MODELLING OF HYDRAULIC FLIP INSIDE A SCALED-UP DIESEL INJECTOR NOZZLE

The ignition process in diesel engines is mainly depending on the quality of mixing process of highly compressed air and fuel. The quality of mixing process here refers to how well the air atoms and fuel atoms are in contact with each other. Mixture of air and fuel particles can induced ignition, but the time frame for a particular ignition is depending on the surrounding parameters. These parameters either delay or furtherance the time frame of ignition. Atomization process that took place in the nozzle and is one of the parameters that enhances the ignition process. Atomization is a process where the fuel in the form of liquid is broken into tiny small particles. Good atomization is required for a better ignition process. The efficiency of atomization is affected by several condition. This paper mainly focused on two conditions. Cavitation and hydraulic flip are those two conditions. Cavitation can enhance atomization process while hydraulic flip reduces the effectiveness of atomization. Hydraulic flip begins when the cavitation bubble goes beyond the super-critical cavitation condition. Eventually, the downstream ambient air which is usually at higher pressure compared to vapor saturation process will enter into the cavitation domain to produce a layer which separates the liquid and the nozzle wall. This phenomenon has a great impact on the structure and atomization of liquid jet. This study is mainly on designing the nozzle which can prevent hydraulic flip. The design of Martynov (2005) was drawn in a computer aided software (SOLIDWORKS, 2014). The validation and simulation of the created nozzle design were performed using computational fluid design software (ANSYS 15.0). Modification of nozzle done by attaching trip wire at the throat of the rectangular nozzle. Trip wire alter the characteristic of the separated shear layer by changing the periodic shedding behavior which dependent on the formation and coalescence of micro-vortex cavity at separated shear layer and re-entrance motion. Shedding frequency increases due to attachment of trip wire. Higher frequency relates to shorter length of cavitation area.