Doctor of Philosophy (PhD)
Mechanical and Industrial Engineering
Ongoing work to find renewable biofuels to function as drop-in replacements or blending components with gasoline has identified a large number of fuel candidates. Given the vast number of potential biomass-derived fuel molecules and limited sample sizes, screening tools are required to down-select candidate fuels having desired physical properties to ensure good engine performance. This work investigates approaches for rapid screening of candidate fuels using micro-liter sample sizes targeting four properties -- surface tension, viscosity, heat of vaporization (HOV), and vapor pressure. Measurement techniques for fuel properties are developed based on unit phenomena for liquid fuel droplets including droplet oscillation and evaporation.
For surface tension and viscosity predictions, the approach uses shape oscillation dynamics of single droplets generated by a piezo-electric device and their decay over time. Lamb’s theory for small-amplitude droplet oscillations is utilized to calculate viscosity and surface tension. Measurements are obtained for both primary reference fuels (isooctane and n-heptane) and bio-derived candidate fuels from four functional groups of interest. Measurements results show that the droplet oscillation based approach is capable of reproducing surface tension and viscosity values for the tested fuels within deviations of 7% and 13% respectively from literature data. Results are obtained using an average of 5 µL per fuel sample per run within about 20 s.
For surface tension and viscosity prediction at elevated temperatures, the measurements show deviations within 10% of reference values obtained from the literature. The simulations are further used to study the relative contribution to deviations in surface tension and viscosity predictions due to heat and mass transfer from the droplet, as well as viscous effects violating the inviscid flow assumption in the droplet oscillation theory.
For HOV and vapor pressure predictions, evaporation of moving heated fuel droplets is studied. Measurement results for n-heptane, isobutanol, and PRF 84 are compared with literature data at different temperatures. The predictions of HOV and vapor pressure have deviations within 10% and 22% respectively from literature data. Extended schemes are proposed involving additional measurements for droplet temperature and velocity. These extended schemes can potentially increase the number and accuracy of predicted fuel properties.
Dang, Wanjun, "Droplet-Based Fuel Property Measurements" (2021). LSU Doctoral Dissertations. 5726.