Burning characteristics of palm-oil biodiesel under long-term storage conditions

The influences of oxidative variables on the burning characteristics of palm-oil biodiesel were investigated experimentally in this study. Biodiesel, which is composed of monoalkyl esters of long-chain fatty acids, generally has an inferior oxidative stability than petrodiesel. Hence, the long-term oxidative stability of palm-oil biodiesel has received much industry attention because it is used widely as an alternative to pure diesel fuel. Palm-oil biodiesel was stored in a constant-temperature water bath at either 60 °C or 20 °C continuously for 3000 h to observe the variation in its oxidative degradation and burning characteristics, such as carbon residue and the amount of heat released, with storage time. The effect of antioxidant addition on the burning characteristics was also investigated. The experimental results reveal that the palm-oil biodiesel suffered greater oxidative degradation at higher storage temperatures and in the absence of an antioxidant, which resulted in a faster decrease in the amount of heat released as the storage time elapsed. The addition of the chain-breaker antioxidant BHT effectively broke the peroxidation reaction mechanism and hence significantly retarded the decrease in heat release. The oxidative stability of the palm-oil biodiesel was worst at a higher storage temperature, a longer storage time, and in the absence of an antioxidant, which caused the more extensive formation of sediments of oxidative products and hence a larger carbon residue after burning. The greater oxidative degradation also caused the more extensive decomposition of unsaturated fatty acids into oxidative products, which decreased the flash point and the cetane index of the fuel.