Analysis on spray behavior of ducted fuel injection under different ambient pressures

Ducted fuel injection (DFI) has the potential to reduce soot emissions with respect to free injection. To explore the spray performance of DFI under different ambient pressures as well as to keep up with the trend of high intensification in diesel engines, a LES numerical model was adopted to investigate and analyze the spray behavior of DFI in the perspectives of spray development and gas entrainment under the ambient gas pressure ranges from 3 MPa to 12 MPa. The numerical results were validated by the visualization experiment. Free spray was targeted for comparison with DFI spray. The investigation results indicated that the difference between DFI spray and free spray is attributed to the spray-duct interaction. The ambient gas between duct wall and spray acts as a pivot to achieve the spray-duct interaction. With ambient pressure increasing, more ambient gas plays the pivotal role. The axial and overall development of DFI spray is faster than those of free spray, and the advantage is more obvious with increasing ambient pressure. The pressure difference between the inside and outside of duct causes a regular gas entrainment at the duct inlet. The pressure drop ratio and the gas entrainment rate both decrease as ambient pressure increases.