Biodiesels Manufactured from Different Feedstock: From Fuel Properties to Fuel Atomization and Evaporation

Different from fossil diesel, biodiesels can be manufactured from different sources of biomass or animal fat. Each biodiesel manufactured from a certain feedstock consists of different fatty acid methyl esters (FAMEs). Its FAME types and fractions are unique and are solely controlled by the mother feedstock and not the manufacturing process. One key feature that makes biodiesels different from their fossil counterparts is the oxygen contained in biodiesels. The oxygen content, FAME types, and FAME fractions vary in a wide range among biodiesels made from different feedstock and this in turn affects the fuel properties and physical processes, including atomization and evaporation. An extensive analysis has been successfully carried out in this study to examine the role of oxygen content, carbon chain length, and unsaturation degree in different biodiesels and the influence of FAMEs on key fuel properties (heating value, cetane number, viscosity, and surface tension). Furthermore, some useful information related to (i) the morphology and density of fuel fragments derived close to the nozzle exit and (ii) drop evaporation is reported. The atomization characteristics are experimentally observed using a high-speed imaging technique developed earlier, while the evaporation study is theoretically conducted using the well-known D-square model. It shows that the oxygen in the biodiesel is directly linked to the carbon chain length and the number of double bonds in the fuel molecules as well as to the key fuel properties. The viscosity of biodiesels and their constituents has a certain impact on the morphology and population of fuel fragments derived in the breakup zone, while the thermal properties have a significant effect on biodiesel evaporation. The dependence of fuel properties on atomization at the downstream locations of the spray, where the breakup process has completed, is minimal.