Schlieren investigation on impacts of duct size on macroscopic spray characteristics of ducted fuel injection

Ducted fuel injection (DFI) is a cutting-edge technology for boosting the air-fuel mixture quality of heavy-duty diesel engines. The present study employs ducts with different lengths and inner diameters to investigate the diesel macroscopic spray characteristics of DFI spray by Schlieren optical technique and compares them with a free spray. The experiment is carried out in a constant-volume spray chamber with a single-hole injector. Injection pressure ranges from 40 to 160 MPa and ambient pressure is set to 6 MPa. Spray morphology, spray tip penetration, spray cone angle and spray area are analysed. It is found that DFI spray with long and small inner diameter duct shows a considerable improvement in spray characteristics compared to those of free spray, especially under higher injection pressure. Besides, the use of long and small inner diameter duct is more comfortable to form a clear mushroom-shaped head spray at the duct outlet. These advantages can be attributed to the enhanced air-fuel mixing.