Visualization and simulation study on the impacts of conical duct geometry on the spray characteristics of ducted fuel injection

In this work, experiment and simulation methods were employed to investigate the spray characteristics of ducted fuel injection (DFI) configured the conical duct. A cylindrical duct was used for comparison. The diameter of the small port of the conical duct is the same as the diameter of the cylindrical duct hole. The conical duct is placed in two ways, namely contracted and expanded placement. The research was conducted under injection pressure of 120 MPa, high ambient density of 65.6 kg/m³ and non-vaporizing conditions. The perspectives of spray dispersion, spray morphology and gas-fuel mixing at the duct inlet were investigated as indicators for evaluating spray performance. Results showed that the duct confinement is the main reason for the difference in spray performance. Under the duct confinement, the fuel adhering to the inner wall of the duct during the spraying process forms a film. Depending on whether the spray collides directly with the duct wall, the interaction of the spray with the duct is interpreted as direct interaction and indirect interaction. The film shows a jitter-like development under the direct interaction and develops smoothly under indirect interaction. Direct interaction is beneficial to improve spray performance, while indirect interaction is the opposite. The duct confinement changes the velocity field, Turbulent Kinetic Energy field and pressure field of the spray, which results in the difference in the spray performance of each spray method. A strong gas entrainment occurs at the duct inlet, contributing to the formation of a high quality gas-fuel mixture. For these spray performances, DFI with the conical duct does not perform as well as that of the cylindrical duct and the conical duct is better placed in contraction than in expansion.