An experimental investigation was conducted to explore the possibility of castor biodiesel to be used as alternative fuel for an existing compression ignition (CI) engine. The castor biodiesel was produced using the transesterification process and the important physico‐chemical properties of various blends were investigated. A series of experiments were carried out on a CI engine fuelled with various castor biodiesel and diesel blends (B10, B20, B30, B40, and B50), over the entire range of engine loading conditions. The comparative analysis of engine performance parameters such as brake thermal efficiency (BTE), specific fuel consumption (SFC), and exhaust gas temperature (EGT); exhaust emissions such as CO, HC, NOx, and smoke opacity; combustion parameters such as cylinder pressure, heat release rate, ignition delay, cumulative heat release, rate of pressure rise, and combustion duration, were carried out. Results were then compared with the base line data for diesel. Further investigations were conducted to estimate the extent to which the castor biodiesel could replace the mineral diesel. The comprehensive analysis of the data collected from the experimentation revealed that the 20% blend of castor biodiesel with diesel (B20) improved the thermal efficiency of the engine and lower exhaust emissions. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 1139–1150, 2017