A high speed flow visualization technique was utilized to study fuel spray development and the fuel-air mixing process in a direct fuel injection motored rotary engine assembly. Kerosene fuel was injected through a single hole nozzle at an angle of 60° from the horizontal axis into the combustion chamber. The nozzle was installed in a Servojet fuel injection system that was mounted in the central housing of a rotary engine. A 40 watt copper vapor laser was sychronized with a high speed rotating prism camera to expose motion picture films at 5000 frames per second (fps). The fuel spray structure was studied at injection pressures of 44 and 70 MPa, and at nominal injection durations of 1.2 and 2.8 ms. The engine shaft speed was 2000 rpm. A sequence of successive frames was selected from high speed films and then used to analyze the fuel spray characteristics. The flow field and rotor motion which had contributing effects on the fuel spray behavior were also considered. The spray tip velocities and penetration distances of the fuel spray were quantified by analyzing the high speed films and were found to be significantly influenced by injection pressures.