Equations for predicting the cetane number of diesel fuels from their physical properties

Twenty-two equations for predicting the cetane number of diesel fuels were tested for accuracy by comparing the predicted values for > 500 fuels with the measured values. All the equations and measured values were taken from the literature. It was found that the predictive capability of certain equations was high: several could predict the cetane number with a standard error of < 2. It is concluded that it is unlikely that the standard error can be reduced significantly below 1.5, because the measured cetane numbers are themselves subject to experimental error. The equations were unable to predict accurately the cetane number of untypical diesel fuels, such as vegetable oils and diesel blends containing alcohols. This was expected, since these empirical equations were constructed from databases for typical diesel fuels only. The measured cetane number of diesel fuels was found to correlate very well with their aniline point. Six of the 22 equations were functions of only the aniline point, and two of them showed very good predictive capability.

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