Biodiesel is an alternative fuel for diesel engines that can be produced from renewable feedstocks such asvegetable oil and animal fats. These feedstocks are reacted with an alcohol to produce alkyl monoesters that can be used inconventional diesel engines with little or no modification. Biodiesel, especially if produced from highly unsaturated oils,oxidizes more rapidly than diesel fuel. This article reports the results of experiments to track the chemical and physicalchanges that occur in biodiesel as it oxidizes. These results show the impact of time, oxygen flow rate, temperature, metals,and feedstock type on the rate of oxidation. Blending with diesel fuel and the addition of antioxidants are explored also.The data indicate that without antioxidants, biodiesel will oxidize very quickly at temperatures typical of diesel engines.This oxidation results in increases in peroxide value, acid value, and viscosity. While the peroxide value generally reaches aplateau of about 350 meq/kg ester, the acid value and viscosity increase monotonically as oxidation proceeds.
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Monyem et al. (1999) studied this question.