Optimization of spray break-up CFD simulations by combining Sigma-Y Eulerian atomization model with a response surface methodology under diesel engine-like conditions (ECN Spray A)

[EN] This work evaluates the performance of the Sigma-Y Eulerian atomization model at reproducing the internal structure of a diesel spray with a special focus on Sauter Mean Diameter (SMD) predictions. Modeling results have been compared to x-ray radiography measurements [21,24,38] which provided unique data within dense spray region. The first step corresponds to accurately reproduce the large scale spray dispersion. Among different RANS turbulence models, the standard k-s with the round jet corrected CIE value (1.60), has shown the best performance, as shown in [12]. Then, the study is devoted to the application and optimization of the predicted interphase surface density (E). In this work, a combination of CFD modeling and the statistical Design of Experiments (DOE) technique known as Response Surface Method (RSM) is applied in order to improve Sauter Mean Diameter (SMD) predictions from E equation compared to experimental measurements. In the investigation, two different optimizations are conducted for the three modeling parameters involved in the equation, following a Central Composite Design (CCD), leading to 15 simulations for each one. After that, both optimum sets of values are validated to assure the accuracy of the method and it is decided the best choice. Finally, different injection and ambient conditions are simulated, with those selected values, providing a remarkable improvement in the modeling performance.Authors acknowledge that part of this work was possible thanks to the Programa de Ayudas de Investigacion y Desarrollo (PAID 2013 3198) of the Universitat Politecnica de Valencia. Also this study was partially funded by the Spanish Ministry of Economy and Competitiveness in the frame of the COMEFF (TRA2014-59483R) project.Pandal-Blanco, A.; Payri, R.; García-Oliver, JM.; Pastor Enguídanos, JM. (2017). Optimization of spray break-up CFD simulations by combining Sigma-Y Eulerian atomization model with a response surface methodology under diesel engine-like conditions (ECN Spray A). Computers & Fluids. 156:9-20. doi:10.1016/j.compfluid.2017.06.022S92015

Combustion modeling in a pressurized gas turbine burner using Large-Eddy Simulations

The research leading to these results has received funding from the European Union's Horizon 2020 Programme under the ESTiMatE project, grant agreement No. 821418. The authors thankfully acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (IM-2020-3-0022, IM-2021-1-0016).García-Oliver, JM.; Pastor Enguídanos, JM.; Olmeda-Ramiro, I.; Both, A.; Mira, D. (2022). Combustion modeling in a pressurized gas turbine burner using Large-Eddy Simulations. 690-699. http://hdl.handle.net/10251/19067769069

A computational analysis of local flow for reacting Diesel sprays by means of an Eulerian CFD model

[EN] An implementation and validation of the coupled Sigma-gamma ADF model is presented in this work for reacting Diesel spray CFD simulations under a RANS turbulence modeling approach. An Approximated Diffusion Flamelet (ADF) model Michel et al. (2008) implemented in the OpenFOAM CFD open-source library by Winklinger (2014)15 fed with the spray description, i.e. mixing formation process, provided by the Sigma-gamma Eulerian atomization model Garcia-Oliver et al. (2013). In the present investigation, the Engine Combustion Network Spray A reference configuration is used for validation. Specifically, the model can provide accurate predictions of typical reacting spray metrics, such as the ignition delay and the lift-off length. Moreover, the internal structure is also fairly reproduced in terms of quasi-steady spatial distribution of formaldehyde and OH, related with low and high temperature reactions respectively. Additionally, modeling results have been compared to recent Particle image velocimetry (PIV) measurements Garcia-Oliver et al. (2017) under both inert and reacting conditions. Flow response to heat release is quantitatively predicted by the model, both in terms of local velocity increase as well as radial dilation. The model has been used to understand combustion-induced reduction in entrainment, in particular around the lift-off length location. Flow confinement does not seem to influence the global flame behaviour, even though some changes in the local flow hint can be observed when moving from an open to a closed domain. (C) 2017 Elsevier Ltd. All rights reserved.Authors acknowledge that this work was possible thanks to the Programa de Ayudas de Investigation y Desarrollo (PAID-2013 3198) of the Universitat Politecnica de Valencia. Also this study was partially funded by the Spanish Ministry of Economy and Competitiveness in the frame of the COMEFF(TRA2014-59483-R) project. Authors thank Gilles Bruneaux from IFPEN for the interesting suggestions and discussions.Pandal-Blanco, A.; García-Oliver, JM.; Novella Rosa, R.; Pastor Enguídanos, JM. (2018). A computational analysis of local flow for reacting Diesel sprays by means of an Eulerian CFD model. International Journal of Multiphase Flow. 99:257-272. https://doi.org/10.1016/j.ijmultiphaseflow.2017.10.010S2572729

A computational analysis of the impact of bore-to-stroke ratio on emissions and efficiency of a HSDI engine

[EN] Research on combustion systems for Internal Combustion Engines (ICE) is guided by the necessity of improving engine efficiency while achieving the pollutant regulations. In this framework, this study identifies and describes the effect of the bore-to-stroke ratio (B/S) on the combustion system performance and emissions by means of computational fluid dynamics (CFD). The study is applied to a 4-cylinder 4-stroke High Speed Direct Injection (HSDI) CI engine. It is divided in two parts, the first part is focused on one operating point and presents a detailed description of the main effects of different B/S ratios configurations, and the second part compares the results with different engine operating conditions. For both parts the air management, injection settings and compression ratio were kept constant in order to isolate the impact of the B/S ratio. The results confirmed that the indicated thermal efficiency was increased for lower B/S ratio because of the combustion chamber surface area decrease and faster combustion. Regarding the emissions, NOx and soot presented a strong and opposed dependence on B/S ratio generated mostly due to enhanced air¿fuel mixing for lower B/S ratio. Finally, those trends were proven to be independent from the operating condition, giving the study a more general value.Authors acknowledge that this work was possible thanks to the Ayuda para la Formation de Profesorado Universitario (FPU 13/02817) belonging to the Subprogramas de Formacion y de Movilidad del Ministerio de Educacion, Cultura y Deporte from Spain. The authors would also like to recognize the funding and technical support from PSA GroupeBenajes, J.; Novella Rosa, R.; Pastor Enguídanos, JM.; Hernández-López, A.; Duverger, T. (2017). A computational analysis of the impact of bore-to-stroke ratio on emissions and efficiency of a HSDI engine. Applied Energy. 205:903-910. https://doi.org/10.1016/j.apenergy.2017.08.023S90391020

Effect of turbulence model and inlet boundary condition on the Diesel spray behavior simulated by an Eulerian Spray Atomization (ESA) model

Simulating liquid spray first and second atomization is not an easy task. Many models have been developed over the past years, but Eulerian ones have proved their better performance for the dense zone of the spray. In this work a new compressible Eulerian model is used to compute the internal flow together with the spray. Up to five two-equation turbulence models have been tested and its influence is remark- able in terms of spray behavior, but also greatly affects the mass flow rate and the momentum flux. At the end, SST k x model proves to be best than the others. Additionally, different types of inlet boundary con- ditions have been also tested and analyzed. Results when compared with previously obtained experimental data show that the commonly used for external flow time-varying velocity boundary condition gives also good performance for the internal flow.This research was funded in the frame of Project "Compresion de la influencia de combustibles no convencionales en el proceso de inyeccion y combustion tipo Diesel" reference TRA2012-36932 from Ministerio de Economia y Competitividad (Spanish Ministry of Economy).Salvador Rubio, FJ.; Gimeno García, J.; Pastor Enguídanos, JM.; Martí Aldaraví, P. (2014). Effect of turbulence model and inlet boundary condition on the Diesel spray behavior simulated by an Eulerian Spray Atomization (ESA) model. International Journal of Multiphase Flow. 65:105-116. https://doi.org/10.1016/j.ijmultiphaseflow.2014.06.003S1051166

Effects of piston bowl geometry on Reactivity Controlled Compression Ignition heat transfer and combustion losses at different engine loads

This work investigates the effects of the piston bowl geometry on RCCI (Reactivity Controlled Compression Ignition) heat transfer and combustion losses and its repercussion on the engine efficiency. For this purpose, three piston geometries with compression ratio 14.4:1 have been studied and compared by means of computational modeling. In addition, the engine operating conditions proposed at low, medium and high load were also validated experimentally in a heavy-duty single-cylinder engine adapted for dual fuel operation. The engine speed was kept constant at 1200 rev/min during the research. Results suggest that heat flux through the piston surface represent the major portion of the heat transfer energy. Thus, the comparison of the three geometries demonstrates that reduced piston surface area and reduced charge motion, are the key factors to improve the gross indicated efficiency over the different engine loads. Moreover, it is found that a shallow piston geometry with a smooth transition from the center to the squish region, with a 16% reduced surface area, strongly improves the gross work at low load. However, this gain diminishes due to increased combustion losses as engine load increases. Finally, an intermediate geometry was confirmed as the best balanced piston geometry for RCCI operation over the three different loads.The authors would like to acknowledge VOLVO Group Trucks Technology for supporting this research and to express their gratitude to CONVERGENT SCIENCE Inc. for their kind support for performing the CFD calculations using CONVERGE software.Benajes Calvo, JV.; García Martínez, A.; Pastor Enguídanos, JM.; Monsalve Serrano, J. (2016). Effects of piston bowl geometry on Reactivity Controlled Compression Ignition heat transfer and combustion losses at different engine loads. Energy. 98:64-77. doi:10.1016/j.energy.2016.01.014S64779

Computational optimization of the combustion system of a heavy duty direct injection diesel engine operating with dimethyl-ether

[EN] A genetic algorithm optimization methodology is applied to the design of the combustion system of a heavy-duty diesel engine fueled with dimethyl ether (DME). The optimization includes the key combustion system related hardware, bowl geometry and injection nozzle design, together with the most relevant air management and injection settings. The GA was linked to the KIVA computational fluid dynamics code and an automated grid generation tool to perform a single-objective optimization. The optimization target focused on maximizing efficiency, while keeping NOx emissions, peak pressure and maximum pressure rise rate under the baseline engine levels. This research work not only provides the optimum combustion system definition, but also the cause-effect relation between the inputs and outputs under investigation, identifying the most relevant parameters controlling the performance of a DME fueled engine. Piston bowl geometry is found to primarily influence heat transfer and combustion efficiency due to its impact on the surface area and fuel distribution, respectively. Mixing is most affected by the injection system parameters. Finally, the optimum DME engine configuration provides 6.9% absolute net indicated efficiency improvement over the baseline engine fueled with DME. This study confirms the potential of DME as a promising fuel for the future generation of compression ignition engines and demonstrates the need to co-optimize the fuel and combustion system.Authors acknowledge that this work was possible thanks to the Ayuda para la Formacion de Profesorado Universitario (FPU 13/02817) belonging to the Subprogramas de Formacion y de Movilidad del Ministerio de Educacion, Cultura y Deporte from Spain.Benajes, J.; Novella Rosa, R.; Pastor Enguídanos, JM.; Hernández-López, A.; Kokjohn, SL. (2018). Computational optimization of the combustion system of a heavy duty direct injection diesel engine operating with dimethyl-ether. Fuel. 218:127-139. https://doi.org/10.1016/j.fuel.2018.01.020S12713921

Optimization of the Combustion System of a Medium Duty Direct Injection Diesel Engine by Combining CFD modeling with Experimental Validation

The research in the field of internal combustion engines is currently driven by the needs of decreasing fuel consumption and CO2 emissions, while fulfilling the increasingly stringent pollutant emissions regulations. In this framework, this research work focuses on describing a methodology for optimizing the combustion system of compression ignition (CI) engines, by combining computational fluid dynamics (CFD) modeling, and the statistical Design of Experiments (DOE) technique known as Response Surface Method (RSM). As a key aspect, in addition to the definition of the optimum set of values for the input parameters, this methodology is extremely useful to gain knowledge on the cause/effect relationships between the input and output parameters under investigation. This methodology is applied in two sequential studies to the optimization of the combustion system of a 4-cylinder 4-stroke Medium Duty Direct Injection (DI) CI engine, minimizing the fuel consumption while fulfilling the emission limits in terms of NOx and soot. The first study targeted four optimization parameters related to the engine hardware including piston bowl geometry, injector nozzle configuration and mean swirl number (MSN) induced by the intake manifold design. After the analysis of the results, the second study extended to six parameters, limiting the optimization of the engine hardware to the bowl geometry, but including the key air management and injection settings. For both studies, the simulation plans were defined following a Central Composite Design (CCD), providing 25 and 77 simulations respectively. The results confirmed the limited benefits, in terms of fuel consumption, around 2%, with constant NOx emission achieved when optimizing the engine hardware, while keeping air management and injection settings. Thus, including air management and injection settings in the optimization is mandatory to significantly decrease the fuel consumption, by around 5%, while keeping the emission limits.Benajes Calvo, JV.; Novella Rosa, R.; Pastor Enguídanos, JM.; Hernández-López, A.; Hasegawa, M.; Tsuji, N.; Emi, M.... (2016). Optimization of the Combustion System of a Medium Duty Direct Injection Diesel Engine by Combining CFD modeling with Experimental Validation. Energy Conversion and Management. 110:212-229. doi:10.1016/j.enconman.2015.12.010S21222911

One-dimensional diesel spray modeling of multicomponent fuels

[EN] The present work reports a one-dimensional model to predict the liquid length and spray penetration of diesel sprays when using blends of single-component fuels. A high-pressure liquid-vapour equilibrium has been implemented by means of fugacity coefficients, together with the hypothesis of a real-gas mixture to calculate the partial enthalpy of each component. The model has been validated in a first step by means of an experimental study using binary blends of n-decane and n-hexadecane, where the temporal evolution of the liquid length and vapor spray penetration have been measured. Results show that the model predicts adequately the spray penetration for the different fuels at various conditions. A six-component fuel has also been investigated. Results indicate that this fuel has a very similar evaporative behavior to n-hexadecane, which is confirmed by both experiments and model predictions.Part of this work has been developed within the frame of project B03T02 Modelling of Emission Formation and Exhaust Gas Aftertreatment, Multicomponent diesel Combustion Modelling and Validation with financial support of the "COMET K2-Competence Centres for Excellent Technologies Programme" of the Austrian Federal Ministry for Transport, Innovation and Technology (BMVIT), the Austrian Federal Ministry of Economy, Family and Youth (BMWFJ), the Austrian Research Promotion Agency (FFG), the Province of Styria, and the Styrian Business Promotion Agency (SFG). Thanks are also given to the supporting industrial and scientific project partners, namely Kompetenzzentrum-Das Virtuelle Fahrzeug Forschungsgesellschaft mbH (ViF), AVL List GmbH, OMV Refining and Marketing GmbH and Institute for Internal Combustion Engines and Thermodynamics (IVT) Graz University of Technology. Support for this research was partially provided by the Generalitat Valenciana inside the program Ajudes per a la realitzacio de projectes d'I+D per a grups de investigacio emergent (reference GV/2013/041), which is gratefully acknowledged. Also, the authors would like to thank the Pontificia Universidad Catolica del Peru for financing the first year of studies of W. Vera-Tudela and making it possible for him to start his program of PhD at the Universitat Politecnica de Valencia.Pastor Soriano, JV.; García Oliver, JM.; Pastor Enguídanos, JM.; Vera-Tudela Fajardo, WM. (2015). One-dimensional diesel spray modeling of multicomponent fuels. Atomization and Sprays. 25(6):485-517. https://doi.org/10.1615/AtomizSpr.2014010370S48551725