Oxygenates may be added to diesel oil to help reduce exhaust emissions from diesel engines. This study evaluates the effect of adding ethyl-tert-butyl ether (ETBE) to diesel oil on the physicochemical properties of the mixture. ETBE is added in volumetric proportions of 5%, 10%, 20%, 30%, and 40%, and its effects on density, viscosity, lubricity, surface tension, miscibility, and cetane number are investigated. While the effects of ETBE addition on density, viscosity, and cetane number have been examined earlier, this is the first study to investigate the effects of ETBE addition on surface tension, lubricity, and miscibility. The impact of ETBE addition on particulate matter (PM) and smoke emissions is also investigated. The results reveal that ETBE addition can significantly reduce PM emission. In particular, it was found that only 10% ETBE can decrease PM emission by 36%. ETBE addition was also found to reduce the smoke opacity, resulting in 70% reduction with 40% ETBE fraction at the engine speed of 1400 rpm and a load of 80 N m. This is the first study that reports the effect of ETBE addition on PM emission from an engine fueled by diesel-ETBE blends. (C) 2012 Elsevier Ltd. All rights reserved.