A review of the effect of the composition of biodiesel on NOx emission, oxidative stability and cold flow properties

This paper will review and attempt to discover the ideal fatty acid composition of biodiesel which exhibits lower NOx emissions, better oxidative stability and cold flow properties. The physicochemical properties of biodiesel strongly depend on their fatty acid composition. A high percentage of unsaturated fatty acid in biodiesel is correlated with higher NOx emissions, poor oxidative stability and better cold flow properties. The presence of saturated fatty acids (SFA), in particular the long chain type, exhibits good oxidative stability and produces lower NOx emissions. SFA do however demonstrate poor cold flow properties. The polyunsaturated fatty acids (PUFA) exhibit better cold flow properties but produces higher NOx emissions and poorer oxidative stability. The ideal requirements of biodiesel properties impose contradictory conditions on the fatty acid composition of biodiesel. For example, coconut and palm kernel oils which have a high percentage of lauric fatty acid are reported to circumvent all three drawbacks of biodiesel. The monounsaturated fatty acids (MUFA), specifically oleic acids, a major component in almost all biodiesel, display the positive characteristics of both SFA and PUFA. Biodiesel properties can therefore be improved by using various remedial methods including genetic engineering, reformulated biodiesel and additives. (C) 2015 Elsevier Ltd. All rights reserved.