Correlation for the estimation of the cetane number of biodiesel fuels and implications on the iodine number

Some European experts on normalization of transport fuels have recently suggested the suppression of the cetane-number limitation from the European biodiesel norm when its final destination is blending with diesel fuel. Although this measure should not affect the range of oils used for biodiesel production (only few of them lead to biodiesel fuels with cetane numbers below this limit), the trend of cetane number to decrease with increasing unsaturation could reinforce the arguments to maintain the iodine-number limitation as an indirect limit for the cetane number. The iodine number has frequently been subjected to controversy because its stringent limitation in Europe prevents from using differently unsaturated fatty oils for biodiesel production. Some of the arguments in favour of extending or eliminating the iodine-number limitation in the norm are exposed here. Previously, a correlation for the estimation of the cetane number based on a literature review is proposed. From this correlation, a procedure is proposed for the estimation of the limiting effect of the current cetane-number limitation on the unsaturation degree of biodiesel fuels. Finally, the impact of the elimination of the cetane-number limitation on the use of different oils for biodiesel production is analyzed.