In an optically accessible direct injection Diesel engine with pressure and temperature conditions close to those of actual engines, the gaseous and liquid phases of the fuel were simultaneously visualized by planar exciplex fluorescence to yield instantaneous information sensitive to droplet breakup and vaporization in a non-combusting spray. Semi-quantitative results were extracted from the technique to give spatially integrated ensemble average data concerning the temporal evolution of the mass concentration of the respective phases. The ensemble scattering polarization ratio technique was also applied to yield the droplet size and concentration at the leading edge of the jet. Within the jet core, planar measurements of the depolarization of elastically scattered light indicated the presence of longitudinal fluctuations in droplet concentration. Cycle to cycle coherence in the depolarization profiles was observed.