In this study, initially, n-butanol at low proportions viz. 5%, 10%, 15%, and 20% is blended with Karanja methyl ester (KME) respective proportions, and the blends are characterized. The blends are denoted as KBB5, KBB10, KBB15 and KBB20 where the numeric value followed by KBB indicates the percentage of n-butanol in the blends. The blends are used as test fuels in a single cylinder, four-stroke, direct injection (DI) diesel engine producing power of 4.4 kW at a constant speed of 1500 rpm. The combustion, performance and emission characteristics of the engine are evaluated and compared with the diesel engine operation. Further, an oxygenated additive: diethyl ether (DEE) in small quantities is added with the optimum blend to examine the reduction of unburnt hydrocarbon (UHC) emission from the engine when it is run with a biodiesel n-butanol blend. Among all the four KME n-butanol blends examined in this study, KBB15 exhibits good performance and less emissions. The results are presented in this paper. (C) 2018 Elsevier Ltd. All rights reserved.