Effect of Fatty Acid Ethyl Esters in Biodiesel on Thermo-physical Properties

Biodiesel fuels generally contain five types of fatty acid ethyl esters (Palmitate, Stearate, Oleate, Linoleate and Linolenate), which affect the thermo-physical properties of biodiesel fuels. The effects of each of the mono ester of fatty acids in biodiesel on the thermo-physical properties (density, viscosity, heating value and cetane number) were examined. Biodiesels were produced by transesterification method using ethanol and sodium hydroxide catalyst and seven types of vegetable oils (sunflower, soybean, canola, olive, corn and grapeseed). Thermo-physical properties of each sample were measured according to ASTM standards. For each of the properties, a nonlinear regression model based on five independent variables of the fatty acids ethyl esters (FAEE) were presented. The correlation coefficient regression models for density, viscosity, heating value and cetane number were obtained equal to 0.9457, 0.9169, 0.9731 and 0.9029, respectively. The results showed that of the ethyl stearate (C18=0) impact factor on the density is equal to 0.803, which is lower than the standard (0.86), and Methyl Linolenat (C18=3) impact factor on the density is 0.913, which is more than the standard (9.0). Ethyl Stearate(C18=0) impact factor on the viscosity is equal to 8.41, which is higher than the standard (6). Also, Ethyl stearate has the greatest impact on heating value of biodiesel, and Ethyl Palmitate (C16=0) and Ethyl Linolenate (C18=3) have the smalles impact. Impact factor of Methyl Linolenate (C18=3) on the cetane number of biodiesel is 19.652, which is less than the standard (47). So, by increasing the amount of saturated fatty acids (especially ethyl stearate), viscosity, heating value and cetane number of biodiesel fuel increase, but the density decreases. If the heating value and cetane number of fuel increase, the engine power is increased, but if the viscosity increases and density dicreases, the atomization of the fuel is incomplete. Therefore, the production of biodiesel from vegetable oils with high saturated fatty acids increases the engine power.