Several diesel injection systems were selected for evaluating the effects of fuel properties on diesel spray characteristics. Fuel properties that were examined were viscosity and specific gravity. The selected injection systems were operated on nine test fuels covering a broad range of viscosity and specific gravity. High-speed movies were taken of the fuels being injected into a high-pressure environment. Penetration and cone angle data were reduced from the movies and used as a basis for fuel-to-fuel comparisons. In addition, drop size distribution data were obtained for one injection system operating on four fuels with different viscosities.Fuel viscosity was found to have an effect on spray tip penetration. For a pintle-type nozzle as fuel viscosity increased, the tip penetration rate decreased. Tip penetration rate from a pressure time injection system was proportional to the fuel viscosity, in that as viscosity increased, tip penetration increased. For a unit injector, viscosity effects on spray tip penetration were not significant. Viscosity effects for the unit injectors were more apparent from examination of the jet break-up length; as viscosity increased, the break-up length increased.The cone angle of the spray did appear to be related to the fuel viscosity for all but one of the injection systems examined. For the pintle-type nozzle, the cone angle was not a function of fuel viscosity. For a unit injector, the cone angle tended to decrease with an increase in viscoity. The cone angle for the pressure-time injector appeared to decrease as viscosity increased. Drop size measurements made on the pintle nozzle indicated that as viscosity increased, the drop diameter also increased.