Optical investigations on Diesel spray dynamics and in-flame soot formation

En las últimas décadas ha avanzado mucho la comprensión científica sobre el proceso de combustión de los chorros diesel de inyección directa gracias al desarrollo de todo tipo de técnicas e instalaciones ópticas. Además, se han desarrollado y mejorado una gran cantidad de modelos de Dinámica de Fluidos Computacional (CFD), los cuales se usan para el desarrollo de motores altamente eficientes y con bajas emisiones. Sin embargo, debido a la complejidad de los procesos físicos y químicos involucrados en este proceso de combustión, así como a las limitaciones significativas de los experimentos, aún hay muchas cuestiones sin responder: ¿Cómo afecta la combustión a la dinámica del chorro? ¿Cómo cuantificar de forma efectiva la cantidad de hollín y la temperatura del mismo en la llama? ¿Cómo afecta el flujo del aire y las inyecciones partidas al desarrollo del chorro y a la formación de hollín en condiciones no quiescente? Para ayudar a resolver las preguntas planteadas, el objetivo de este trabajo se pone en investigar al dinámica del chorro y la formación de hollín de los chorros Diesel de inyección directa en condiciones quiescentes y no quiescentes por medio de diferentes técnicas ópticas. El trabajo se ha dividido en dos bloques principales. El primero está centrado en el estudio de las modificaciones inducidas por la combustión en la dinámica del chorro, así como la caracterización de la formación de hollín en la llama, todo ello en condiciones quiescentes. Dichas condiciones son proporcionadas por una maqueta de flujo continuo a alta presión y temperatura. La expansión radial y axial del chorro reactivo se ha investigado usando n-dodecano, n-heptano y una mezcla binaria de combustibles primarios de referencia (80% n-heptano y 20% iso-octano en masa), basándose en una base de datos existente medida mediante visualización de schlieren. Se ha estudiado tanto el papel de las condiciones de operación como las propiedades del combustible. A continuación se ha desarrollado por primera vez una técnica combinada de extinción-radiación, aplicada a la medida de hollín en llamas diesel. Gracias a esta técnica, tanto la fracción volumétrica de hollín como la temperatura se obtuvieron simultáneamente considerando los efectos de la autoabsorción en la radiación. Todo este trabajo se ha desarrollado dentro del marco de actividades de la Engine Combustion Network (ECN). El segundo bloque corresponde a la caracterización de la dinámica del chorro y de la formación de hollín en condiciones no quiescentes, que ocurren en la cámara de combustión de un motor monocilíndrico de dos tiempos con accesos ópticos. En esta parte, se ha llevado a cabo en primer lugar la visualización del chorro para una inyección única en condiciones no-reactivas y reactivas. Se han aplicado la visualización simultánea de schlieren y de la quimioluminiscencia del radical OH* para obtener la penetración del chorro y la longitud de despegue de la llama, mientras que la visualización de la extinción de ombroscopía difusa (DBI) se ha aplicado para cuantificar la formaciónde hollín. Los resultados se han comparado con los de la base de datos de la Engine Combustion Network antes mencionados, para estudiar los efectos del movimiento del aire inducido por el movimiento del pistón sobre el desarrollo del chorro y del hollín. Finalmente, se han usado diferentes estrategias de inyección partida para estudiar cómo la primera inyección afecta a los procesos de mezcla y a formación de hollín de la segunda, al cambiar el tiempo de separación entre ambos eventos de inyección o la cantidad inyectada en el primer pulso.In recent decades, the scientific understanding of the combustion process of direct injection diesel spray has progressed a lot, thanks to the development of all kinds of optical facilities and techniques. In addition, a large amount of efficient and accurate Computational Fluid Dynamics (CFD) models, which are used for the design of highly efficient, low emission engines has been developed and improved. However, because of the complexity of the physical and chemical process involved in this combustion process, as well as significant experimental limitations and uncertainties, there are still a lot of remaining questions: How does combustion affect spray dynamics? How can in-flame soot amount and soot temperature be quantified effectively? How do the airflow and split-injection affect spray development and soot formation under non-quiescent conditions? To help solve these raised questions, the objective of this work is set to investigate the spray dynamics and soot formation process of direct injection diesel sprays under both quiescent and non-quiescent conditions by means of different optical techniques. The work has been divided into two main blocks. The first one is focused on the study of combustion-induced modifications in spray dynamics, as well as the characterization of in-flame soot formation under quiescent conditions. The quiescent conditions are provided by a kind of high-temperature high-pressure constant flow vessel. The radial and axial reacting spray expansion were 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 an existing database from Schlieren imaging technique. Both operating conditions and fuel properties on this combustion-induced expansion were studied. Next, a combined extinction-radiation technique was first developed and applied in diesel spray soot measurement. Thanks to this technique, both the in-flame soot volume fraction and temperature were obtained simultaneously by considering the self-absorption effect on radiation. All this work has been carried out within the framework of activities of the engine combustion network (ECN). The second block corresponds to the characterization of spray dynamics and soot formation under non-quiescent conditions, which occur within the combustion chamber of a single-cylinder two-stroke optical engine. In this part, the spray visualization for single-injection under both non-reacting and reacting operating conditions was conducted first. Schlieren and OH * chemiluminescence were simultaneously applied to obtain the spray tip penetration and flame lift-off length, while the Diffuse Back Illumination (DBI) extinction imaging was applied to quantify the instantaneous soot formation. Results were compared with Engine Combustion Network database mentioned above to study the airflow effects induced by piston movement on spray and soot development. Finally, different split-injection strategies were used to study how the first injection affects the mixing and soot formation processes of the second one, by changing the dwell time between both injection events or the first injection quantity.En les últimes dècades ha avançat molt la comprensió científica sobre el procés de combustió dels dolls dièsel d'injecció directa gràcies al desenvolupament de tot tipus de tècniques i instal·lacions òptiques. A més, s'han desenvolupat i millorat una gran quantitat de models de Dinàmica de Fluids Computacional (CFD), els quals s'usen per al desenvolupament de motors altament eficients i amb baixes emissions. No obstant açò, a causa de la complexitat dels processos físics i químics involucrats en aquest procés de combustió, així com de les limitacions significatives dels experiments, encara hi ha moltes qüestions sense respondre: Com afecta la combustió a la dinàmica del doll? Com quantificar de forma efectiva la quantitat de sutge i la temperatura del mateix en la flama? Com afecta el flux de l'aire i les injeccions partides al desenvolupament del doll i a la formació de sutge en condicions no quiescents? Per a ajudar a resoldre les preguntes plantejades, l'objectiu d'aquest treball es posa a investigar al dinàmica del doll i la formació de sutge dels dolls Dièsel d'injecció directa en condicions quiescents i no quiescents per mitjançant diferents tècniques òptiques. El treball s'ha dividit en dos blocs principals. El primer està centrat en l'estudi de les modificacions induïdes per la combustió en la dinàmica del doll, així com la caracterització de la formació de sutge en la flama, tot açò en condicions quiescents. Aquestes condicions són proporcionades per una maqueta de flux continu a alta pressió i temperatura. L'expansió radial i axial del doll reactiu s'ha investigat usant n-dodecà, n-heptà i una mescla binària de combustibles primaris de referència (80% n-heptà i 20% iso-octà en massa), basant-se en una base de dades existent mesura mitjançant visualització de schlieren. S'ha estudiat tant el paper de les condicions d'operació com les propietats del combustible. A continuació s'ha desenvolupat per primera vegada una tècnica combinada d'extinció-radiació, aplicada a la mesura de sutge en flames dièsel. Gràcies a aquesta tècnica, tant la fracció volumètrica de sutge com la temperatura es van obtenir simultàniament considerant els efectes de l'autoabsorció en la radiació. Tot aquest treball s'ha desenvolupat dins del marc d'activitats de la Engine Combustion Network (ECN). El segon bloc correspon a la caracterització de la dinàmica del doll i de la formació de sutge en condicions no quiescents, que ocorren en la cambra de combustió d'un motor monocilíndric de dos temps amb accessos òptics. En aquesta part, s'ha dut a terme en primer lloc la visualització del doll per a una injecció única en condicions no-reactives i reactives. S'han aplicat la visualització simultània de schlieren i de la quimioluminescència del radical OH* per a obtenir la penetració del doll i la longitud d'enlairament de la flama, mentre que la visualització de l'extinció d'ombroscopia difusa (DBI) s'ha aplicat per a quantificar la formaciónde sutge. Els resultats s'han comparat amb els de la base de dades de la Engine Combustion Network abans esmentats, per a estudiar els efectes del moviment de l'aire induït pel moviment del pistó sobre el desenvolupament del doll i del sutge. Finalment, s'han usat diferents estratègies d'injecció partida per a estudiar com la primera injecció afecta als processos de mescla i a formació de sutge de la segona, en canviar el temps de separació entre tots dos esdeveniments d'injecció o la quantitat injectada en el primer pols.Xuan, T. (2017). Optical investigations on Diesel spray dynamics and in-flame soot formation [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/94626TESI

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

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

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). 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An Experimental Study on Diesel Spray Injection into a Non-Quiescent Chamber

[EN] Visualization of single-hole nozzles into quiescent ambient has been used extensively in the literature to characterize spray mixing and combustion. However in-cylinder flow may have some meaningful impact on the spray evolution. In the present work, visualization of direct diesel injection spray under both non-reacting and reacting operating conditions was conducted in an optically accessible two-stroke engine equipped with a single-hole injector. Two different high-speed imaging techniques, Schlieren and UV-Light Absorption, were applied here to quantify vapor penetration for non-reacting spray. Meanwhile, Mie-scattering was used to measure the liquid length. As for reacting conditions, Schlieren and OH* chemiluminescence were simultaneously applied to obtain the spray tip penetration and flame lift-off length under the same TDC density and temperature. Additionally, PIV was used to characterize in-cylinder flow motion. Results were compared with those from the Engine Combustion Network database obtained under quiescent ambient conditions in a high pressure high temperature vessel. Because of the air flow induced by piston movement, in-cylinder conditions in the two-stroke engine during the spray injection are highly unsteady, which has a significant impact on the spray development and interference on the spray visualization. From the comparison with quiescent data from the Engine Combustion Network, air flow induced by piston movement was found to slow down tip penetration. Moreover, both ignition delay and lift-off length under unsteady flow conditions show less sensitivity with ambient temperature than that of quasi-steady conditions.This work was partially funded by the Government of Spain through COMEFF Project (TRA2014-59483-R). In addition, the authors acknowledge that some equipment used in this work has been partially supported by FEDER project funds (FEDER-ICTS-2012-06), framed in the operational program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain. The authors want also to express their gratitude to CONVERGENT SCIENCE Inc for their kind support for this research.Pastor, JV.; García-Oliver, JM.; García Martínez, A.; Zhong, W.; Micó Reche, C.; Xuan, T. (2017). An Experimental Study on Diesel Spray Injection into a Non-Quiescent Chamber. SAE International Journal of Fuel and Lubricants. 10(2):1-13. https://doi.org/10.4271/2017-01-0850S11310

In-flame soot quantification of diesel sprays under sooting/non-sooting critical conditions in an optical engine

[EN] Because of the challenge of meeting stringent emissions regulations for internal combustion engines, some advanced low temperature combustion modes have been raised in recent decades to improve combustion efficiency. Therefore, detailed understanding and capability for accurate prediction of in-flame soot processes under such low sooting conditions are becoming necessary. Nowadays, a lot of investigations have been carried out to quantify in-flame soot in Diesel sprays under high sooting conditions by means of different optical techniques. However, no information of soot quantification can be found for sooting/non-sooting critical conditions. In current study, the instantaneous soot production in a two-stroke optical engine under low sooting conditions has been measured by means of a Diffused back-illumination extinction technique (DBI) and two-color method (2C) simultaneously. The fuels used were n-dodecane and n-heptane, which have been injected separately though two different injectors equipped with single-hole nozzles. A large cycle-to-cycle variation on soot production can be observed under such operating conditions, however the in-cylinder heat release traces were quite repeatable. It is the same with the well-known trends of soot amount to operating conditions that the probability of sooting cycles increases with higher ambient temperature, higher ambient density and lower injection pressure. Both techniques present a pretty good agreement on soot amount when the peak of KL value is close to 1. However, the KL value of two-color method becomes bigger than that of DBI and the difference increases with lower sooting conditions.This study was partially funded by the Natural Science Foundation of China (No. 51876083), China Postdoctoral Science Foundation (2018M642176) and High-tech Research Key laboratory of Zhenjiang (SS2018002)Xuan, T.; Pastor, JV.; García-Oliver, JM.; García Martínez, A.; He, Z.; Wang, Q.; Reyes, M. (2019). In-flame soot quantification of diesel sprays under sooting/non-sooting critical conditions in an optical engine. Applied Thermal Engineering. 149:1-10. https://doi.org/10.1016/j.applthermaleng.2018.11.112S11014

A study on diesel spray tip penetration and radial expansion under reacting conditions

The shape of Diesel spray was investigated at real engine conditions in a constant pressure combustion chamber. Schlieren imaging technique was used to make quantitative measurements of spray tip penetration and radial width stressing the impact that the fuel combustion and heat release have on the spray shape. The heat-release region and the Lift-off length were identified measuring OH* chem-iluminescence. The fuel (n-dodecane) as well as the operating conditions and the injector used (single axially-oriented hole, 89 mu m-diameter) were chosen following the guidelines of the Engine Combustion Network. The effects of different operating parameters on the axial and radial expansion were also investigated. According to the results the reacting spray can be divided into three parts: an inert part, a transient one, and a quasi-steady one that lays between the two other regions. A new method for evaluating this radial expansion of reacting spray was developed, which was evaluated under the different operating conditions. Results show that the radial expansion increases with increasing injection pressure and decreasing ambient temperature and ambient density. The oxygen concentration has no obvious effect on the radial expansion. (C) 2015 Elsevier Ltd. All rights reserved.Authors acknowledge that some equipment used in this work has been partially supported by FEDER project funds (FEDER-ICTS-2012-06), framed in the operational program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain.Payri, R.; García Oliver, JM.; Xuan, T.; Bardi, M. (2015). A study on diesel spray tip penetration and radial expansion under reacting conditions. Applied Thermal Engineering. 90:619-629. https://doi.org/10.1016/j.applthermaleng.2015.07.042S6196299

Fundamental studies of diesel flame dynamics and soot process

[EN] This work has been divided into two parts. The first part is the study of the effects of injection pressure and ambient conditions on diesel spray tip penetration and radius expansion under reacting condition. An experimental database of tip penetration and radius expansion of a diesel single-hole nozzle fuelled with Dodecane, which was recorded by schlieren imaging under different conditions were deeply analyzed. For the second part, the effects of injection pressure and ambient conditions on liquid phase penetration, lift-off length and soot were investigated with a multi-hole injector.[ES] El presente trabajo ha sido dividido en dos partes. La primera parte consta del estudio de los efectos de la presión de inyección y condiciones de cámara en la penetración y expasión radial de un chorro diesel bajo condiciones reactivas. Una base de datos con resultados experimentales de penetración y expansión radial en un inyector mono-orificio con dodecano, los cuales fueron realizados mediante la técnica óptica de schlieren fueron analizados con detalle. Como segunda parte, los efectos de la presión de inyección y condiciones de cámara sobre la longitud líquida, longitud de desprendimiento de llama y generación de hollín fueron investigados con un inyecton multi-orificio.Xuan, T. (2014). Fundamental studies of diesel flame dynamics and soot process. http://hdl.handle.net/10251/59622Archivo delegad

A numerical study of the effects of injection rate shape on combustion and emission of diesel engines

The spray characteristics including spray droplet sizes, droplet distribution, spray tip penetration length and spray diffusion angle directly affects the mixture process of fuel and oxygen and then plays an important role for the improvement of combustion and emission performance of diesel engines. Different injection rate shapes may induce different spray characteristics and then further affect the subsequent combustion and emission performance of diesel engines. In this paper, the spray and combustion processes based on four different injection rate shapes with constant injection duration and injected fuel mass were simulated in the software of AVL FIRE. The numerical models were validated through comparing the results from the simulation with those from experiment. It was found that the dynamic of diesel engines with the new proposed hump shape of injection rate and the original saddle shape is better than that with the injection rate of rectangle and triangle shape, but the emission of NOX is higher. And the soot emission is lowest during the late injection period for the new hump-shape injection rate because of a higher oxidation rate with a better mixture between fuel and air under the high injection pressure