The cetane number is a widely used diesel fuel quality parameter related to the ignition delay time (and combustion quality) of a fuel. It has been applied to alternative diesel fuels such as biodiesel and its components. In this work, the cetane numbers of numerous straight-chain and branched fatty acid esters were determined. Specifically, 29 samples of esters of methyl, ethyl, n-propyl, n-butyl, iso-propyl, iso-butyl, 2-butyl, and 2-ethylhexyl esters of palmitic, stearic, oleic and linoleic acid were investigated. It was found that branching in the ester moiety does not significantly affect cetane number compared to the straight-chain esters. Therefore, branched esters, which have been suggested as a possible improvement for the cold-flow properties of biodiesel, can be employed without significantly affecting ignition properties compared to the more common methyl esters. Unsaturation in the fatty acid chain was again observed to be the most significant factor causing lower cetane numbers. Cetane numbers were determined in an Ignition Quality Tester (IQT) which is a newly developed, automated rapid method using only small amounts of material for determining cetane numbers. The IQT is as applicable to biodiesel and its components as previous cetane-testing methods.
