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[EN] This article presents a study of the impact on engine efficiency of the heat loss reduction due to in-cylinder coating insulation. A numerical methodology based on one-dimensional heat transfer model is developed. Since there is no analytic solution for engines, the one-dimensional model was validated with the results of a simple "equivalent" problem, and then applied to different engine boundary conditions. Later on, the analysis of the effect of different coating properties on the heat transfer using the simplified one-dimensional heat transfer model is performed. After that, the model is coupled with a complete virtual engine that includes both thermodynamic and thermal modeling. Next, the thermal flows across the cylinder parts coated with the insulation material (piston and cylinder head) are predicted and the effect of the coating on engine indicated efficiency is analyzed in detail. The results show the gain limits, in terms of engine efficiency, that may be obtained with advanced coating solutions., The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The equipment used in this work has been partially supported by FEDER project funds "otacion de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energetica y Medioambiental de Sistemas de Transporte (CiMeT)'' (Grant No. FEDER-ICTS-2012-06), framed in the operational program of unique scientific and technical infrastructure of the Spanish Government. This project has received funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 724084.

[EN] In this article, a numerical methodology for assessing combustion noise in compression ignition engines is described with the specific purpose of analysing the unsteady pressure field inside the combustion chamber. The numerical results show consistent agreement with experimental measurements in both the time and frequency domains. Nonetheless, an exhaustive analysis of the calculation convergence is needed to guarantee an independent solution. These results contribute to the understanding of in-cylinder unsteady processes, especially of those related to combustion chamber resonances, and their effects on the radiated noise levels. The method was applied to different combustion system configurations by modifying the spray angle of the injector, evidencing that controlling the ignition location through this design parameter, it is possible to decrease the combustion noise by minimizing the resonance contribution. Important efficiency losses were, however, observed due to the injector/bowl matching worsening which compromises the performance and emissions levels., The authors want to express their gratitude to CONVERGENT SCIENCE Inc. and Convergent Science GmbH for their kind support for performing the CFD calculations using CONVERGE software.

[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].

[EN] In this paper, the unsteady behaviour of a compression-ignited (CI) engine combustion chamber is studied by analysing the results of a Computational Fluid Dynamics (CFD) model through the application of different flow decomposition techniques, aiming to resolve the underlying modal structure of the process. Experimental validation for the combustion simulation is provided, and a methodology for extracting coherent pressure information is proposed in order to provide a suitable input for different analysis methods. These range from straightforward Fourier transform techniques to more sophisticated modal decomposition approaches. In particular Proper Orthogonal Decomposition (POD) is shown to provide valuable insight into the time-spatial structure of the combustion flow field, allowing the establishment of correlations between pressure modes and physical parameters of the combustion, such as the injection timing or the chamber geometry. Dynamic Mode Decomposition (DMD) on the other hand is proven to successfully highlight the link between the frequency of the unsteady energy components and their spatial distribution within the chamber. Advantage is then taken of the modal characterization of the unsteady behaviour in the chamber to showcase how physical parameters such as the spray angle can be modified to optimize the acoustic signature of the combustion process, helping CI internal combustion engines reduce their acoustic environmental impact (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved., The equipment used in this work has been partially supported by FEDER project funds "Dotacidn de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energetica y Medioambiental de Sistemas de Transporte (CiMeT)" [grant number FEDER-ICTS-2012-06], framed in the operational program of unique scientific and technical infrastructure of the Spanish Government.

[EN] This paper presents a numerical methodology based on Computational Fluid Dynamics (CFD) simulations to understand the physics of heat losses through the cylinder walls coated with different materials, taking into account other important factors such as surface roughness and near wall flow velocity in a turbocharged spark-ignited (SI) engine. Engine closed cycle simulations have been performed to estimate the thermodynamic evolution of the charge inside the cylinder and therefore, to evaluate the effect of roughness on heat transfer and combustion at real operating conditions. The model has been validated by using experimental data for two different steady-state operation conditions of a fully instrumented engine. In general, the maximum rate of heat release is reduced as the roughness is increased. Observed trends indicate that the heat transfer variation is mainly caused by changes in the combustion process due to the surface roughness, rather than to the effects of the coating material properties/characteristics (the increase of the effective contact area, porosity, etc.). Lastly, the comparison between uncoated and coated engine have shown that maximal gains around 5% in heat loss could be achieved, with very limited efficiency improvement, whereas the knock tendency increases., J. Gomez-Soriano is partially supported through the Programa de Apoyo para la Investigation y Desarrollo (PAID) of Universitat Politecnica de Valencia [Grant No. FPI-S2-2016-1353].

En un marco global de creciente preocupación por la salud y el medio ambiente, el sector de la automoción se ha visto afectado por el endurecimiento de las normativas anticontaminación. Este hecho ha llevado a la comunidad científica al desarrollo de nuevos conceptos y tecnologías para, por una parte, conseguir reducciones importantes en los niveles de emisiones y por otra adecuarse a las exigencias del consumidor. La combinación del concepto de combustión parcialmente premezclada -PPC- uti-lizando combustibles con octanaje similar a la gasolina, el ciclo de trabajo de los motores dos tiempos y un diseño de baja cilindrada surge como una solución prome-tedora para conseguir reducciones simultáneas de óxidos de nitrógeno y partículas de hollín, para producir menores cantidades de dióxido de carbono y aumentar el rango de carga. Así pues, en base a estas premisas, el objetivo de esta investigación consiste en la evaluación del comportamiento de las emisiones contaminantes en un motor dos tiempos HSDI de pequeña cilindrada, operando con el concepto PPC gasolina con ayuda de la herramienta CFD. Los resultados obtenidos confirman cómo es posible implementar el concepto PPC en este motor a cargas medias-altas; obteniendo niveles muy bajos de N􀀀��Ox y partículas junto con moderados niveles de CO y 􀀂��HC. Sin embargo, un complejo proceso de optimización de la configuración del motor es necesario para obtener sus máximos beneficios.