The effects of different ethanol-diesel blended fuels on the performance and emissions of diesel engines have been evaluated experimentally and compared in this paper. The purpose of this project is to find the optimum percentage of ethanol that gives simultaneously better performance and lower emissions. The experiments were conducted on a water-cooled single-cylinder Direct Injection (DI) diesel engine using 0% (neat diesel fuel), 5% (E5-D) 10% (E10-D), 15% (E15-D), and 20%, (E20-D) ethanol-diesel blended fuels. With the same rated power for different blended fuels and pure, diesel fuel, the engine performance parameters (including power, torque, fuel consumption, and exhaust temperature) and exhaust emissions [Bosch smoke number, CO, No-x, total hydrocarbon (THC)] were measured. The results indicate that: the brake specific fuel consumption and brake thermal efficiency increased with an increase of ethanol contents in the blended fuel at overall operating conditions; smoke emissions decreased with ethanol-diesel blended fuel, especially with E10-D and E15-D. CO and NOx emissions reduced for ethanol-diesel blends. but THC increased significantly when compared to neat diesel fuel. (C) 2004 Elsevier Ltd. All fights reserved.