations has been proposed to predict the physical time associated with ignition delay in diesel diffusion flames. This physical time depends significantly on the nozzle geometry, and its influence is not captured in traditional Arrhenius-like correlation. To assess this influence, three multi-hole nozzles with different degrees of conicity (expressed in terms of k-factor) have been tested onan optically accessible 2-stroke single-cylinder engine. First, the hydraulic behavior of the nozzles is assessed from the point of view of injection rate and spray momentum. Later, the effect of the geometry on vapor spray angle has been analyzed through a Schlieren visualization technique. Mie-scattering has allowed to determine the stabilized liquid length. Then, chemiluminescence imaging was used to obtain the temporal and spatial appearance of OH radicals, which are used as indicators to the ignition delay. Finally, all the results are combined with a one-dimensional spray model to determine the physical induction time and include it into a new ignition delay correlation, which shows up to 4% accuracy improvement compared to a traditional Arrhenius equation. (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.Payri, R.; Salvador, F.; De La Morena, J.; Pagano, V. (2017). Using a one-dimensional spray model to improve liquid length and ignition delay estimations for diesel flames. Applied Thermal Engineering. 124:1090-1102. https://doi.org/10.1016/j.applthermaleng.2017.06.1021090110212

Experimental investigation of the effect of orifices inclination angle in multihole diesel injector nozzles. Part 2-Spray characteristics

[EN] Diesel spray development is a key research topic due to its impact on the combustion characteristics. On the current paper, the effect of the orifices inclination angle on the spray penetration characteristics is evaluated. For this purpose, three nozzles with included angles of 90, 140 and 155 degrees are selected. Visualization tests are performed on a room-temperature constant-pressure vessel pressurized with a high-density gas (SF6), in order to reproduce the density conditions inside the combustion chamber at the start of the injection event. Both frontal and lateral Mie-scattering visualization are used, depending on the particular nozzle configuration. Results show how the spray penetration is slower as the inclination angle increases, which is linked to its lower nozzle outlet velocity. A statistical correlation of the spray penetration as a function of the area and velocity coefficients is obtained and discussed.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.Payri, R.; Salvador, FJ.; De La Morena, J.; Pagano, V. (2018). Experimental investigation of the effect of orifices inclination angle in multihole diesel injector nozzles. Part 2-Spray characteristics. Fuel. 213:215-221. https://doi.org/10.1016/j.fuel.2017.07.076S21522121

Effects of cavitation in common-rail diesel nozzles on the mixing process

[EN] A study to experimentally analyze the effect of cavitation on the mixing process in diesel nozzles was carried out. The mixing process was studied through the spray cone angle. It was characterized in two different scenarios: with the liquid length (nearly realistic conditions, that is, evaporative but non-reactive spray) and the heat release fraction (fully realistic conditions, that is, evaporative and reactive spray). In both studied scenarios, the increase in spray cone angle caused by the cavitation phenomenon, which leads to a better mixing process, has been confirmed. Nevertheless, when the variations of the effective injection velocity and the spray cone angle obtained by comparing a cylindrical nozzle (i.e. a nozzle that promotes the cavitation phenomenon) with a conical nozzle (i.e. a nozzle that inhibits this phenomenon) were analyzed together, it was found that, for the cases studied here, the mixing process worsens with the cylindrical nozzle.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors thank the FPU program of the Spanish Ministry of Education for supporting the PhD studies of Oscar A de la Garza (grant: AP2008-01913) and also thank the PSA Peugeot-Citroen, National Council of Science and Technology (CONACYT) of the Mexican Government (project: CB-239943) and the Royal Academy of Engineering, United Kingdom (project: NRCP/1415/238) for supporting this research.López, JJ.; De La Garza De Leon, O.; De La Morena, J.; Martínez Martínez, S. (2017). Effects of cavitation in common-rail diesel nozzles on the mixing process. International Journal of Engine Research. 18(10):1017-1034. https://doi.org/10.1177/1468087417697759S10171034181

Experimental Characterization of Real Driving Cycles in a Light-Duty Diesel Engine under Different Dynamic Conditions

[EN] This paper studies the behavior of a Euro 6 diesel engine tested under dynamic conditions corresponding to different real driving emissions (RDE) scenarios. RDE cycles have been performed in an engine test bench by simulating its operation in a long van application. A computer tool has been designed to define the cycle accounting for different dynamic characteristics and driver behaviors to study their influence on CO2 and pollutant emissions, particularly CO, THC, and NOX. Different dynamic parameters have been established in terms of power, torque, engine speed, or vehicle speed. Additionally, a tool to estimate the emission of an RDE cycle from steady-state maps has been developed, helping to identify emission trends in a clearer way. Finally, the conclusions suggest that driving patterns characterized by lower engine speeds lead to fewer emissions. In addition, the analysis of RDE cycles from stationary maps helps to estimate the final tailpipe emissions of CO2 and NOX, offering the possibility to rely on tests carried out on engine test bench, dynamometer, or on the road.FundingThis research has been supported by Grant PID2020-114289RB-I00 funded by MCIN/AEI/10.13039/501100011033.Luján, JM.; Piqueras, P.; De La Morena, J.; Redondo-Puelles, F. (2022). Experimental Characterization of Real Driving Cycles in a Light-Duty Diesel Engine under Different Dynamic Conditions. Applied Sciences. 12(5):1-20. https://doi.org/10.3390/app1205247212012

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

Assessment of compressibility effects on internal nozzle flow in diesel injectors at very high injection pressures

[EN] Diesel fuel injection systems are being used at higher injection pressure conditions over time because of more stringent emissions requirements. Thus, the importance to properly take into account the fluid compressibility on injection CFD simulations is also increasing. In this paper, an investigation of the compressibility effects in nozzle flow simulations has been carried out for injection pressures up to 250 MPa. To do so, the fluid properties (including density, viscosity and speed of sound) have been measured in a wide range of boundary conditions. These measurements have allowed to obtain correlations for the fluid properties as a function of pressure and temperature. Then, these equations have been incorporated to a CFD solver to take into account the variation of the fluid properties with the pressure changes along the computational domain. The results from these simulations have been compared to experimental mass flow rate and momentum flux results, showing a significant increase in accuracy with respect to an incompressible flow solution.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 authors would like also to thank the computer resources, technical expertise and assistance provided by Universidad de Valencia in the use of the supercomputer "Tirant". Mr. Jaramillo's Thesis is funded by "Conselleria d'Educacio, Cultura i Esports" of Generalitat Valenciana in the frame of the program "Programa VALI+D para investigadores en formacion, Reference ACIF/2015/040.Salvador, F.; De La Morena, J.; Martínez López, J.; Jaramillo-Císcar, D. (2017). Assessment of compressibility effects on internal nozzle flow in diesel injectors at very high injection pressures. Energy Conversion and Management. 132:221-230. https://doi.org/10.1016/j.enconman.2016.11.03222123013

Influence of Pre-Turbine Small-Sized Oxidation Catalyst on Engine Performance and Emissions under Driving Conditions

[EN] The earlier activation of the catalytic converters in internal combustion engines is becoming highly challenging due to the reduction in exhaust gas temperature caused by the application of CO2 reduction technologies. In this context, the use of pre-turbine catalysts arises as a potential way to increase the conversion efficiency of the exhaust aftertreatment system. In this work, a small-sized oxidation catalyst consisting of a honeycomb thin-wall metallic substrate was placed upstream of the turbine to benefit from the higher temperature and pressure prior to the turbine expansion. The change in engine performance and emissions in comparison to the baseline configuration are analyzed under driving conditions. As an individual element, the pre-turbine catalyst contributed positively with a relevant increase in the overall CO and HC conversion efficiency. However, its placement produced secondary effects on the engine and baseline aftertreatment response. Although small-sized monoliths are advantageous to minimize the thermal inertia impact on the turbocharger lag, the catalyst cross-section is in trade-off with the additional pressure drop that the monolith causes. As a result, the higher exhaust manifold pressure in pre-turbine pre-catalyst configuration caused a fuel consumption increase higher than 3% while the engine-out CO and HC emissions did around 50%. These increments were not completely offset despite the high pre-turbine pre-catalyst conversion efficiency (>40%) because the partial abatement of the emissions in this device conditioned the performance of the close-coupled oxidation catalyst.This research has been partially supported by FEDER and the Government of Spain through project TRA2016-79185-R and by Universitat Politecnica de Valencia under a grant with reference number FPI-2018-S2-10 to the Ph.D. student Maria Jose Ruiz.Serrano, J.; Piqueras, P.; De La Morena, J.; Ruiz-Lucas, MJ. (2020). Influence of Pre-Turbine Small-Sized Oxidation Catalyst on Engine Performance and Emissions under Driving Conditions. Applied Sciences. 10(21):1-17. https://doi.org/10.3390/app10217714S1171021Serrano, J. R., Novella, R., & Piqueras, P. (2019). Why the Development of Internal Combustion Engines Is Still Necessary to Fight against Global Climate Change from the Perspective of Transportation. Applied Sciences, 9(21), 4597. doi:10.3390/app9214597Road Transport: Reducing CO2 Emissions from Vehicles. European Commissionhttps://ec.europa.eu/clima/policies/transport/vehicles/carsJoshi, A. (2020). Review of Vehicle Engine Efficiency and Emissions. SAE Technical Paper Series. doi:10.4271/2020-01-0352Gohil, D. B., Pesyridis, A., & Serrano, J. R. (2020). Overview of Clean Automotive Thermal Propulsion Options for India to 2030. Applied Sciences, 10(10), 3604. doi:10.3390/app10103604Jain, A., Krishnasamy, A., & V, P. (2020). Computational optimization of reactivity controlled compression ignition combustion to achieve high efficiency and clean combustion. International Journal of Engine Research, 22(7), 2213-2232. doi:10.1177/1468087420931730Claßen, J., Pischinger, S., Krysmon, S., Sterlepper, S., Dorscheidt, F., Doucet, M., … Thewes, S. C. (2020). Statistically supported real driving emission calibration: Using cycle generation to provide vehicle-specific and statistically representative test scenarios for Euro 7. International Journal of Engine Research, 21(10), 1783-1799. doi:10.1177/1468087420935221Di Maio, D., Beatrice, C., Fraioli, V., Napolitano, P., Golini, S., & Rutigliano, F. G. (2019). Modeling of Three-Way Catalyst Dynamics for a Compressed Natural Gas Engine during Lean–Rich Transitions. Applied Sciences, 9(21), 4610. doi:10.3390/app9214610Reitz, 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:10.1177/1468087419877990Kawaguchi, A., Wakisaka, Y., Nishikawa, N., Kosaka, H., Yamashita, H., Yamashita, C., … Tomoda, T. (2019). Thermo-swing insulation to reduce heat loss from the combustion chamber wall of a diesel engine. International Journal of Engine Research, 20(7), 805-816. doi:10.1177/1468087419852013Luján, J. M., Serrano, J. R., Piqueras, P., & Diesel, B. (2019). Turbine and exhaust ports thermal insulation impact on the engine efficiency and aftertreatment inlet temperature. Applied Energy, 240, 409-423. doi:10.1016/j.apenergy.2019.02.043Arnau, F. J., Martín, J., Pla, B., & Auñón, Á. (2020). Diesel engine optimization and exhaust thermal management by means of variable valve train strategies. International Journal of Engine Research, 22(4), 1196-1213. doi:10.1177/1468087419894804Maniatis, P., Wagner, U., & Koch, T. (2018). A model-based and experimental approach for the determination of suitable variable valve timings for cold start in partial load operation of a passenger car single-cylinder diesel engine. International Journal of Engine Research, 20(1), 141-154. doi:10.1177/1468087418817119Luján, J. M., Bermúdez, V., Piqueras, P., & García-Afonso, Ó. (2015). Experimental assessment of pre-turbo aftertreatment configurations in a single stage turbocharged diesel engine. Part 1: Steady-state operation. Energy, 80, 599-613. doi:10.1016/j.energy.2014.05.048Luján, J. M., Serrano, J. R., Piqueras, P., & García-Afonso, Ó. (2015). Experimental assessment of a pre-turbo aftertreatment configuration in a single stage turbocharged diesel engine. Part 2: Transient operation. Energy, 80, 614-627. doi:10.1016/j.energy.2014.12.017Serrano, J. R., Climent, H., Piqueras, P., & Angiolini, E. (2014). Analysis of fluid-dynamic guidelines in diesel particulate filter sizing for fuel consumption reduction in post-turbo and pre-turbo placement. Applied Energy, 132, 507-523. doi:10.1016/j.apenergy.2014.07.043Joergl, V., Keller, P., Weber, O., Mueller-Haas, K., & Konieczny, R. (2008). Influence of Pre Turbo Catalyst Design on Diesel Engine Performance, Emissions and Fuel Economy. SAE International Journal of Fuels and Lubricants, 1(1), 82-95. doi:10.4271/2008-01-0071Serrano, J. R., Bermúdez, V., Piqueras, P., & Angiolini, E. (2017). On the impact of DPF downsizing and cellular geometry on filtration efficiency in pre- and post-turbine placement. Journal of Aerosol Science, 113, 20-35. doi:10.1016/j.jaerosci.2017.07.014Kröcher, O., Elsener, M., Bothien, M.-R., & Dölling, W. (2014). Pre-Turbo Scr - Influence of Pressure on NOx Reduction. MTZ worldwide, 75(4), 46-51. doi:10.1007/s38313-014-0140-xBermúdez, V., Serrano, J. R., Piqueras, P., & García-Afonso, O. (2011). Assessment by means of gas dynamic modelling of a pre-turbo diesel particulate filter configuration in a turbocharged HSDI diesel engine under full-load transient operation. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 225(9), 1134-1155. doi:10.1177/0954407011402278Payri, F., Serrano, J. R., Piqueras, P., & García-Afonso, O. (2011). Performance Analysis of a Turbocharged Heavy Duty Diesel Engine with a Pre-turbo Diesel Particulate Filter Configuration. SAE International Journal of Engines, 4(2), 2559-2575. doi:10.4271/2011-37-0004Serrano, J. R., Guardiola, C., Piqueras, P., & Angiolini, E. (2014). Analysis of the Aftertreatment Sizing for Pre-Turbo DPF and DOC Exhaust Line Configurations. SAE Technical Paper Series. doi:10.4271/2014-01-1498Klaewkla, R., Arend, M., & F., W. (2011). A Review of Mass Transfer Controlling the Reaction Rate in Heterogeneous Catalytic Systems. Mass Transfer - Advanced Aspects. doi:10.5772/22962Piqueras, P., García, A., Monsalve-Serrano, J., & Ruiz, M. J. (2019). Performance of a diesel oxidation catalyst under diesel-gasoline reactivity controlled compression ignition combustion conditions. Energy Conversion and Management, 196, 18-31. doi:10.1016/j.enconman.2019.05.111Sampara, C. S., Bissett, E. J., & Chmielewski, M. (2007). Global Kinetics for a Commercial Diesel Oxidation Catalyst with Two Exhaust Hydrocarbons. Industrial & Engineering Chemistry Research, 47(2), 311-322. doi:10.1021/ie070813

Comparative study of the internal flow in diesel injection nozzles at cavitating conditions at different needle lifts with steady and transient simulations approaches

[EN] The motion of the needle during the injection process of a diesel injector has a marked influence on the internal flow, the fuel characteristics at the nozzle exit, the spray pattern and the fuel-air mixing process. The current paper is focused on the computational study of the internal flow and cavitation phenomena during the injection process, with inclusion of the opening where the needle is working at partial lifts. This study has been performed with a homogeneous equilibrium model (OpenFOAM) customized by the authors to simulate the real motion of the needle. The first part of the study covers the analysis of the whole injection process with a moving mesh using the boundary conditions provided by a one-dimensional (1D) model of the injector created in AMESim. This 1D model has offered the possibility of reproducing the movement of the needle with real lift law and real injection pressure evolution during the injection. Thus, it has been possible to compare the injection rate profiles provided by OpenFOAM against those obtained both in AMESim and experimentally. The second part compares the differences in mass flow, momentum flux, effective velocity and cavitation appearance between steady (fixed lifts) and transient (moving mesh) simulations. The aim of this comparison is to establish the differences between these two approaches. On the one hand is a more realistic approach in its use of transient simulations of the injection process and where the needle movement is taken into account. On the other hand, is the use of steady simulations at partial needle lifts. This analysis could be of interest to researchers devoted to the study of the diesel injection process since it could help to delimit the uncertainties involved in using the second approach which is more easily carried out, versus the first which is supposed to provide more realistic results.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 'Ministerio de Economa 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.; De La Morena, J.; Crialesi Esposito, M.; Martínez López, J. (2018). Comparative study of the internal flow in diesel injection nozzles at cavitating conditions at different needle lifts with steady and transient simulations approaches. Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering. 232(8):1060-1078. https://doi.org/10.1177/0954407017725672S10601078232

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