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. 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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. 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Evaluation of swirl effect on the Global Energy Balance of a HSDI Diesel engine

[EN] In the last years, a growing interest about increasing engine efficiency has led to the development of new engine technologies. Since air motion in the chamber is a key issue in internal combustion engines to improve the air-fuel mixing process and achieve faster burning rates, modern Diesel engines are designed to generate gas vorticity (swirl) that lead to enhanced turbulence in the combustion chamber. However, the use of swirl has a direct effect on fuel consumption due to the changes in the in-cylinder processes, affecting indicated efficiency, and also on the air management. An analysis, based on the engine Global Energy Balance (GEB), is presented to thoroughly assess the behavior of a high speed direct injection Diesel engine under variable swirl levels at different operating points. The tests have been performed keeping constant both the conditions at intake valve closing and combustion phasing, thus minimizing the variability due to in-cylinder conditions and the combustion process. The analysis includes a combination of theoretical (0D models) and experimental tools (heat rejection and wall temperature measurement) used to ensure control of in-cylinder conditions and to provide detailed explanation of the different phenomena affecting engine efficiency when swirl ratio is modified. Based on these tools, impact of swirl on the engine GEB is analyzed in detail paying special attention to engine efficiency and heat transfer in the chamber. Results show that increasing swirl has two main effects regarding the gross indicated efficiency (eta(i)): on one hand chamber heat rejection increases and therefore eta(i) diminishes about -0.5% at low load and 0.4% at high load; on the other hand combustion development is affected and thus a eta(i) improvement higher to 1.5% is achieved at low load and speed. The combination of these effects leads to a gross indicated efficiency increase higher to 1% at an optimum swirl ratio that diminishes when engine speed increases. In addition, pumping losses effect dominates brake efficiency behavior, which always diminishes (from 0.9% to 1.4%) when swirl increases. (C) 2017 Elsevier Ltd. All rights reserved.The support of GM Global R&D and the Spanish Ministry of Economy and Competitiveness (TRA2013-41348-R) is greatly acknowledged.Benajes, J.; Olmeda, P.; Martín, J.; Blanco-Cavero, D.; Warey, A. (2017). Evaluation of swirl effect on the Global Energy Balance of a HSDI Diesel engine. Energy. 122:168-181. https://doi.org/10.1016/j.energy.2017.01.082S16818112

Swirl ratio and post injection strategies to improve late cycle diffusion combustion in a light-duty diesel engine

[EN] Nitrogen oxides (NOx) and soot emissions are the most important pollutants from direct-injection diesel engines. In particular, soot formation and oxidation determine the net engine-out soot emissions. These phenomena are complex and competing processes during diesel combustion. Despite many researches implicate the mechanisms of soot formation with soot emissions, the enhancement of the late cycle soot oxidation is the dominant mechanism for a reduction of engine-out soot emissions. The mixing process and the in-cylinder bulk temperature are two important parameters in the development of soot oxidation process. The current research compares different engine strategies to enhance the late cycle mixing controlled combustion process and therefore enhance soot oxidation while maintaining similar gross indicated efficiency in a light-duty engine. For this purpose, a simplified methodology has been used, which analyzes the effect of mixing process and in-cylinder bulk gas temperature on soot oxidation during the late cycle combustion. For carrying out this research, theoretical and experimental tools were used. In particular, the experimental measurements were made in a single-cylinder direct-injection light-duty diesel engine varying the swirl ratio and the injection pattern as injection pressure, Start of Energizing (SoE), Energizing Time (ET) and number of injections events. To analyze soot emissions, the combustion luminosity was measured by an optoelectronic probe and the optical thickness parameter (KL) was evaluated by the two-color pyrometry method. The apparent combustion time (ACT-1) was used as mixing time tracer. Results show that an increase in swirl ratio implies an improvement on the mixing process and higher values of average bulk temperature during the late-cycle diffusion combustion. Both phenomena produce an enhancement in the soot oxidation process. In the lowest swirl ratio case, a suitable injection strategy based on multiple injections, provides similar results of soot oxidation process (and therefore, the emissions) as high swirl ratio case. (C) 2017 Elsevier Ltd. All rights reserved.Benajes, J.; Martín, J.; García Martínez, A.; Villalta-Lara, D.; Warey, A. (2017). Swirl ratio and post injection strategies to improve late cycle diffusion combustion in a light-duty diesel engine. Applied Thermal Engineering. 123:365-376. doi:10.1016/j.applthermaleng.2017.05.101S36537612

Thermodynamic analysis of an absorption refrigeration system used to cool down the intake air in an Internal Combustion Engine

[EN] This paper deals with the thermodynamic analysis of an absorption refrigeration cycle used to cool down the temperature of the intake air in an Internal Combustion Engine using as a heat source the exhaust gas of the engine. The solution of ammonia-water has been selected due to the stability for a wide range of operating temperatures and pressures and the low freezing point. The effects of operating temperatures, pressures, concentrations of strong and weak solutions in the absorption refrigeration cycle were examined to achieve proper heat rejection to the ambient. Potential of increasing Internal Combustion Engine efficiency and reduce pollutant emissions was estimated by means of theoretical models and experimental tests. In order to provide boundary conditions for the absorption refrigeration cycle and to simulate its effect on engine performance, a OD thermodynamic model was used to reproduce the engine performance when the intake air is cooled. Furthermore, a detailed experimental work was carried out to validate the results in real engine operation. Theoretical results show how the absorption refrigeration system decreases the intake air flow temperature down to a temperature around 5 degrees C and even lower by using the bottoming waste heat energy available in the exhaust gases in a wide range of engine operating conditions. In addition, the theoretical analysis estimates the potential of the strategy for increasing the engine indicated efficiency in levels up to 4% also at the operating conditions under evaluation. Finally, this predicted benefit in engine indicated efficiency has been experimentally confirmed by direct testing. (C) 2016 Elsevier Ltd. All rights reserved.Authors want to acknowledge the "Apoyo para la investigacion y Desarrollo (PAID)" grant for doctoral studies (FPI S2 2015 1067).Novella Rosa, R.; Dolz, V.; Martín, J.; Royo-Pascual, L. (2017). Thermodynamic analysis of an absorption refrigeration system used to cool down the intake air in an Internal Combustion Engine. Applied Thermal Engineering. 111:257-270. https://doi.org/10.1016/j.applthermaleng.2016.09.084S25727011

New 0-D methodology for predicting NO formation under continuously varying temperature and mixture composition conditions

The development of new diesel combustion modes characterized by low combustion temperatures, to minimize the NOx emissions, has caused a noticeable change in the diesel spray s structure and in the NOx chemistry, gaining relevance the N2O and the prompt routes in detriment of the thermal mechanism.Therefore, to accurately predict the NOx emissions, the detailed chemistry and physics must be taken into account, with the consequence of increasing the computational cost. The authors propose in the current study a new predictive methodology associated to low computational cost, where detailed chemistry and simplified physics are considered. To diminish even more the computational cost, the chemistry was tabulated as a function of temperature and oxygen excess mass fraction (parameter which effectively couples the equivalence ratio and the EGR rate). This tool has been developed with the objective of being applicable in continuously varying temperature and mixture fraction conditions (the diffusion diesel spray context) and was validated with the Two-Stage Lagrangian model (TSL-model) and with real engine measurements. The results in both validation scenarios reflect a high degree of accuracy making it applicable, at least, to perform qualitative predictions. By extension, it is expected to perform similarly in continuously varying temperature conditions (i.e.: homogenous charge compression ignition diesel combustion modes) which are less demanding computationally speaking.The authors would like to acknowledge the contribution of the Spanish Ministry of Economic and Competitively for the financial support of the present research study associate to the projects TRA 2008-06448 (VELOSOOT) and to Dr. V. Golovitchev for his valuable comments and suggestions.Benajes Calvo, JV.; López Sánchez, JJ.; Molina Alcaide, SA.; Redón Lurbe, P. (2015). New 0-D methodology for predicting NO formation under continuously varying temperature and mixture composition conditions. Energy Conversion and Management. 91:367-376. https://doi.org/10.1016/j.enconman.2014.12.010S3673769

Thermal effects on the diesel injector performance through adiabatic 1D modelling. Part I: Model description and assessment of the adiabatic flow hypothesis

[EN] The fuel flow along common-rail injectors is usually treated as isothermal, although the expansions across the injector orifices lead to variations in the fuel temperature that in turn modify the fuel properties influencing injector dynamics. This investigation introduces the hypothesis of adiabatic flow to account for local temperature variations in the computational model of a solenoid injector previously introduced by the authors in its isothermal variant. The main contribution of the study consists on the assessment of the validity of this hypothesis by qualitatively estimating the relative importance of the heat transfer processes during the injection event and in the time lapse among injections. Results of this tentative assessment for engine-like conditions imply that heat transfer is usually still occurring by the time of a new injection, meaning any initial temperature difference among the fuel and the injector wall is not expected to be completely mitigated before each injection event. The magnitude of reduction of this temperature difference depends on the injection frequency through engine speed and load. Anyway, the assumption of adiabatic flow seems to hold once the steady conditions of the injection are reached, meaning that any temperature change predictions considered with the adiabatic hypothesis may be valid as long as a certain temperature change is accounted for at the injector inlet. In a second part of the paper, the capabilities of this new model are validated against experimental data, allowing the use of the model to explore the influence of the thermal effects on the injection event.This work was partly sponsored by FEDER and the Spanish "Ministerio de Economia y Competitividad" in the frame of the project "Desarrollo de modelos de combustion y emisiones HPC para el analisis de plantas propulsivas de transporte sostenible (CHEST)", reference TRA2017-89139-C2-1-R-AR. The support of General Motors Global Research and Development (US) concerning the experimental measurements in the engine is gratefully acknowledged by the authors. The authors would also like to thank Jose Enrique del Rey, Leo Thiercelin and Mariano Sanchez for their technical help.Salvador, FJ.; Gimeno, J.; Martín, J.; Carreres, M. (2020). Thermal effects on the diesel injector performance through adiabatic 1D modelling. Part I: Model description and assessment of the adiabatic flow hypothesis. 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Effect of nozzle orifice geometry on spray, combustion, and emission characteristics under diesel engine conditions. Fuel, 90(3), 1267-1276. doi:10.1016/j.fuel.2010.10.048Salvador, F. J., Carreres, M., Jaramillo, D., & Martínez-López, J. (2015). Analysis of the combined effect of hydrogrinding process and inclination angle on hydraulic performance of diesel injection nozzles. Energy Conversion and Management, 105, 1352-1365. doi:10.1016/j.enconman.2015.08.035Nguyen, D., Duke, D., Kastengren, A., Matusik, K., Swantek, A., Powell, C. F., & Honnery, D. (2017). Spray flow structure from twin-hole diesel injector nozzles. Experimental Thermal and Fluid Science, 86, 235-247. doi:10.1016/j.expthermflusci.2017.04.020Salvador, F. J., de la Morena, J., Carreres, M., & Jaramillo, D. (2017). Numerical analysis of flow characteristics in diesel injector nozzles with convergent-divergent orifices. 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Thermo- and Fluid-Dynamic Processes in Direct Injection Engines. THIESEL2016 special issue

Payri, R.; Margot, X. (2017). Thermo- and Fluid-Dynamic Processes in Direct Injection Engines. THIESEL2016 special issue. International Journal of Engine Research. 18(1-2):3-5. doi:10.1177/1468087416680663S35181-

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

Linking instantaneous rate of injection to X-ray needle lift measurements for a direct-acting piezoelectric injector

Internal combustion engines have been and still are key players in today's world. Ever increasing fuel consumption standards and the ongoing concerns about exhaust emissions have pushed the industry to research new concepts and develop new technologies that address these challenges. To this end, the diesel direct injection system has recently seen the introduction of direct-acting piezoelectric injectors, which provide engineers with direct control over the needle lift, and thus instantaneous rate of injection (ROI). Even though this type of injector has been studied previously, no direct link between the instantaneous needle lift and the resulting rate of injection has been quantified. This study presents an experimental analysis of the relationship between instantaneous partial needle lifts and the corresponding ROI. A prototype direct-acting injector was utilized to produce steady injections of different magnitude by partially lifting the needle. The ROI measurements were carried out at CMT-Motores Termicos utilizing a standard injection rate discharge curve indicator based on the Bosch method (anechoic tube). The needle lift measurements were performed at the Advanced Photon Source at Argonne National Laboratory. The analysis seeks both to contribute to the current understanding of the influence that partial needle lifts have over the instantaneous ROI and to provide experimental data with parametric variations useful for numerical model validations. Results show a strong relationship between the steady partial needle lift and the ROI. The effect is non-linear, and also strongly dependent on the injection pressure. The steady lift value at which the needle ceases to influence the ROI increases with the injection pressure. Finally, a transient analysis is presented, showing that the needle velocity may considerably affect the instantaneous ROI, because of the volume displaced inside the nozzle. Results presented in this study show that at constant injection pressure and energizing time, this injector has the potential to control many aspects of the ROI and thus, the heat release rate. Also, data presented are useful for numerical model validations, which would provide detailed insight into the physical processes that drive these observations, and potentially, to the effects of these features on combustion performance.The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (Argonne). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.Viera-Sotillo, JP.; Payri, R.; Swantek, AB.; Duke, DJ.; Sovis, N.; Kastengren, AL.; Powell, CF. (2016). Linking instantaneous rate of injection to X-ray needle lift measurements for a direct-acting piezoelectric injector. Energy Conversion and Management. 112:350-358. https://doi.org/10.1016/j.enconman.2016.01.038S35035811

Numerical approach for assessing combustion noise in compression-ignited Diesel engines

[EN] Diesel combustion noise has become a crucial aspect for the engine manufacturers due to its impact on human health and influence on the customer purchasing decision. The interaction of the pressure waves after mixture self-ignition induces cavity resonances inside the combustion chamber. This complex phenomenon produces high-frequency pressure oscillations, hence traditional in-cylinder measurements do not provide enough information to characterise the in-cylinder acoustic field. In this paper, a numerical methodology is proposed for assessing the Diesel combustion as a noise source and to overcome measurement limitations. An optimisation procedure is also presented in order to determine the numerical calculation parameters, boundary conditions definition and initialization. Results show that local flow conditions at the start of combustion have a strong influence on the acoustic response of the in-cylinder noise source. These particular conditions are only achievable by the proposed methodology which considers entire engine cycle simulations with the complete cylinder domain. Therefore, traditional Computational Fluid Dynamic (CFD) approaches, such those used for predicting combustion stability or pollutant emissions, are not suitable for reproducing the physical mechanisms of noise generation and they cannot be used for acoustic purposes. The reliability of the proposed methodology to simulate the acoustic field accurately inside the combustion chamber has been validated by comparison with experiments.The equipment used in this work has been partially supported by FEDER project funds "Dotacion de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energdtica y Medioambiental de Sistemas de Transporte (CiMeT), (FEDER-ICTS-2012-06)", framed in the operational program of unique scientific and technical infrastructure of the Spanish Ministerio de Economia y Competitividad. J. Gomez-Soriano is partially supported through the "Programa de Apoyo para la Investigacion y Desarrollo (PAID)" of Universitat Politecnica de Valencia [Grant No. FPI-S2-2016-1353].Torregrosa, AJ.; Broatch, A.; Gil, A.; Gómez-Soriano, J. (2018). Numerical approach for assessing combustion noise in compression-ignited Diesel engines. Applied Acoustics. 135:91-100. https://doi.org/10.1016/j.apacoust.2018.02.006S9110013