INVESTIGATION OF BIODIESEL THERMAL STABILITY UNDER SIMULATED IN-USE CONDITIONS

Abstract

Biodiesel is an alternative diesel fuel produced by transesterification of vegetable oils or animal fats. Whilebiodiesel provides numerous environmental benefits such as reduced exhaust emissions, it is more prone to oxidation thanpetroleum-based diesel fuel and this can alter its properties. When oxidation occurs at ordinary temperatures, the initialproducts are hydroperoxides. As the oxidation continues, the peroxides may split and form aldehydes, ketones, and shortchain acids that produce unpleasant odors. Sediment and gums are formed through polymerization of the peroxides andcan cause fuel filter plugging. The objective of this study was to relate the chemical and physical processes associatedwith biodiesel oxidation to the conditions that affect diesel fuel system performance. A relationship was sought betweenthe test that is used by the engine industry to define engine fuel stability requirements (ASTM D2274) and the tests used bythe fats and oils industry to characterize oxidation (Peroxide Value and Acid Value). It was found during the course of thisstudy that the ASTM fuel stability method is not suitable for biodiesel. While oxidation causes the fuel viscosity toincrease, fuel filter plugging was not necessarily a natural consequence of biodiesel oxidation even when the fuel wasoxidized to a level beyond what would be observed in practice. The effect of fuel temperature and blending with diesel fuelon the oxidation was investigated and the interrelationship between the fuels acid value and viscosity is shown.