Experimental investigation of a common rail direct injection diesel engine is carried out, when working with diesel fuel in blends with 10% (B10), 15% (B15) and 20% (B20) n- butanol at different loads and speeds. The cetane number of the blends is lower than basic fuel and is corrected to these of the neat diesel fuel. The differences in brake specific fuel consumption (BSFC) and exhaust emissions are compared with the baseline operations (when working with the neat diesel fuel). The cetane improver 2-EthylHexil Nitrate is used. Six types of fuels are investigated: B10 and B10 with cetane improver, B15 and B15 with cetane improver, B20 and B20 with cetane improver. This approach shows that the BSFC for fuel blends with corrected cetane number is closer to this with neat diesel fuel, especially at higher engine speeds. The exhaust smoke (D) for blends with corrected cetane number is lower than the neat diesel fuel and blends without cetane improver. There is no clear trend for NOx emission.