A theoretical model was developed to evaluate the performance, characteristics and combustion parameters of vegetable oil esters like Jatropha, Mahua and Neem Oil esters. The predicted results of these fuels are compared with result of diesel fuel. The vegetable oil esters are produced   by transesterification method. In this process, the raw vegetable oil reacts with methanol and forms esterified vegetable oil in the presence of NaOH (or) KOH that acts as a catalyst. A four zone model based on the existing two zone model is developed to predict the pressures, various zone temperatures and volumes at various crank angle positions. The combustion characteristics and performance parameters such as heat release, heat transfer, work done, mean effective pressure, thermal efficiency, specific fuel consumption and power are predicted for different vegetable oil esters and for various engine conditions such as injection timing, spray cone angle and load conditions. The maximum performance is predicted for all fuels at an optimum engine conditions. The optimum engine conditions include three fourth of load, injection timing of 14oBTDC, spray cone angle of 18o. From the predicted results, the heat release and work done are reduced by about 5% for Jatropha, 19% for Mahua and 25% for Neem oil esters when compared to diesel. There is a slight drop in the values of pressure, thermal efficiency, power and mean effective pressure for vegetable oil esters when compared to diesel.  However SFC shows an increase. The performance is considerably increased with respect to increase of cone angle from 14o to 20o. The optimum performance is found at cone angle of 18o for all fuels. From the investigation, it is concluded that performance of vegetable oil esters such as Jatropha, Mahua and Neem oil esters are in good agreement with diesel performance at optimum engine conditions.  Thus the developed model is highly compatible for simulation work with bio diesel as an alternative fuel.