Keywords: microemulsion, renewable fuel, critical micelle concentration, micelle, nanoscale chemistry
Summary:The authors have developed a technology to blend biomass-derived oxygenates - alcohols, free fatty acids, neutralizer, and water – together to form a renewable blendstock. When blended into diesel, the resulting microemulsion fuel has been used to power unmodified diesel engines. We have been working to characterize the structural properties of the resulting fuel system because we believe this will enable us to design a superior fuel system meeting energy and environmental needs while overcoming biofuel commercialization challenges. Ethanol, water, and polar hydrophilic compounds have limited solubility with diesel and nonpolar long-chain hydrocarbons, and are therefore prone to phase separation, but Sylvatex’s technology uses high concentrations of combustible, renewable fatty acids that act as a surfactant to form inverse micelles where the ethanol components are concentrated inside of a bubble surrounded by the surfactant’s polar carboxylate head, while the long hydrophilic tail of the surfactant faces outward, solubilizing with the diesel, to result in a microemulsion system that is thermodynamically stable. The presence of spherical reverse micelles in our alternative fuel system has been confirmed using dynamic light scattering (DLS). We have identified the lower critical micelle concentration as 3-5 % (vol.) depending on formulation, and characterized micelles that form optimal micelle diameter ranges of 4.5 - 50 nm. Additionally, we have observed that micelle formation and size can be attributed to surfactant length and the existent polar oxygenate concentration. Additional projects to corroborate this data with Small Angle Neutron Scatterings (SANS) and Small Angle X-Ray Scattering (SAXS) studies are underway. The benefit to a nanostructured fuel is that the ethanol and oxygenates have a “cooling effect” on the combustion temperature of the fuel, thereby reducing unwanted side products of particulate matter (PM) and nitrogen oxides (NOx). Commercialization of this technology will have the following impacts: availability of an affordable cleaner burning renewable alternative diesel fuel that will meet the Low Carbon Fuel Standard and does not compete with food crops, reduced emissions of nitrogen oxides and particulate matter, and reduced dependence on petroleum. To date, we have completed performance evaluation on emissions and fuel consumption, accumulated over 10,000 miles in on-road vehicle demonstrations, characterized the physical, chemical and structural properties of the microemulsion system, and assessed the compatibility of the resulting fuel product with elastomers and metals. We have also been developing processing methods to economically derive the renewable surfactant from waste products, and will be studying the impacts of micelle size on engine performance.  Effect of Oxygenated Fuel on Combustion and Emissions in a Light-Duty Turbo Diesel Engine. Juhun Song , Kraipat Cheenkachorn , Jinguo Wang ,Joseph Perez Energy Fuels, 2002, 16 (2), pp 294301  Effect of Performance and Emissions on DI Diesel Engine Using Ethanol Diesel Blends. Daheriya, L., Shrivastaba, N., International Journal of Engineering Research and Technology, 2012, 1(6).  Evaluation of Diesel Fuel - Ethanol Microemulsions. Goering, C.E., Pryde, E.H., Boruff, P.A., Schwab, A.W., Transactions of the ASAE, 1982, 25(1), p. 47-53.