As the use of alternative fuels increases, it is increasingly important to understand the influence of chemical and physical properties on flame behavior. The objective of this paper is to explore the impact of adding O-2 to the fuel side of opposed-flow diffusion flames, where the multicomponent fuel is delivered as liquid droplets of varying diameter. The approach is based on the computational simulation of ideal opposed-flow stagnation flames with a separation distance of 5 mm between the fuel and air inlets. The fuel composition is a mixture of n-heptane, n-dodecane, and n-hexadecane, which is selected to represent a Fischer-Tropsch fuel. Gas-phase chemical kinetics is modeled using a reduced, but detailed, reaction mechanism containing 196 species. The influence of the finite vaporization rate is evaluated by comparing predictions with pre-vaporized fuel to those with monodispersed initial fuel droplet diameters of 20 and 30 pm. The effects of O-2 in the fuel stream are assessed using simulations with 0%, 5% or 10% O-2 incorporated into the N-2 carrier gas. In all cases the pressure is 10 atm, the inlet gases are at 950 K, the droplets are initially at room temperature, and the inlet velocities of the fuel droplets and carrier gas is 1 m s(-1). The fuel loading is adjusted to achieve an overall equivalence ratio of unity. The predictions illustrate substantially different behavior under different conditions; these differences can be related to the time available for fuel vapor to react with the premixed O-2. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.