Gasoline direct injection (G-DI) engines offer several advantages over traditional Port Fuel Injection (PFI) engines with regards to achieving substantial improvement in fuel economy and emissions without deteriorating engine performance. The motivation of this thesis is to contribute to the development of new optical techniques for analysis of 'air-fuel' mixing processes occurring in G-DI engines, particularly spray impact and spray evaporation. A 3-dimensional laser induced fluorescence technique is developed to quantify the thickness and spatial distribution of transient liquid fuel films formed as a result of spray-wall interaction. Calibrated temporally-resolved benchmark results of a transient spray from a gasoline direct injector impinging on a flat quartz crown are presented, with observations and discussion of the transient development of the fuel film. Experimental results for atmospheric and elevated ambient pressures are presented and discussed, providing an insight on the influence of elevated ambient density in the deposition of fuel films. The technique proved successful at characterising, qualitatively and quantitatively, the development of fuel films, particularly describing the transient effect of the fuel film thickness and shape. The calibrated measurements are consistent with previous qualitative studies of spray impact and demonstrate the applicability of the technique for appraisal of CFD predictions. For the analysis of spray mass transfer, a Laser Induced Exciplex Fluorescence (LIEF) technique is also developed. LIEF is an optical diagnostic technique that generates spectrally separated fluorescence signals from liquid and vapour phases of a spray, providing temporal and spatial resolution of both species simultaneously. Experiments at three sets of ambient conditions are presented to examine the influence of temperature and pressure variations on airborne liquid/vapour mass ratio. Quantitative analysis of vapour concentrations is discussed along with potential limitations for quantitative results, particularly for dense sprays. Finally, a simulation on a commercially available CFD code is presented to explore the potential of TIR-LIF for validation of spray impingement models. CFD results are compared with TIR-LIF experimental data, showing good comparison of quantitative trends and fuel film characteristics. However, areas for further development are identified and discussed.