An optical investigation on spray macroscopic characteristics of ducted fuel injection

Ducted fuel injection (DFI) spray is a new spray method that mimics Bunsen burner and has shown a great potential to reduce soot emissions and improve thermal efficiency for heavy-duty diesel engines. But the mechanism has not been revealed clearly. The present study focuses on how the duct impacts the spray characteristics compared to free spray considering the importance of air-fuel mixing. Experiments were performed in a constant-volume spray chamber with a single-hole injector. Schlieren visualization technique was used to capture vapor-phase of sprays under different injection pressures. It was found that DFI spray is more dispersed compared to free spray. DFI spray could increase spray penetration significantly compared to free spray, especially under higher injection pressures. DFI spray could also increase spray cone angle by about 4° compared to free spray. Since diesel spray was trapped in the duct, when the spray penetrated through the duct, DFI spray area was smaller than that of free spray during initial period, but quickly exceeded that of free spray and became larger and larger. These advantages indicate DFI is able to improve the air-fuel mixing process.