Ducted fuel injection (DFI) is a developing strategy for reducing in-cylinder soot formed during mixing-controlled combustion in diesel compression ignition engines. Fuel injection through a small duct has the effect of extending the lift-off length and reducing the equivalence ratio at ignition. In this work, the feasibility of ducted fuel injection to reduce soot and to enable leaner lifted flame combustion is investigated for a single diesel jet injected from a 138µm orifice into engine relevant (60-120 bar, 800-950K) quiescent conditions. High speed imaging and natural luminosity measurements of combusting sprays have been used to quantify duct effects on jet penetration, ignition delay, lift-off length, and soot emission in a constant volume high-temperature-pressure-vessel (HTPV). Measurements show an order of magnitude lower soot luminosity when using an optimized duct configuration at 800K and 120bar. As ambient temperature and/or duct diameter increase, soot reduction benefits tend to diminish. ‘Pre-ignition’ prior to the duct exit and degraded performance were observed for ducts with excessive standoff distance. Computational simulations of free and ‘ducted’ fuel injections are capturing many of these and other trends in jet penetration, lift-off length, and soot luminosity, thereby elucidating key physics of ducted fuel injection.