Synthetic phenolic antioxidants to biodiesel: path toward NOx reduction of an unmodified indirect injection diesel engine

Biodiesel is a green alternative fuel produced from renewable resources. The major disadvantage of biodiesel is the substantial increase in NOx emission. This study examined the effects of antioxidant-treated coconut biodiesel on the performance and exhaust emission characteristics of an indirect injection diesel engine. Coconut biodiesel was produced by transesterification using potassium hydroxide as a catalyst. Two low-cost synthetic antioxidants, 2(3)-tert-butyl-4-methoxyphenol (BHA) and 2,6-di-tert-butyl-4-methylphenol (BHT), were added at 2000 ppm to 20% coconut methyl ester in diesel (CB20). Tests were conducted on a 55 kW 2.5 L four-cylinder diesel engine at a constant load varying speed. Results showed that the antioxidants significantly reduced NOx emission with a slight effect on brake thermal efficiency. The addition of BHA and BHT to CB20 reduced the average NOx emission by 7.78% and 3.84%, and the average brake specific fuel consumption by 1.77% and 1.46%, respectively. The antioxidant addition increased CO, HC, and smoke opacity, but the extent of increase was still below the diesel level. Thus, the addition of antioxidants presents a promising option for NOx reduction.