The oxidative stability of FAME in the model Crankcase environment

• Main Author: Hall, James
• Other Authors: Davies, Rob ; Long, Nicholas
• Published: Imperial College London 2012
• Subjects: 547
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.693865

The use of biodiesel has increased in recent years due to the implementation of governmental policies driven by environmental, economic and political reasons. Biodiesel is composed of fatty acid methyl esters (FAME), which can be derived from plant, marine and animal sources. There have been reports of some potential problems associated with biodiesel use in modern diesel engines, with lubricant dilution by blended biodiesel fuels leading to accumulation of FAME in the oil sump in the crankcase. This project focuses on the design and implementation of an experimental model based on the Rancimat apparatus that can simulate certain aspects of the FAME degradation chemistry occurring in the crankcase and oil sump. An analysis procedure to compliment the experimental model is applied to carry out product distribution analysis on a series of (C18) model FAME, identifying and quantifying the oxidation products formed under the experimental conditions, where epoxides are the major monomeric degradation. Some oxidation kinetic parameters have been investigated using biodiesel samples, with noticeable differences in oxidation rates found when FAME are oxidised individually and when in mixtures. Kinetic factors of FAME and model base oil in single and multi-component systems have also been investigated, with the base oil displaying good oxidative stability in mixtures as well as on its own The influence of antioxidants on stabilising various model systems has shown synergistic effects. Combinations of primary and secondary antioxidants have displayed good synergy, with the suppression of the rate of hydroperoxide formation by primary antioxidants enhancing the effectiveness of the secondary antioxidant. Primary antioxidants have been observed to affect the onset of oxidation, whilst secondary antioxidants decrease the hydroperoxide and epoxide, but increase the alcohol yields as a result of autoxidation.