A biodiesel is a clean-burning alternative fuel. It has drawn attention of the energy researchers over the last two decades as a solution to problems of environmental concerns, rising fossil fuel price, increasing dependency on foreign energy sources. However, it is susceptible to oxidative degradation due to autoxidation in the presence of oxygen, which hinders its widespread use. The addition of an antioxidant to it reduces this phenomenon significantly. It is expected that antioxidants may affect the clean burning characteristic of a biodiesel. Coconut (Cocos nucifera) and Jatropha (Jatropha curcas) are two promising feedstock growing in the South-East Asian region. This paper presents an experimental investigation of the effect of addition of an antioxidant on the performance and emission characteristics of a four-cylinder diesel engine fueled with 20% blends of two biodiesels (CB20 and JB20). A biodiesel from coconut oil was produced by transesterification process using potassium hydroxide (KOH) as a catalyst. Jatropha biodiesel production was preceded by an esterification step, using sulfuric acid as a catalyst. To study the antioxidant effect, two low-cost synthetic antioxidants, 2(3)-tert-butyl-4-methoxyphenol (BHA) and 2,6-di-tert-butyl-4-methylphenol (BHT), at a concentration of 2000. ppm, were used in this study. Addition of antioxidants increased their oxidation stability without causing any negative effect on other physicochemical properties. BHT and BHA were found to increase the stability of JB20 and CB20, respectively. Performance results indicate that JB20 and CB20 showed, respectively, 0.95% and 2.97% lower mean brake power (BP) and 5.02% and 4.76% higher mean brake-specific fuel consumption (BSFC) than to diesel. The addition of antioxidants increased BP and reduced BSFC slightly. Emission results show that untreated JB20 and untreated CB20 increased nitrogen monoxide (NO) emission by 5.52% and 8.02%, but reduced carbon monoxide (CO) and hydrocarbon (HC) emission. Antioxidant-treated blends reduced NO emission by 2.6-5.0%, but increased CO emission by 4.9-20.8% and HC emission by 23.2-40.2% compared to B20 depending on feedstock. Thus, antioxidant-treated JB20 and CB20 blends can be used in diesel engines without any modification. © 2014 Elsevier B.V.
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