Very high pressures for injecting gasoline in internal combustion (i.c.) engines are recently explored for improving the air/fuel mixing process in order to control unburned hydrocarbons (UBHC) and particulate matter emissions such as for investigating new combustion concepts. The challenge remains the improvement of the spray parameters in terms of atomization, smaller droplets and their spread in the combustion chamber in order to enhance the combustion efficiency. In this framework, the raise of the injection pressure plays a key role in GDI engines for the trade-off of CO2 vs other pollutant emissions. This study aims contributing to the knowledge of the physical phenomena and mechanisms occurring when fuel is injected at ultra-high pressures for mapping and controlling the mixture formation. Liquid and vapor phases of the fuel, injected by a GDI multi-hole device, were investigated to highlight the pressure role (up to 100 MPa) on the spray morphology under different ambient conditions. Commercial gasoline was injected in a constant volume vessel by a prototypal 5-hole, L/d: 2.6, solenoid activated GDI injector. Nitrogen gas was pressurized in the vessel to realize densities ranging from 0.2 to 11.5 kg/m3, at temperatures variable between room and 473 K.
Mie-scattering, for the liquid phase, and shadowgraph techniques, for the liquid + vapor phases, were adopted to depict the fuel spread, registering images on a high-speed C-Mos camera. The influences of the ambient gas and injection conditions were of particular interest providing fundamental of the physics insight the fuel penetration and vaporization. The spray profiles indicated a strong sensitivity against the ambient conditions. Under flash-boiling settings, very high injection pressures induced a loss of the classic mushroom morphology, related to the spray-collapse, because the increased droplet velocities, along the axial direction, become a dominant effect.