The fuel injection process has been studied since the internal combustion engine was developed. Direct injection has been an integral part to the success of diesel engines, where there is minimal time for the fuel to mix with the compressed air. The benefits of fuel injection center on: fuel efficiency and lower toxic emissions. As the world depletes more fossil fuels each year it is imperative to concentrate research on techniques to lower fuel consumption. Past research on fuel sprays using laser techniques were limited by cross sensitivity in regards to the regions with both liquid and vapor phases present. Quantitative schlieren techniques have been proposed and investigated since the first half of the 20th century, but only recently with the rapid development of digital imaging techniques and computers have they have been used for quantitative analysis. This thesis presents the results for a new hardware installation for a rainbow schlieren diagnostic method. Experiments were performed using a constant pressure flow vessel (CPFV) and a modern common rail diesel injector to obtain high-speed images of the vaporizing fuel sprays. The CPFV ran under steady ambient thermodynamic conditions where the pressure and temperatures were controlled variables. Two cameras were used, Mie scatter liquid phase data and the rainbow schlieren vapor phase data were captured simultaneously. Quantitative results indicate that the axial and radial variation in the fuel sprays seem to match the well-validated variable profile model.