This research aims to analyze the potential possibility of the butyl ether (BE, oxygenates of di-ether group) as a fuel additives for a naturally aspirated direct injection diesel engine fuel. Compared with the diesel fuel, smoke emission decreased approximately 26% by applying the blended fuel(diesel fuel 80 vol-% + BE 20vol-%) at the engine speed of 2,500 rpm and with full engine load. There was none significant difference between the blended fuel and the diesel fuel on the power, torque, and brake specific energy consumption rate of the diesel engine. But, NOx emission from the blended fuel was higher than that of the commercial diesel fuel. As a counter plan, the EGR method was employed to reduce the NOx. We found the possible area where the simultaneous reduction of the smoke and the NOx emission from the diesel engine was achieved by applying the BE blended fuel and the cooled EGR method.