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The heat from the exhaust gas of diesel engines can be an important heat source to provide additional power using a separate Rankine Cycle (RC) or an Organic Rankine Cycle (ORC). Water is the best working fluid for this type of applications in terms of efficiency of the RC system, availability and environmental friendliness. However, for small engines and also at part load operations, the exhaust gas temperature is not sufficient enough to heat the steam to be in superheated zone, which after expansion in the turbine needs to be in superheated zone. Ammonia was found to be an alternate working fluid for these types of applications which can run at low exhaust temperatures. Computer simulation was carried out with an optimized heat exchanger to estimate additional power with water and ammonia as the working fluids. ANSYS 14.0 CFX software was used for the simulation.

Exhaust gases from diesel engines can be an adequate source of energy to run a bottoming Rankine cycle to increase the overall efficiency of the engine as it contains a significant portion of input energy. In this research, an automotive diesel engine was tested to estimate the available energy in the exhaust gas. Shell and tube heat exchangers were used to extract the heat from the exhaust gas and the performance of the two shell and tube heat exchangers were investigated with parallel and counter flow arrangements using water as the working fluid. The results obtained were below satisfactory as these heat exchangers were purchased from the marketplace and not optimized for this particular application. Thus attempts were made to optimize the design of the heat exchanger by computer simulation using the available experimental data.