Impact of additives on storage stability of Karanja (Pongamia Pinnata) biodiesel blends with conventional diesel sold at retail outlets

• Effect of the addition of antioxidants on storage stability blends of diesels with KOME.
• Strong correlation between KOME concentration and storage stability.
• Oxidation stability of neat KOME and its diesel blends were found to increase significantly with addition of antioxidants.
• PY and PrG were found most effective antioxidants among all.
• Difference in physicochemical properties shown variation in the storage stability of diesel biodiesel blends.

Biodiesel has been recognized as a “green fuel”, being the most attractive substitute to the conventional petro-diesel. The unsaturated fatty acids present in biodiesel are susceptible to oxidation. One of the main criteria used for the quality assessment of biodiesel is ‘storage oxidation stability’. Oxidation of the esters during the long-term storage can lead to problems for the utilization of biodiesel in the engine directly. Therefore, the addition of additives is required to protect the oxidation of biodiesel. This study investigates the effect of antioxidant additives on oxidation stability of neat biodiesel [Karanja oil methyl ester (KOME)] and its diesel blends. KOME was prepared by methanolic KOH catalyzed transesterification of Karanja oil, which was produced from a non-edible oil feedstock from Indian sub-continent. Various diesel–biodiesel blends (B5, B10, B15, B20, B25 and B40) were prepared with conventional diesels sold at retail outlets of Northern India. Butylated hydroxy anisole (BHA), Butylated hydroxy toluene (BHT), tert-Butylhydroxyquinone (TBHQ), Propyl-gallate (PrG) and Pyrogallol (PY) antioxidant additives were selected for this study. Significant improvement in oxidation stability as well as in density and kinematic viscosity of diesel–biodiesel blends was observed with all antioxidants studied. PY, PrG and BHA were found most effective among all antioxidants tested, and their use in diesel/biodiesel blends showed a greater stabilizing potential. All the samples were stored at room temperature in air-tight bottles under ambient conditions. The aim of this study is to find the minimum required concentration of most effective antioxidant to meet the storage oxidation stability specifications.