Ducted Fuel Injection: An Experimental Study on Optimal Duct Size

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Ducted Fuel Injection: An Experimental Study on Optimal Duct Size

Martin, Glen / Svensson, Kenth / Fitzgerald, Russell

Ducted fuel injection (DFI), a concept that utilizes fuel injection through ducts, was implemented in a constant pressure High Temperature Pressure Vessel at 60 bar ambient pressure, 800-1000 K ambient temperature, and 21 % oxygen. The ducts were 14 mm long and placed 3-4.7 mm from the orifice exit. The duct diameters ranged from 1.6-3.2 mm and had a rounded inlet and a tapered outlet. Diesel fuel was used in single-orifice fuel injectors operating at 250 MPa rail pressure.The objective of this work was to study soot reduction for various combinations of orifice and duct diameters. A complete data set was taken using the 150 μm orifice. A smaller data set was acquired for a 219 μm orifice, showing similar trends.Soot reduction peaked at an optimal duct diameter of 2-2.25 mm, corresponding to an 85-90 % spray area reduction for the 150 μm orifice. Smaller or larger duct diameters were less effective. Duct diameter had a minimal effect on ignition delay.Ambient temperature had an apparent strong effect on soot reduction. At 800 K, where the reaction rates were slower, DFI reduced soot by more than 94 % via longer lift-off lengths regardless of the duct geometry. At 1000 K, where the lift-off length was much shorter, apparent DFI soot reduction peaked at 42 %. For the larger orifice diameter, duct effectiveness was less sensitive to duct diameter.