Flash Boiling Evidences of a Multi-Hole GDI Spray under Engine Conditions by Mie-Scattering Measurements 2015-01-1945

During an injection process, a fluid undergoes a sudden pressure drop across the nozzle. If the pressure downstream the injector is below the saturation value of the fluid, superheated conditions are reached and thermodynamic instabilities realized. In internal combustion engines, flashing conditions greatly influence atomization and vaporization processes of a fuel as well as the mixture formation and combustion.

This paper reports imaging behavior of a fuel under both flash boiling and non-flash boiling conditions. A GDI injector, eight-hole, 15.0 cc/s @ 10 MPa static flow, injected a single-component fluid (iso-octane), generating the spray. Experiments were carried out in an optically-accessible constant-volume quiescent vessel by Mie-scattering technique. A C-Mos high-speed camera was used to acquire cycle-resolved images of the spray evolving in the chamber filled with N₂ which pressure ranged between 0.05 and 0.3 MPa. Two sets of measurements were carried out with the injector and fuel temperature constant at ambient and 363 K, respectively. A single pulse strategy was adopted, 0.68 ms in duration, with two injection pressures: 10.0 and 20.0 MPa. Tip penetrations, cone-angles, and spray enlargements are reported at all the injection settings.