String Cavitation and 3D PIV in Multi-Hole Injector = String Cavitation and 3D PIV in Multi-Hole Injector

다국어 초록 (Multilingual Abstract)

It is essential to control fuel spray characteristics in diesel engines for cleaning up exhaust gases and improving combustion efficiency. Turbulent cavitating flow in fuel injectors plays an important role in fuel spray characteristics. String cavitation may occur in a sac and nozzles of multi-hole fuel injectors, which strongly affects fuel spray characteristics. It should be caused by the vortex flow in the sac. However, the occurrence mechanism of string cavitation has not been clarified yet. The purpose of this study is to clarify the mechanism and condition of string cavitation occurrence by conducting a high-speed visualization experiment in a transparent injector of cavitation and a discharged liquid jet at various needle lifts and flow rates. We also measure the three-dimensional flow field in the sac by 3D PIV. The transparent acrylic multi-hole mini-sac nozzle is designed to visualize cavitation. Sodium iodide aqueous solutions or diesel oil with α-methyl naphthalene is used as a working fluid to avoid the refraction at the surface of the acrylic walls and these liquids. As a result, it is found that at low needle lift string cavitation often occurs which is surrounded by a vortical flow in the sac and increases the discharged hollow-cone liquid jet angle, while at high needle lift thin and short string cavitation may occur, which does not strongly influence discharged liquid jet and spray. The probability of the string cavitation appearance under various conditions as well as the transient motion of string cavitation and liquid jet is also clarified.