Assessment of a numerical model for multi-hole gasoline sprays to be employed in the simulation of spark ignition GDI engines with a jet-guided combustion mode

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 FireTM 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. Initial droplets size is hypothesised according to a log-normal distribution based on a physical reasoning. Comparisons between the achieved numerical results and the experimentally evaluated penetration lengths allow to establish the droplets distribution shape and the physical models better approximating the actual spray behaviour. In a second part of the paper the assessed model is used to simulate the mixture formation process in a high speed four-stroke spark ignition engine. The influence on the engine performances of different orientations of the injector, chosen compatibly with constructive constraints, is highlighted.