Effect of piezo-driven and solenoid-driven needle opening of common-rail diesel injectors on internal nozzle flow and spray development

Abstract

A prototype piezo-driven diesel injector has been developed and characterized in terms of measured flowrate, predicted cavitating nozzle hole flow distribution, and visual spray development. Results are compared with those obtained for a conventional solenoid-driven diesel injector equipped with the same micro-sac multi-hole injection nozzle. The response time and the needle lift trace for both injectors have been predicted for injection pressures up to 1300 bar using a hydraulic simulation model. Mie spray images obtained using a high-speed camera and utilizing diffusion illumination light, have allowed estimation of the spray tip penetration and spray cone angle under a variety of back pressures. The experimental results show that the piezo-driven injector produces longer spray tip penetration and smaller spray cone angle. This has been supported by CFD simulations of the internal nozzle hole cavitating flow obtained using the transient needle profile of the solenoid- and the piezo-driven injectors. Model predictions suggest an increase in the fuel exit momentum of the piezo-driven nozzle during the opening phase of the needle, relative to those of the solenoid-driven one.