Visualization of Cavitation Phenomena at a Nozzle Hole and a Seat in a Fuel Injection Nozzle by Neutron Radiography

It is supposed that cavitation occurs in a fuel injection nozzle of a Diesel engine and affects the fuel spray. Cavitation phenomenon have been observed in the optically transparent nozzles simulating the Diesel engine fuel injection nozzle. However, no visualization in a real nozzle was reported since the real nozzle was made of metal and opaque to optical rays. Nucleation phenomena like cavitation are affected much on the wall surface and the liquid conditions. Therefore, visualization of the fuel behaviors in the real nozzle is important to the study of the cavitation phenomena. Neutron radiography is suitable for visualizing the fuel behaviors inside the metallic nozzle since neutron attenuation in the fuel is much higher than that in the nozzle body made of iron. Visualization of cavitation in a one-hole nozzle of a Diesel engine fuel injector was carried out by using neutron radiography systems at KUR in Research Reactor Institute of Kyoto University and at HANARO in Korea Atomic Energy Research Institute. Neutron pulses made by a chopper synchronized to the injector rotation were irradiated to the fuel injection nozzle for high shutter speed exposures. Real metallic nozzles and light oil were used. The nozzle hole size was 0.38 mm and the maximum pressure was 20 MPa. The revolution number was changed from 360 rpm to 600 rpm. A multi-exposure method was applied to obtain a clear image as an ensemble average of the synchronized images. The Abel transformation was applied to the images to obtain axial-symmetric distributions of the fuel from the projection images. The fuel behaviors at the nozzle hole and the seat were observed. The cavitation phenomena were observed at both the nozzle hole and the seat.