This paper presents a computational study of the effect of water-spray characteristics on the suppression of a large-scale (2 m x 2 m) JP-8 pool fire in a 10 m x 10 m x 10 m compartment with an open ceiling. The numerical model is based on an unsteady Reynolds-averaged Navier-Stokes formulation using a stochastic separated flow approach for the droplets that includes detailed descriptions of the interaction between water droplets and fire plume. Simulation results indicate that water-spray injection causes the gas temperature to rise due to the initial enhancement of the turbulent mixing. A threshold suppression condition is achieved when the injected droplet carries enough momentum (injection speed range is 20-80 m/s) to penetrate the fire plume and evaporate in the flame regions where most of the gas-phase combustion is taking place. In addition, the droplet size (ranging from 100-800 mu m) should be small enough to yield quick evaporation when in contact with the flame surface for efficient cooling. Based on a parametric study, a preferred fire suppression configuration is recommended for the systems considered.