Similar properties of biodiesel to conventional diesel have made biodiesel as a promising fuel. However, its NOx emission was reported higher by most researchers in the world. In this study, antioxidants are used in the effort of improving the oxidation stability of biodiesel and reducing the NOx emission while maintaining the engine performance. p-Phenylenediamine (PPD) and N,N’-diphenyl-p-phenylenediamine (DPPD) are added in 0.025 wt% and 0.15 wt% concentrations, respectively into palm oil methyl ester-diesel blend. The performance characteristics of biodiesel
blends are tested on a single cylinder engine with an attached emission analyser. The addition of
the PPD and DPPD antioxidants improved the oxidation stability of biodiesel without affecting much in the density and kinematic viscosity. For B20 (20% biodiesel + 80% Euro 5 diesel), the addition of DPPD showed the best results by reducing NO (0.8% lower on average), CO (10.8% lower on average) and HC emission (32.9% lower on average), as compared to B7 blend. However in terms of engine performance, B20+DPPD showed higher BSFC and lower brake power when
compared to B7 blend.