The purpose of this work is to investigate the effect of butanol-biodiesel blends on the emissions and performance characteristics of a four-stroke, naturally aspirated, water-cooled, indirect injection diesel engine (IDI). Testing was performed comparing butanol blended with biodiesel, standard diesel (D100) and neat biodiesel (B100) at four engine loads. The biodiesel-butanol blends were 5%, 10%, and 20% butanol in volume basis (B95Bu5, B90Bu10, B80Bu20). Compared to biodiesel, butanol blended fuels showed lower exhaust gas temperatures and nitrogen oxides (NOx) emissions while exhibiting higher carbon monoxide (CO) and unburned hydrocarbons (HC) emissions. Butanol blended fuels produced lower CO and higher NOx emissions than diesel fuel for low concentrations of butanol (5% and 10%), but there was no significant change in terms of HC emissions. The biodiesel blend containing the highest concentration of butanol (20%) caused higher CO and HC emissions and lower NOx emission than diesel. Brake specific fuel consumption increased with biodiesel and biodiesel blended fuels as compared to diesel. (C) 2014 Elsevier Ltd. All rights reserved.