ABSTRACT

KEYWORDS: Droplet evaporation; multicomponent fuel; surface regression; evaporation constant; biodiesel; Marangoni convection; high pressure ambience; gas solubility; fugacity; real gas effects; phase equilibrium

Liquid fuels are atomized to droplets and used in several applications. Understanding the evaporation process of the droplets is important in applications such as internal combustion engines, industrial oil furnaces, gas turbine engines and liquid-propellant rockets. Depending upon the application, the operating pressure can be low, moderate or high. Therefore, detailed understanding of the evaporation characteristics under different ambient conditions is crucial. This will facilitate achieving better combustion efficiency and reducing emissions in spray combustion devices. In this thesis, comprehensive numerical simulations of Indian based biodiesel droplets and binary liquid fuel droplets are reported. Here, ambient temperatures and pressures are chosen considering applications such as pre-vaporizer, internal combustion engines as well as in lab-scale experiments reported in literature.
Numerical results of evaporation characteristics of suspended droplets of biodiesels of Indian origin and their individual fatty acid methyl ester (FAME) components in air at atmospheric pressure under normal gravity condition have been presented systematically, as biodiesel is an alternative fuel that contains six to seven fatty acid esters. Two approaches are considered for this purpose. In the first approach, biodiesel is considered as a single component fuel, and its properties are estimated from the mixture of its fatty acid components using appropriate mixing rules. In the second approach, all the individual fatty acid components are separately considered in a multicomponent manner. Predicted evaporation characteristics have been compared satisfactorily against the experimental data from literature. Vaporization characteristics of biodiesels have been explained in terms of the evaporation characteristics of their FAME components. The effects of ambient temperature, fuel type, convection velocity and presence of a bead on evaporation characteristics are studied in detail. Flow, temperature and species fields in and around the droplets of biodiesels and their blends are also reported. A correlation based on long chain saturation factor (LCSF) has been proposed to estimate time averaged evaporation constant of a droplet, which will be quite useful for estimating the evaporation constant of biodiesels.
Numerical results of evaporation characteristics of binary droplets at high ambient pressures have been presented. Predictions have been validated satisfactorily against experimental data from literature. The effects of pressure, temperature, initial liquid-phase composition and convection velocity on evaporation characteristics have been presented in detail. Flow, temperature and species fields in and around the droplets of the binary fuel droplets are also reported.