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This is the author's version of a work that was accepted for publication in International Journal of Engine Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published as https://doi.org/10.1177/1468087420921584., [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.

[ES] En la situación actual existente, el mundo en general y la industria en especial, buscan reducir las emisiones de especies contaminantes por tal de cumplir con la normativa vigente establecida como barrera al empeoramiento del medio ambiente. Este contexto, ha llevado a buscar nuevas alternativas a la combustión de combustibles fósiles (gasolina) como es el caso del hidrógeno. Aquí, aparece el interés del trabajo que se va a llevar a cabo, donde un estudio de gas natural e hidrógeno como combustible, combinados con técnicas como una mayor dilución en aire o la recirculación de gases de escape, serán analizadas cualitativa y cuantitativamente. Además, se hará una comparación de valores entre estos, buscando los mejores resultados y viendo las deficiencias presentes en las distintas situaciones a analizar. De este modo, y con la búsqueda de una reducción de emisiones (especialmente del dióxido de carbono y de los óxidos de nitrógeno) como premisa a seguir, se tratará de obtener toda la información posible para un caso de 2000 rpm que opera con un alta carga, teniendo un caso de validación experimental, que dotará al documento de una mayor exactitud, [EN] Nowadays, the world in general, and the industry in particular, are seeking to reduce pollutant emissions in order to meet the current regulations established in relation to the environment. This context has led to the search for new alternatives to the combustion of fossil fuels (petrol) such as hydrogen. The current study analyses qualitatively and quantitatively the natural gas and hydrogen considered as fuel, combined with techniques such as further dilution in air or exhaust gas recirculation. In addition, a comparison of results is carried out, finding the best outcomes, and looking at the deficiencies in the different situations. Therefore, with the aim of reducing emissions (especially carbone dioxide and nitrogen oxides) as a target, all possible information is obtained for a 2000 rpm case operating at high load. Having an experimental case gives the study greater accuracy, [CA] En la situació actual existent, el món en general i la indústria en concret, busquen reduir les emissions d’espècies contaminants per tal d’acomplir amb la normativa vigent establida com a barrera a l’empijorament del medi ambient. Aquest context, ha portat a buscar noves alternatives a la combustió de combustibles fòssils (gasolina) com és el cas de l’hidrogen. Ací apareix l’interés del treball que es desenvoluparà, on l’estudi de gas natural i hidrogen com a combustible, combinats amb tècniques com una major dilució en aire o la recirculació de gasos d’escap, seràn analitzades qualitativavent i quantitativa. A més, es farà una comparació de valors entre aquests, buscant els millors resultats i veient les deficiències presents en les diferents situacions a analitzar. D’aquesta manera, i amb la cerca d’una reducció d’emissions (especialment del diòxi de carboni i dels òxids de nitrogen) com a premissa a seguir, es tractarà d’obtindre tota la informació possible per a un cas de 2000 rpm que opera amb un alta càrrega, tenint un cas de validació experimental, que dotarà al document d’una major exactitud

[ES] El presente Trabajo Fin de Grado plantea como objetivo principal el estudio de un aspecto crítico en los sistemas de encendido por precámara de tipo pasivo como es el impacto de los diferentes parámetros que definen la geometría de la propia precámara, fundamentalmente su volumen y el área de paso de los orificios que conectan dicha precámara con la cámara de combustion principal, sobre las prestaciones de este concepto de ignición de aplicación a motores de encendido provocado. Para alzcanzar este objetivo se utilizará una herramienta de simulación 1D que permite reproducir los flujos termofluidodinámicos característicos en este tipo de motores, incluyendo aquellos que se desarrollan en el interior de la precámara una vez integrada en el modelo completo del motor, junto con un modelo 1D de chorro gaseoso que posibilita el análisis de las características fundamentales de los chorros eyectados desde la precámara hacia la cámara principal. Una vez establecidas las herramientas y seleccionados los parámetros con los que se evaluará las prestaciones del concepto, se procederá a realizar una serie de estudios parámetricos diseñados para identificar el efecto aislado de cada uno de los parámetros geométricos para entender no sólo la sensibilidad del concepto de encendido sino también para establecer criterios de diseño que permitan optimizarlo en el futuro. Este Trabajo Fin de Grado pretende contribuir a generar el conocimiento necesario para desarrollar motores de encendido provocado de nueva generación más eficientes y con menos emisiones de CO2 de aplicación al sector de transporte por carretera, en línea con las líneas estratégicas establecidas por las instituciones Europeas y Españolas., [CA] El present Treball Fi de Grau planteja com a objectiu principal l'estudi d'un sistema d'encesa per precambra de tipus passiu per a motors d'encesa provocat i les seves prestacions enfront de diferents combustibles alternatius, a més de gasolina. A més, es posarà atenció a l'impacte dels diferents paràmetres que defineixen la geometria de la pròpia precámara, fonamentalment el seu volum i l'àrea de pas dels orificis que connecten aquesta precámara amb la cambra de combustió principal. Per assolir aquest objectiu s'utilitzarà una eina de simulació 1D que permet reproduir els fluxos termofluidodinámicos característics en aquest tipus de motors, incloent aquells que es desenvolupen a l'interior de la precámara un cop integrada en el model complet de l'motor, juntament amb un model 1D de raig gasós que possibilita l'anàlisi de les característiques fonamentals dels dolls ejectats des de la precámara cap a la càmera principal. Un cop establertes les eines i seleccionats els combustibles alternatius i paràmetres amb els quals s'avaluarà les prestacions de l'concepte, es procedirà a realitzar una sèrie d'estudis dissenyats per identificar l'efecte aïllat de cada un d'aquests factors per entendre no només la sensibilitat de l'concepte d'encesa sinó també per establir criteris de disseny que permetin optimitzar en el futur. Aquest Treball Fi de Grau pretén contribuir a generar el coneixement necessari per desenvolupar motors d'encesa provocat de nova generació més eficients i amb menys emissions de CO2 d'aplicació a el sector de transport per carretera, en línia amb les línies estratègiques establertes per les institucions Europees i espanyoles, [EN] The main objective of this Final Degree Project is to study a critical aspect in passive-type pre-chamber ignition systems, such as the impact of the different parameters that define the geometry of the pre-chamber itself, mainly its volume and the area of passage of the orifices that connect said pre-chamber with the main combustion chamber, on the performance of this ignition concept applied to spark-ignition engines. To achieve this objective, a 1D simulation tool will be used that allows to reproduce the thermofluid-dynamic flows characteristic of this type of engine, including those that develop inside the pre-chamber once it has been integrated into the complete engine model, together with a 1D model. of gaseous jet that allows the analysis of the fundamental characteristics of the jets ejected from the pre-chamber to the main chamber. Once the tools have been established and the parameters used to evaluate the performance of the concept have been selected, a series of design parametric studies will be carried out to identify the isolated effect of each of the geometric parameters to understand not only the sensitivity of the concept of on but also to establish design criteria to optimize it in the future. This Final Degree Project aims to contribute to generating the necessary knowledge to develop new generation spark-ignition engines that are more efficient and with less CO2 emissions applicable to the road transport sector, in line with the strategic lines established by the European institutions and Spanish.

[ES] Debido a la creciente preocupación por el cambio climático, las emisiones de gases de efecto invernadero causadas por los motores de combustión interna se encuentran en el punto de mira. Es necesario optimizar el rendimiento y reducir tanto el consumo como la contaminación causada por estos motores debido a las restrictivas normativas que se están implementando, además de mejorar la calidad del aire que respiramos. Los motores de encendido provocado (MEP) son el sistema propulsivo más utilizado en el sector del transporte de pasajeros. Estos motores han demostrado tener un mayor control de las emisiones contaminantes que los motores de encendido por compresión (MEC), sin embargo, la eficiencia de los MEP es peor que la de los MEC. Una estrategia novedosa para mejorar el rendimiento de los MEP es el uso del sistema de ignición por precámara. No obstante, el uso de esta tecnología no ha sido optimizado hasta el momento, y aún se desconocen varios aspectos relacionados al diseño interno de la precámara que podrían mejorar sus prestaciones y aumentar su tolerancia a la dilución con gases de escape. Por ello, en este trabajo se ha desarrollado un diseño de experimentos (DOE) para estudiar el sistema de encendido por precámara en un MEP mediante herramientas avanzadas de dinámica de fluidos computacional (CFD). El trabajo parte de un modelo numérico calibrado con medidas experimentales para una precámara de referencia estudiada anteriormente, con el objetivo de proponer una nueva arquitectura de precámara cónica, con el volumen y diámetro de los orificios previamente optimizados para obtener mejores prestaciones de los chorros, y evaluar el impacto de tres parámetros geométricos de esta precámara sobre los procesos de renovación de la carga y combustión: el ángulo tangencial de los agujeros de la precámara, el ángulo azimutal (vertical) de los agujeros y la longitud de la garganta de la precámara. Los resultados han permitido entender aspectos claves de esta arquitec, [EN] Due to growing concern about climate change, greenhouse gas emissions caused by internal combustion engines are in the spotlight. It is necessary to optimize the performance and reduce both consumption and pollution caused by these engines due to the restrictive regulations that are being implemented, in addition to improving the quality of the air we breathe. Spark Ignition (SI) engines are the most widely used propulsion system in passenger car applications. These engines have shown to have greater control of pollutant emissions than compression ignition (CI) engines, however, the efficiency of SI engines is worse than the equivalent CI engines. A novel strategy to improve the thermal efficiency of SI engines is the use of the pre-chamber ignition system. However, the use of this technology has not been optimized so far, and several aspects related to the internal design of the pre-chamber that could improve its performance and increase its tolerance to dilution with exhaust gases are still unknown. Therefore, in this work a design of experiments (DOE) has been developed to study the pre-chamber ignition system in a SI engine using advanced computational fluid dynamics (CFD) tools. The work is based on a numerical model calibrated with experimental measurements for a previously studied reference pre-chamber, with the aim of proposing a new conical pre-chamber architecture, with the volume and diameter of the holes previously optimized to obtain better performance from the jets, and evaluate the impact of three geometric parameters of this new pre-chamber design on the air management and combustion processes: the tangential angle of the pre-chamber holes, the azimuthal (vertical) angle of the holes and the length of the throat of the pre-chamber. The results have allowed to understand key aspects of this pre-chamber architecture, necessary to optimize the operation of the concept., [CA] A causa de la creixent preocupació pel canvi climàtic, les emissions de gasos d'efecte hivernacle causades pels motors de combustió interna es troben en el punt de mira. Cal optimitzar el rendiment i reduir tant el consum com la contaminació causada per aquests motors a causa de les restrictives normatives que s'estan implementant, a més de millorar la qualitat de l'aire que respirem. Els motors d'encesa provocada (MEP) són el sistema propulsiu més utilitzat en el sector de l'transport de passatgers. Aquests motors han demostrat tenir un major control de les emissions contaminants que els motors d'encesa per compressió (MEC), però, l'eficiència dels MEP és pitjor que la dels MEC. Una estratègia innovadora per millorar el rendiment dels MEP és l'ús de sistema d'ignició per precambra. No obstant això, l'ús d'aquesta tecnologia no ha estat optimitzat fins al moment, i encara es desconeixen diversos aspectes relacionats a el disseny intern de la precámara que podrien millorar les seves prestacions i augmentar la seva tolerància a la dilució amb gasos d'escapament. Per això, en aquest treball s'ha desenvolupat un disseny d'experiments (DOE) per estudiar el sistema d'encesa per precámara en un MEP mitjançant eines avançades de dinàmica de fluids computacional (CFD). El treball parteix d'un model numèric calibrat amb mesures experimentals per a una precámara de referència estudiada anteriorment, amb l'objectiu de proposar una nova arquitectura de precambra cònica, amb el volum i diàmetre dels orificis prèviament optimitzats per obtenir millors prestacions dels dolls, i avaluar l'impacte de tres paràmetres geomètrics d'aquesta precámara sobre els processos de renovació de la càrrega i combustió: l'angle tangencial dels forats de la precámara, l'angle azimutal (vertical) dels forats i la longitud del coll de la precámara. Els resultats han permès entendre aspectes claus d'aquesta arquitectura de precámara, necessaris per a optimitzar el funcionament de l'concepte.

[ES] Los procesos físico-químicos que ocurren en la cámara de combustión de sistemas de propulsión actuales se caracterizan por ser complejos y no-lineales. En general, la predicción de estos procesos se realiza a partir de modelos de dinámica de fluido computacional (CFD), los cuales son modelos que han sido altamente desarrollados, pero son costosos. En este trabajo se proponen modelos de regresión basados en el autoaprendizaje que permiten reproducir el comportamiento no lineal de las variables de estudio, y que proporcionan resultados en un tiempo razonable de cálculo., [CA] Els processos fisicoquímics que es produeixen a l’interior de la cambra de combustió dels motors d’encesa per compressió, i a qualsevol altre sistema de propulsió actual, són complexos i no-lineals. De forma habitual, aquests processos es simulen amb mètodes numèrics, entre els quals destaquen els models de dinàmica de fluids computacional (CFD). Aquest tipus de models han sigut altament desenvolupats durant els últims anys i els seus resultats són, generalment, molt exactes, no obstant això, presenten la problemàtica de requerir un cost computacional molt elevat. En este treball es proposen models alternatius capaços de predir els òxids de nitrogen i el consum específic a partir de diferents variables de disseny referides al sistema de combustió en un temps de càlcul raonablement menor. Estos models alternatius consistixen en models de regressió basats en l’autoaprenentatge. Els models de regressió proposats són les xarxes neuronals, el Super Learner i les gramàtiques d’eixam. Al llarg d’aquest treball es desenvolupen tant el seu funcionament com la implementació de cada un d’ells i es comparen les seues respectives capacitats d’ajust entre si, així com el cost computacional que requereixen. Prèviament a l’estudi dels algoritmes es realitza una revisió de diversos aspectes relacionats amb el procés de combustió en motors d’encesa per compressió, amb la finalitat d’entendre l’àmbit en què s’apliquen els algoritmes i conéixer, conceptualment, tant les variables que es prediuen com aquelles a partir de les quals es du a terme la predicció., [[EN] The physico-chemical processes that occur inside the combustion chamber of compression ignition engines, and in any other current propulsion system, are complex and non-linear. These processes are usually simulated with numerical methods, especially with fluid dynamics models (CFD). These kind of models have been highly developed during the last years and their results are, in general, very accurate, however, they have a problem with requiring a very high computational cost. This paper proposes alternative models which are able to predict nitrogen oxides and specific consumption from different design variables referred to the combustion system in a reasonably shorter calculation time. These alternative models consist in self-learning regression models. The proposed regression models are neural networks, the Super Learner and Grammatical Swarm. In this document, it is explained how they work and their implementation. It is also included a comparation between their respective adjustment capabilities, as well as the computational cost that they require. Before the study of the algorithms, a review of different aspects related to the combustion process in compression ignition engines is included, in order to understand the field in which the algorithms are applied and to know, conceptually, the variables that are predicted and those from which the predictions are done.

[EN] Passive pre-chamber ignition concept has been proven to be an excellent strategy to increase the ignition energy and enhance the combustion velocity even when spark-ignition engines are operating in diluted conditions. Other benefits of this system are the increased combustion stability and combustion efficiency, reducing hydrocarbons and carbon monoxide emissions. However, these advantages are limited at some operation conditions such as low engine load or diluted conditions since both the energy available in the pre-chamber and the scavenge of combustion products are compromised. In this framework, numerical studies using two different computational tools, based on one-dimensional modeling, are utilized to gain knowledge about the governing parameters and to improve the design of a pre-chamber when the engine operates at these restrictive conditions. In particular, the impact of the pre-chamber volume, the total cross sectional area of the holes and tangential angle of the nozzles have been numerically evaluated. Different pre-chamber designs were proposed and experimentally tested in a single-cylinder, high compression ratio turbocharged spark-ignition engine fueled with compressed natural gas and operating on Miller cycle. Results give valuable insight into the key aspects of the internal geometry and some relevant design paths to follow for a suitable pre-chamber definition.

[EN] In this study, a numerical methodology for the optimization of the combustion chamber in compression ignited engines using OME as fuel is presented. The objective is to obtain a dedicated combustion system for an engine that is fueled with this alternative fuel improving the efficiency and reducing the emissions of NOx. This article proposes the integration between the optimization algorithm and CFD codes to evaluate the behavior of an engine fuelled with the low sooting fuel OME. Based on a diesel model validated against experimental data, a further model for OME fuel was implemented for evaluating the performance of the engine. The particle swarm algorithm (PSO) was modified based on the Novelty Search concepts and used as optimization algorithm. Several tools are coupled in order to create each CFD case where all the tools and optimization algorithm are coupled in a routine that automates the entire process. The result is an optimized combustion system that provides an increase of the efficiency (about 2.2%) and a NOx reduction (35.7%) in comparison with the baseline engine with conventional fuel. In addition, a neuronal network was trained with all the results of all simulations performed during the optimization process, studying the influence of each parameter on the emissions and efficiency. From this analysis it was concluded that the EGR rate and injection pressure affects the NOx emissions with a range of variability of 63% and 38% respectively.

[EN] In view of the increasing restrictions for CO2 mitigation, the evaluation of alternative fuels to ensure sustainability of transportation is becoming increasingly important. Since some of these alternatives can be refined from renewable sources, they are interesting from the perspective of both: the use of the current power-plants and the CO2 emission. In this sense, natural gas arises as an interesting propellant to substitute fossil fuels. Therefore, combining this fuel with specific combustion strategies can help to decrease the environmental footprint of transportation in the broadest sense. In this paper, an evaluation of the possible advantages of this combination has been conducted. The investigation has been carried out in a port fueled turbocharged spark-ignition engine, using compressed natural gas (CNG) and a passive pre-chamber ignition system. The effects of the CNG fuel properties on combustion have been analyzed and the global impact of using CNG for transportation has been appraised by means of the life cycle assessment. Results show that combustion of CNG refined by different renewable sources not only reduces the global CO2 emission but also can contribute to remove the existent pollution. In addition, they show an increase of the engine thermal efficiency when combining CNG and the pre-chamber ignition concept.

[EN] Hydrogen is one of the most promising alternative fuels for the transportation industry. The use of hydrogen to enable lean burn in internal combustion engines is an attractive solution for reducing CO2 emissions from two points of views: the substitution of carbon-based fuels and the increased thermal efficiency due to lean operation. Combining this strategy with the passive pre-chamber ignition system with gasoline/hydrogen blends is even more interesting. The main limitations of the passive pre-chamber concept in a high compression ratio spark-ignition engine were shown through engine experiments. A numerical study was then performed to evaluate the chance of extending the dilution limit by using hydrogen along with this technology. Results show how the use of hydrogen provides considerable benefits in the main chamber combustion process by enhancing the thermo-chemical properties of the mixture, increasing the flame speed, and improving the flame structure. Using an adequate gasoline-hydrogen blend proved to enable optimum burning rates at lean conditions, leading to a relevant thermal efficiency gain.

[EN] Experimental results from a study on the evolution of gas jets ejected through the orifices of a pre-chamber in a heavy-duty optical engine are presented. The work examines conditions without fuel inside the main-chamber, which helps to describe the dynamics of the ejected gas jets without the interference of subsequent combustion in the main-chamber. Experimental diagnostics consist of high-speed visible intensified imaging and low-speed infrared imaging. Additionally a one-dimensional gas jet model is used to characterize the spatial distribution of the ejected flow, including parameters such as tip penetration, which are then validated based on experimental results. Different stages in the ejection of pre-chamber jets are identified, with chemical activity restricted to a maximum distance of 5 to 10 orifice diameters downstream of the orifice as indicated by the recorded visible radiation. Sensitivity of cycle-to-cycle variations in pre-chamber jet development to the air-to-fuel ratio in the pre-chamber observed in the experiments is in most part attributed to the variations in the timing of combustion initiation in the pre-chamber. The influence of the ejection flow on the penetration of the gas jet on a cycle-tocycle basis is presented using the one-dimensional model. The one-dimensional model also indicates that the local flow exhibits highest sensitivity to operating conditions during the start of ejection until the timing when maximum flow is attained. Differences that exist during the decreasing mass-flow ejection time-period tend to smear out in part due to the transient slowdown of the ejection process

[EN] The need to improve the thermal efficiency of gasoline engines used in hybrid vehicles, has led to explore new solutions for reducing engine heat losses. Hence, it is important for the car manufacturers to be able to predict the heat transfer in the engine components. Numerical methods such as CFD (Computational Fluid Dynamics) or CHT (Conjugate Heat Transfer) can be used to assess the heat losses through the combustion chamber walls, but they are long and costly. In this regard, it is particularly interesting for the industry to use simplified models, which may play a key role in the design stage. In this work a 1D model integrated with 3D finite elements based on a commercial software is used to calculate the heat losses in a single-cylinder gasoline direct injection engine. The model is first validated, then a detailed heat transfer analysis is performed, and its results compared to those of a full CFD-CHT simulation. Results demonstrate that this approach is suitable to predict in a short time the heat losses and the spatial temperature distribution in the solid regions of an internal combustion engine. The model also yields accurate values in terms of engine performance

[EN] The achievement of a carbon-free emissions economy is one of the main goals to reduce climate change and its negative effects. Scientists and technological improvements have followed this trend, improving efficiency, and reducing carbon and other compounds that foment climate change. Since the main contributor of these emissions is transportation, detaching this sector from fossil fuels is a necessary step towards an environmentally friendly future. Therefore, an evaluation of alternative fuels will be needed to find a suitable replacement for traditional fossil-based fuels. In this scenario, hydrogen appears as a possible solution. However, the existence of the drawbacks associated with the application of H-2-ICE redirects the solution to dual-fuel strategies, which consist of mixing different fuels, to reduce negative aspects of their separate use while enhancing the benefits. In this work, a new combustion modelling approach based on machine learning (ML) modeling is proposed for predicting the burning rate of different mixtures of methane (CH4) and hydrogen (H2). Laminar flame speed calculations have been performed to train the ML model, finding a faster way to obtain good results in comparison with actual models applied to SI engines in the virtual engine model framework.

Los perfiles NACA de 4 dígitos, desarrollados por el National Advisory Committee for Aeronautics, se basan en una formulación matemática que define el concepto geométrico del perfil alar con cuatro parámetros según la nomenclatura: NACA 1234. Donde el primer dígito representa la ordenada máxima de la línea media en porcentaje de la cuerda. El segundo dígito caracteriza la posición de la ordenada máxima en décimas de la cuerda. Y los dígitos 3 y 4 definen el espesor máximo en porcentaje de la cuerda. Este laboratorio virtual se centra en la generación de perfiles alares NACA a partir de sus 4 dígitos característicos. Con la obtención del perfil (normalizado respecto a las coordenadas transversales del ala), el alumno será capaz de evaluar las características principales del ala y como se va a comportar esta una vez instalada en el avión. Por tanto, el objetivo de este laboratorio virtual es involucrar al alumno en el propio proceso de diseño del ala, contribuyendo al entendimiento de la relación entre la nomenclatura del perfil y sus características de diseño. A través de la aplicación, el alumno es capaz de generar su propio diseño a partir de sus dígitos característicos, adaptado a las necesidades de su problema.

[ES] El presente estudio se desarrolla en la marco de la combustión en motores de gasolina y se centra en el análisis del concepto de encendido por precámara. El proyecto trata del estudio numérico del proceso combustión en la cámara principal de un motor de las características anteriores, identificando, cuantificando y modelando los fenómenos básicos que intervienen en este proceso. En un principio, se ha diseñado un dominio computacional simplificado para evitar el ruido generado por todos los efectos laterales vinculados al funcionamiento de un motor real. Manteniendo constantes las condiciones iniciales en la precámara, la combustión en la cámara principal se ha investigado variando tanto la energía cinética turbulenta inicial como la tasa de dilución del aire. Los resultados del análisis permitieron identificar los dos mecanismos de combustión involucrados, la combustión de alta turbulencia y la propagación del frente de la llama. El primero de ellos se deteriora rápidamente a medida que se desplaza el proceso de combustión hacia mezclas pobres, y por ello se exploraron dos estrategias adicionales para superar este inconveniente. En primer lugar, incrementar la temperatura inicial demostró ser una solución robusta para mantener las prestaciones del concepto encendido por precámara cuando la combustión de la cámara principal se desarrolla en condiciones ultra-pobres. Desafortunadamente, las emisiones de óxidos de nitrógeno se revelaron inaceptables para cumplir con las normativas anticontaminación. En segundo lugar, se analizó el efecto de la estructura del chorro turbulento en el proceso de combustión en la cámara principal. Con este fin se realizaron un conjunto de simulaciones cambiando parámetros geométricos como el diámetro del orificio y/o su conicidad, y el diámetro de la precámara. Entre ellos, sólo la configuración de orificio de geometría divergente permitió mejorar ligeramente el proceso de combustión durante la etapa dominada por el mecanismo inicial, [EN] The present study is developed in the frame of petrol engine combustion and is focused on the analysis of a Turbulent Jet Ignition concept. The project deals with the numerical investigation of the main chamber combustion by identifying, quantifying and modelling the basic phenomena involved in this process. In the beginning, an extremely simplified computational domain was designed to lose track of all the side effects linked to the functioning of a real engine. Keeping constant the pre-chamber initial conditions, the main chamber combustion was investigated by varying both the initial turbulent kinetic energy and the air dilution rate. The results of the post-processing detected two combustion mechanisms, high turbulence combustion and flame front propagation. Especially, the former is strongly compromised by moving towards lean conditions. Thus, two further strategies were explored to overcome this drawback. Firstly, the increase of the initial temperature proved to be a robust solution to keep the effectiveness of the Turbulent Jet Ignition concept when the main chamber combustion is compromised by the ultra-lean operation. Unfortunately, the nitrogen oxides emissions revealed unacceptable to comply with the ever-increasing anti-pollution regulations. Secondly, the effect of the turbulent jet structure on the combustion process was analyzed. In order to do that, several simulations were carried out changing geometric parameters such as orifice diameter and/or conicity, and pre-chamber diameter. Among them, only the divergent configuration enabled to achieve slightly enhanced combustion during the stage controlled by the initial mechanism.

[EN] As computational capabilities continue to grow, exploring the limits of computational fluid dynamics to capture complex and elusive phenomena, which are otherwise difficult to study by experimental techniques, is one of the main targets for the research community. This paper presents a detailed analysis of the physical processes that lead to combustion noise emissions in internal combustion engines. In particular, diesel combustion in a compression-ignition (CI) engine is studied in order to understand the singular behavior of the in-cylinder flow field responsible for the acoustic emissions. The main objective is, therefore, to improve the understanding of the phenomena involved in CI engine noise using large eddy simulations. Several visualization methods are employed to investigate the connection between combustion behavior and its effects on the pressure field. In addition, proper orthogonal decomposition is used to analyze the modal energy distribution among all the acoustic modes. The results show that the acoustic signature is fundamentally conditioned by the intensity of the premixed combustion rather than by the pressure oscillations generated by turbulent fluctuations in the flame surface established during the diffusion stage.

[EN] In this paper, a computational study was performed using a combination of several numerical tools to better understand the limiting aspects of combustion in a passive pre-chamber ignition system when operating at lean conditions. A specific methodology was developed to analyze in detail the scavenging and combustion processes of this ignition concept. Results show how the scavenging of passive pre-chambers is primarily dependent on the force that the piston makes on the gas during the compression stroke, being independent of the pre-chamber geometry as along as the ratio between the total cross sectional area of the pre-chamber holes and the prechamber volume is kept within a suitable range. Moreover, a successful lean combustion, with an air-to-fuel ratio around 2, cannot be achieved as the burning rates inside the pre-chamber significantly decrease due to the low laminar flame speeds, that results in low quality jets. Further results show that increasing the flow temperature can help to recover competitive combustion rates when knocking combustion is not a limiting factor. The contribution of the heat losses through the pre-chamber walls to the overall energy balance of the pre-chamber has been estimated, showing that their impact is negligible (< 5%). Alternatives for increasing the laminar flame speed were proposed in order to improve combustion inside the pre-chamber. Although the pre-chamber combustion profile was successfully improved, none of the proposed solutions were able to completely burn the main chamber charge with the current pre-chamber design.

[ES] Hoy en día, los efectos negativos del calentamiento global generan una gran preocupación sobre las emisiones de los gases de efecto invernadero y sus consecuencias. Debido al consumo de combustibles fósiles en el sector del transporte, las emisiones de CO2 están aumentando de forma alarmante, siendo este uno de los principales contribuyentes. Además, el uso de estos combustibles también genera una serie de emisiones contaminantes nocivas para el ser humano que degradan la calidad del aire localizadas en las zonas de alta habitabilidad; entre los más conocidos están los óxidos de nitrógeno (NOx) y las partículas de hollín. En este contexto, la optimización de los actuales motores de encendido provocado (MEP) muestra ciertas ventajas respecto a sus principales competidores; los motores de encendido por compresión (MEC). Aunque estos últimos cuentan con un mayor rendimiento térmico que se traduce en menos emisiones de CO2, las futuras normativas anticontaminación están forzando a los fabricantes de motores a evaluar otras alternativas. La integración de un sistema de encendido por precámara en MEP ofrece ciertas ventajas en términos de rendimiento térmico y CO2 sin comprometer el coste del motor en exceso. Sin embargo, la complejidad añadida al incorporar este sistema de encendido hace necesario el desarrollo de nuevas estrategias de diseño que permitan acelerar el desarrollo y la optimización del concepto. Por tanto, en este trabajo se ha desarrollado una metodología de diseño para este novedoso sistema de encendido en un MEP de nueva generación. La metodología se basa en tres herramientas numéricas con diferente grado de complejidad. En primer lugar, un modelo de acción de ondas se utiliza para estimar los flujos entre la precámara y la cámara de combustión. Además, se ha utilizado un modelo unidimensional de chorro para predecir las características de éstos. Y, por último, se ha utilizado un modelo avanzado basado en la dinámica de fluidos computacional (CFD) p, [VL] Les creixents emissions dels gasos d'efecte d'hivernacle estan creant una gran preocupació sobre l’escalfament global i les seues conseqüències. Un dels principals sectors de consum de petroli en el món és el del transport de persones. Per a això s’utilitzen motors de combustió interna alternatius que necessiten combustibles fòssils per al seu funcionament, els quals generen una gran quantitat de CO₂, nociva per al medi ambient. Tot això comporta una degradació de la qualitat de l'aire que respirem i l'augment de malalties respiratòries. La preocupació per la salut i el medi ambient continua creixent a causa a les continues millores de la indústria. Especialment ha sigut el sector de l'automoció el que s'ha vist afectat per la dura normativa anti-contaminació. En aquest marc, els efectes negatius de la contaminació ambiental i sonora estan arribant a límits realment preocupants, sent aquests especialment aparents en els principals nuclis urbans, on les autoritats estan, fins i tot, restringint la circulació dels vehicles tèrmics. Per tant, en aquest treball s'ha desenvolupat una metodologia de disseny per a un nou sistema d'encesa en un motor d'encesa provocada de nova generació. La metodologia es basa en tres eines numèriques amb diferent grau de complexitat. En primer lloc, un model d'acció d'ones s'utilitza per a estimar els fluxos entre la pre-cambra i la cambra de combustió. A més, s'ha utilitzat un model unidimensional per a predir les característiques de l’intercanvi de massa entre les cambres. I, finalment, s'ha utilitzat un model més avançat basat en la dinàmica de fluids computacional (CFD) per a validar els anteriors models i entendre millor el concepte. Els resultats mostren una bona correlació amb les mesures experimentals, demostrant la validesa i utilitat de la metodologia. Utilitzant aquesta metodologia, s'ha proposat un disseny òptim del sistema que augmenta el rang d'operació i la flexibilitat del concepte., [EN] Nowadays, the negative effects of global warming are causing great concern about greenhouse gas emissions and their consequences. Due to the consumption of fossil fuels in the transport sector, CO2 emissions are increasing at a critical rate, with the transport sector being one of the main contributors. In addition, the use of these fuels also generates a number of pollutant emissions harmful to humans that degrade the air quality in areas of high habitability; being nitrogen oxides (NOx) and soot particles among the best known. In this context, the optimization of existing Spark-Ignition (SI) engines shows certain advantages over their main competitor, the Compression-Ignition (CI) engines. Although the latter have a higher thermal efficiency resulting in lower CO2 emissions, future anti-pollution regulations are forcing engine manufacturers to evaluate other alternatives. The integration of a pre-chamber ignition system in SI engines offers advantages in terms of thermal efficiency and CO2 without compromising the cost of the engine in excess. However, the added complexity of incorporating this ignition system requires the development of new design strategies to accelerate the development and optimization of the concept. Therefore, in this work a design methodology has been developed for this novel ignition system in a new generation MEP. The methodology is based on three numerical tools with different degrees of complexity. Firstly, a wave action model is used to estimate the flows between the prechamber and the combustion chamber. In addition, a one-dimensional jet model has been used to predict the characteristics of these. And finally, an advanced model based on computational fluid dynamics (CFD) has been used to validate the previous models and to perform a detailed analysis of the concept. The results show a good correlation with the experimental measurements, demonstrating the validity and applicability of the methodology. Based on these, an optimal sy

[EN] The engine oil contamination by both particulate matter (PM) and fuel is becoming an important problem since strategies to control pollutant emissions in internal combustion engines (ICE) significantly increase their presence in engine oil. As a consequence, the engine oil loses its tribological properties compromising engine lubrication and leading to potential problems in engine such as wear, corrosion, etc. For that reason, the study of the oil degradation and contamination due to these strategies have a special interest to the engine manufacturers and engine oil formulators. In this paper, the engine oil soot content and fuel dilution is analysed under real engine conditions. The study is addressed from two different but complementary points of views. First, on-line measurements at several engine operating conditions are performed in order to further understand how the soot generation correlates with the oil soot content and other derived problems on oil performance. Then, experimental data available after the experimental campaign is used to calibrate a numerical model, based on Computational Fluid Dynamics (CFD), that estimate the amount of soot particles settled in the engine oil. Results show that soot particles are more present in oil when operating high load-speed conditions and during the Diesel Particulate Filter (DPF) regeneration cycles. Regarding the fuel dilution, delayed post-injections are critical since they significantly increase the amount of fuel in the engine oil. Numerical results also show the relationships between the soot particles generated during combustion and the amount of soot in engine oil, giving an enhanced comprehension of soot-in-oil deposition mechanisms.

[EN] As the focus of research and development is put into innovative combustion concepts with the goal of reducing harmful chemical pollutants while keeping or even improving the efficiency of conventional Diesel combustion, it is necessary to consider the impact on noise pollution brought by those innovative concepts. However, the question arises as to what extent the noise characterization and optimization strategies currently applied to conventional Diesel compression-ignited engines are applicable to these innovative combustion concepts. In this paper, we apply experimental noise characterization techniques based on pressure trace decomposition to two compression-ignited engines: a baseline conventional Diesel engine and an innovative 2-stroke engine operating with the gasoline partially premixed combustion concept. Analysis of the results reveals that the underlying physical phenomena responsible for the spectral signature of the noise are still shared between the new and the conventional concepts. However, results evince a significant change in the relevance of these physical sources, leading to necessary changes in optimization strategies for future compression-ignited engine development.

[EN] The pre-chamber ignition concept is an attractive strategy to enable the operation of spark-ignition engines in lean or diluted conditions keeping a suitable combustion process. According to the results the benefits in lean conditions include the combustion process shortening, the improvement of combustion stability and the increase of combustion efficiency by lowering carbon monoxide and hydrocarbons emissions. Thus, the pre-chamber ignition concept, especially in its passive version, arises as a promising alternative for future spark-ignition engines for passenger car applications. In this framework, an experimental investigation has been carried out to evaluate the potential of passive pre-chamber ignition concept in a high compression ratio, turbocharged, port fueled spark-ignition engine, using 95 Research Octane Number gasoline. As a first step, a 1D Wave Action Model was generated to design the pre-chamber geometry taking the fuel available at the start of pre-chamber combustion and the pressure difference between the main chamber and pre-chamber as key parameters. In a second step, these pre-chamber designs were experimentally validated at high load/speed conditions (4500¿rpm, 12.5¿bar Indicated Mean Effective Pressure) and compared with the conventional spark-ignition concept. Experimental results show how the passive pre-chamber concept increases efficiency with good combustion stability and high combustion efficiency in stoichiometric conditions. Nevertheless, maximum lambda attainable with the passive system is similar than that of the conventional spark and much lower compared to the maximum levels reported for the active system.

[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.

[EN] Knock is a major bottleneck to achieving higher thermal efficiency in spark-ignited (SI) engines. The overall tendency to knock is highly dependent on fuel anti-knock quality as well as engine operating conditions. It is, therefore, critical to gain a better understanding of fuel-engine interactions in order to develop robust knock mitigation strategies. In the present work, a numerical model based on three-dimensional (3-D) computational fluid dynamics (CFD) was developed to capture knock in a Cooperative Fuel Research (CFR) engine. For combustion modeling, a hybrid approach incorporating the G-equation model to track turbulent flame propagation, and a homogeneous reactor multi-zone model to predict end-gas auto-ignition ahead of the flame front and post-flame oxidation in the burned zone, was employed. In addition, a novel methodology was implemented wherein a laminar flame speed lookup table generated a priori from a chemical kinetic mechanism could be used to provide flame speed as an input to the G-equation model, instead of using conventional empirical correlations. Multi-cycle Reynolds-Averaged Navier Stokes (RANS) simulations were performed for two different spark timings (STs) corresponding to non-knocking and knocking conditions, with other operating conditions kept the same as those of a standard Research Octane Number (RON) test. Iso-octane was considered as the fuel for the numerical study. Two different reduced kinetic mechanisms were employed to describe end-gas auto-ignition chemistry and to generate the flame speed lookup table. Experimental data, including intake/exhaust boundary conditions, was provided by a spark timing sweep study conducted in an in-house CFR engine. Moreover, cylinder wall/valve/port surface temperatures and residual gas fraction (RGF) were estimated using a well-calibrated one-dimensional (1-D) model. On the other hand, a novel methodology was also developed to analyze experimental data for the knocking case and identify

[EN] It is challenging to develop highly efficient and clean engines while meeting user expectations in terms of performance, comfort and drivability. One of the critical aspects in this regard is combustion noise control. Combustion noise accounts for about 40 percent of the overall engine noise in typical turbocharged diesel engines. The experimental investigation of noise generation is difficult due to its inherent complexity and measurement limitations. Therefore, it is important to develop efficient numerical strategies in order to gain a better understanding of the combustion noise mechanisms. In this work, a novel methodology was developed, combining computational fluid dynamics (CFD) modeling and genetic algorithm (GA) technique to optimize the combustion system hardware design of a high-speed direct injection (HSDI) diesel engine, with respect to various emissions and performance targets including combustion noise. The CFD model was specifically set up to reproduce the unsteady pressure field inside the combustion chamber, thereby allowing an accurate prediction of the acoustic response of the combustion phenomena. The model was validated by simulating several steady operating conditions and comparing the numerical results against experimental data, in both temporal and frequency domains. Thereafter, a GA optimization was performed with the goal of minimizing indicated specific fuel consumption (ISFC) and combustion noise, while restricting pollutant (soot and NOx) emissions to their respective baseline values. Eight design variables were selected pertaining to piston bowl geometry, nozzle inclusion angle, number of injector nozzle holes and in-cylinder swirl. An objective merit function based on the emissions, ISFC and combustion noise, was constructed to quantify the strength of the engine designs, and was determined using the CFD model as the function evaluator. The in-cylinder noise level was characterized by the total resonance energy of local pressure

[EN] In the present work, a numerical methodology based on three-dimensional (3D) computational fluid dynamics (CFD) was developed to predict knock in a 2-Stroke engine operating with gasoline Partially Premixed Combustion (PPC) concept. Single-cycle Unsteady Reynolds-Averaged Navier Stokes (URANS) simulations using the renormalization group (RNG) k - epsilon model were performed in parallel while the initial conditions are accordingly perturbed in order to imitate the variability in the in-cylinder conditions due to engine operation. Results showed a good agreement between experiment and CFD simulation with respect to cycle-averaged and deviation of the ignition timing, combustion phasing, peak pressure magnitude and location. Moreover, the numerical method was also demonstrated to be capable of predicting knock features, such as maximum pressure rise rate and knock intensity, with good accuracy. Finally, the CFD solution allowed to give more insight about in-cylinder processes that lead to the knocking combustion and its subsequent effects.

[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.

[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.

[EN] This paper evaluates the potential advantages of introducing a new injector concept with a dual set of orifices in a 2-stroke engine operating with gasoline partially premixed combustion (PPC gasoline), specially in terms of combustion noise reduction. The injector is based on a configuration with two concentric needle valves and dual actuators, which allows to switch among two independent crowns of holes. The first set of orifices is controlled by the primary needle valve while an additional needle valve manages the secondary holes crown. Moreover, both valves are coupled with the two actuators separately, providing enhanced selective control over injection with an extra degree of freedom. In this investigation, a combination of Computational Fluid Dynamics (CFD) simulations and the Design of Experiments (DoE) technique is proposed with the specific purpose of optimizing this new injector configuration. In addition to determining the most convenient design, this method is extremely useful to establish cause/effect relationships between the injection design parameters and their impact on the engine performance and emissions. Results show how this solution could increase the operating range of the PPC gasoline concept by improving the combustion stability while acoustic emissions are reduced

[EN] As noise pollution remains one of the biggest hurdles posed by thermal engines, increasing efforts are made to alleviate the generation of combustion noise from the early design stage of the chamber. Since the complexity of both modern chamber geometries and the combustion process itself precludes robust analytic solutions, and since the resonant, highly 3D pressure field is difficult to be measured experimentally, focus is put on the numerical modelling of the process. However, in order to optimize the resources devoted to this simulation, an informed decision must be made on which formulations are followed. In this work, the experimental cyclic dispersion of the in-cylinder pressure is analyzed in two typical compression-ignited (CI) and spark-ignited (SI) engines. Acoustic signatures and pressure rise rates are derived from this data, showing how while the preponderance of flame front propagation and dependency of previous cycle in SI engine noise usually calls for multi-cycle, more complex turbulence modelling such as Large Eddy Simulation (LES), simpler Unsteady Reynolds-Averaged Navier-Stokes (URANS) formulations can accurately characterize the more consistent pressure spectra of CI thermal engines, which feature sudden autoignition as the main noise source.

[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.

Las crecientes exigencias de la industria están cambiando la forma en que entendemos la sociedad y el entorno en el que vivimos. Frente a la necesidad de un comercio rápido y globalizado, están emergiendo varios problemas de sostenibilidad. Por una parte, ciertos sectores resultan favorecidos, como es el caso del transporte y su radical incremento de actividades. Por otra parte, esto causa un impacto negativo considerable en los ecosistemas terrestres. En este marco, los efectos negativos de la contaminación ambiental y sonora están llegando a límites realmente preocupantes, siendo estos especialmente visibles en los principales núcleos urbanos, donde las autoridades están incluso restringiendo la circulación de los vehículos térmicos. Particularmente, el ruido producido por la quema del combustible en vehículos propulsados por motores de combustión interna alternativos, siendo una de las principales fuente acústicas por delante de otras como la aviación o el ferrocarril, está siendo objeto de recientes estudios para reducir sus efectos perjudiciales en la población. El objetivo principal de esta tesis se centra en el estudio y caracterización de la combustión como fuente de emisiones acústicas. Concretamente, esta investigación tiene como propósito dar respuesta a cuáles son los fenómenos físicos asociados a la generación del ruido en motores de encendido por compresión, así como proponer algunas directrices que ayuden a entender y mejorar -desde el punto de vista de emisiones acústicas y consumo- el diseño de los motores actuales. En una primera aproximación, se recurre a técnicas experimentales de medida para, con el registro de la presión instantánea dentro de la cámara de combustión, caracterizar el origen de las perturbaciones acústicas. A pesar de que la información aportada por estos métodos es relevante, existen limitaciones para recrear la espacialidad del campo acústico y, por tanto, dificultan la comprensión de los fenómenos no estacionarios asociados a, Les creixents exigències de la indústria estan canviant la forma en què entenem la societat i l'entorn en què vivim. Davant la necessitat d'un comerç ràpid i globalitzat estan sorgint diversos problemes de sostenibilitat que, per una part afavoreixen que sectors com el del transport incrementen les seues activitats de forma radical, però que per l'altra, causen un impacte negatiu en els ecosistemes terrestres. En aquest context, els efectes negatius de la contaminació ambiental i sonora estan arribant a límits realment preocupants, sent aquests especialment visibles als principals nuclis urbans on les autoritats estan inclús restringit la circulació dels vehicles tèrmics. Particularment, el soroll causat per la crema de combustible en vehicles propulsats per motors de combustió interna alternatius, sent una de les principals fonts acústiques per davant d'altres com l'aviació o el ferrocarril, està sent objecte de recents estudis per tal de reduir els efectes perjudicials en la població. L'objectiu principal d'aquesta tesi es centra en l'estudi i caracterització de la combustió com a font d'emissions acústiques. Concretament, aquesta investigació té com a propòsit donar resposta a quins són els fenòmens físics associats a la generació de soroll en motors d'encès per compressió, així com proposar algunes directrius que ajuden a entendre i millorar -des del punt de vista de les emissions acústiques i consum- el disseny dels motors actuals. En una primera aproximació, es recorre a tècniques experimentals de mesura per a, amb el registre de la pressió instantània en la cambra de combustió, caracteritzar l'origen de les pertorbacions acústiques. Tot i que la informació aportada per aquests mètodes és rellevant, existeixen limitacions per a reconstruir l'espacialitat del camp acústic i, per tant, dificulten la comprensió dels fenòmens no estacionaris associats a aquest. Per aquesta raó, en posteriors estudis es recorre a l'ús de la dinàmica de fluids computacional o CFD, s, The ever-increasing demands of industry are changing the way we understand society and the environment in which we live. In the face of the need for rapid and globalised trade, a number of sustainability issues are emerging which, on the one hand, encourage sectors such as transport to radically increase their activities, but, on the other hand, cause a negative impact on terrestrial ecosystems. In this context, the negative effects of environmental and noise pollution are reaching really worrying limits, these being especially visible in the main urban areas where the authorities are even restricting the circulation of vehicles powered with thermal engines. In particular, the noise produced by the fuel burning in vehicles powered by reciprocating internal combustion engines, being one of the main acoustic sources ahead of others such as aviation or railways, is being the focus of recent studies to reduce its harmful effects on the population. The main objective of this thesis focuses on the study and characterization of combustion as a source of noise emissions. Specifically, this research focuses on addressing the physical phenomena associated with noise generation in compression-ignited engines, as well as proposing some guidelines in order to better understand and improve -from the point of view of noise emissions and fuel consumption- the design of current engines. In a first approach, experimental techniques are used to characterise the source of the acoustic disturbances by recording the instantaneous pressure inside the combustion chamber. Although the information provided by these methods is relevant, there are some limitations to recreate the spatiality of the acoustic field and, therefore, make it difficult to understand the non-stationary phenomena associated with it. For this reason, in subsequent studies the Computational Fluid Dynamics or CFD approach is utilized, thereby overcoming the limitations of experimental techniques and allowing a complete vi

[EN] Research efforts in the automotive sector focus on developing new combustion concepts for mitigating the emissions of nitrous oxides and soot of conventional Diesel combustion. One of the most promising concept is the Premixed Charge Compression Ignition. In this, the fuel burns in premixed conditions, avoiding the formation of soot whereas nitrous oxides are controlled using large amounts of exhaust gas recirculation. Because of the premixed combustion, high fuel-burning velocities are produced, whence combustion noise is deteriorated. In order to mitigate this drawback, different blends of gasoline and Diesel fuels are being considered due to their suitability for this combustion characteristics. The effect of these fuel blends on emissions, performance and engine noise is analysed in this paper with the aim to provide additional knowledge of the fundamental issues of this particular combustion mode. The study also includes sweeps of both the start of injection and the amount of exhaust gas recirculation, in order to evaluate further degrees of freedom in the optimisation of the engine settings. Results show that the consideration of the engine noise together with both performance and emissions, reduces dramatically the margin of variation of the combustion settings, limiting therefore the operation range of the engine. (C) 2017 Elsevier Ltd. All rights reserved.

[EN] In this paper, a numerical Computational Fluid Dynamics (CFD) study is carried out with the purpose of understanding how the injector design may impact on the in-cylinder processes, which cause noise emission. This study is based on a combination of the gasoline partially premixed combustion concept with a new high speed direct injection 2-stroke engine, which emerges as a promising solution able to comply with nitrous oxides and particulate matter emissions standards, while ensuring combustion control and stability. The original engine configuration is varied by modifying the included spray angle and the number of injector nozzles in order to evaluate other design solutions for mitigating combustion noise. Results show that the maximum pressure time-derivative achieved during the combustion is the most influential parameter on the acoustic response of the in-cylinder noise source. However, they also evidence that for some operation conditions the resonance phenomena can enhance their contribution, thus playing a relevant role in the engine noise level. Further analysis allowed to identify three combustion related parameters, which characterise this phenomenon and allow identifying key paths to minimize its levels. (C) 2017 Elsevier Ltd. All rights reserved.

In the last decade, different advanced combustion concepts based on generating totally or partially premixed conditions have been investigated in CI (compression ignition) engines with the aim of achieving lower NOx (nitrous oxides) and soot emissions. Most of the drawbacks inherent to this type of combustions, such as the combustion phasing control or combustion stability, can be mitigated by combining the PPC (Partially Premixed Combustion) concept fueled by gasoline and a small 2-stroke HSDI (high speed direct ignition) engine. However, combustion noise issue remains unsolved while it is a critical aspect due to its strong influence in the customer purchasing decision and compliance of more stringent regulations. In this work, an analysis of the combustion noise generated by PPC combustion concept is performed in order to identify the most influential parameters and to define key paths for controlling the noise level. In addition, 3D CFD (Computational Fluid Dynamics) simulations have been performed to further understand the combustion noise generation mechanisms. Results evidence how the strong impact of the maximum pressure time-derivative achieved during combustion process renders all other sources of noise generation irrelevant. The trade-off between combustion noise and combustion efficiency of this PPC concept has been confirmed, while the intrinsic relation between such parameters and the engine efficiency has been also evaluated.