Modelling of primary breakup process of a multi-hole spray for Gasoline Direct Engine applications

The paper proposes a numerical methodology for the simulation of a gasoline spray generated by a multi-hole injector of a current production wall-guided Gasoline Direct Injection engine. Particular care is dedicated to the accurate representation of the spray primary breakup by means of an atomization model. The model is purposely implemented to take into account cavitation phenomena and turbulent effects induced by the nozzle geometry through a simplified approach. Since a high primary breakup rate is expected, an initial distribution of atomized droplets is predicted at the nozzle hole exit by the numerical approach. The spray is at first experimentally investigated in a test vessel at non-evaporative ambient conditions and under quiescent conditions, injecting commercial gasoline at two different injection pressures (10.0 and 20.0 MPa). The spray is characterised in terms of both instantaneous mass flow rate and morphology. Numerical simulations are performed and then compared against experiments in order to evaluate their capability to correctly predict liquid spray penetration, droplet size distribution and spray morphology. The new approach is a fairly simple yet reliable solution able to predict the influence of the nozzle hole (in terms of discharge coefficient, diameter and length) and neglecting geometrical details usually far from being easily accessed by engine developers.