Effect of molecular weights of fatty acid esters on cetane numbers as diesel fuels

Abstract

Cetane numbers for various esters of the saturated fatty acids from C8 to C18 have been determined according to ASTM D‐613. For the methyl esters the cetane numbers were found to increase in a non‐linear relationship with the chain length of the fatty acid. Cetane numbers of esters in which the fatty acid is kept constant while the alcohol esterified is altered also increased with the molecular weight of the ester. However, increases in the molecular weight of the fatty acid portion of the ester produce greater increases in cetane number than the same change in molecular weight in the alcohol portion of the ester. Except for the esters of octanoic acid, all of the esters tested had cetane numbers above the value of 40, which is specified as the minimum cetane number for commercial diesel fuel.

Precombustion of fatty acids and esters of biodiesel. A possible explanation for differing cetane numbers

“…Other factors may also play a role. For example, there is a positive correlation between CN and boiling point of a fatty compound (18). Another work, in which regression analyses were conducted, showed that boiling point was the most reliable property for predicting the CN of fatty compounds (19).…”

Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

“…The present work is intended to provide a reliable kinetic model for a methyl ester fuel that is much larger than the previous methyl butanoate. Instead of the 4 carbon atoms chain of methyl butanoate, the current work provides a kinetic mechanism for methyl decanoate (cetane number of about 47 [ 6,7]), with a chain of 10 carbon atoms with a methyl ester group attached ( Figure 1). …”

Fuel Properties and Performance of Biodiesel

“…The infl uence of compound structure on CNs of fatty compounds was discussed (Harrington, 1986 ) and hypotheses confi rmed by practical cetane tests (Freedman et al , 1990 ;Ladommatos et al , 1996 ;Klopfenstein, 1985 ;. CNs of neat fatty compounds are given in Table 1.1 .…”

“…Transesterifi cation of fats or oils with medium -chain alcohols may increase CN, a parameter that can infl uence ignition quality and exhaust emissions (Klopfenstein, 1985 ). On the other hand, increased branching in saturated hydrocarbon chains also decreases CN.…”