Experimental study on influence of pressure fluctuation and cavitation characteristics of nozzle internal flow on near field spray

To investigate the causal relationship between the multi-frequency pressure fluctuations and the characteristics of the cavitation in the nozzle, as well as the influence mechanism on the near-field spray, a high-speed microscopic imaging technique was used to carry out the visualization experiment of the real-size tapered hole nozzle under different common rail pressures. The research show that the fluctuation trends such as pressure drop, fluctuation duration as well as coupling characteristics of high and low frequency can reflect the injection quantity, effective injection duration and cavitation morphology in the nozzle to some extent. The hydraulic servo action under different injection pressures affects the needle valve displacement, which in turn affects the throttling position and cavitation morphology during the injection process. After cavitation occurs, the pressure wave velocity and pressure wave transmission frequency in the pipe are obviously changed by affecting the bulk elastic modulus of the gas-mixed liquid. When geometry-induced cavitation occurs, the pressure fluctuates at low frequency, and the whole is relatively smooth. When string cavitation occurs, high-frequency pressure fluctua-tions tend to occur. The maximum lift and effective duration of needle valve determine the overall trend of pressure fluctuations, and cavitation characteristics affect the frequency characteristics and propagation speed of pressure fluctuations. The research provides theoretical support for the prediction method of fuel flow and cavitation characteristics in high-pressure nozzle based on high-low frequency identification of pressure fluctuations.