Gasoline Direct Injection(GDi) engines are critically challenged by the new Euro6d regulations and the RDE testing methodology with its greater range of loads, temperatures and altitudes. The main stream GDi engines are based on the pre-mixed homogeneous combustion concept. Therefore it is of key importance to achieve good fuel-gas mixing to have overall homogeneous stochiometric fuel-gas mixture in the combustion chamber at time of ignition under all possible real driving operating conditions. This is an essential requirement for good fuel efficiency (CO2 emission) and low particulate and HC, CO emissions. The NOx emission of a homogeneous combustion engine can be effectively treated by the after-treatment system. The major concern in GDi engine development is the particulate emission. This is especially critical at high load operating conditions for a downsized engine, where the spray layout (spray targeting and individual jet mass distribution) has a key influence on engine combustion and soot emission performance. Engineering research and optimization is required to achieve optimal fuel-air mixing and to avoid liquid wetting on cold components in the combustion chamber. Another main contributor for soot is the diffusion flame caused by the injector tip fuel wetting and the residual fuel in the nozzle sac volume after needle closure. This phenomenon involves very complex physical and chemical processes and is so far not well understood. This project work is dedicated to develop CFD methodology and combustion modelling for investigating these particulate emissions production phenomena. With complete package of numerical tool chain for combustion chamber wall film, mixture homogeneity, injector tip wetting and diffusion flame, injector nozzle design influence on combustion and emission characteristics could be analyzed in a more scientific way and thus enabling ‘knowledge based’ approach for injector nozzle design optimization to meet stringent performance and emission requirements for RDE cycle.