The present study deals with combustion, emission and performance characteristics of a single cylinder, four‐stroke DI, water cooled diesel engine fuelled with diesel, Simarouba glauca oil added with ethanol as additives and its various blends. In current research, experiments were conducted to study the effect of viscosity, calorific value and density on combustion, performance and emission characteristics of S. glauca oil with ethanol as additives, and its different blends, including BD50, BD50E5%, and BD50E10%. The result shows that diesel has the lowest brake specific fuel consumption with other biodiesel, whereas BD50E10% showed the lowest value as compared to other biodiesel. Furthermore, it was found that Brake Thermal Efficiency of diesel was the highest as compared to other biodiesel while BD50E10% was the highest among all. The maximum peak pressures for diesel, BD50, BD50E5%, and BD50E10% are 74.71 bar, 69.26 bar, 71.40 bar, and 73.69 bar, respectively, at 100% load condition. The HRR for BD50E10% was the highest at 100% load condition as compared with diesel and biodiesel. Conclusively, the findings of this study indicate that BD50E10% is the best alternative fuel for diesel engines. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13146, 2019