Effect of nozzle geometrical and dynamic factors on cavitating and turbulent flow in a diesel multi-hole injector nozzle

• A flow visualization experiment with a transparent 4-hole mini-sac nozzle was done.
• Geometrical and dynamic factors on cavitating flow were studied together.
• Critical conditions of cavitation inception for different nozzles were got.
• Critical conditions of cavitation inception for different working conditions were got.
• Effect of nozzle sac volume and needle eccentricity on cavitating flow were got.

The presence of cavitation and turbulence in a diesel injector nozzle has significant effect on the subsequent spray characteristics. However, the mechanism of the flow dynamics and its effect on the subsequent spray is unclear because of the complexities of the nozzle flow, such as the cavitation phenomena and turbulence. A flow visualization experiment system with a transparent scaled-up multi-hole injector nozzle tip was setup for getting the experimental data to make a comparison to validate the calculated results from the three dimensional numerical simulation of cavitating flow in the nozzle with mixture multi-phase cavitating flow model and finally a good agreement was seen between the two sets of data. The critical conditions for cavitation inception were derived as well as the relationship between the discharge coefficient and non-dimensional cavitation parameter in numerical simulations. Afterward, the testified numerical models were used to analyze the effects of the nozzle sac volume, orifice inlet curvature, orifice inclination angle, injector needle lift and needle eccentricity on the cavitating flow inside the nozzle. Numerical simulation results can clearly reveal the three-dimensional nature of the nozzle flow and the location and shape of the cavitation induced vapor distribution, which can help understand the nozzle flow better and eventually put forward the optimization ideas of diesel injectors.