Oxidative stability and emission profiles of biodiesel from hemp, karanja, castor, and amla oils: impact of natural antioxidants

Abstract

Biodiesel is a renewable fuel with great potential, but its quality can decline over time due to oxidation, which forms harmful compounds like peroxides, aldehydes, and alcohols. This study examines the oxidative stability and storage life of biodiesel made from non-edible oils such as hemp, karanja, castor, and amla. The stability was evaluated using parameters, like peroxide value, totox value, conjugated diene and triene values, and para-anisidine value. To improve stability, both synthetic and natural antioxidants were tested. Butylated hydroxyanisole (BHA) was used as a synthetic antioxidant, while natural antioxidants used were aqueous extract of Moringa oleifera leaves, citrus fruit residues, and olive pomace. BHA provided the best overall protection, and among the natural antioxidants, olive pomace extract performed the best. Engine emission tests were also carried out to study the environmental impact of these additives. The results showed that Moringa oleifera extract reduced the high NO_x emissions commonly seen with biodiesel, while all antioxidants caused only a slight increase in CO and unburned hydrocarbons. Overall, the emissions from biodiesel remained lower than those from conventional diesel fuel.