Thesis (M.Eng.)--Chulalongkorn University, 2006

Because of the current energy crisis, an increase in fuel price and a decrease in its supply rise an increasing attention of an alternative fuel. Biodiesel is one of the most interesting alternative fuels which can be produced from many plants. Meanwhile drop size and dynamic of its spray has not been investigated clearly yet. Such detailed measurements play an important role in an enhancement of combustion efficiency, it would be employed for optimizing heat transfer, controlling evaporation, and lessening emission. In order to obtain this initial information, a PDA technique was used to measure the local drop size and velocity of mixture of diesel and palm oil. The method is based on light scattering interferometry. From frequency change, it provides information on droplet velocity while the droplet size is evaluated from the phase change of the laser. The atomizer used in this work is a two-fluid atomizer which has been applied for combustion aid because it can atomize high viscosity liquids like vegetable oil fuel. It was experimentally observed that the atomizer generates a spray with large drops at low air injection pressure. Large droplets are produced along traveling distance. Therefore, the large drops with low velocity are found at downstream distances far from the nozzle tip. Moreover, the properties of liquid fuel such as viscosity, affect the atomization and the droplet size distribution. Liquids with high viscosity cause poor atomization, resulting in larger drops. However, liquid viscosity could provide only a small effect on the velocity profile if compressed with the air injection pressure.