Gasoline and gasoline-like fuels (naphtha) have high volatility, which results in flash boiling spray in gasoline engines when operated at throttling or low load conditions. Flash boiling can achieve better atomization, thus benefit fuel evaporation and fuel-air mixing. However, when flash boiling occurs, spray morphology, and fuel distribution are dramatically varied from the injectors' intentional design. This difference will affect the performance of combustion and emissions. Thus it is essential to investigate the spray collapse phenomenon regarding varied conditions. The currently developing gasoline compression ignition (GCI) engines, also has throttled stoichiometric spark ignition operation mode, which inevitably has flash boiling possibility. However, there is a lack of research on flash boiling spray with a GCI injector, which has a large designed cone angle. This work aims to understand the spray collapse phenomenon and fill the gap in GCI flash boiling spray. Simultaneous side-view diffused back illumination (DBI) and front-view mie-scattering are used to capture the liquid spray development. Simultaneous shadowgraph from side and front view are used for recording the liquid+vapor phase spray development. Criteria for distinguishing different spray regimes have been established from these results. It shows this GCI injector is more resistant to collapse than the other conventional gasoline direct injection (GDI) injectors reported in the literature. A combination of DBI and space-time tomographic algorithm is validated in this work, achieving 3D reconstruction of the spray volume development from non-flashing to collapsed spray regime at low cost. The 3D results help elucidate the spray collapse procedure and provide validation data for CFD simulation. Structured laser illumination planar imaging (SLIPI) is firstly implemented in flash boiling spray study in this work to suppress the multiple scattering effect. Reconstructed 3D results from slice sweeping by SLIPI methods exposes the hollow structure in the spray's collapsed central jet, which has not been reported previously by other methods. Different spray motion types are summarized for the transitional and collapsed spray regime from the SLIPI slice and confirmed by the particle image velocimetry (PIV) technique.

Le moteur essence à allumage par compression (GCI), reposant sur la combustion partiellement prémélangée de l'essence (GPPC), peut potentiellement assurer des opérations efficaces et propres. Le moteur GCI s'est avéré efficace à forte charge, mais l'indice d'octane élevé de l'essence limite considérablement les opérations à faible charge. Le présent travail étudie le potentiel de l'utilisation de l'ozone, fort agent oxydant, pour améliorer la réactivité de l'essence et permettre le fonctionnement à faible charge de GCI. L'ozone peut être produit on board en équipant le moteur d'un générateur d'ozone, sans impact dramatique sur le coût du moteur et sur la complexité du contrôle du moteur. Les essais effectués avec un moteur monocylindre ont montré que l'ozone favorise la combustion HCCI de l'essence, permettant d'étendre la limite d’auto-inflammation et de réduire la température minimale nécessaire de celle-ci. Les diagnostics optiques ont montré que ces propriétés sont liées à une prolifération radicale accrue, amenées par des réactions à basse température induites par l'ozone. En parallèle, le processus de combustion GCI a été étudié dans des conditions de faible charge. Sans ozone, la température d'admission doit être considérablement augmentée pour permettre l'auto-inflammationdes mélanges essence-air pauvres. De plus, les résultats indiquent que le monoxyde d’azote (NO) contenu dans les gaz brûlés résiduels peut, dans certaines conditions, favoriser fortement la combustion GCI. Ensuite,l'effet de l'ozone a été étudié dans des conditions d'injection directe GCI. Les résultats démontrent qu’une stratégie avec double injection est nécessaire pour maximiser l’effet promoteur de l’ozone et pour contrôler le processus de combustion GCI. Enfin, l'utilisation d’une forte concentration d’ozone a permis d’atteindre des opérations à faible charge en mode GCI, avec des faibles émissions de NOx et de suie, et cela, sans avoir besoin d'augmenter la température ou la pression d'admission. / Gasoline Compression Ignition (GCI) engine, relying on Gasoline Partially Premixed Combustion (GPPC) has potential for efficient and clean operations. GCI engine showed to be effective at high load, however, the highoctane number of gasoline dramatically limits low load operations. The present work investigates the potential of using ozone, a strong oxidizing agent, to improve gasoline reactivity and enabling low load GCI operation.Ozone can be produced in-situ and on-demand by equipping the engine with an ozone generator, without a dramatic impact on the engine cost and the engine control complexity. Experiments in a single cylinder engine showed that ozone promotes gasoline HCCI combustion, making possible to extend the lean limit and reducing the minimum temperature needed for autoignition. Optical diagnostics showed that these properties are related to an increased radical proliferation related to ozone-induced low temperature reactions. In parallel, GCI combustion process was investigated under low load conditions. Without ozone, the intake temperature should be considerable increased to enable auto ignition of lean gasoline-air mixtures. Moreover, results indicated that the NO contained into residual burnt gases can strongly promote GCI low load combustion. Finally, the effect of ozone was investigated under GCI direct-injection conditions, demonstrating that low load GCI operation with low NOx and Soot emission can be achieved by seeding the intake of the engine with ozone without needing of increasing the intake charge temperature or boosting the intake pressure.