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Three high pressure multi-hole GDI injectors, one manufactured by Continental, two manufactured by Bosch, are experimentally characterized under various injection strategies in terms of instantaneous mass flow rate and fuel dispersion. Spray visualization within an optically accessible pressure vessel allows the measurement of the single jet cone angle and penetration length. A portable numerical model for the issuing spray dynamics is developed within the AVL Fire code, exploiting a log-normal distribution for the initial droplets diameter, whose expected value and variance are properly defined as a function of the main physical parameters. Tuning of the entering constants is realized by means of an automatic optimization procedure. An example of application of the spray model within a 3D simulation of the in-cylinder process of a GDI engine is presented. Effects of splitting injection into two successive events are discussed.

The work relates to the use of multidimensional modelling as a tool for improving the robustness of combustion of a Gasoline Direct Injection (GDI) Spark Ignition (SI) engine. A procedure is assessed for the prediction of the thermo-fluid-dynamic processes occurring in a single-cylinder, four-stroke engine, characterised by a bore-to-stroke ratio close to the unity, and a pent-roof head with four valves. The engine is at a design stage, under development for application on two wheels vehicles. A new generation six-holes Bosch injector is considered as realising a jet guided combustion mode. This last is preferred for its potential in realising effective charge stratification and great combustion stability under various operating conditions. The three-dimensional (3D) numerical model is developed within the AVL FIRE™ software environment.

Results of an experimental campaign conducted on a multi-hole gasoline injector are used to assess a numerical model for the spray dynamics suitable to be employed for the prediction of a GDI engine pressure cycle. The considered injector generates a spray with a hollow-ellipsoid footprint structure on a plane perpendicular to the spray axis. Spray penetration lengths and cone angles are measured at different injection pressures and total injected masses in an optically accessible vessel containing nitrogen at controlled conditions of temperature and pressure. Injected mass flow rate is measured on a Bosch tube. The numerical simulation is performed within the AVL Fire™ code environment. As a first step, the gasoline is considered as entering a constant volume environment containing nitrogen, in order to reproduce the effected experiments. Measured injection flow rates and cone angles are used as input variables for the model.