Study of the Effect of Storage Time on the Oxidation and Thermal Stability of Various Biodiesels and Their Blends

Biodiesel can be described as a safe alternative fuel, which can replace petroleum diesel in the future. It consists of long-chain fatty acid methyl esters (FAME). Biodiesel has high lubricity and is a clean burning fuel. It also produces less air pollution, is renewable biodegradable, and is safer for the environment. Since biodiesel is produced from vegetable oil, animal fats, used cooking oil, and so forth, which may contain more or less unsaturated fatty acids that are prone to oxidation accelerated by exposure to air during storage and at high temperature, it may yield polymerized compounds. The oxidation and thermal stability of the fuel changes with storage time due to the formation of oxidation. Therefore, the aim of this study to evaluate the stabilities of biodiesel according to measured fuel properties, such as density, viscosity, flash point, total acid number (TAN), and total base number (TBN), by using various methodologies. In addition, oxidation stability of the samples was measured by the induction period using a Rancimat instrument. In this experiment, palm oil methyl ester (PME), palm biodiesel blend (40% PME and 60% diesel fuel), jatropha methyl ester (JME), jatropha biodiesel blend (40% JME and 60% diesel fuel), coconut oil methyl ester (COME), and conventional diesel fuel were used. Experiments were carried out at intervals over a 12-week test period. The experimental results for JME and PME showed similar performance in terms of flash point. All samples met the standard specification of the American Society for Testing and Materials (ASTM) D6751. (3 h) regarding the induction period, except for JME and its biodiesel blend, which did not meet the EN 14214 (6 h) standard specification. Among the fuel samples giving the worst results for TBN value due to oxidation, overall, among the biodiesels, PME and COME were found to give better results with respect to oxidation and storage stabilities.