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. Spray macroscopic characteristics such as penetration, cone angle and spray area are compared with the fuel mass injected from each hole by specially designed equipment. For further understanding, the orifice geometries, in terms of orifice coning, inner and outer diameter, k factor, rounding radius, are measured through the 3-D models of these two nozzles, which are established based on synchrotron X-ray micro-tomography provided by SSRF (Shanghai Synchrotron Radiation Facility).
The results show that the sprays of these two nozzles are distributed unevenly in space, and its variance can reach to circa 15%. The fuel mass measurements correspondingly support this conclusion, as fuel mass injected from each orifice present 10% difference in weight. Compared to the orifice coning, inner and outer diameter, the rounding radius at each inlet orifice differ the most and has the most effects on spray performance.