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The performance of Gasoline Direct Injection (GDI) engines is governed by multiple physical processes such as the internal nozzle flow and the mixing of the liquid stream with the gaseous ambient environment. A detailed knowledge of these processes even for complex injectors is very important for improving the design and performance of combustion engines all the way to pollutant formation and emissions. However, many processes are still not completely understood, which is partly caused by their restricted experimental accessibility. Thus, high-fidelity simulations can be helpful to obtain further understanding of GDI injectors. In this work, advanced simulation and experimental methods are combined in order to study the spray characteristics of two different 3-hole GDI injectors.

In recent times, due to the improvement of internal cylinder flow analysis technology with Computational Fluid Dynamics (CFD), the prediction accuracy of fuel consumption and emission has improved. However, small motorcycles often have complex intake ports which restrict the layout of injectors. Therefore optimization of injection spray to achieve high combustion efficiency and less wall wetting is a challenge. In this study, we predicted fuel consumption and emission performance by the simulation result of air fuel distribution and wall wetting amount with an actual motorcycle engine model. We optimized injector nozzle length, spray angle and spray tip penetration. After the optimization, we evaluated the emission performance and fuel consumption with an actual engine. As a result, we were able to confirm the improvement of fuel consumption and emission performance.