This work studied the impact of hydrous ethanol and n-butanol fumigation on the combustion characteristics, performance, pollutant emissions, particle number concentration and size distribution of an automotive diesel engine. Independently of engine load, both alcohols exhibited higher premixed combustion peaks, faster combustion process, and higher coefficient of variation of indicated mean effective pressure (imep) and reduced maximum in-cylinder temperature, in comparison with ultra low sulfur diesel (ULSD). Neither n-butanol nor hydrous ethanol presented better brake thermal efficiency (bte) and brake specific fuel consumption (bsfc) than ULSD. Engine performance with alcohol fumigation is highly susceptible to operating mode. Therefore, it is necessary to optimize the specific thermal conditions for implementing a fumigation strategy. Both alcohols increased carbon monoxide (CO) and total hydrocarbons (THC) and reduced nitrogen oxides (NOx) and particulate matter (PM), in comparison with ULSD fuel. However, the magnitude of this reduction was markedly affected by engine operating mode. The n-butanol showed the best trade-off (PM vs NOx + THC) among all fuels. In comparison with ULSD, hydrous ethanol fumigation decreased the total number concentration of particles while maintaining or increasing the geometric mean diameter, depending on the engine load. In comparison with ULSD, n-butanol maintained or reduced the total number concentration of particles and exhibited the opposite trend for the geometric mean diameter. The particle number concentration (PNC) and size distribution were not affected by engine load for n-butanol. (C) 2015 Elsevier Ltd. All rights reserved.