The three-dimensional KIVA code has been used to study the effects of multicomponent fuel droplet vaporization on diesel engine performance under both standard and cold-starting conditions. The code has also been updated with state-of-the-art submodels including: a wave breakup atomization model, drop drag with drop distortion, spray/wall interaction with sliding, rebounding, and breaking-up drops, multistep kinetics ignition and laminar-turbulent characteristic time combustion, wall heat transfer with unsteadiness and compressibility, and a crevice flow model. The baseline computational results are compared with experimental data from a single-cylinder Caterpillar research engine equipped with a high-pressure, electronically-controlled fuel injection system. The effect of multicomponent fuel droplet vaporization is studied, with particular attention to the effects of the injection ambient temperatures. The vaporization model, besides being able to describe bicomponent fuels, accounts for high pressure effects, variable properties, and variable Lewis number. The model was tested and compared with experimental data for single droplets, and comparisons between the model results and the available data are satisfactory. The multicomponent fuel vaporization model was extended to model diesel sprays under typical diesel conditions. Necessary modifications were also carried out in the atomization and collision sub-models. The spray results indicate the importance of multicomponent fuel effects in conditions where ambient temperatures are relatively low, such as in cold-starting. The model was successfully applied to engine cases.