Effect of oxidation under accelerated conditions on fuel properties of methyl soyate (biodiesel)

Biodiesel derived from transesterification of soybean oil and methanol is an attractive alternative fuel for combustion in direct-injection compression ignition (diesel) engines. During long-term storage, oxidation due to contact with air (autoxidation) presents a legitimate concern with respect to maintaining fuel quality of biodiesel. This work examines the effects of oxidation under controlled accelerated conditions on fuel properties of methyl soyate (SME). SME samples from four separate sources with varying storage histories were oxidized at elevated temperature under a 0.5 standard cm(3)/min air purge and with continuous stirring. Results showed that reaction time significantly affects kinematic viscosity (v). With respect to increasing reaction temperature, v, acid value (AV), PV, and specific gravity (SG) increased significantly, whereas cold flow properties were minimally affected for temperatures up to 150degreesC. Antioxidants TBHQ and alpha-tocopherol showed beneficial effects on retarding oxidative degradation of SME under conditions of this study. Results indicated that v and AV have the best potential as parameters for timely and easy monitoring of biodiesel fuel quality during storage.