Spray morphology transformation of propane, n-hexane and iso-octane under flash-boiling conditions

Spray collapse has been widely observed under both flash-boiling and non-flash-boiling conditions when multi-hole gasoline direct injection (GDI) injectors with compact nozzle configurations were used. The main objective of this study is to further understand the collapse mechanisms by using liquids with appreciably different properties (propane, n-hexane and iso-octane). The tests were carried out in a constant volume vessel with ambient pressures ranging from 0.6 bar to 11.0 bar and fuel temperatures from 30 °C to 110 °C. Flashing propane sprays presented a non-collapse feature under elevated-ambient-pressures but flash-boiling conditions. By close-up examination of flashing propane sprays over a wide range of liquid temperatures and ambient pressures, it was found that there should be an ambient pressure threshold between 1.0 and 3.0 bar between the collapsed and the non-collapse sprays for propane. The spray collapse occurred as the ambient pressure is below the threshold. The non-collapse feature for flashing propane sprays under the ambient pressures beyond the threshold was attributed to the prohibition of nucleation and bubble growth under elevated ambient pressures.