Impact of essential oils from agro waste as antioxidants on biodiesel long-term storage stability for CI engines: Fresh and aged evaluations

This research aims to ameliorate the oxidation and storage stability of Prosopis juliflora Methyl Ester (PJME) using the Rancimat method (EN14112). Agricultural waste-derived essential oils (AWEOs), such as Citrus Aurantifolia L. (CA), Curcuma longa L. (CL), and Eucalyptus camaldulensis Dehn (EC), were used as natural antioxidants alongside the commonly used synthetic antioxidant TBHQ. The concentrations of antioxidants ranged from 0% to 4% (v/v % of biodiesel). Results indicated that adding 4% CA to raw PJME extended the induction period (IP) from 2.64 h to 11.2 h at the end of 60 days, meeting EN14214 standards and exhibiting the highest antioxidant activity. TBHQ is less effective at lower concentrations; however, it is comparable to CL at higher concentrations. At 4% TBHQ with PJME, the IP was 9.9, 8.8, and 8.1 hours at the end of 15, 30, and 45 days of storage, respectively. Furthermore, this study uniquely compared the performance and emissions of a CI engine fuelled with a fresh B30 blend, B30 blends stored for 60 days (aged) without and with the addition of an optimal 4% CA antioxidant. The results showed that adding 4% CA to the B30 blend extended its IPs to 34.5 hours, meeting EN590 standards for FAME blends. Compared to B30–60d, the B30+4CA-60d blend exhibited a 9.4% increase in BTE and a 6.5% decrease in BSFC at a BMEP of 4.15 bar. It has an emission reduction potential of 47.8% for CO, 8% for HC, along with a marginal decrease in NOXemissions. Compared to D100, it significantly reduced CO emissions by 37.5%, HC emissions by 8%, and NOXemissions by 16.3%. These findings indicate that natural antioxidants effectively inhibit free radical formation and maintain biodiesel quality over extended storage on par with synthetic antioxidants. This finding is significant as it maintains engine performance and addresses global energy and environmental concerns.