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The continually increasing stringent requirements in terms of emissions and performance lead to the demand for further development of gasoline engines, in order to satisfy the regulations and to be competitive in the market. One of the main limitations in simultaneously improving the efficiency and performance of SI engines is the knock behaviour. This phenomenon limits either the possibility to adopt a higher compression ratio, which would be beneficial for the engine efficiency, or it causes a poor combustion timing which leads to a higher fuel consumption and a lag in performance. As a result, having the possibility to judge the risk of knock during the design phase can be beneficial to increase the potentials of the engine. In this work, a methodology for the prediction of the knock tendency in spark ignition engines using a 3D-CFD software has been developed.

In this work the formation and the evolution of the fuel spray emerging from a hollow-cone swirl injector were investigated. The first aim of the work was to set up a tool for fuel spray simulation in a CFD analysis that can offer a reasonable accuracy with no significant increment in the computational time. The analysis started from a theoretical formulation of the fuel flow inside the injector, based on the potential theory, obtaining an injector model which allows the calculation of the main spray characteristics usually required by the CFD analysis (i.e. droplet velocity, fuel film thickness, droplet size distribution). These parameters can be obtained only from spray cone angle and mass flow rate, which are the data commonly provided by injector manufacturers. Furthermore, a phenomenological approach was also presented, in order to properly simulate in CFD analysis the spray tip penetration in the dense spray zone, without requiring an increase of the spatial grid resolution.