Composition Effects on Thermo-Physical Properties and Evaporation of Suspended Droplets of Biodiesel Fuels

From the energy security and environment standpoint, the biodiesel fuels derived from vegetable oils or animal fats appear to be promising alternative to fossil diesel. Although the engine experiments prove their viability, the scientific data base for characterizing biodiesel combustion is limited. Detailed studies on the characterization of biodiesel fuels and their effects on fundamental engine processes like droplet evaporation and combustion are essential. The present study evaluates the useful thermo-physical properties and droplet evaporation characteristics of biodiesel fuels. The droplet evaporation measurements are carried out using suspended droplet experiments on five biodiesel fuels of Indian origin viz. jatropha, pongamia (karanja), neem, mahua and palm. The droplet evaporation rates of these fuels are related to properties such as binary diffusivity and molecular weight, which in turn depend on their fatty acid composition. It is observed that palm methyl ester has the highest evaporation constant value of 0.1634 mm2/s and thus the lowest life time among the biodiesel fuels investigated. This value is attributed to its lowest molecular weight and highest molecular mass diffusivity. On the other hand, a reverse trend is observed for karanja biodiesel resulting in the highest lifetime among the fuel tested.