A theoretical model was developed for various equivalence ratios to evaluate the performance characteristics and combustion parameters of vegetable oil esters like Jatropha, Mahua and Neem and they are compared to diesel fuel. The combustion characteristics and performance parameters were predicted for different vegetable oil esters and for various equivalence ratios. From the predicted results, it was found that the heat release and work done were reduced by about 4% for Jatropha, 6% for Mahua and 8% for Neem oil esters when compared to diesel. However, slight increase was observed for specific fuel consumption. The harmful pollutants such as HC, CO, NOx and smoke were reduced in the vegetable oil esters than diesel fuel. From the investigation it was concluded that the performance of vegetable oil esters such as Jatropha, Mahua, and Neem are much better. Thus the developed model was highly capable for simulation work with bio-diesel as a suitable alternative fuel for diesel.