The objective of the present study is to explore the effects of the minor addition of 1-pentanol and benzyl alcohol, classified respectively as aliphatic and aromatic type alcohols based on the classified hydroxyl group position in their molecular structure. Simarouba glauca and diesel blends (B20 and B40) were prepared and tested to study the CI engine performance, emission and combustion characteristics under different load conditions. To each of the four combination fuel samples prepared for B20 and B40, 1-pentanol and benzyl alcohol additives were added at 5% and 10% concentrations by volume. Experimental tests for all of the different fuels were performed in a single cylinder, four-stroke and constant speed CI engine and the engine characteristics were compared with diesel and biofuel blends. The experimental study reveals that the poor performance of B20 and B40 is enhanced with 1-pentanol (P) and benzyl alcohol (Bn) addition. The improvement in performance is considerable with an increase in the concentrations of alcohol in B20 and B40 blends. Higher HC, CO and smoke emissions associated with B20 and B40 blend fuels are reduced with alcohol addition. NOx emissions are also reduced with the addition of alcohol blends and 1-pentanol shows more promising results in terms of low NOx emissions compared to benzyl alcohol. Alcohol addition with B20 and B40 extended the ignition delay period due to low cetane number. However, combustion phasing is reduced as a result of improved combustion. The outcome of this research work is that poor combustion characteristics of the biofuel-diesel blend can be improved with the minor addition of aliphatic and aromatic alcohol. Except for comparatively higher NOx emissions, benzyl alcohol showed promising results in terms of performance parameters like efficiency, emission and combustion improvement.