Soot temperature characterization of spray a flames by combined extinction and radiation methodology

[EN] Even though different optical techniques have been applied on 'Spray A' in-flame soot quantification within Engine Combustion Network in recent years, little information can be found for soot temperature measurement. In this study, a combined extinction and radiation methodology has been developed with different wavelengths and applied on quasi-steady Diesel flame to obtain the soot amount and temperature distribution simultaneously by considering self-absorption issues. All the measurements were conducted in a constant pressure combustion chamber. The fuel as well as the operating conditions and the injector used were chosen following the guidelines of the Engine Combustion Network. Uncertainty caused by wavelength selection was evaluated. Additionally, temperature-equivalence ratio maps were constructed by combining the measurements with a 1D spray model. Temperature fields during the quasi-steady combustion phase show peak temperatures around the limit of the radiation field, in agreement with a typical diffusion flame structure. Effects of different operating parameters on soot formation and temperature were investigated. Soot temperature increases dramatically with oxygen concentration, but it shows much less sensitivity with ambient temperature and injection pressure, which on the other hand have significant effects on soot production. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.This study was partially funded by the Ministerio de Economia y Competitividad from Spain in the frame of the CHEST Project (TRA2017-89139-C2-1-R) and China Postdoctoral Science Foundation (2018M642176). This study was also partially supported by State Key Laboratory of Engines, Tianjin University.Xuan, T.; Desantes J.M.; Pastor, JV.; García-Oliver, JM. (2019). Soot temperature characterization of spray a flames by combined extinction and radiation methodology. Combustion and Flame. 204:290-303. https://doi.org/10.1016/j.combustflame.2019.03.02329030320

Experimental validation and analysis of seven different chemical kinetic mechanisms for n-dodecane using a Rapid Compression-Expansion Machine

[EN] Seven different chemical kinetic mechanisms for n-dodecane, two detailed and five reduced, have been evaluated under Engine Combustion Network (ECN) thermodynamic conditions by comparison to experimental measurements in a Rapid Compression-Expansion Machine (RCEM). The target ECN conditions are imposed at Top Dead Center (TDC), which cover a wide range of temperatures (from 850 K to 1000 K), oxygen molar fractions (0.21 and 0.15) and equivalence ratios (0.8, 0.9 and 1), while the pressure is fixed to keep a constant density at TDC equal to 22.8 kg/m(3). The results obtained have been used to validate the chemical kinetic simulations, which have been performed with CHEMKIN, by comparing both cool flames and high temperature ignition delays, as well as the heat released in each stage of the combustion process in case of having a two-stage ignition pattern. The experimental results show good agreement with the chemical kinetic simulations. In fact, the mean relative deviation in ignition delay between experiments and simulations among all the chemical mechanisms is equal to 18.0% (3 CAD) for both cool flames and high temperature ignition. In general, closer correspondence has been obtained for the ignition delay referred to the high-temperature stage of the process, being the cool flames phenomenon more difficult to reproduce. Moreover, the differences between the reduced mechanisms and the most detailed one have been analyzed, concluding that the enhanced specific reaction rates of the most reduced mechanisms cause differences not only on the ignition delays, but also on the Negative Temperature Coefficient (NTC) behavior and on the heat released during cool flames. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.The authors would also like to thank the Spanish Ministry of Education for financing the PhD. Studies of Dario Lopez-Pintor (grant FPU13/02329). This study was partially funded by the Spanish Ministry of Economy and Competitiveness in the frame of the COMEFF (TRA2014-59483-R) project.Desantes, J.; López, JJ.; García-Oliver, JM.; López-Pintor, D. (2017). Experimental validation and analysis of seven different chemical kinetic mechanisms for n-dodecane using a Rapid Compression-Expansion Machine. Combustion and Flame. 182:76-89. https://doi.org/10.1016/j.combustflame.2017.04.004S768918

A phenomenological explanation of the autoignition propagation under HCCI conditions

[EN] A phenomenological explanation about the autoignition propagation under HCCI conditions is developed in this paper. To do so, diffusive effects from the burned zones to the fresh mixture, pressure waves based effects and expansion effects caused by combustion are taken into account. Additionally, different Damkohler numbers have been defined and evaluated in order to characterize the phenomenon and quantify the relevance of each effect. The theoretical explanation has been evaluated by means of chemiluminescence measurements performed in a Rapid Compression Expansion Machine (RCEM), which allow to estimate the velocity of propagation of the autoignition front. The results showed that under HCCI conditions the autoignition propagation is controlled, in general, by the pressure waves established in the combustion chamber, since the characteristic time of the autoignition propagation is too short to assume the absence of pressure gradients in the chamber. Thus, the thermodynamic conditions reached behind the pressure wave promote the autoignition and explain the high propagation velocities associated to the reaction front. Besides, the results also showed that the contribution of diffusive phenomena on the propagation is negligible, since the characteristic time of diffusion is too long compared to the characteristic time of the autoignition propagation. Finally, the experimental measurements showed that the autoignition propagation is affected by a really relevant cycle-to-cycle variation. The turbulence generated by the combustion has, by definition, an aleatory behavior, leading to random heterogeneity distribution and, therefore, to somewhat random autoignition propagation.The authors would like to thank different members of the CMT-Motores TTrmicos team of the Universitat Politecnica de Valencia for their contribution to this work. The authors would also like to thank the Spanish Ministry of Education for financing the PhD. Studies of Dario Lopez-Pintor (grant FPU13/02329). This research has been partially funded by FEDER and the Spanish Government through project TRA2015-67136-R.Desantes, J.; López, JJ.; García-Oliver, JM.; López-Pintor, D. (2017). A phenomenological explanation of the autoignition propagation under HCCI conditions. Fuel. 206:43-57. https://doi.org/10.1016/j.fuel.2017.05.075S435720

A numerical study of the effect of nozzle diameter on diesel combustion ignition and flame stabilization

This is the author's version of a work that was accepted for publication in International Journal of Engine Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published as https://doi.org/10.1177/1468087419864203.[EN] The role of nozzle diameter on diesel combustion is studied by performing computational fluid dynamics calculations of Spray A and Spray D from the Engine Combustion Network. These are well-characterized single-hole sprays in a quiescent environment chamber with thermodynamic conditions representative of modern diesel engines. First, the inert spray evolution is described with the inclusion of the concept of mixing trajectories and local residence time into the analysis. Such concepts enable the quantification of the mixing rate, showing that it decreases with the increase in nozzle diameter. In a second step, the reacting spray evolution is studied focusing on the local heat release rate distribution during the auto-ignition sequence and the quasi-steady state. The capability of a well-mixed-based and a flamelet-based combustion model to predict diesel combustion is also assessed. On one hand, results show that turbulence-chemistry interaction has a profound effect on the description of the reacting spray evolution. On the other hand, the mixing rate, characterized in terms of the local residence time, drives the main changes introduced by the increase of the nozzle diameter when comparing Spray A and Spray D.The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: The work was partially funded by the Government of Spain through the CHEST Project (TRA2017-89139-C2-1-R) and by Universitat Politecnica de Valencia through the Programa de Ayudas de Investigaciony Desarrollo (PAID-01-16).Desantes Fernández, JM.; García-Oliver, JM.; Novella Rosa, R.; Pachano-Prieto, LM. (2020). A numerical study of the effect of nozzle diameter on diesel combustion ignition and flame stabilization. International Journal of Engine Research. 21(1):101-121. https://doi.org/10.1177/1468087419864203S101121211Pickett, L. M., & Siebers, D. L. (2002). An investigation of diesel soot formation processes using micro-orifices. Proceedings of the Combustion Institute, 29(1), 655-662. doi:10.1016/s1540-7489(02)80084-0Pickett, L. M., & Siebers, D. L. (2005). Orifice Diameter Effects on Diesel Fuel Jet Flame Structure. Journal of Engineering for Gas Turbines and Power, 127(1), 187-196. doi:10.1115/1.1760525Du, C., Andersson, S., & Andersson, M. (2018). Two-dimensional measurements of soot in a turbulent diffusion diesel flame: the effects of injection pressure, nozzle orifice diameter, and gas density. Combustion Science and Technology, 190(9), 1659-1688. doi:10.1080/00102202.2018.1461850Ishibashi, R., & Tsuru, D. (2016). An optical investigation of combustion process of a direct high-pressure injection of natural gas. Journal of Marine Science and Technology, 22(3), 447-458. doi:10.1007/s00773-016-0422-xPang, K. M., Jangi, M., Bai, X.-S., Schramm, J., & Walther, J. H. (2017). Effects of Nozzle Diameter on Diesel Spray Flames: A numerical study using an Eulerian Stochastic Field Method. Energy Procedia, 142, 1028-1033. doi:10.1016/j.egypro.2017.12.350Pickett, L. M., Manin, J., Genzale, C. L., Siebers, D. L., Musculus, M. P. B., & Idicheria, C. A. (2011). Relationship Between Diesel Fuel Spray Vapor Penetration/Dispersion and Local Fuel Mixture Fraction. SAE International Journal of Engines, 4(1), 764-799. doi:10.4271/2011-01-0686García-Oliver, J. M., Malbec, L.-M., Toda, H. B., & Bruneaux, G. (2017). A study on the interaction between local flow and flame structure for mixing-controlled Diesel sprays. Combustion and Flame, 179, 157-171. doi:10.1016/j.combustflame.2017.01.023Dahms, R. N., Paczko, G. A., Skeen, S. A., & Pickett, L. M. (2017). Understanding the ignition mechanism of high-pressure spray flames. Proceedings of the Combustion Institute, 36(2), 2615-2623. doi:10.1016/j.proci.2016.08.023Gimeno, J., Martí-Aldaraví, P., Carreres, M., & Peraza, J. E. (2018). Effect of the nozzle holder on injected fuel temperature for experimental test rigs and its influence on diesel sprays. International Journal of Engine Research, 19(3), 374-389. doi:10.1177/1468087417751531Matusik, K. E., Duke, D. J., Kastengren, A. L., Sovis, N., Swantek, A. B., & Powell, C. F. (2017). High-resolution X-ray tomography of Engine Combustion Network diesel injectors. International Journal of Engine Research, 19(9), 963-976. doi:10.1177/1468087417736985Pandurangi, S. S., Bolla, M., Wright, Y. M., Boulouchos, K., Skeen, S. A., Manin, J., & Pickett, L. M. (2016). Onset and progression of soot in high-pressure n-dodecane sprays under diesel engine conditions. International Journal of Engine Research, 18(5-6), 436-452. doi:10.1177/1468087416661041Aubagnac-Karkar, D., Michel, J.-B., Colin, O., & Darabiha, N. (2017). Combustion and soot modelling of a high-pressure and high-temperature Dodecane spray. International Journal of Engine Research, 19(4), 434-448. doi:10.1177/1468087417714351Ihme, M., Ma, P. C., & Bravo, L. (2018). Large eddy simulations of diesel-fuel injection and auto-ignition at transcritical conditions. International Journal of Engine Research, 20(1), 58-68. doi:10.1177/1468087418819546Yue, Z., & Reitz, R. D. (2017). An equilibrium phase spray model for high-pressure fuel injection and engine combustion simulations. International Journal of Engine Research, 20(2), 203-215. doi:10.1177/1468087417744144Bhattacharjee, S., & Haworth, D. C. (2013). Simulations of transient n-heptane and n-dodecane spray flames under engine-relevant conditions using a transported PDF method. Combustion and Flame, 160(10), 2083-2102. doi:10.1016/j.combustflame.2013.05.003Pei, Y., Hawkes, E. R., & Kook, S. (2013). Transported probability density function modelling of the vapour phase of an n-heptane jet at diesel engine conditions. Proceedings of the Combustion Institute, 34(2), 3039-3047. doi:10.1016/j.proci.2012.07.033Pang, K. M., Jangi, M., Bai, X.-S., Schramm, J., & Walther, J. H. (2018). Modelling of diesel spray flames under engine-like conditions using an accelerated Eulerian Stochastic Field method. Combustion and Flame, 193, 363-383. doi:10.1016/j.combustflame.2018.03.030D’Errico, G., Lucchini, T., Contino, F., Jangi, M., & Bai, X.-S. (2014). Comparison of well-mixed and multiple representative interactive flamelet approaches for diesel spray combustion modelling. Combustion Theory and Modelling, 18(1), 65-88. doi:10.1080/13647830.2013.860238Kösters, A., Karlsson, A., Oevermann, M., D’Errico, G., & Lucchini, T. (2015). RANS predictions of turbulent diffusion flames: comparison of a reactor and a flamelet combustion model to the well stirred approach. Combustion Theory and Modelling, 19(1), 81-106. doi:10.1080/13647830.2014.982342Lucchini, T., D’Errico, G., Onorati, A., Frassoldati, A., Stagni, A., & Hardy, G. (2017). Modeling Non-Premixed Combustion Using Tabulated Kinetics and Different Fame Structure Assumptions. SAE International Journal of Engines, 10(2), 593-607. doi:10.4271/2017-01-0556Pal, P., Keum, S., & Im, H. G. (2015). Assessment of flamelet versus multi-zone combustion modeling approaches for stratified-charge compression ignition engines. International Journal of Engine Research, 17(3), 280-290. doi:10.1177/1468087415571006Pope, S. B. (1978). An explanation of the turbulent round-jet/plane-jet anomaly. AIAA Journal, 16(3), 279-281. doi:10.2514/3.7521Novella, R., García, A., Pastor, J. M., & Domenech, V. (2011). The role of detailed chemical kinetics on CFD diesel spray ignition and combustion modelling. Mathematical and Computer Modelling, 54(7-8), 1706-1719. doi:10.1016/j.mcm.2010.12.048CONVERGE manual. Madison, WI: Convergent Science, 2016.Yao, T., Pei, Y., Zhong, B.-J., Som, S., Lu, T., & Luo, K. H. (2017). A compact skeletal mechanism for n-dodecane with optimized semi-global low-temperature chemistry for diesel engine simulations. Fuel, 191, 339-349. doi:10.1016/j.fuel.2016.11.083Perez E. Application of a flamelet-based combustion model to diesel-like reacting sprays. Unpublished PhD Thesis, Universitat Politècnica de València, Valencia, 2019.Peters, N. (2000). Turbulent Combustion. doi:10.1017/cbo9780511612701Naud, B., Novella, R., Pastor, J. M., & Winklinger, J. F. (2015). RANS modelling of a lifted H2/N2 flame using an unsteady flamelet progress variable approach with presumed PDF. Combustion and Flame, 162(4), 893-906. doi:10.1016/j.combustflame.2014.09.014Payri, R., García-Oliver, J. M., Xuan, T., & Bardi, M. (2015). A study on diesel spray tip penetration and radial expansion under reacting conditions. Applied Thermal Engineering, 90, 619-629. doi:10.1016/j.applthermaleng.2015.07.042Narayanaswamy, K., Pepiot, P., & Pitsch, H. (2014). A chemical mechanism for low to high temperature oxidation of n-dodecane as a component of transportation fuel surrogates. Combustion and Flame, 161(4), 866-884. doi:10.1016/j.combustflame.2013.10.012Kahila, H., Wehrfritz, A., Kaario, O., Ghaderi Masouleh, M., Maes, N., Somers, B., & Vuorinen, V. (2018). Large-eddy simulation on the influence of injection pressure in reacting Spray A. Combustion and Flame, 191, 142-159. doi:10.1016/j.combustflame.2018.01.004Pang, K. M., Jangi, M., Bai, X.-S., Schramm, J., Walther, J. H., & Glarborg, P. (2019). Effects of ambient pressure on ignition and flame characteristics in diesel spray combustion. Fuel, 237, 676-685. doi:10.1016/j.fuel.2018.10.020Tagliante, F., Poinsot, T., Pickett, L. M., Pepiot, P., Malbec, L.-M., Bruneaux, G., & Angelberger, C. (2019). A conceptual model of the flame stabilization mechanisms for a lifted Diesel-type flame based on direct numerical simulation and experiments. Combustion and Flame, 201, 65-77. doi:10.1016/j.combustflame.2018.12.00

Optical study on characteristics of non-reacting and reacting diesel spray with different strategies of split injection

[EN] Even though studies on split-injection strategies have been published in recent years, there are still many remaining questions about how the first injection affects the mixing and combustion processes of the second one by changing the dwell time between both injection events or by the first injection quantity. In this article, split-injection diesel sprays with different injection strategies are investigated. Visualization of n-dodecane sprays was carried out under both non-reacting and reacting operating conditions in an optically accessible two-stroke engine equipped with a single-hole diesel injector. High-speed Schlieren imaging was applied to visualize the spray geometry development, while diffused backgroundillumination extinction imaging was applied to quantify the instantaneous soot production (net result of soot formation and oxidation). For non-reacting conditions, it was found that the vapor phase of second injection penetrates faster with a shorter dwell time and independently of the duration of the first injection. This could be explained in terms of onedimensional spray model results, which provided information on the local mixing and momentum state within the flow. Under reacting conditions, interaction between the second injection and combustion recession of the first injection is observed, resulting in shorter ignition delay and lift-off compared to the first injection. However, soot production behaves differently with different injection strategies. The maximum instantaneous soot mass produced by the second injection increases with a shorter dwell time and with longer first injection duration.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was partially funded by the Spanish Ministry of Economy and Competitiveness in the frame of the advanced spray combustion models for efficient powertrains (COMEFF) (TRA2014-59483-R) project. Funding for Tiemin Xuan's PhD studies was granted by Universitat Politecnica de Valencia through the Programa de Apoyo para la Investigacion y Desarrollo (PAID) (grant reference FPI-2015-S2-1068)Desantes, J.; García-Oliver, JM.; García Martínez, A.; Xuan, T. (2019). Optical study on characteristics of non-reacting and reacting diesel spray with different strategies of split injection. International Journal of Engine Research. 20(6):606-623. https://doi.org/10.1177/1468087418773012S606623206Arrègle, J., Pastor, J. V., López, J. J., & García, A. (2008). Insights on postinjection-associated soot emissions in direct injection diesel engines. Combustion and Flame, 154(3), 448-461. doi:10.1016/j.combustflame.2008.04.021Mendez, S., & Thirouard, B. (2008). Using Multiple Injection Strategies in Diesel Combustion: Potential to Improve Emissions, Noise and Fuel Economy Trade-Off in Low CR Engines. SAE International Journal of Fuels and Lubricants, 1(1), 662-674. doi:10.4271/2008-01-1329He, Z., Xuan, T., Jiang, Z., & Yan, Y. (2013). Study on effect of fuel injection strategy on combustion noise and exhaust emission of diesel engine. Thermal Science, 17(1), 81-90. doi:10.2298/tsci120603159hKook, S., Pickett, L. M., & Musculus, M. P. B. (2009). Influence of Diesel Injection Parameters on End-of-Injection Liquid Length Recession. SAE International Journal of Engines, 2(1), 1194-1210. doi:10.4271/2009-01-1356Musculus, M. P. B., & Kattke, K. (2009). Entrainment Waves in Diesel Jets. SAE International Journal of Engines, 2(1), 1170-1193. doi:10.4271/2009-01-1355O’Connor, J., Musculus, M. P. B., & Pickett, L. M. (2016). Effect of post injections on mixture preparation and unburned hydrocarbon emissions in a heavy-duty diesel engine. Combustion and Flame, 170, 111-123. doi:10.1016/j.combustflame.2016.03.031O’Connor, J., & Musculus, M. (2013). Post Injections for Soot Reduction in Diesel Engines: A Review of Current Understanding. SAE International Journal of Engines, 6(1), 400-421. doi:10.4271/2013-01-0917O’Connor, J., & Musculus, M. (2014). In-Cylinder Mechanisms of Soot Reduction by Close-Coupled Post-Injections as Revealed by Imaging of Soot Luminosity and Planar Laser-Induced Soot Incandescence in a Heavy-Duty Diesel Engine. SAE International Journal of Engines, 7(2), 673-693. doi:10.4271/2014-01-1255Bruneaux, G., & Maligne, D. (2009). Study of the Mixing and Combustion Processes of Consecutive Short Double Diesel Injections. SAE International Journal of Engines, 2(1), 1151-1169. doi:10.4271/2009-01-1352Pickett, L. M., Kook, S., & Williams, T. C. (2009). Transient Liquid Penetration of Early-Injection Diesel Sprays. SAE International Journal of Engines, 2(1), 785-804. doi:10.4271/2009-01-0839Skeen, S., Manin, J., & Pickett, L. M. (2015). Visualization of Ignition Processes in High-Pressure Sprays with Multiple Injections of n-Dodecane. SAE International Journal of Engines, 8(2), 696-715. doi:10.4271/2015-01-0799Bolla, M., Chishty, M. A., Hawkes, E. R., & Kook, S. (2017). Modeling combustion under engine combustion network Spray A conditions with multiple injections using the transported probability density function method. International Journal of Engine Research, 18(1-2), 6-14. doi:10.1177/1468087416689174Blomberg, C. K., Zeugin, L., Pandurangi, S. S., Bolla, M., Boulouchos, K., & Wright, Y. M. (2016). Modeling Split Injections of ECN «Spray A» Using a Conditional Moment Closure Combustion Model with RANS and LES. SAE International Journal of Engines, 9(4), 2107-2119. doi:10.4271/2016-01-2237Cung, K., Moiz, A., Johnson, J., Lee, S.-Y., Kweon, C.-B., & Montanaro, A. (2015). Spray–combustion interaction mechanism of multiple-injection under diesel engine conditions. Proceedings of the Combustion Institute, 35(3), 3061-3068. doi:10.1016/j.proci.2014.07.054Moiz, A. A., Cung, K. D., & Lee, S.-Y. (2017). Simultaneous Schlieren–PLIF Studies for Ignition and Soot Luminosity Visualization With Close-Coupled High-Pressure Double Injections of n-Dodecane. Journal of Energy Resources Technology, 139(1). doi:10.1115/1.4035071Maes, N., Bakker, P. C., Dam, N., & Somers, B. (2017). Transient Flame Development in a Constant-Volume Vessel Using a Split-Scheme Injection Strategy. SAE International Journal of Fuels and Lubricants, 10(2), 318-327. doi:10.4271/2017-01-0815Moiz, A. A., Ameen, M. M., Lee, S.-Y., & Som, S. (2016). Study of soot production for double injections of n-dodecane in CI engine-like conditions. Combustion and Flame, 173, 123-131. doi:10.1016/j.combustflame.2016.08.005PASTOR, J., JAVIERLOPEZ, J., GARCIA, J., & PASTOR, J. (2008). A 1D model for the description of mixing-controlled inert diesel sprays. Fuel, 87(13-14), 2871-2885. doi:10.1016/j.fuel.2008.04.017Desantes, J. M., Pastor, J. V., García-Oliver, J. M., & Pastor, J. M. (2009). A 1D model for the description of mixing-controlled reacting diesel sprays. Combustion and Flame, 156(1), 234-249. doi:10.1016/j.combustflame.2008.10.008Pastor, J., Garcia-Oliver, J. M., Garcia, A., Zhong, W., Micó, C., & Xuan, T. (2017). An Experimental Study on Diesel Spray Injection into a Non-Quiescent Chamber. SAE International Journal of Fuels and Lubricants, 10(2), 394-406. doi:10.4271/2017-01-0850Settles, G. S. (2001). Schlieren and Shadowgraph Techniques. doi:10.1007/978-3-642-56640-0Pastor, J. V., Payri, R., Garcia-Oliver, J. M., & Briceño, F. J. (2013). Schlieren Methodology for the Analysis of Transient Diesel Flame Evolution. SAE International Journal of Engines, 6(3), 1661-1676. doi:10.4271/2013-24-0041Pastor, J. V., Garcia-Oliver, J. M., Novella, R., & Xuan, T. (2015). Soot Quantification of Single-Hole Diesel Sprays by Means of Extinction Imaging. SAE International Journal of Engines, 8(5), 2068-2077. doi:10.4271/2015-24-2417Pickett, L. M., & Siebers, D. L. (2004). Soot in diesel fuel jets: effects of ambient temperature, ambient density, and injection pressure. Combustion and Flame, 138(1-2), 114-135. doi:10.1016/j.combustflame.2004.04.006Ko¨ylu¨, U. O., & Faeth, G. M. (1994). Optical Properties of Overfire Soot in Buoyant Turbulent Diffusion Flames at Long Residence Times. Journal of Heat Transfer, 116(1), 152-159. doi:10.1115/1.2910849Manin, J., Pickett, L. M., & Skeen, S. A. (2013). Two-Color Diffused Back-Illumination Imaging as a Diagnostic for Time-Resolved Soot Measurements in Reacting Sprays. SAE International Journal of Engines, 6(4), 1908-1921. doi:10.4271/2013-01-2548Choi, M. Y., Mulholland, G. W., Hamins, A., & Kashiwagi, T. (1995). Comparisons of the soot volume fraction using gravimetric and light extinction techniques. Combustion and Flame, 102(1-2), 161-169. doi:10.1016/0010-2180(94)00282-wKnox, B. W., & Genzale, C. L. (2015). Reduced-order numerical model for transient reacting diesel sprays with detailed kinetics. International Journal of Engine Research, 17(3), 261-279. doi:10.1177/1468087415570765Burke, S. P., & Schumann, T. E. W. (1928). Diffusion Flames. Industrial & Engineering Chemistry, 20(10), 998-1004. doi:10.1021/ie50226a005Desantes, J. M., García-Oliver, J. M., Xuan, T., & Vera-Tudela, W. (2017). A study on tip penetration velocity and radial expansion of reacting diesel sprays with different fuels. Fuel, 207, 323-335. doi:10.1016/j.fuel.2017.06.108Nerva, J.-G. (s. f.). An Assessment of fuel physical and chemical properties in the combustion of a Diesel spray. doi:10.4995/thesis/10251/29767Payri, R., Salvador, F. J., Gimeno, J., & Bracho, G. (2008). A NEW METHODOLOGY FOR CORRECTING THE SIGNAL CUMULATIVE PHENOMENON ON INJECTION RATE MEASUREMENTS. Experimental Techniques, 32(1), 46-49. doi:10.1111/j.1747-1567.2007.00188.xPayri, R., Gimeno, J., Novella, R., & Bracho, G. (2016). On the rate of injection modeling applied to direct injection compression ignition engines. International Journal of Engine Research, 17(10), 1015-1030. doi:10.1177/1468087416636281Malbec, L.-M., Eagle, W. E., Musculus, M. P. B., & Schihl, P. (2015). Influence of Injection Duration and Ambient Temperature on the Ignition Delay in a 2.34L Optical Diesel Engine. SAE International Journal of Engines, 9(1), 47-70. doi:10.4271/2015-01-1830Payri, R., García-Oliver, J. M., Xuan, T., & Bardi, M. (2015). A study on diesel spray tip penetration and radial expansion under reacting conditions. Applied Thermal Engineering, 90, 619-629. doi:10.1016/j.applthermaleng.2015.07.042Knox, B. W., & Genzale, C. L. (2017). Scaling combustion recession after end of injection in diesel sprays. Combustion and Flame, 177, 24-36. doi:10.1016/j.combustflame.2016.11.021García-Oliver, J. M., Malbec, L.-M., Toda, H. B., & Bruneaux, G. (2017). A study on the interaction between local flow and flame structure for mixing-controlled Diesel sprays. Combustion and Flame, 179, 157-171. doi:10.1016/j.combustflame.2017.01.02

A study on tip penetration velocity and radial expansion of reacting diesel sprays with different fuels

[EN] The reacting diesel spray structure was investigated using n-dodecane, n-heptane and one binary blend of Primary Reference Fuels (80% n-heptane and 20% iso-octane in mass) based on the existing database from previous experimental results from Schlieren imaging technique in a constant pressure combustion chamber. The spray tip velocity was derived from the derivative of tip penetration versus time. The operating conditions and the injector used (single axially-oriented hole, 89 mm-diameter) were chosen following the guidelines of the Engine Combustion Network. A 1D spray model was also applied here to support the analysis of experimental results. Parametric variations of injection pressure, ambient temperature and oxygen concentration have been performed for each fuel. Analysis of radial expansion and reacting tip velocity was performed in terms of an average spray radial increase (DR) and a constant (k) defining the tip penetration velocity. k values of reacting cases are always bigger than those from inert ones for both experimental and theoretical results. Based upon this parameter, quasi-steady tip penetration under the investigated conditions seems not to be affected by ambient temperature, oxygen content or fuel cetane number. Three cases with different fuels and similar ignition delay and lift-off length were further analyzed, which shows that the reactivity of the mixture has an effect on the transition timing from inert to reacting states, as well as on the initial penetration stages, but not on the quasi-steady phase. Apart from the similar tip velocity during quasi-steady phase, the full transient evolution of the tip is highly similar. The fact that this full overlap does not occur for other operating conditions indicates that early penetration stages are highly affected by the transient chemistry development, which largely depends on fuel cetane number.This study was partially funded by the Spanish Ministry of Economy and Competitiveness in the frame of the COMEFF (TRA2014-59483-R) project. Funding for Tiemin Xuan's PhD studies was granted by Universitat Politecnica de Valencia through the Programa de Apoyo para la Investigacion y Desarrollo (PAID) (Grant reference FPI-2015-S2-1068).Desantes J.M.; García-Oliver, JM.; Xuan, T.; Vera-Tudela-Fajardo, WM. (2017). A study on tip penetration velocity and radial expansion of reacting diesel sprays with different fuels. Fuel. 207:323-335. https://doi.org/10.1016/j.fuel.2017.06.108S32333520

Application of an unsteady flamelet model in a RANS framework for spray A simulation

[EN] In the present investigation the Spray A reference configuration defined in the framework of the Engine Combustion Network (ECN) has been modeled by means of an Unsteady Flamelet Model (USFM) including detailed parametric studies to evaluate the impact of ambient temperature, oxygen concentration and density. The study focuses on the analysis of the spray ignition delay, the flame lift-off length and the internal structure of the spray and flame according to the experimental information nowadays available for validating the results provided by the model. Promising results are obtained for the nominal case and also for the parametric variations (temperature, oxygen...) in terms of liquid and vapor penetration, ignition delay (ID) and lift-off length (LOL). The model permits to predict the ID and the LOL which constitute two parameters of key importance for describing the characteristics of transient reacting sprays. Valuable insight on the details of the combustion process is obtained from the analysis of formaldehyde (CH2O), acetylene (C2H2) and hydroxide (OH) species in spatial coordinates and also in the so-called phi-T maps. Important differences arise in the inner structure of the flame in the quasi-steady regime, which is closely linked to soot formation, when varying the ambient boundary conditions. Additionally, the auto-ignition process is investigated in order to describe in detail the spatial onset and propagation of combustion. Results confirm the impact of the ambient conditions on the regions of the spray where start of combustion takes place, so the relation between the local scalar dissipation rate and mixture fraction variance is also discussed. This investigation provides an insight of the potential of the USFM combustion model to describe the physical and chemical processes involved in transient spray combustion.Authors acknowledge that this work was possible thanks to the Ayuda para la Formacion de Profesorado Universitario (FPU 14/03278) belonging to the Subprogramas de Formacion y de Movilidad del Ministerio de Educacion, Cultura y Deporte from Spain. Also this study was partially funded by the Ministerio de Economia y Competitividad from Spain in the frame of the COMEFF (TRA2014-59483-R) national project.Desantes, J.; García-Oliver, JM.; Novella Rosa, R.; Pérez-Sánchez, EJ. (2017). Application of an unsteady flamelet model in a RANS framework for spray A simulation. Applied Thermal Engineering. 117:50-64. https://doi.org/10.1016/j.applthermaleng.2017.01.101S506411

LES Eulerian diffuse-interface modeling of fuel dense sprays near- and far-field

[EN] Engine fuel spray modeling still remains a challenge, especially in the dense near-nozzle region. This region is difficult to experimentally access and also to model due to the complex and rapid liquid and gas interaction. Modeling approaches based on Lagrangian particle tracking have failed in this area, while Eulerian modeling has proven to be particularly useful. Interface resolved methods are still limited to primary atomization academic configurations due to excessive computational requirements. To overcome those limitations, the single-fluid diffuse interface model known as Sigma-Y, arises as a single-framework for spray simulations. Under the assumption of scale separation at high Reynolds and Weber numbers, liquid dispersion is modeled as turbulent mixing of a variable density flow. The concept of surface area density is used for representing liquid structures, regardless of the complexity of the interface. In this work, a LES based implementation of the Sigma-Y model in the OpenFOAM CFD library is applied to simulate the ECN Spray A configuration. Model assessment is performed for both near- and far-field spray development regions using different experimental diagnostics available from ECN database. The CFD model is able to capture near-nozzle fuel mass distribution and, after Sigma equation constant calibration, interfacial surface area. Accurate predictions of spray far-field evolution in terms of liquid and vapor tip penetration and local velocity can be simultaneously achieved. Model accuracy is lower when compared to mixture fraction axial evolution, despite radial distribution profiles are well captured.This work was partially funded by the Spanish Ministerio de Economia y Competitividad within the frame of the CHEST (TRA2017-89139-C2-1-R) project. The computations were partially performed on the Tirant III cluster of the Servei d'Informatica of the University of Valencia (vlc38-FI-2018-2-0006). Authors acknowledge the computer resources at Picasso and the technical support provided by Universidad de Malaga (UMA) (RES-FI-2018-1-0039).Desantes Fernández, JM.; García-Oliver, JM.; Pastor Enguídanos, JM.; Olmeda-Ramiro, I.; Pandal, A.; Naud, B. (2020). LES Eulerian diffuse-interface modeling of fuel dense sprays near- and far-field. International Journal of Multiphase Flow. 127:1-13. https://doi.org/10.1016/j.ijmultiphaseflow.2020.103272S113127Andreini, A., Bianchini, C., Puggelli, S., & Demoulin, F. X. (2016). Development of a turbulent liquid flux model for Eulerian–Eulerian multiphase flow simulations. International Journal of Multiphase Flow, 81, 88-103. doi:10.1016/j.ijmultiphaseflow.2016.02.003Anez, J., Ahmed, A., Hecht, N., Duret, B., Reveillon, J., & Demoulin, F. X. (2019). Eulerian–Lagrangian spray atomization model coupled with interface capturing method for diesel injectors. International Journal of Multiphase Flow, 113, 325-342. doi:10.1016/j.ijmultiphaseflow.2018.10.009Baldwin, E. T., Grover, R. O., Parrish, S. E., Duke, D. J., Matusik, K. E., Powell, C. F., … Schmidt, D. P. (2016). String flash-boiling in gasoline direct injection simulations with transient needle motion. International Journal of Multiphase Flow, 87, 90-101. doi:10.1016/j.ijmultiphaseflow.2016.09.004Bardi, M., Payri, R., Malbec, L. M., Bruneaux, G., Pickett, L. M., Manin, J., … Genzale, C. (2012). ENGINE COMBUSTION NETWORK: COMPARISON OF SPRAY DEVELOPMENT, VAPORIZATION, AND COMBUSTION IN DIFFERENT COMBUSTION VESSELS. Atomization and Sprays, 22(10), 807-842. doi:10.1615/atomizspr.2013005837Battistoni, M., Som, S., & Powell, C. F. (2019). Highly resolved Eulerian simulations of fuel spray transients in single and multi-hole injectors: Nozzle flow and near-exit dynamics. Fuel, 251, 709-729. doi:10.1016/j.fuel.2019.04.076Beheshti, N., Burluka, A. A., & Fairweather, M. (2007). Assessment of Σ−Y liq model predictions for air-assisted atomisation. Theoretical and Computational Fluid Dynamics, 21(5), 381-397. doi:10.1007/s00162-007-0052-3Chesnel, J., Reveillon, J., Menard, T., & Demoulin, F.-X. (2011). LARGE EDDY SIMULATION OF LIQUID JET ATOMIZATION. Atomization and Sprays, 21(9), 711-736. doi:10.1615/atomizspr.2012003740CMT, 2018. Virtual injection rate generator.Crua, C., Heikal, M. R., & Gold, M. R. (2015). Microscopic imaging of the initial stage of diesel spray formation. Fuel, 157, 140-150. doi:10.1016/j.fuel.2015.04.041Crua, C., Manin, J., & Pickett, L. M. (2017). On the transcritical mixing of fuels at diesel engine conditions. Fuel, 208, 535-548. doi:10.1016/j.fuel.2017.06.091Dahms, R. N., Manin, J., Pickett, L. M., & Oefelein, J. C. (2013). Understanding high-pressure gas-liquid interface phenomena in Diesel engines. Proceedings of the Combustion Institute, 34(1), 1667-1675. doi:10.1016/j.proci.2012.06.169Demoulin, F.-X., Beau, P.-A., Blokkeel, G., Mura, A., & Borghi, R. (2007). A NEW MODEL FOR TURBULENT FLOWS WITH LARGE DENSITY FLUCTUATIONS: APPLICATION TO LIQUID ATOMIZATION. Atomization and Sprays, 17(4), 315-345. doi:10.1615/atomizspr.v17.i4.20Demoulin, F.-X., Reveillon, J., Duret, B., Bouali, Z., Desjonqueres, P., & Menard, T. (2013). TOWARD USING DIRECT NUMERICAL SIMULATION TO IMPROVE PRIMARY BREAK-UP MODELING. Atomization and Sprays, 23(11), 957-980. doi:10.1615/atomizspr.2013007439Desantes, J. M., García-Oliver, J. M., Pastor, J. M., Pandal, A., Baldwin, E., & Schmidt, D. P. (2016). Coupled/decoupled spray simulation comparison of the ECN spray a condition with the -Y Eulerian atomization model. International Journal of Multiphase Flow, 80, 89-99. doi:10.1016/j.ijmultiphaseflow.2015.12.002Dukowicz, J. K. (1980). A particle-fluid numerical model for liquid sprays. Journal of Computational Physics, 35(2), 229-253. doi:10.1016/0021-9991(80)90087-xDuret, B., Reveillon, J., Menard, T., & Demoulin, F. X. (2013). Improving primary atomization modeling through DNS of two-phase flows. International Journal of Multiphase Flow, 55, 130-137. doi:10.1016/j.ijmultiphaseflow.2013.05.004ECN, 2014. LVF data archive.ECN, 2018. Engine combustion network data archive.Garcia-Oliver, J. M., Pastor, J. M., Pandal, A., Trask, N., Baldwin, E., & Schmidt, D. P. (2013). DIESEL SPRAY CFD SIMULATIONS BASED ON THE Σ-Υ EULERIAN ATOMIZATION MODEL. Atomization and Sprays, 23(1), 71-95. doi:10.1615/atomizspr.2013007198Gorokhovski, M., & Herrmann, M. (2008). Modeling Primary Atomization. Annual Review of Fluid Mechanics, 40(1), 343-366. doi:10.1146/annurev.fluid.40.111406.102200Hussein, H. J., Capp, S. P., & George, W. K. (1994). Velocity measurements in a high-Reynolds-number, momentum-conserving, axisymmetric, turbulent jet. Journal of Fluid Mechanics, 258, 31-75. doi:10.1017/s002211209400323xIlavsky, J., & Jemian, P. R. (2009). Irena: tool suite for modeling and analysis of small-angle scattering. Journal of Applied Crystallography, 42(2), 347-353. doi:10.1107/s0021889809002222Jasak, H., Weller, H. G., & Gosman, A. D. (1999). High resolution NVD differencing scheme for arbitrarily unstructured meshes. International Journal for Numerical Methods in Fluids, 31(2), 431-449. doi:10.1002/(sici)1097-0363(19990930)31:23.0.co;2-tKastengren, A., Ilavsky, J., Viera, J. P., Payri, R., Duke, D. J., Swantek, A., … Powell, C. F. (2017). Measurements of droplet size in shear-driven atomization using ultra-small angle x-ray scattering. International Journal of Multiphase Flow, 92, 131-139. doi:10.1016/j.ijmultiphaseflow.2017.03.005Kastengren, A. L., Tilocco, F. Z., Powell, C. F., Manin, J., Pickett, L. M., Payri, R., & Bazyn, T. (2012). ENGINE COMBUSTION NETWORK (ECN): MEASUREMENTS OF NOZZLE GEOMETRY AND HYDRAULIC BEHAVIOR. Atomization and Sprays, 22(12), 1011-1052. doi:10.1615/atomizspr.2013006309Kastengren, A. L., Tilocco,F. Z., Duke, D. J., Powell, C. F., Seoksu, M., Xusheng, Z., 2012b. Time-resolved x-ray radiography of diesel injectors from the engine combustion network. ICLASS Paper (1369).Kastengren, A. L., Powell, C. F., Wang, Y., Im, K.-S., & Wang, J. (2009). X-RAY RADIOGRAPHY MEASUREMENTS OF DIESEL SPRAY STRUCTURE AT ENGINE-LIKE AMBIENT DENSITY. Atomization and Sprays, 19(11), 1031-1044. doi:10.1615/atomizspr.v19.i11.30Klein, M., Sadiki, A., & Janicka, J. (2003). A digital filter based generation of inflow data for spatially developing direct numerical or large eddy simulations. Journal of Computational Physics, 186(2), 652-665. doi:10.1016/s0021-9991(03)00090-1Kraichnan, R. H. (1970). Diffusion by a Random Velocity Field. Physics of Fluids, 13(1), 22. doi:10.1063/1.1692799Lacaze, G., Misdariis, A., Ruiz, A., & Oefelein, J. C. (2015). Analysis of high-pressure Diesel fuel injection processes using LES with real-fluid thermodynamics and transport. Proceedings of the Combustion Institute, 35(2), 1603-1611. doi:10.1016/j.proci.2014.06.072Lebas, 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.2008.11.005Ma, P. C., Wu, H., Jaravel, T., Bravo, L., & Ihme, M. (2019). Large-eddy simulations of transcritical injection and auto-ignition using diffuse-interface method and finite-rate chemistry. Proceedings of the Combustion Institute, 37(3), 3303-3310. doi:10.1016/j.proci.2018.05.063Macian, V., Bermudez, V., Payri, R., & Gimeno, J. (2003). NEW TECHNIQUE FOR DETERMINATION OF INTERNAL GEOMETRY OF A DIESEL NOZZLE WITH THE USE OF SILICONE METHODOLOGY. Experimental Techniques, 27(2), 39-43. doi:10.1111/j.1747-1567.2003.tb00107.xManin, J., Bardi, M., Pickett, L. M., & Manin, J. (2012). SP2-4 Evaluation of the liquid length via diffused back-illumination imaging in vaporizing diesel sprays(SP: Spray and Spray Combustion,General Session Papers). The Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines, 2012.8(0), 665-673. doi:10.1299/jmsesdm.2012.8.665Matheis, J., & Hickel, S. (2018). Multi-component vapor-liquid equilibrium model for LES of high-pressure fuel injection and application to ECN Spray A. International Journal of Multiphase Flow, 99, 294-311. doi:10.1016/j.ijmultiphaseflow.2017.11.001Naber, J., Siebers, D., 1996. Effects of gas density and vaporization on penetration and dispersion of diesel sprays. SAE Technical Paper (960034).Nicoud, F., Toda, H. B., Cabrit, O., Bose, S., & Lee, J. (2011). Using singular values to build a subgrid-scale model for large eddy simulations. Physics of Fluids, 23(8), 085106. doi:10.1063/1.3623274Oefelein, J., Dahms, R., & Lacaze, G. (2012). Detailed Modeling and Simulation of High-Pressure Fuel Injection Processes in Diesel Engines. SAE International Journal of Engines, 5(3), 1410-1419. doi:10.4271/2012-01-1258Pandal, A., Pastor, J. M., Payri, R., Kastengren, A., Duke, D., Matusik, K., … Schmidt, D. (2017). Computational and Experimental Investigation of Interfacial Area in Near-Field Diesel Spray Simulation. SAE International Journal of Fuels and Lubricants, 10(2), 423-431. doi:10.4271/2017-01-0859Pandal, A., Payri, R., García-Oliver, J. M., & Pastor, J. M. (2017). Optimization of spray break-up CFD simulations by combining Σ-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.2017.06.022Pastor, J. V., Garcia-Oliver, J. M., Pastor, J. M., & Vera-Tudela, W. (2015). ONE-DIMENSIONAL DIESEL SPRAY MODELING OF MULTICOMPONENT FUELS. Atomization and Sprays, 25(6), 485-517. doi:10.1615/atomizspr.2014010370Pickett, L. M., Manin, J., Genzale, C. L., Siebers, D. L., Musculus, M. P. B., & Idicheria, C. A. (2011). Relationship Between Diesel Fuel Spray Vapor Penetration/Dispersion and Local Fuel Mixture Fraction. SAE International Journal of Engines, 4(1), 764-799. doi:10.4271/2011-01-0686Pickett, L. M., Manin, J., Kastengren, A., & Powell, C. (2014). Comparison of Near-Field Structure and Growth of a Diesel Spray Using Light-Based Optical Microscopy and X-Ray Radiography. SAE International Journal of Engines, 7(2), 1044-1053. doi:10.4271/2014-01-1412Poinsot, T. ., & Lelef, S. . (1992). Boundary conditions for direct simulations of compressible viscous flows. Journal of Computational Physics, 101(1), 104-129. doi:10.1016/0021-9991(92)90046-2Pope, S. B. (2004). Ten questions concerning the large-eddy simulation of turbulent flows. New Journal of Physics, 6, 35-35. doi:10.1088/1367-2630/6/1/035Poursadegh, F., Lacey, J. S., Brear, M. J., & Gordon, R. L. (2017). On the Fuel Spray Transition to Dense Fluid Mixing at Reciprocating Engine Conditions. Energy & Fuels, 31(6), 6445-6454. doi:10.1021/acs.energyfuels.7b00050Ricou, F. P., & Spalding, D. B. (1961). Measurements of entrainment by axisymmetrical turbulent jets. Journal of Fluid Mechanics, 11(1), 21-32. doi:10.1017/s0022112061000834Robert, A., Martinez, L., Tillou, J., & Richard, S. (2013). Eulerian – Eulerian Large Eddy Simulations Applied to Non-Reactive Transient Diesel Sprays. Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, 69(1), 141-154. doi:10.2516/ogst/2013140Schmidt, D. P., Gopalakrishnan, S., & Jasak, H. (2010). Multi-dimensional simulation of thermal non-equilibrium channel flow. International Journal of Multiphase Flow, 36(4), 284-292. doi:10.1016/j.ijmultiphaseflow.2009.11.012Shin, D., Sandberg, R. D., & Richardson, E. S. (2017). Self-similarity of fluid residence time statistics in a turbulent round jet. Journal of Fluid Mechanics, 823, 1-25. doi:10.1017/jfm.2017.304Shinjo, 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.2010.03.008Taub, G. N., Lee, H., Balachandar, S., & Sherif, S. A. (2013). A direct numerical simulation study of higher order statistics in a turbulent round jet. Physics of Fluids, 25(11), 115102. doi:10.1063/1.4829045Trask, N., Schmidt, D. P., Lightfoot, M., & Danczyk, S. (2012). Compressible Modeling of the Internal Two-Phase Flow in a Gas-Centered Swirl Coaxial Fuel Injector. Journal of Propulsion and Power, 28(4), 685-693. doi:10.2514/1.b34102Wehrfritz, A., Kaario, O., Vuorinen, V., & Somers, B. (2016). Large Eddy Simulation of n-dodecane spray flames using Flamelet Generated Manifolds. Combustion and Flame, 167, 113-131. doi:10.1016/j.combustflame.2016.02.019Weller, H. G., Tabor, G., Jasak, H., & Fureby, C. (1998). A tensorial approach to computational continuum mechanics using object-oriented techniques. Computers in Physics, 12(6), 620. doi:10.1063/1.168744Xue, Q., Battistoni, M., Powell, C. F., Longman, D. E., Quan, S. P., Pomraning, E., … Som, S. (2015). An Eulerian CFD model and X-ray radiography for coupled nozzle flow and spray in internal combustion engines. International Journal of Multiphase Flow, 70, 77-88. doi:10.1016/j.ijmultiphaseflow.2014.11.012Xue, Q., Som, S., Senecal, P. K., & Pomraning, E. (2013). LARGE EDDY SIMULATION OF FUEL-SPRAY UNDER NON-REACTING IC ENGINE CONDITIONS. Atomization and Sprays, 23(10), 925-955. doi:10.1615/atomizspr.201300832

Theoretical development of a new procedure to predict ignition delays under transient thermodynamic conditions and validation using a Rapid Compression-Expansion Machine

An experimental and theoretical study about the autoignition phenomenon has been performed in this article. A new procedure to predict ignition delays under transient (i.e. variable) thermodynamic conditions has been developed starting from the Muller's chemical kinetics mechanism. The results obtained have been compared with those obtained from the Livengood & Wu integral method, as well as with direct chemical kinetic simulations. All simulations have been performed with CHEMKIN, employing a detailed chemical kinetic mechanism. The simulations have been validated in the working range versus experimental results obtained from a Rapid Compression-Expansion Machine (RCEM). The study has been carried out with n-heptane as a diesel fuel surrogate. The experimental results show a good agreement with the direct chemical kinetic simulations. Besides, better predictions of the ignition delay have been obtained from the new procedure than the ones obtained from the classic Livengood & Wu expression. (C) 2015 Elsevier Ltd. All rights reserved.The authors would like to thank different members of the CMT-Motores Termicos team of the Universitat Politecnica de Valencia for their contribution to this work. The authors would also like to thank the member of ITQ, Joaquin Martinez, for his help with the gas chromatography. The authors are grateful to the Generalitat Valenciana for the financial support to acquire the RCEM (references PPC/2013/011 and FEDER Operativo 2007/2013 F07010203PCI00CIMETUPV001). Finally, the authors would like to thank the Spanish Ministry of Education for financing the PhD. Studies of Dario Lopez-Pintor (grant FPU13/02329). This work was partly founded by the Generalitat Valenciana, project PROME-TEOII/2014/043.k.Desantes Fernández, JM.; López, JJ.; Molina, S.; López Pintor, D. (2016). Theoretical development of a new procedure to predict ignition delays under transient thermodynamic conditions and validation using a Rapid Compression-Expansion Machine. Energy Conversion and Management. 108:132-143. https://doi.org/10.1016/j.enconman.2015.10.077S13214310

An experimental analysis on the evolution of the transient tip penetration in reacting Diesel sprays

Schlieren imaging has helped deeply characterize the behavior of Diesel spray when injected into an oxygen-free ambient. However, when considering the transient penetration of the reacting spray after autoignition, i.e. the Diesel flame, few studies have been found in literature. Differences among optical setups as well as among experimental conditions have not allowed clear conclusions to be drawn on this issue. Furthermore, soot radiation may have a strong effect on the image quality, which cannot be neglected. The present paper reports an investigation on the transient evolution of Diesel flame based upon schlieren imaging. Experimental conditions have spanned values of injection pressure, ambient temperature and density for typical Diesel engine conditions. An optimized optical setup has been used, which makes it possible to obtain results without soot interference. Based on observations for a long injection event (4 ms Energizing Time), the analysis has resorted to extensive comparison of inert and reacting sprays parameters, which have made it possible to define different phases after autoignition. Shortly after autoignition, axial and radial expansion of the spray have been observed in terms of tip penetration and radial cone angle. After that, during a stabilization phase, the reacting spray penetrates at a similar rate as the inert one. Later, the reacting spray undergoes an acceleration period, where it penetrates at a faster rate than the inert one. Finally, the flame enters a quasi-steady penetration phase, where the ratio of reacting and inert penetration stabilizes at a nearly constant value. The duration of the reacting spray penetration stages shows modifications when varying engine parameters such as air temperature, air density, injection pressure, and nozzle diameter. However, the proportionality between reacting and inert penetration has been observed to depend mainly on temperature, in agreement with observed reductions in entrainment when shifting from inert to reacting conditions. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.This work was partially funded by the Spanish Ministry of Science and Technology through the "EFFICIENT AND CLEAN COMBUSTION IN COMPRESSION IGNITION ENGINES USING THE DUAL-FUEL CONCEPT" Project (TRA2011-26359). Mr. Francisco J. Briceno wishes to acknowledge financial support through a PhD studies Grant (AP2008-02231) also sponsored by the Spanish Ministry of Education and Science. Last, but not least, authors would like to express their gratitude to Jose Enrique del Rey for his enthusiasm, proactiveness and help during data acquisition.Desantes Fernández, JM.; Pastor, JV.; García Oliver, JM.; Briceño Sánchez, FJ. (2014). An experimental analysis on the evolution of the transient tip penetration in reacting Diesel sprays. Combustion and Flame. 161(8):2137-2150. https://doi.org/10.1016/j.combustflame.2014.01.022S21372150161