Algae, Canola, or Palm Oils—Diesel Microemulsion Fuels: Phase Behaviors, Viscosity, and Combustion Properties

Abstract

Vegetable oils are being considered as a renewable energy alternative for diesel. The high viscosity of vegetable oils causes injector fouling and durability problems in compression–ignition engines. Microemulsification can be used to reduce vegetable oil viscosity without complex chemical transformation processes. The goal of our work is to formulate reverse micellar microemulsions of vegetable oils and No. 2 diesel fuel blended with ethanol using different combinations of surfactants and co-surfactants. Ethanol, also a renewable fuel, was used as a viscosity modifier. We studied three vegetable oils (canola, palm, and algae oils) to blend with diesel fuel. The microemulsion fuels were tested for temperature stability, viscosity, water tolerance, and their combustion performance in terms of flame radiation and pollutant (CO, NO_x) emissions. With appropriate surfactant and co-surfactant systems, we successfully formulated canola and algae/diesel microemulsions with cloud points and points that satisfy the ASTM standards. Among all formulations, palm/diesel microemulsion fuels solidified at 6–6.5°C due to high saturated triglyceride content. While the formulated microemulsion fuels had approximately 10% lower heating value than diesel fuel, their CO emission and flame radiation were superior to those of diesel fuel. NO_x emissions were also lower with the blends containing no nitrate additives, but were higher than with diesel fuel in the presence of nitrate additives. Thus, these results show that microemulsification can produce biofuels with desirable viscosity, fuel properties can be adjusted via formulation variables, and microemulsions can replace chemical processes for producing biofuels.

Keywords:

• Algae
• Palm
• Canola
• Biofuels
• Microemulsions
• Combustion test
• Phase behaviors
• Emissions
• Viscosity

ACKNOWLEDGMENTS

The authors would like to thank Norman Love, Megan Salisbury, and Anh Mai for experimental assistance. Funding for this work has been provided through the Oklahoma Center for Advancement of Science and Technology (OCAST) and Oklahoma Bioenergy Center. Partial support was provided by industrial sponsors of the Institute for Applied Surfactant Research at the University of Oklahoma: Clorox, Conoco/Phillips, Church and Dwight, Ecolab, GlaxoSmithKline, Halliburton, Huntsman, S.C. Johnson & Son, Oxiteno, Procter & Gamble, Sasol North America, Shell Chemical, and from Dr. Sabatini's Sun Oil Company endowed chair and Dr. Harwell's Conoco/Dupont endowed professorship.