ID 267

Flash Boiling Spray of a Hollow Cone GDI Injector under Low Ambient Pressure

 

Abstract:

Good spray atomization facilitates the fuel evaporation in a gasoline engine, thus contributes to higher fuel effi-ciency and lower emission. Flash boiling is a phenomenon which leads to internal boiling of the fuel, causing vapor bubbles to form within the droplet. Then explosion and collapse of the vapor bubbles can significantly boost the droplet breakup and evaporation. During certain stages of a gasoline direct injection (GDI) engine, the combination of increased fuel temperature and sub-atmospheric cylinder pressure during injection can lead to flash boiling con-dition. In this study, experimental studies were carried out to study the flash boiling spray of a hollow cone GDI piezoelectric injector. Different sets of heating devices were used to ensure the fuel, injector and ambient tempera-ture are all kept at same value, and the temperature ranges from 25 C to 125 C. The fuel being used is pure isooc-tane and the ambient pressure ranges from 1 bar to 0.01 bar. By the combination of different temperature and am-bient pressure, different superheat degree (SD) and different ambient-to-saturation ratio (Pa/Ps) can be achieved. The spray development under non-flash boiling and flash boiling condition were compared. For a hollow cone injec-tor, the flare flash boiling spray can cause the cone shape spray to expand, both inwards and outwards, comparing to the cone spray under non-flash boiling conditions. This is different from the flash boiling spray of a multi-hole injector, which would collapse towards the axis. The axisymmetric inward expansion would converge together and form a fast axial development of the spray. Shock wave phenomenon was also produced by flash boiling spray penetration front under high superheated conditions.