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In this study, in order to form a wide range of ambient gas density, Nitrogen and sulfur hexafluoride (SF6) are employed as ambient gas. Based on the common rail and high speed imaging system, the spray characteristics in extremely high ambient density and different ambient temperature are investigated in a constant volume vessel, and the influences of gas physical property on the spray characteristics have also been analyzed. The investigation results show that: the spray tip penetration and spray cone angle vary phenomenally with the increase of the ambient gas density. Due to the generation of shock wave, the results of the spray characteristics from two ambient gas densities are different nevertheless the same densities. Furthermore, the spray tip penetrations from the different ambient gases do not vary obviously from each other until the detachment of the shock wave from the spray tip.

Spray behavior is regarded as one of main factors which influence engine performance, fuel consumption and emissions for diesel engine. In practice, spray characteristics from each orifice from a multi-hole nozzle are normally arranged symmetrically, while the hole-to-hole spray variation is unavoidable. This variation will cause spatial uneven distribution of spray and combustion degrade, which will be no longer inconsiderable in face of the more and more stringent emission rules. In this paper, two methods including spray macro-characteristics experiment and separated fuel mass measurement are employed to test the hole-to-hole spray variation of two six-hole symmetric VCO injectors of different brands, and experiments are operated under different conditions including different injection pressures, back pressures and injection durations.

In this study, the orifice inlet rounding radii of four diesel nozzles with different hydro erosive grinding time were measured based on the x-ray CT scan technology provided by Shanghai Synchrotron Radiation Facility (SSRF), and a wide parametrical study of the spray macroscopic behavior in the first 18 mm from the nozzle tip have been carried out with high speed camera. And then the influence of orifice inlet rounding radius on the spray behavior in the near-nozzle field was thoroughly investigated. The investigation results show that: the mean values of orifice inlet rounding radii of different nozzles are measured to be on the order of 21.5-56.8 μm. Although the spray tip penetrations of different nozzles tend to increase with the hydro erosive grinding time through statistical analyzing method, the variations of penetration from nozzles are less than 15% according to different hydro erosive grinding timing.