Optimizing Energy Recovery from Marine Diesel Engines: A Thermodynamic Investigation of Supercritical Carbon Dioxide Cycles

Since the population and economic activities have increased energy demands, researchers and scientists have turned to recover wasted energy in various systems. This study aims to maximize energy recovery from marine diesel engines through heat exchange in four different types of wasted streams (exhaust gas, engine coolant, and engine oil coolant). In this research, four cycles of carbon dioxide critical recovery have been designed and modeled to utilize wasted heat energy from marine diesel engines (MAN B W L35MC6-TII). The EES engineering software has been used for mathematical calculations. In each cycle, the effect of various parameters such as compressor outlet pressure, compressor inlet temperature, and turbine inlet temperature on output power, exergy efficiency, and compressor power consumption has been investigated. The results of this study indicate that the use of a heat recovery cycle in a diesel engine prevents the loss of a significant amount of energy in the engine. Additionally, increasing the fluid temperature at the compressor inlet reduces the output power and exergy efficiency in all recovery cycles. Increasing the fluid temperature at the turbine inlet reduces the compressor power consumption, increases the output power, and enhances the exergy efficiency in all recovery cycles. When the engine body coolant is used in the recovery cycle, the output power and energy system efficiency increase. Moreover, the cycle includes a generator to recover the heat output of carbon dioxide from the turbine. According to the findings of this study, despite the highest turbine output power (611.5 kW) belonging to the exhaust gas recovery system with two heat exchangers, the recovery system with a single heat exchanger has the highest usable output power (228.3 kW). This system had the highest energy and exergy efficiency of 17.72% and 12.85%, respectively.