Effects of lubricant oil additive on the characterization of particles from a four-cylinder turbocharged diesel engine were investigated. Neat diesel and blended fuel containing oil pour point depressant (PPD) additive were chosen as the test fuels. Effects of different fuels on size distribution, morphology, and nanostructure of the diesel particles were studied. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) were employed to study the morphology and nanostructure parameters. Particle size distribution was measured by fast particulate spectrometer (DMS 500). According to the experimental results, distribution of the primary particles size of the two fuels conforms to Gaussian distribution, whereas the mean diameter of blended fuel is larger than that of neat diesel at 1200 rpm, which is contrarily smaller at 2400 rpm. Besides, fractal dimension (D-f) of aggregates increases close to 2 (D-f = 1.991), indicating that the structure became compacter with adding PPD. As to the nanostructure parameters of the blended fuel particles, the layer fringe length decreases from 1.191 nm to 1.064 nm, while both the separation distance and tortuosity increase. The changes in the nanostructure parameters indicate that the particles are more ordered and compressed with burning pure diesel. Results of blended fuel from DMS show that more particles, particularly nucleation mode particles, were discharged. In addition, its size distribution become bimodal logarithmic at 2400 rpm. All these results can provide new information of the effects of oil PPD additive on the formation and characterization of diesel particles. (C) 2014 Elsevier Ltd. All rights reserved.