Enhancement of fuel/air mixing is one path towards enabling future diesel engines to increase efficiency and control emissions. Air-assist fuel injections have shown potential for low pressure applications and the current work aims to extend air-assist feasibility understanding to high pressure environments. Analyses were completed and carried out for traditional high pressure fuel-only, internal air-assist, and external air-assist fuel/air mixing processes. A combination of analytical 0-D theory and 3D CFD were used to help understand the processes and guide the design of the air-assisted setup. The internal air-assisted setup was determined to have excellent liquid fuel vaporization, but poorer fuel dispersion than the traditional high-pressure fuel injections. The external air-assist setup showed potential in enhancing the fuel/air mixing process by a reduction in local equivalence ratios, and was selected over the internal air-assisted concept for manufacturing and experimental testing.Experiments in a constant volume combustion reactor were completed using a pre-burn technique to prepare the ambient gases to diesel auto-ignition temperature ranges (+750 K). High-speed Schlieren photography and laser extinction measurements were employed to assess both the qualitative and quantitative nature of the fuel/air mixing process and sooting tendency.