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

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

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

Study of mass and momentum transfer in diesel sprays base on X-ray mass distribution measurements and on a theoretical derivation

[EN] In this paper, a research aimed at quantifying mass and momentum transfer in the near-nozzle field of diesel sprays injected into stagnant ambient air is reported. The study combines X-ray measurements for two different nozzles and axial positions, which provide mass distributions in the spray, with a theoretical model based on momentum flux conservation, which was previously validated. This investigation has allowed the validation of Gaussian profiles for local fuel concentration and velocity near the nozzle exit, as well as the determination of Schmidt number at realistic diesel spray conditions. This information could be very useful for those who are interested in spray modeling, especially at high-pressure injection conditions. © 2010 Springer-Verlag.This work was partly sponsored by "Vicerrectorado de Investigacion, Desarrollo e Innovacion'' of the "Universidad Politecnica de Valencia'' in the frame of the project "Estudio del flujo en el interior de toberas de inyeccion Diesel'', reference no. 3150 and by "Generalitat Valenciana'' in the frame of the project with the same title and reference GV/2009/031. This support is gratefully acknowledged by the authors.Desantes, J.; Salvador Rubio, FJ.; López, JJ.; De La Morena, J. (2011). Study of mass and momentum transfer in diesel sprays base on X-ray mass distribution measurements and on a theoretical derivation. Experiments in Fluids. 50(2):233-246. https://doi.org/10.1007/s00348-010-0919-8S233246502Abramovich GN (1963) The theory of turbulent jets. MIT Press, Cambridge, MAAdler D, Lyn WT (1969) The evaporation and mixing of a liquid fuel spray in a Diesel air swirl. Proc Instn Mech Eng 184:171–180Coghe A, Cossali GE (1994) Phase Doppler characterisation of a Diesel spray injected into a high density gas under vaporisation regimes. In: 7th international symposium on application of laser techniques to fluid mechanics, LisbonCorreas D (1998) Theoretical and experimental study of isothermal Diesel free sprays (in Spanish). PhD Thesis, Universidad Politécnica de ValenciaCossali GE (2001) An integral model for gas entrainment into full cone sprays. J Fluid Mech 439:353–366Dent JC (1971) A basis for the comparison of various experimental methods for studying spray penetration. SAE Paper 710571Desantes JM, Payri R, Salvador FJ, Gil A (2006a) Deduction and validation of a theoretical model for a free diesel Spray. Fuel 85:910–917Desantes JM, Arrègle J, López JJ, Cronhjort A (2006b) Scaling laws for free turbulent gas jets and Diesel-like sprays. Atomization Spray 16:443–473Desantes JM, Payri R, García JM, Salvador FJ (2007) A contribution to the understanding of isothermal diesel spray dynamics. Fuel 86:1093–1101Dumouchel C (2008) On the experimental investigation on primary atomization of liquid streams. Exp Fluids 45:371–422Heimgärtner C, Leipertz A (2000) of the primary spray break-up close to the nozzle of a common-rail high pressure diesel injection system. SAE Paper 2000-01-1799Hinze JO (1975) Turbulence. McGraw Hill, New YorkHiroyasu H, Arai M (1990) Structures of fuel sprays in diesel engines. SAE Paper 900475Jawad B, Gulari E, Henein NA (1992) Characteristics of intermittent fuel sprays. Combust Flame 88:384–396Lefèbvre AH (1989) Atomization and sprays. Hemisphere, New YorkLeick P, Riedel T, Bittlinger G, Powell CF, Kastengren AL, Wang J (2007) X-Ray measurements of the mass distribution in the dense primary break-up region of the spray from a standard multi-hole common-rail diesel injection system. In: Proc 21st ILASS (Europe)Linne M, Paciaroni M, Hall T, Parker T (2006) Ballistic imaging of the near field in a diesel spray. Exp Fluids 40:836–846Naber J, Siebers DL (1996) Effects of gas density and vaporisation on penetration and dispersion of diesel sprays. SAE Paper 960034Payri F, Bermúdez V, Payri R, Salvador FJ (2004) The influence of cavitation on the internal flow and the Spray characteristics in diesel injection nozzles. Fuel 83:419–431Payri R, García JM, Salvador FJ, Gimeno J (2005) Using spray momentum flux measurements to understand the influence of diesel nozzle geometry on spray characteristics. Fuel 84:551–561Payri R, Tormos B, Salvador FJ, Araneo L (2008) Spray droplet velocity characterization for convergent nozzles with three different diameters. Fuel 87:3176–3182Post S, Iyer V, Abraham J (2000) A study of near-field entrainment in gas jets and sprays under diesel conditions. ASME J Fluids Eng 122:385–395Prasad CMV, Kar S (1976) An investigation on the diffusion of momentum and mass of fuel in a diesel fuel spray. ASME J Eng Power 76-DGP-1:1–11Rajaratnam N (1976) Turbulent jets. Elsevier, AmsterdamRamirez AI, Som S, Aggarwal SK, Kastengren AL, El-Hannouny EM, Longman DE, Powell CF (2009) Quantitative X-ray measurements of high-pressure fuel sprays from a production heavy duty diesel injector. Exp Fluids 47:119–134Reitz RD, Bracco FV (1982) Mechanism of atomisation of a liquid jet. Phys Fluids 25(10):1730–1742Ricou FP, Spalding DB (1961) Measurements of entrainment by axisymmetrical turbulent jets. J Fluid Mech 11:21–32Rife J, Heywood JB (1974) Photographic and performance studies of diesel combustion with a rapid compression machine. SAE Paper 740948Roisman IV, Tropea C (2001) Flux measurements in sprays using phase doppler techniques. Atomization Spray 11:667–699Roisman IV, Araneo L, Tropea C (2007) Effect of ambient pressure on penetration of a diesel spray. Int J Multiphase Flow 33(8):904–920Saliba R, Baz I, Champoussin JC, Lance M, Marié JL (2004) Cavitation effect on the near nozzle spray development in high-pressure diesel injection. In: Proc 19th ILASS (Europe)Schlichting H (1978) Boundary layer theory. McGraw Hill, New YorkSinnamon JF, Lancaster DR, Stiener JC (1980) An experimental and analytical study of engine fuel spray trajectories. SAE Paper 800135Sou A, Hosokawa S, Tomiyama A (2007) Effects of cavitation in a nozzle on liquid jet atomization. Int J Heat Mass Tran 50(17–18):3575–3582Spalding DB (1979) Combustion and mass transfer. Pergamon Press, New YorkSubramaniam S (2001) Statistical modelling of a spray as using the droplet distribution function. Phys Fluids 13(3):624–642Tanner FX, Feigl A, Ciatti SA, Powell CF, Cheong S-K, Liu J, Wang J (2006) Structure of high-velocity dense sprays in the near-nozzle region. Atomization Spray 16:579–597Way RJB (1977) Investigation of interaction between swirl and jets in direct injection diesel engines using a water model. SAE Paper 770412Wu KJ, Santavicca DA, Bracco FV (1984) LDV measurements of drop velocity in diesel-type sprays. AAIA J 22(9):1263–1270Wu KJ, Reitz RD, Bracco FV (1986) Measurements of drop size at the spray edge near the nozzle in atomising liquid jets. Phys Fluids 29(4):941–951Yue Y, Powell CF, Poola R, Wang J, Schaller JK (2001) Quantitative measurements of diesel fuel spray characteristics in the near-nozzle region using X-ray absorption. Atomization Spray 11(4):471–49

Experimental assessment of the fuel heating and the validity of the assumption of adiabatic flow through the internal orifices of a diesel injector

[EN] In this paper an experimental investigation on the heating experienced by the fuel when it expands through the calibrated orifices of a diesel injector is carried out. Five different geometries corresponding to the control orifices of two different commercial common-rail solenoid injectors were tested. An experimental facility was used to impose a continuous flow through the orifices by controlling the pressures both upstream and downstream of the restriction. Fuel temperature was controlled prior to the orifice inlet and measured after the outlet at a location where the flow is already slowed down. Results were compared to the theoretical temperature increase under the assumption of adiabatic flow (i.e. isenthalpic process). The comparison points out that this assumption allows to predict the fuel temperature change in a reasonable way for four of the five geometries as long as the pressure difference across the orifice is high enough. The deviations for low imposed pressure differences and the remaining orifice are explained due to the low Reynolds numbers (i.e. flow velocities) induced in these cases, which significantly increase the residence time of a fuel particle in the duct, thus enabling heat transfer with the surrounding atmosphere. A dimensionless parameter to quantify the proneness of the flow through an orifice to exchange heat with the surroundings has been theoretically derived and calculated for the different geometries tested, allowing to establish a boundary that defines beforehand the conditions from which heat losses to the ambient can be neglected when dealing with the internal flow along a diesel injector.This work was partly sponsored by “Ministerio de Economía y Competitividad”, of the Spanish government, in the frame of the project “Estudio de la interacción chorro-pared en condiciones realistas de motor”, reference TRA2015-67679-c2-1-R. This support is gratefully acknowledged by the authors.Salvador, F.; Gimeno, J.; Carreres, M.; Crialesi Esposito, M. (2017). Experimental assessment of the fuel heating and the validity of the assumption of adiabatic flow through the internal orifices of a diesel injector. Fuel. 188:442-451. https://doi.org/10.1016/j.fuel.2016.10.061S44245118

Validity of the Livengood & Wu correlation and theoretical development of an alternative procedure to predict ignition delays under variable thermodynamic conditions

A theoretical study about the autoignition phenomenon has been performed in this article. The hypotheses of the Livengood & Wu integral have been revised, concluding that the critical concentration of chain carriers is not constant. However, its validity under engine conditions has been justified. Expressions to characterize the temporal evolution of the concentration of chain carriers, as well as the critical concentration of active radicals and the ignition delay, have been obtained starting from the Glassman s model. A new expression to predict ignition delays under variable conditions has been developed and the results obtained with this expression have been compared with those obtained from the Livengood & Wu integral. Two different fuels have been studied: isooctane (as a gasoline surrogate) and n-heptane (as a diesel fuel surrogate). The new method to predict ignition delays under variable conditions has shown, in general, better results than the classic Livengood & Wu integral, but the inability of the Glassman s model to reproduce the negative temperature coefficient regime should be improved in future works.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 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 PROMETEOII/2014/043.k.Desantes Fernández, JM.; López Sánchez, JJ.; Molina Alcaide, SA.; López Pintor, D. (2015). Validity of the Livengood & Wu correlation and theoretical development of an alternative procedure to predict ignition delays under variable thermodynamic conditions. Energy Conversion and Management. 105:836-847. https://doi.org/10.1016/j.enconman.2015.08.013S83684710

ECU-oriented models for NOx prediction. Part 1: a mean value engine model for NOx prediction

The implantation of nitrogen oxide sensors in diesel engines was proposed in order to track the emissions at the engine exhaust, with applications to the control and diagnosis of the after-treatment devices. However, the use of models is still necessary since the output from these sensors is delayed and filtered. The present paper deals with the problem of nitrogen oxide estimation in turbocharged diesel engines combining the information provided by both models and sensors. In Part 1 of this paper, a control-oriented nitrogen oxide model is designed. The model is based on the mapping of the nitrogen oxide output and a set of corrections which account for the variations in the intake and ambient conditions, and it is designed for implementation in commercial electronic control units. The model is sensitive to variations in the engine's air path, which is solved through the engine volumetric efficiency and the first-principle equations but disregards the effect of variation in the injection settings. In order to consider the effect of the thermal transients on the in-cylinder temperature, the model introduces a dynamic factor. The model behaves well in both steady-state operation and transient operation, achieving a mean average error of 7% in the steady state and lower than 10% in an exigent sportive driving mountain profile cycle. The relatively low calibration effort and the model accuracy show the feasibility of the model for exhaust gas recirculation control as well as onboard diagnosis of the nitrogen oxide emissions.Guardiola, C.; Pla Moreno, B.; Blanco-Rodriguez, D.; Calendini, PO. (2015). ECU-oriented models for NOx prediction. Part 1: a mean value engine model for NOx prediction. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. 229(8):992-1015. doi:10.1177/0954407014550191S9921015229

Optimal heat release shaping in a reactivity controlled compression ignition (RCCI) engine

[EN] The present paper addresses the optimal heat release (HR) law in a single cylinder engine operated under reactivity controlled compression ignition (RCCI) combustion mode to minimise the indicated specific fuel consumption (ISFC) subject to different constraints including pressure related limits (maximum cylinder pressure and maximum cylinder pressure gradient). With this aim, a 0-dimensional (0D) engine combustion model has been identified with experimental data. Then, the optimal control problem of minimising the ISFC of the engine at different operating conditions of the engine operating map has been stated and analytically solved. To evaluate the method viability a data-driven model is developed to obtain the control actions (gasoline fraction) leading to the calculated optimal HR, more precisely to the optimal ratio between premixed and diffusive combustion. The experimental results obtained with such controls and the differences with the optimal HR are finally explained and discussed.This work was supported by Ministerio de Economía y Competitividad through Project TRA2016-78717-R.Guardiola, C.; Plá Moreno, B.; García Martínez, A.; Boronat-Colomer, V. (2017). Optimal heat release shaping in a reactivity controlled compression ignition (RCCI) engine. Control Theory and Technology. 15(2):117-128. https://doi.org/10.1007/s11768-017-6155-5S117128152F. Payri, J. M. Luján, C. Guardiola, et al. A challenging future for the IC engine: New technologies and the control role. Oil & Gas Science and Technology–Revue D IFP Energies Nouvelles, 2015, 70(1): 15–30.H. Yanagihara, Y. Sato, J. Minuta. A simultaneous reduction in NOx and soot in diesel engines under a new combustion system (Uniform Bulky Combustion System–UNIBUS). Proceedings of the 17th international Vienna Motor Symposium, Vienna, 1996: 303–314.D. A. Splitter, M. L. Wissink, T. L. Hendricks, et al. Comparison of RCCI, HCCI, and CDC operation from low to full load. THIESEL 2012 conference on thermo-and fluid dynamic processes in direct injection engines. Valencia, 2012.J. Benajes, J. V. Pastor, A. García, et al. The potential of RCCI concept to meet EURO VI NOx limitation and ultra-low soot emissions in a heavy-duty engine over the whole engine map. Fuel, 2015, 159(1): 952–961.J. Benajes, A. García, J. Monsalve-Serrano, et al. An assessment of the dual-mode reactivity controlled compression ignition/conventional diesel combustion capabilities in a EURO VI medium-duty diesel engine fueled with an intermediate ethanol-gasoline blend and biodiesel. Energy Conversion and Management, 2016, 123(1): 381–391.S. Molina, A. García, J. M. Pastor, et al. Operating range extension of RCCI combustion concept from low to full load in a heavy-duty engine. Applied Energy, 2015, 143: 211–227.D. A. Splitter, R. D. Reitz. Fuel reactivity effects on the efficiency and operational window of dual-fuel compression ignition engines. Fuel, 2014, 118(5): 163–175.J. Benajes, S. Molina, A. García, et al. Effects of low reactivity fuel characteristics and blending ratio on low load RCCI (reactivity controlled compression ignition) performance and emissions in a heavy-duty diesel engine. Energy, 2015, 90: 1261–1271.J. Benajes, S. Molina, A. García, et al. An investigation on RCCI combustion in a heavy duty diesel engine using incylinder blending of diesel and gasoline fuels. Applied Thermal Engineering, 2014, 63(1): 66–76.J. Li, W. M. Yang, H. An, et al. Numerical investigation on the effect of reactivity gradient in an RCCI engine fueled with gasoline and diesel. Energy Conversion and Management, 2015, 92(1): 342–352.J. Benajes, S. Molina, A. García, et al. Effects of direct injection timing and blending ratio on RCCI combustion with different low reactivity fuels. Energy Conversion and Management, 2015, 99(1): 193–209.J. Benajes, J. V. Pastor, A. García, et al. A RCCI operational limits assessment in a medium duty compression ignition engine using an adapted compression ratio. Energy Conversion and Management, 2016, 126(1): 497–508.F. Zurbriggen, T. Ott, C. Onder, et al. Optimal control of the heat release rate of an internal combustion engine with pressure gradient, maximum pressure, and knock constraints. Journal of Dynamic Systems, Measurement, and Control, 2014, 136(6): DOI 10.1115/1.4027592.L. Eriksson, M. Sivertsson. Computing optimal heat release rates in combustion engines. SAE International Journal of Engines, 2015, 8(3): 1069–1079.L. Eriksson, M. Sivertsson. Calculation of optimal heat release rates under constrained conditions. SAE International Journal of Engines, 2016, 9(2): 1143–1162.Y. Zhang, T. Shen. Model based combustion phase optimization in SI engines: Variational analysis and spark advance determination. IFAC-PapersOnLine, 2016, 49(11): 679–684.F. Payri, P. Olmeda, J. Martín, et al. A new tool to perform global energy balances in DI diesel engines. SAE International Journal of Engines, 2014, 7(7): 43–59.S. Yu, M. Zheng. Ethanol-diesel premixed charge compression ignition to achieve clean combustion under high loads. Proceedings of the Institution of Mechanical Engineers–Part D: Journal of Automobile Engineering, 2016, 30(4): 527–541.D. Klos, D. Janecek, S. Kokjohn. Investigation of the combustion instability-NOx tradeoff in a dual fuel reactivity controlled compression ignition (RCCI) engine. SAE International Journal of Engines, 2015, 8(2): 821–830.G. Woschni. A Universally Applicable Equation for the Instantaneous Heat Transfer Coefficient in the Internal Combustion Engine. SAE Technical Paper. 1967: DOI 10.4271/670931.C. Guardiola, J. López, J. Martín, et al. Semi-empirical in-cylinder pressure based model for NOx prediction oriented to control applications. Applied Thermal Engineering, 2011, 31(16): 3275–3286.C. Guardiola, J. Martín, B. Pla, et al. Cycle by cycle NOx model for diesel engine control. Applied Thermal Engineering, 2017, 110: 1011–1020.J. M. Desantes, J. J. López, P. Redón, et al. Evaluation of the Thermal NO formation mechanism under low temperature diesel combustion conditions. International Journal of Engine Research, 2012, 13(6): 531–539.O. Sundstrm, L. Guzzella. A generic dynamic programming Matlab function. IEEE International Conference on Control Applications/International Symposium on Intelligent Control, St Petersburg: IEEE, 2009: 1625–1630.J. Benajes, A. García, J. M. Pastor, et al. Effects of piston bowl geometry on reactivity controlled compression ignition heat transfer and combustion losses at different engine loads. Fuel, 2016, 98(1): 64–77.J. Benajes, J. V. Pastor, A. García, et al. An experimental investigation on the influence of piston bowl geometry on RCCI performance and emissions in a heavy-duty engine. Energy Conversion and Management, 2015, 103: 1019–1031.J. M. Desantes, J. Benajes, A. García, et al. The role of the incylinder gas temperature and oxygen concentration over low load RCCI combustion efficiency. Energy, 2014, 78(SI): 854–868

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