Heat available in the exhaust gas of a diesel engine can be an important heat source to provide additional power using separate Rankine Cycle (RC). In this current work, experiments were conducted to measure the available exhaust heat from a 40kW diesel engine generator set. Performance of an available shell and tube heat exchanger using water as the working fluid was conducted. With the available experimental data, computer simulation was carried out to optimize the design of the heat exchanger. This optimized heat exchanger was then used to estimate additional power considering actual turbine efficiency. Two heat exchangers were used for this purpose. One is used to generate vapour and the other to generate super-heated vapour. Two organic fluids namely Ammonia and HFC-134a were used in this study. The water was also used as working fluid to compare the results. The proposed heat exchanger can produce 10%, 9% and 8% additional power by using water, ammonia and HFC-134a as the working fluids respectively