Experimental tests on an Euro III compression ignition engine were performed with blends of diesel B15 fuel with ethanol (0-20 vol%) and 1 vol% of an original additive, defined as a mixture of 72.5 vol% of castor oil, 17.5 vol% of soybean biodiesel and 10 vol% of n-butanol. Such mixtures were compared to commercial diesel B7 E0 fuel. The results showed that the addition of ethanol implied an increase of the ignition delay, a faster heat release and a decrease of maximum pressure. Without any optimization of injection timing and combustion, results showed a better conversion of ethanol chemical energy into brake power, when compared with a commercial flex fuel spark ignition engine. In addition, a small increase in the indicated efficiency, in particular at low loads (25% of the maximum torque obtained with commercial fuel under the same rotation), was also observed. Specific fuel consumption increased almost 2% for each 5 vol% of anhydrous ethanol in the blends since the density and the lower heating value of the fuel decreased. A significant decrease of maximum torque was also observed, due to a reduction of the injected volume of fuel (up to 30% in diesel B15 E20 fuel). (C) 2019 Elsevier Ltd. All rights reserved.