Investigation of the Parameters Affecting the Cetane Number of Biodiesel

The cetane number is the most significant property for measuring the ignition quality of fuels for compression ignition diesel engines. In this study, the derived cetane number (DCN) of several types of biodiesel, biodiesel components and ultra-low sulfur diesel (ULSD) was determined using an Ignition Quality Tester (IQT™). The chemical structure of FAME leads to a higher cetane number of biodiesel compared to ULSD. The contribution to DCN from minor components present in biodiesel is not significant. Oxidation of biodiesel samples results in higher DCN values while depending on the conditions of oxidation. A greater than 25% increase was observed when oxidation was carried out in a way to retain volatile oxidative products such as carboxylic acids and aldehydes. Accelerated oxidation of cotton seed oil (CSO) biodiesel at 110 °C and 10 L/min air flow rate after 210 min resulted in a loss of 14% of the FAME content, of which 10% can be attributed to the oxidation of methyl linoleate (C18:2), whereas oxidation of soy bean oil (SBO) biodiesel resulted in a loss of 21% total FAME after 210 min. A significant amount of methyl linolenate (C18:3) remained un-reacted after 210 min of oxidation. Ambient oxidation of distilled biodiesel samples resulted in a very high cetane number. Oxidative products such as aldehydes, hydroperoxides and oligomers of FAME are probably responsible for this higher DCN. This study enhances the understanding of the effect of composition on the cetane number of biodiesel as well as the effect of oxidative aging on both biodiesel composition and the resultant DCN.