Visual experiment of transient cavitating flow characteristics in the real-size diesel injector nozzle

Cavitating flow inside diesel injector nozzles affects subsequent atomization behaviors and then spray characteristics which is decisive for diesel engine performance and pollutant formation. In this paper, particular attention was focused on the transient flow characteristics in the real-size diesel nozzle. An experimental study under different pressures was conducted to analyze the evolution of cavitation inside diesel nozzle, and it was found that higher injection pressure leads to earlier cavitation inception. The bubble “suction” from orifice exit at the end of injection and the bubble “discharge” at the initial stage of the next injection were observed as well. Moreover two types of “string cavitation” were observed and the “string cavitation” as a special cavitation phenomenon which considerably boost the spray angle was investigated in details. It was found that the occurrence of “string cavitation” has a strong relationship with the location of needle, the injection pressure, and the shape of sac. Furthermore the effects of these three factors on the occurrence regularity of the “string cavitation” were also investigated.