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Today, Direct-Injection systems are widely used on Spark-Ignition engines in combination with turbo-charging to reduce the fuel-consumption and the knock risks. In particular, the spread of Gasoline Direct Injection (GDI) systems is mainly related to the use of new generations of multi-hole, high-pressure injectors whose characteristics are quite different with respect to the hollow-cone, low-pressure injectors adopted in the last decade. This paper presents the results of an experimental campaign conducted on the spray produced by a GDI six-holes injector into a constant volume vessel with optical access. The vessel was filled with air at atmospheric pressure. Different operating conditions were considered for an injection pressure ranging from 3 to 20 MPa. For each operating condition, spray images were acquired by a CCD camera and then post processed to evaluate the spray penetration and cone angles.

The preparation of the air-fuel mixture represents one of the most critical tasks in the definition of a clean and efficient SI engine. Therefore it becomes necessary to consolidate the numerical methods which are able to describe such a complex physical process. Within this context, the authors developed a CFD methodology into an open-source code to investigate the air-fuel mixture formation process in PFI engines. Attention is focused on moving mesh algorithms, Lagrangian spray modeling and spray-wall interaction modeling. Since moving grids are involved and the mesh quality during motion strongly influences the computed in-cylinder flow-field, a FEM-based automatic mesh motion solver combined with topological changes was adopted to preserve the grid quality in presence of high boundary deformations like the interaction between the piston bowl and the valves during the valve-overlap period.

During the last years the deep re-examination of the engine design for lowering engine emissions involved two-wheel vehicles too. The IC engine overall efficiency plays a fundamental role in determining final raw emissions. From this point of view, the optimization of the in-cylinder flow organization is mandatory. In detail, in SI engines the generation of a coherent tumble vortex having dimensions comparable to the engine stroke could be of primary importance to extend the engines' ignition limits toward the field of the dilute/lean mixtures. For motorbike and motor scooter applications, the optimization of the tumble generation is considered an effective way to improve the combustion system efficiency and to lower emissions, considering also that the two-wheels layout represents an obstacle in adopting the advanced post-treatment concepts designed for automotive applications.