Experimental investigation was carried out to study the combustion, engine performance and emission characteristics of a single cylinder, naturally aspirated, air cooled, constant speed compression ignition engine, fuelled with two modified fuel blends, B20 (Diesel soybean biodiesel) and diesel soybean biodiesel ethanol blends, with alumina as a nanoadditive (D80SBD15E4S1 + alumina), and the results are compared with those of neat diesel. The nanoadditive was mixed in the fuel blend along with a suitable surfactant by means of an ultrasonicator, to achieve stable suspension. The properties of B20, D80SBD15E4S1 + alumina fuel blend are changed due to the mixing of soybean biodiesel and the incorporation of the alumina nanoadditives. Some of the measured properties are compared with those of neat diesel, and presented. The cylinder pressure during the combustion and the heat release rate, are higher in the D80SBD15E4S1 + alumina fuel blend, compared to neat diesel. Further, the exhaust gas temperature is reduced in the case of the D80SED15E4S1 + alumina fuel blend, which shows that higher temperature difference prevailing during the expansion stroke could be the major reason for the higher brake thermal efficiency in the case of D80SBD15E4S1 + alumina fuel blend. The presence of oxygen in the soybean biodiesel, and the better mixing capabilities of the nanoparticles, reduce the CO and UBHC appreciably, though there is a small increase in NOx at full load condition. (C) 2015 Elsevier Ltd. All rights reserved.