Feasibility Study on the Utilization of Soybean Oil and Butanol Blends as an Alternative Fuel Source for Combustion Applications

A variety of concepts have been investigated in an effort to categorize simply mixed blends of soybean oil-butanol fuel as a suitable alternative fuel source for combustion applications. Basic physical property testing carried out in accordance with ASTM standardized methods proved that the addition of butanol to the highly viscous soybean oil (SBO) lowered viscosity, density, and surface tension and improved cold flow properties. The high energy density of pure SBO proved to increase the heating value of the fuel blend. Mixing rules and estimation methods were developed to predict basic property values as a function of temperature and composition with good accuracy. Evaporation studies on single fuel droplets revealed that there is a diffusion-like gasification mechanism present when SBO/butanol blends are exposed to pure vaporization at or below 225°C. All blends exhibit evaporation constants similar to pure butanol suggesting that the mass diffusion of butanol toward the surface is faster than the surface regression rate of the droplet. Combustion tests results suggested that there is a mixed mode gasification mechanism dominated by that of a diffusion rate limiting one present during combustion of single SBO/butanol droplets. Disruptive burning and microexplosions occur because of the mass diffusion of butanol toward the droplet surface being slower than that of the surface regression during combustion. This results in the trapping of butanol within the surface of the droplet allowing for it to be superheated and causing obliteration of the fuel droplet. All blends proved to exhibit incomplete combustion however it was less likely for droplets of near equal concentrations. Blends of near equal concentration (Bu50 and Bu40) proved to have a higher tendency for microexplosions to occur and they were more violent. Strategic droplet size measurements throughout their lifetime provided insight that this is likely due to the amount of butanol burned prior to droplet microexplosions. An economical analysis provided information suggesting that simply mixed SBO/butanol blends could be a feasible alternative fuel source for various combustion applications.