Visualization and Simulation Study on Impacts of Wall Roughnesson Spray Characteristics of Ducted Fuel Injection

The creative proposal of ducted fuel injection (DFI) in the application of heavy-duty diesel engines is to improve the quality of gas-fuel mixture in the combustion zone. The present research employed experimental and simulation methods to investigate the impact of the roughness of the inner wall of the duct on DFI spray characteristics. The study was carried out under high injection pressure of 120 MPa and high ambient density of 54.2 kg/m3. It was found that DFI spray configured with the smooth-walled and rough-walled duct both accelerate the axial diffusion with respect to free spray, and the smooth-walled duct performs best. The duct confinement is attributed to this by allowing the spray inside the duct to flow axially at a high velocity, and slowing down the momentum decay compared to the mass exchange between the spray and the ambient gas. DFI spray with smooth-walled duct shows better overall diffusion compared to that of free spray, but the rough-walled duct shows the opposite, highlighting the strong spray-film interaction of the smooth wall promotes the overall diffusion, while the weak interaction of the rough wall accelerates the attenuation of the overall diffusion momentum with respect to free spray. Regardless of the smooth-walled or rough-walled duct, the pumping effect caused by the huge pressure difference between the inside and outside of the duct formed by the duct confinement causes strong gas entrainment at the duct inlet, promoting the formation of a sufficient and uniform gas-fuel mixture inside the duct, which is beneficial to the formation of leaner combustion