Effect of synthetic and aromatic amine antioxidants on oxidation stability, performance, and emission analysis of waste cooking oil biodiesel.

In the present study, an attempt was made to improve the oxidation stability of biodiesel by adding antioxidants to waste cooking oil biodiesel, and their impact on performance and emissions was analyzed. Two types of antioxidants were chosen for the analysis: an aromatic amine antioxidant, diphenylamine (DPA), and synthetic oxidants, tert-butylhydroxyquinone (TBHQ) and pyrogallol (PY). All the antioxidants were added to the biodiesel at doses of 200 ppm and 500 ppm to evaluate their effect. The oxidation stability was found as per the ASTM standard by mixing 500 ppm antioxidants for all three antioxidant-treated biodiesel blends. DPA yielded similar results as TBHQ, although PY had a better oxidation stability according to the Rancimat test. Gas chromatography and mass chromatography were also performed on the neat biodiesel. Performance and emission tests were performed on the antioxidant-treated biodiesel blends and diesel. The brake thermal efficiency of the tested fuel increased by 9.8%, 6.9%, and 15.88% when the DPA, TBHQ, and PY antioxidants were added to the test fuel compared to that of the test fuel without added antioxidant. The brake specific energy consumption of the test fuel decreased by 9.05% with DPA, 7.03% with TBHQ, and 14.08% with PY compared to that of the test fuel without antioxidant. The NOx emissions of the antioxidant-treated test fuels were reduced by 14.65% with DPA, 11.22% with TBHQ, and 23.10% with PY compared to those of the test fuel without antioxidants. Additionally, the aromatic amine antioxidant (DPA) was found to be effective in enhancing the performance and lowering the exhaust emissions compared to diesel for unmodified diesel engines.