Good spray atomization facilitates fuel evaporation in a gasoline engine, thus contributes to higher fuel efficiency and lower emissions. Flash boiling is a phenomenon which leads to internal fuel boiling. It causes vapor bubbles to form within the droplet and promotes droplet breakup and evaporation. During certain operations 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 condition. In this study, experiments 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 that the fuel, injector and ambient temperature are all kept at same value, and the temperature ranges from 25 °C to 125 °C. The fuel used is pure isooctane and the ambient pressure ranges from 1 kPa to 100 kPa. By the combination of different temperature and ambient pressure, different superheat degrees and different ambient-to-saturation pressure ratios (Pa/Ps) can be achieved. For a hollow cone injector, 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. The axisymmetric inward expansion would converge together and form a fast developing plume shape, and the transition point is around 0.5 for Pa/Ps ratio. The peak penetration velocity and spray axial penetration are compared between different experimental conditions. When Pa/Ps is larger than 0.5, the spray development is dominated by the injection momentum and the effect of flash boiling is minor. When Pa/Ps is reduced to below 0.5, the flash boiling effect takes place and changed the spray dynamics. The peak penetration velocity start increasing rapidly with the superheated degree only when Pa/Ps ratio is smaller than 0.5. The spray axial penetration results showed three regimes corresponding to Pa/Ps value.
|Original language||English (US)|
|Title of host publication||14th International Conference on Liquid Atomization and Spray Systems, ICLASS 2018|
|Publisher||ILASS � Europe, Institute for Liquid Atomization and Spray Systems|
|State||Published - Jan 1 2020|