Effect of sac-volume on the relationship among ball behavior, injection and initial spray characteristics of ultra-high pressure GDI injector

Abstract The purpose of this study is to analyze the effect of sac-volume in high-pressure gasoline direct injection (GDI) injector on ball behavior, initial spray characteristics, and the post-injection after the end of injection. In this study, the advanced visualization technique, X-ray phase contrast imaging (XPCI), used to visualize and analyze the ball behavior inside the injector, and the initial spray behavior within several millimeter (mm) from the nozzle tip. Using XPCI and Mie-scattering techniques, the relationship between spray characteristics and the internal flow could be analyzed at injection pressures of 10 MPa and 35 MPa, for injection duration of 0.52 ms and 1.5 ms. Results showed that the ball was further away from the center of the nozzle when testing with a smaller sac volume. Regarding spray characteristics, smaller sac volume led to increased spray tip penetration due to a lower average ball lift. In addition, as the sac volume decreases, the amount of residual fuel discharged at the end of injection was less; additionally, ligaments and droplets formed were smaller.