Fuel mixture formation and spray characteristics are crucial for the advancement of Gasoline Compression Ignition (GCI) engine. For investigations of spray characteristics, a high-pressure high-temperature spray chamber with constant volume has been designed, tested and commissioned at CCRC, KAUST. Back light illumination technique has been applied to investigate the macroscopic spray properties of an outwardly opening piezoelec- tric injector. Three parameters including injection pressure, ambient pressure, and ambient temperature have been involved. A total of 18 combinations of experimental conditions were tested under non-reactive conditions. Through qualitative analysis of spray morphology under different operating conditions, an apparent distinction of spray morphology has been noticed. Spray morphology and propagation have shown strong dependencies on ambient pressure and ambient tempera- ture while injection pressure has a negligible effect on spray shape. Increasingly compact and bushier spray patterns were observed in the cases of high ambient pressure due to in- creasing aerodynamic drag force on spray boundary. It should also be noted that ambient temperature plays a fairly important role in fuel evaporation rate. At 200 °C, oscillating and considerably short spray shape was produced. Also, circumferential ring-like vortices and distinctive string-like structures have been identified for the fuel spray exiting this hollow cone injector. It has been observed that high ambient pressure conditions (Pamb = 4 bar and 10.5 bar) are favorable to the vortices generation, which has also been reported in previous literature. The quantitative description of macroscopic spray properties reveals that ambient pres- sure and ambient temperature are found to be the most influential parameters on liquid penetration length. The rise of ambient pressure results in considerably shorter liquid pen- etration length. Ambient temperature also appears to be a very effective factor of reducing penetration length. Injection pressure contributes to a notable increase of liquid penetra- tion length under ambient pressure of 1 atm. However, the influence of injection pressure is substantially reduced under ambient pressures of 4 bar and 10.5 bar, which indicates that ambient pressure exerts much stronger influence than injection pressure on liquid penetra- tion length. Furthermore, it has been revealed that the increase of injection pressure and ambient pressure are the predominant sources contributing to the enlargement of spray cone angle. The effect of injection pressure on spray cone angle has been amplified by the increase of ambient pressure. With increasing ambient pressure, the penetration of injected fuel tends to propagate axially in a much slower manner that leads to wider fuel distribution in the radial direction. Ambient temperature exerts a similar influence on spray cone angle as on liquid penetration length. The spray cone angle experiences a noticeable decline when ambient gas is increased to 200 °C.

Une analyse exhaustive de la piézoélectricité a été réalisée par la modélisation moléculaire basée sur l'application des principes de la mécanique quantique. La calibration de la méthode et des paramètres du calcul est d'abord examinée en comparant les résultats calculés concernant les oxydes de silicium et de Germanium à leurs homologues expérimentaux. Ensuite, les paramètres microscopiques qui influencent chaque contribution de cette propriété macroscopique de réponse sont distinctement rationalisés. Enfin, après la rationalisation de la propriété piézoélectrique, la conception de matériaux montrant un effet piézoélectrique élevé a été tentée. Nous avons montré que la grande piézoélectricité induite par un dopage dans le plan du graphène tendra vers une valeur unique, ni nulle ni infinie, et de façon indépendante de la nature physique ou chimique particulière du défaut. L'induction d'une piézoélectricité hors du plan du graphène en brisant sa planéité selon la direction-z est également étudiée. La réponse piézoélectrique obtenue est largement améliorée par rapport à la limite finie de la piézoélectricité dans le plan, mais aux grandes concentrations du défaut seulement. En effet, contrairement à la composante dans le plan de la piézoélectricité, la composante hors du plan, dépend de la nature du défaut et diminue jusqu'à tendre vers zéro à dilution infinie. / An exhaustive analysis of the technologically important piezoelectric phenomena is here done by applying quantum chemical simulations. At first, the calibration of the assumed computational scheme is examined by comparing our calculated piezoelectric properties of the well-known piezoelectric quartz to their experimental counterparts. Secondly, the microscopic parameters that influence each contribution of piezoelectric macroscopic property are distinctly rationalized. After the rationalization of the piezoelectric property, the design of materials that exhibiting a high piezoelectric effect has been attempted. It has been shown that a large in-plane piezoelectricity induced in graphene by doping can be acquired by including any in-plane defect(s). Moreover, in the limit of vanishing defect concentration, the piezoelectric response tends toward a unique value, neither null nor infinite, regardless of the particular chemical or physical nature of the defect. The induction of an out-of-plane piezoelectricity in graphene by breaking its planarity through the non-periodic z-direction is stated, where the obtained piezoelectric response is largely improved compared to the finite in-plane piezoelectric limit, at however higher concentration of the defect. Contrarily to what has been discussed for the in-plane piezoelectric effect, the out-of-plane one eventually vanishes as far as the limit of infinite defect dilution is reached, and so it relies ultimately on the nature of the defect.

Trois systèmes ternaires (SAS, BAS et ZAS) ont été étudiés dans le cadre de la thèse. Les principaux objectifs étaient l’élaboration et la caractérisation de verres aluminosilicatés de Sr, Ba et Zn peu étudiés auparavant. Une étude systématique a été réalisée sur des aluminosilicates vitreux et dans certains cas sur des aluminosilicates fondus avec différents rapports MO/Al₂O₃ (M = Sr, Ba, Zn) et SiO₂/Al₂O₃. Les compositions étudiées couvrent une partie significative des diagrammes ternaires (des silicates aux verres peralumineux, des compositions pauvres en silice à celles riches en silice). Cela a permis d'accroître nos connaissances sur les domaines de vitrification de ces systèmes. Afin d’obtenir des informations sur la structure et les propriétés macroscopiques des verres SAS, BAS et ZAS, une approche multi-technique a été mise en place. Une telle approche permet d’avoir une vue d’ensemble sur les systèmes étudiés et de trouver des origines nano- à microscopiques aux propriétés macroscopiques. La spectroscopie de résonance magnétique nucléaire, la diffractométrie de neutrons et la spectroscopie Raman ont été utilisées au cours de la thèse afin de sonder l'échelle à courte et à moyenne distance. Les propriétés macroscopiques mesurées ont été : la densité, la viscosité et la température de transition vitreuse. Les données issues de cette thèse permettent une meilleure compréhension des changements de structures et des propriétés macroscopiques des verres aluminosilicatés produits par les variations de MO/Al₂O₃ ou SiO₂/Al₂O₃, ou par la nature des cations non-formateurs de réseau. / Three ternary systems (SAS, BAS and ZAS) have been investigated within the framework of the PhD thesis. The main goals were the elaboration and characterization of previously poorly studied Sr, Ba and Zn aluminosilicate glasses. A systematic study has been carried out on glasses and in some cases on melts with various MO/Al₂O₃ (M = Sr, Ba, Zn) and SiO₂/Al₂O₃ ratios. The compositions studied cover a significant part of the ternary diagrams (from silicates to peraluminous glasses, from silica-poor to silica-rich compositions). This allowed expanding our knowledge of the vitrification domains in these systems. In order to obtain information on the structure and macroscopic properties of SAS, BAS and ZAS glasses, a multi-technique approach has been implemented. Such approach allows having a broad view on the systems and finding nano- to microscopic origins of macroscopic properties. The techniques used during the thesis probe short- (NMR, ND) to medium-range (Raman) scale and among the properties studied were density, viscosity and glass transition temperature. The data resulting from this thesis provides a better understanding of the changes in the structure and macroscopic properties of the aluminosilicate glasses produced by variations in MO/Al₂O₃ or SiO₂/Al₂O₃, or by the nature of non-network forming cation.