Measurement of the Nucleation and Growth Kinetics of Some Middle Distillate Fuels and Their Blends with a Model Biodiesel Fuel

Abstract

The nucleation kinetics and crystal growth rates of both middle distillates and their blends with a model biodiesel were determined. As middle distillates are complex mixtures of hydrocarbons, a strategy was taken to define the solute and solvent. Different mixtures were prepared from different fuels, and a mixture law was used to calculate the mass percentages of each n-paraffin in the mixture; the difference between experimental and estimated compositions was negligible. An experimental device was set up to obtain the solubility curve of a distillate, for the first time. The application of classical homogeneous nucleation theory and Nývlt’s semiempirical approach allowed the nucleation rate, interfacial tension, and nucleation order to be obtained. The presence of esters did not have an influence on the solubility curve slope, but they had higher kinetic parameters and influenced the interfacial tension. The values found using the Nývlt law were typical for organic systems. Images were taken as a function of temperature and time, using thermomicroscopy, and image analysis enabled the crystal growth rates to be obtained. In general, the mixtures containing esters had higher growth rates. The solvent nature was found to play an important role in the growth, as the other alternative fuels studied have considerably higher growth rates.