In this study, the effects of hazelnut oil–diesel (H30), corn oil–diesel (C30), soybean oil–diesel (S30), sunflower oil–diesel (Su30), canola oil–diesel (Ca30) and Crambe abyssinica oil–diesel (Cr30) and diesel fuel blends were investigated on combustion characteristics, engine performance and NOx, CO, HC, and soot emissions. A single cylinder, four stroke, direct injection diesel engine was operated at maximum brake torque engine speed of 2200 rpm and 7.5, 11.25, 15, and 18.75 Nm engine loads. Test results showed that thermal efficiency decreased by about 3.1, 6.44, 7.08, 7.40, 8.76, and 11.68% with H30, C30, S30, Su30, Ca30, and Cr30 compared to D100 at full load, respectively. There was no big differences on cylinder pressure between test fuels. However, higher heat release rate was obtained with D100 according to fuel blends due to higher calorific value of D100. Test results also showed that HC, CO, and soot emissions decreased with biodiesel fuel blends compared to diesel fuel for all engine loads while NOx emissions increased. At full load, HC and CO decreased by about 81.2 and 21.5%, respectively, with C30 compared to diesel. Similarly, soot reduced 51.3% with Su30 compared to diesel at the same engine load. However, NOx increased 15.8% with C30 according to diesel at full load. It was concluded that biodiesel–diesel fuel blends can be used efficiently in a diesel engine. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1438–1447, 2018.