The cetane number is one of the most significant properties to specify the ignition quality of a fuel for use in a diesel engine. The cetane number of biodiesel fuels is considerably influenced by their fatty acid methyl ester composition. The determination of cetane number of biodiesel is an expensive and time-consuming process. The objective of the present work is to predict the cetane numbers of different biodiesels using their fatty acid ester composition. Fifteen different biodiesel (including three blends) fuels were prepared and their cetane numbers were experimentally measured. An extensive literature review was made and the measured cetane numbers were compared with the reported values. To predict the cetane numbers of biodiesel fuels from their fatty acid methyl ester composition, a multiple linear regression model was developed. The cetane numbers and fatty acid compositions of 57 biodiesel fuels and 7 pure fatty acid methyl esters from the available literature were given as inputs. The experimentally measured cetane numbers and fatty acid compositions of four biodiesel fuels were also given as inputs to develop the regression model. The regression model has yielded an R 2 value of 0.953 and a standard deviation of 2.271. The predicted cetane numbers are comparable with the experimentally measured cetane numbers. The maximum prediction error from the present model was found to be 8 per cent. Similarly, the present model was compared with the available litrature models. The maximum prediction error from the literature models was found to be 15 per cent. The present model also shows a good agreement with the measured cetane numbers.

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Biodiesel is a renewable fuel that is suitable for both stationary and automotive engines. It consists of fatty acid methyl esters and fatty acid ethyl esters when vegetable oils are transesterified with methanol and ethanol respectively. The structural configuration and properties of individual fatty acid methyl esters can significantly influence the biodiesel properties. The purpose of the present work is to review the effects of the properties and the structural configurations of fatty acid methyl esters on various biodiesel properties. The structural configuration includes the molecular structure, the chain length, the saturated or unsaturated nature, the degree of unsaturation and the position of double bonds. Important properties of fatty acid methyl esters are reviewed, and a large number of data consisting of their reported values are given. The viscosity, the cetane number, the heat of combustion, the density, the bulk modulus and compressibility, the iodine value, the oxidative stability, the low-temperature properties, the boiling point, the lubricity, the saponification value, the surface tension, the specific heat, the latent heat of vaporization and the flash point are reviewed in the present study. The reported mathematical equations for estimating the properties of fatty acid compounds and biodiesel are presented. A few studies that recommend enrichment of a particular fatty acid (or acids) which is possible through genetic modification to improve the overall biodiesel properties are also cited. The contribution of a particular fatty acid (or acids) favours some properties while it has an undesirable effect on other properties. Hence the specification of one particular fatty acid profile to improve all the properties of biodiesel is not possible. Considering the low-temperature properties and the oxidative stability, a combination of both saturated fatty acids and unsaturated fatty acids is necessary. Therefore, it is important to decide whether a biodiesel should contain a larger amount of saturated fatty acid esters or unsaturated fatty acid esters in order to obtain better fuel properties. The inherent genetic modification of the fatty acid profile could be the best possibility for addressing several fuel property issues simultaneously.

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