Thermodynamic Analysis of Combined ORC-VCR Powered by Waste Energy from Diesel Engine

To efficiently utilize the waste energy from both exhaust gases and cooling water of a Diesel engine, an organic Rankine cycle-vapor compression refrigeration (ORC-VCR) combined system is employed and a thermodynamic model is developed, analyzed and optimized. Four hydro-carbon working fluids R600 (butane), R600a (isobutane), R601 (pentane), R601a (isopentane) are analyzed and evaluated in order to find a suitable working fluid for the combined system which may yield high system efficiencies for same waste energies from the diesel engine. The overall coefficient of performance (COP) and working fluid mass flow rate of per kW cooling capacity (MKW) are chosen as key performance indicators. The boiler pressure in the sub-critical range, the condenser temperature and evaporator temperature are taken to be the decision variables for optimization. Comparison between selected working fluids for their optimized systems is done on the basis of COP, MKW, condenser pressure, boiler temperature, expansion ratio (EPR) and compression ratio (CMR). The analysis shows that among the selected working fluid, R600 is the best for the ORC-VCR system for waste energy utilization from both exhaust gases and cooling water a diesel engine.