Comparisons in spray and atomization characteristics with/without hydro-erosive (HE) grinding in nozzle orifice under non-evaporation and evaporation conditions

摘要

Cavitation in nozzle orifices plays an important role on atomization and spray. In the industrial manufacturing, the processing method, especially the fluid grinding technology seriously affects the geometry of the orifice, such as the inlet rounding and roughness of inner orifice, which may result in the cavitation and turbulence of the internal flow. Therefore, the effect of grinding nozzle orifice on fuel spray was studied in this paper. Two mini-sac injectors with the same single orifice were used to compared. One was electrical discharge machining (EDM) nozzle orifice with Hydro-Erosive (HE) Grinding, and the other was EDM orifice without grinding. The spray experiments were conducted in the constant volume chamber. Firstly, the discharged coefficient (C-d) was calculated by controlling the injection duration and quantity. Secondly, non-evaporating characteristics were obtained through Mie scattering method. The spray tip penetration, spray area, spray cone angle and spray angle were defined and analyzed. Then, evaporating behaviors were characterized by laser absorption scattering (LAS) measurement as well as vapor mass and evaporation ratio. Finally, microscopic behaviors of near-nozzle spray and droplets were compared with the help of particle image analysis (PIA) technology. Results showed that owing to the cavitation without grinding process, C-d decreased sharply, leading to less spray area and angle. But the evaporation was promoted by the cavitation and turbulence. More vapor mass and evaporation ratio can be obtained without HE Grinding. Furthermore, droplet size becomes smaller without grinding due to the better atomization by turbulence. However, the mean velocity decreases sharply, and the coefficient of variation (COV) increases without grinding, which should be considered carefully in the injector design.