The present work evaluates the impact of properties of four very common bio-fuels, viz. vegetable oil (cottonseed), or its derived (methyl ester) bio-diesel, or ethanol, or n-butanol, in blends of various proportions with diesel fuel, on the combustion and exhaust emissions of a fully instrumented, six-cylinder, four-stroke, heavy-duty direct injection (HDDI), 'Mercedes-Benz' bus diesel engine, bearing a waste-gate turbocharger with after-cooler, running under steady and transient conditions. Under steady-state operation, exhaust smoke, nitrogen oxides (NOx), carbon monoxide (CO), and total unburned hydrocarbons (HC) were measured and compared with those of the baseline operation (with neat diesel fuel) and among themselves. Fuel injection, combustion chamber pressure, and heat release rate (HRR) diagrams revealed interesting features of the combustion mechanisms. These results and the different physical and chemical properties of those bio-fuels are used to aid the interpretation of the observed engine behavior. As regards the transient engine operation, measurements for three accelerations tests were examined with the engine fueled on bio-diesel or n-butanol diesel fuel blends. The test bed was complemented with fast response instruments to capture the development of key engine and turbocharger variables, depicted in analytical diagrams, using ultra-fast response instrumentation for the instantaneous measurements of the exhaust NO and smoke opacity. Again, these results and the different physical and chemical properties of bio-fuels are used to aid the interpretation of the engine behavior. Finally, a comparison is made for the influence of bio-fuels properties (bio-diesel and n-butanol) on the NOx and smoke emissions between steady-state and transient operating conditions, under the recognition of the different non-fuel factors affecting the transient operating schedules. (C) 2015 Elsevier Ltd. All rights reserved.