Estimation of cetane index for esters of fatty acids

Cetane indexes have been calculated for the esters of the individual saturated fatty acids in the C8-C24 range plus palmitoleic, oleic, linoleic, and linolenic acids. Two methods were used for these calculations: ASTM 976 and a method involving simultaneous equations relating the experimentally determined cetane numbers for several transesterified oils and the fatty acid compositions of the oils. Cetane indexes calculated according to ASTM 976 produced values which were too low for ester mixtures high in saturated acids and low in polyunsaturated acids, and were somewhat high for ester mixtures high in polyunsaturated acids. When cetane indexes calculated according to the simultaneous equation method were applied to the fatty acid mixtures, the agreement with those experimentally determined was approximately the error of determination of the cetane number.