Les mécanismes d’évolution spatio-temporelle des structures turbulentes instationnaires tridimensionnelles, et en particulier ceux rencontrés aux plus grandes échelles, sont à l’origine de phénomènes d’instabilité qui conduisent très souvent à une diminution de la performance des systèmes énergétiques. C’est le cas des variations cycle-à-cycle dans le moteur à combustion interne. Malgré les progrès substantiels réalisés par la simulation numérique en mécanique des fluides, les approches expérimentales demeurent essentielles pour l’analyse et la compréhension des phénomènes physiques ayant lieu. Dans ce travail de thèse, deux types de vélocimétrie par image de particules (PIV) ont été appliqués et adaptés au banc moteur optique du laboratoire Coria pour étudier l’écoulement en fonction de six conditions de fonctionnement du moteur. La PIV Haute Cadence 2D2C a permis d’abord d’obtenir un suivi temporel de l’écoulement dans le cylindre durant un même cycle moteur ainsi qu’identifier ces variations cycliques. La PIV Tomographique 3D3C a permis ensuite d’étendre les données mesurées vers l’espace tridimensionnel. La Tomo-PIV fait intervenir 4 caméras en position angulaire visualisant un environnement de géométrie complexe, confinée, ayant un accès optique restreint et introduisant des déformations optiques importantes. Cela a nécessité une attention particulière vis-à-vis du processus de calibration 3D des modèles de caméras. Des analyses conditionnées 2D et 3D de l’écoulement sont effectuées en se basant principalement sur la décomposition propre orthogonale (POD) permettant de séparer les différentes échelles de structure et le critère Γ permettant l’identification des centres des tourbillons. / The unsteady evolution of three-dimensional large scale flow structures can often lead to a decrease in the performance of energetic systems. This is the case of cycle-to-cycle variations occurring in the internal combustion engine. Despite the substantial advancement made by numerical simulations in fluid mechanics, experimental measurements remain a requirement to validate any numerical model of a physical process. In this thesis, two types of particle image velocimetry (PIV) were applied and adapted to the optical engine test bench of the Coria laboratory in order to study the in-cylinder flow with respect to six operating conditions. First, the Time-Resolved PIV (2D2C) allowed obtaining a temporal tracking of the in-cylinder flow and identifying cyclic variabilities. Then tomographic PIV (3D3C) allowed extending the measured data to the three-dimensional domain. The Tomo-PIV setup consisted of 4 cameras in angular positioning, visualizing a confined environment with restricted optical access and important optical deformations. This required a particular attention regarding the 3D calibration process of camera models. 2D and 3D conditional analyses of the flow were performed using the proper orthogonal decomposition (POD) allowing to separate the different scales of flow structures and the Γ criterion allowing the identification of vortices centres.

Most mature oil reservoirs or fields tend to perform below expectations, owing to high level of associated gas production. This creates a sub-optimal performance of the oil production surface facilities; increasing oil production specific operating cost. In many scenarios oil companies flare/vent this gas. In addition to oil production constraints, associated gas flaring and venting consists an environmental disasters and economic waste. Significant steps are now being devised to utilise associated gas using different exploitation techniques. Most of the technologies requires large associated gas throughput. However, small-scale associated gas resources and non-associated natural gas reserves (commonly referred to as stranded gas or marginal field) remains largely unexploited. Thus, the objective of this thesis is to evaluate techno- economic of gas turbine engines for onsite electric power generation called gas- to-wire (GTW) using the small-scaled associated gas resources. The range of stranded flared associated gas and non-associated gas reserves considered is around 10 billion to 1 trillion standard cubic feet undergoing production decline. The gas turbine engines considered for power plant in this study are based on simple cycle or combustion turbines. Simple cycle choice of power-plant is conceived to meet certain flexibility in power plant capacity factor and availability during production decline. In addition, it represents the basic power plant module cable of being developed into other power plant types in future to meet different local energy requirements. This study developed a novel gas-to-wire techno-economic and risk analysis framework, with capability for probabilistic uncertainty analysis using Monte Carlo simulation (MCS) method. It comprises an iterative calculation of the probabilistic recoverable reserves with decline module and power plant thermodynamic performance module enabled by Turbomatch (an in-house code) and Gas Turb® software coupled with economic risk modules with @Risk® commercial software. This algorithm is a useful tool for simulating the interaction between disrupted gas production profiles induced by production decline and its effect on power plant techno-economic performance over associated gas utilization economic life. Furthermore, a divestment and make- up fuel protocol is proposed for management of gas turbine engine units to mitigate economical underperformance of power plant regime experienced due to production decline. The results show that utilization of associated gas for onsite power generation is a promising technology for converting waste to energy. Though, associated gas composition can be significant to gas turbine performance but a typical Nigerian associated gas considered is as good as a regular natural gas. The majority of capital investment risk is associated with production decline both natural and manmade. Finally, the rate of capital investment returns decreases with smaller reserves.

Currently environmental concerns are driving internal combustion engine manufacturers to seek greater fuel efficiency, more refinement and lower emissions. Cyclic variation is a known obstacle to achieving the greatest potential against these goals and therefore an understanding of how to reduce these is sought. It is widely accepted that cyclic variation in in-cylinder flow motions is a key contributor to overall cyclic variation and therefore the characterisation of factors affecting these is an important step in the process of achieving a better understanding and ultimately control of cyclic variation. This thesis reports the development of a novel optical engine research facility in which high speed digital particle image velocimetry (HSDPIV) has been applied to the study of flow field behaviour within a direct injection spark ignition (DISI) engine. This study investigates the spatial and temporal development of flow structures over and within many engine cycles. Flow field PIV measurements have been captured with a high spatial resolution and temporal frequencies up to 5 kHz from a number of measurement locations at a large range of crank angles. The major contributions from this work have included the use of the novel measurement technique to investigate spatial and temporal flow field development in the intake runner, valve jet, in-cylinder tumble and swirl planes and the pent roof. The gathered data have been used to investigate cycle by cycle variations in both high and low frequency flow structures. Major findings of this work have included the observation of highly varying flow fields throughout the engine cycle. Frequency analysis of these flows has allowed the low frequency bulk motions and higher frequency turbulent components to be studied. The low frequency flow field components are shown to create varying flow field interactions within the cylinder that also affect the manner in which the flow develops over the course of the cycle. The intensity of the turbulence fluctuations, u , has been calculated based upon the high frequency components within the flow and variations within this are shown to correlate with pressure related combustion parameters.

Cette étude est motivée par la protection de l'environnement et la réduction des émissions de CO2 émis par les moteurs à combustion interne. L'objectif de la thèse est d'étudier les possibilités de la réduction de la consommation de carburant d'un moteur diesel d’automobile grâce à la récupération de la chaleur des gaz d'échappement basée sur un cycle de Rankine. Afin de déterminer l'énergie perdue, le moteur a été testé sur un banc d’essais et les paramètres des gaz d’échappement ont été mesurés. Un modèle de simulation du moteur a également été développé et validé grâce aux résultats expérimentaux. Le potentiel de récupération de chaleur sur les gaz d’échappement et sur le refroidissement a été estimé. Cette analyse a révélé que le potentiel sur les gaz d’échappement est plus élevé que celui sur le refroidissement. Grâce au modèle numérique et aux essais, la puissance et l'efficacité du cycle de Rankine ont été étudiées. Enfin, l'impact du système de récupération d’énergie sur les performances du moteur a été analysé. Les résultats montrent que la puissance du moteur augmente de 4,3% au point de puissance maximale du moteur. / This study is motivated by the environment protection and the reduction of emissions CO2 from internal combustion engines. The aim of the thesis is to study the possibilities of fuel consumption reduction of a diesel engine intended for a passenger car by means of waste heat recovery from exhaust gases based on thermodynamic cycle (Rankine cycle). In order to determine the waste heat, the engine was tested on a test bench as the exhaust parameters were measured. A simulation model of the engine has also been developed and validated by means of experimental results. The recovery potential of the exhaust gases and the cooling system has been estimated. This analysis revealed that the waste heat recovery potential of the exhaust gases is higher that the cooling sys-tem. By means of Rankine cycle numerical model and experimental test, the output power and efficiency of the Rankine cycle were studied. Finally, the impact of the heat recovery system on engine performance was studied. The results revealed that the engine power increases by 4.3% at the operating point which corresponds to the maximum engine power. / Това изследване е мотивирано от опазването на околната среда и намаляването на емисиите на CO2 от двигателите с вътрешно горене. Целта на дисертацията е да проучи възможнос-тите за намаляване на разхода на гориво на дизелов двигател, предназначен за лек автомо-бил, чрез рекупериране на енергия с цикъл на Ранкин. За да се определи неоползотворената енергия в отработилите газове бе използван изпитателен стенд. Симулационен модел на двигателя е разработен и валидиран чрез експерименталните резултати. Направена е оценка на потенциала за рекупериране на енергия от отработилите газове и охладителната система. Този анализ показва, че потенциала за рекупериране е по-голям в изпускателната система. С помощта на експериментален стенд и числен модел на цикъла на Ранкин са установени мощността и ефективността на системата. Въздействието на системата за рекупериране на енергия е изследвано. Данните показват, че мощността на двигателя се увеличава с до 4,3%.

L’allumage par claquage laser non résonant des mélanges réactifs considérés à l’état gazeux et au repos est étudié dans ce travail, principalement avec des mélanges n-décane/air (C₁₀H₂₂+N₂+O₂). Ce système est considéré comme étant prometteur dans les différentes stratégies futures concernant les systèmes d’allumages équipant les moteurs à combustion interne. Le plasma d’allumage est généré en focalisant un faisceau laser de haute intensité pendant quelques nanosecondes. Le laser Nd :YAG opère à 1064 nm, il est choisi comme source laser pour l’ensemble des expériences menées en laboratoire afin de montrer l’effet des paramètres physiques, optiques, thermodynamiques (pression) et chimiques (additifs : H₂O, Ar) sur les caractéristiques de l’allumage. Cette étude met en oeuvre une approche statistique sur l’ensemble des expériences en prenant en compte l’ensemble des mesures prises lors de la combustion. Ce manuscrit offre une base de données expérimentale permettant d’appréhender la combustion et la phénoménologie de claquage laser. / Ignition by non-resonant laser breakdown of quiescent reactive mixtures was considered in this experimental study working with gaseous state. In this work, we mainly study the ignition of n-decane / air (C₁₀H₂₂+N₂+O₂) mixtures. This system is considered promising in different future strategies regarding ignitions systems for internal combustion engines. The breakdown is generated by focusing a high intensity laser beam for a few nanoseconds using Nd: YAG laser operating at 1064 nm, it is chosen as the laser source for all experiments conducted here. The experimental plan conducted allows to examine the effect of physical, optical, thermodynamic (pressure) and chemicals (additives: H₂O, Ar) on the characteristics of the laser ignition. This study implements a statistical approach on all the experimental cases taking into account all the measures during breakdown and combustion. This manuscript provides bibliographic basis for understanding combustion and laser breakdown phenomenology.

Cette thèse présente la Simulation des Grandes Echelles (LES) de l’injection, de la pulvérisation et de la cavitation dans un injecteur pour les applications liées aux moteurs à combustion interne. Pour la modélisation de l’atomisation, on utilise le modèle ELSA (Eulerian Lagrangian Spray Atomization). Le modèle résout la fraction volumique du combustible liquide ainsi que la densité de surface d’interface liquide-gaz pour décrire le processus complet d’atomisation. Dans cette thèse, l’écoulement à l’intérieur de l’injecteur est également pris en compte pour une étude ultérieure de l’atomisation. L’étude présente l’application du modèle ELSA à un injecteur Diesel typique, à la fois dans le contexte de RANS et de LES.Le modèle est validé à l’aide de données expérimentales disponibles dans Engine Combustion Network (ECN). Le modèle ELSA, qui est normalement conçu pour les interfaces diffuses (non résolues), lorsque l’emplacement exact de l’interface liquide-gaz n’est pas pris en compte, est étendu pour fonctionner avec une formulation de type Volume of Fluid (VOF) de flux à deux phases, où l’interface est explicitement résolu. Le couplage est réalisé à l’aide de critères IRQ (Interface Resolution Quality), qui prennent en compte à la fois la courbure de l’interface et la quantité modélisée de la surface de l’interface. Le modèle ELSA est développé en premier lieu en considérant les deux phases comme incompressibles. L’extension à la phase compressible est également brièvement étudiée dans cette thèse. Il en résulte une formulation ELSA compressible qui prend en compte la densité variable de chaque phase. En collaboration avec l’Imperial College de Londres, la formulation de la fonction de densité de probabilité (PDF) avec les champs stochastiques est également explorée afin d’étudier l’atomisation. Dans les systèmes d’injection de carburant modernes, la pression locale à l’intérieur de l’injecteur tombe souvent en dessous de la pression de saturation en vapeur du carburant, ce qui entraîne une cavitation. La cavitation affecte le flux externe et la formulation du spray. Ainsi, une procédure est nécessaire pour étudier le changement de phase ainsi que la formulation du jet en utilisant une configuration numérique unique et cohérente. Une méthode qui couple le changement de phase à l’intérieur de l’injecteur à la pulvérisation externe du jet est développée dans cette thèse. Ceci est réalisé en utilisant le volume de formulation de fluide où l’interface est considérée entre le liquide et le gaz; le gaz est composé à la fois de vapeur et d’airambiant non condensable. / This thesis presents Large Eddy Simulation (LES) of fuel injection, atomization and cavitation inside the fuel injector for applications related to internal combustion engines. For atomization modeling, Eulerian Lagrangian Spray Atomization (ELSA) model is used. The model solves for volume fraction of liquid fuel as well as liquid-gas interface surface density to describe the complete atomization process. In this thesis, flow inside the injector is also considered for subsequent study of atomization. The study presents the application of ELSA model to a typical diesel injector, both in the context of RANS and LES. The model is validated with the help of experimental data available from Engine Combustion Network (ECN). The ELSA model which is normally designed for diffused (unresolved) interfaces, where the exact location of the liquid-gas interface is not considered, is extended to work with Volume of Fluid (VOF) type formulation of two phase flow, where interface is explicitly resolved. The coupling is achieved with the help of Interface Resolution Quality (IRQ) criteria, that takes into account both the interface curvature and modeled amount of interface surface. ELSA model is developed first considering both phases as incompressible, the extension to compressible phase is also briefly studied in this thesis, resulting in compressible ELSA formulation that takes into account varying density in each phase. In collaboration with Imperial College London, the Probability Density Function (PDF) formulation with Stochastic Fields is also explored to study atomization. In modern fuel injection systems, quite oftenthe local pressure inside the injector falls below the vapor saturation pressure of the fuel, resulting in cavitation. Cavitation effects the external flow and spray formulation. Thus, a procedure is required to study the phase change as well as jet formulation using a single and consistent numerical setup. A method is developed in this thesis that couples the phase change inside the injector to the external jet atomization. This is achieved using the volume of fluid formulation where the interface is considered between liquid and gas; gas consists of both the vapor and non condensible ambient air.