Thesis (M.Sc.)--Chulalongkorn University, 2000

The effect of antioxidants on the stability of diesel fuel in this research was performed by using modified method to determine stability of diesel fuel blended with antioxidants. The fuel samples were oxidized in an oxidation bomb with fixed amount of oxygen pressure at 690 kPa. The stability of diesel fuel was characterized by induction period, peroxide value, total insoluble and color development. Investigations were operated by varying in temperature at 25-100 ํC, type and concentration of antioxidants, heteroatom, aromatic content, and component distribution. Additionallly, the effects on storage condition were also studied. Antioxidants were found to improve fuel stability from degradation by increasing of induction period, decreasing peroxide value, prevention of insoluble formation and color development after oxidation. There were four significant factors that led to instability of diesel fuel that were the percentage of hydrocracked fraction, amount of heteroatom, temperature and storage conditions. Although antioxidants could retard oxidation, however they acted as antioxidant by different mechanism. Amine type was more effective in delay oxidation better than phenol type and others. However the reqirement of synergistic benefit to improve stability would be possible with the combination of additives. The optimum dosage of antioxidants to be used for 1 year storage at normal storage condition was about 40-60 mg/l.