Thermodynamic, Economic, and Environmental Analysis and Optimization of a Multi-Heat-Source Organic Rankine Cycle for Large Marine Diesel Engine

The Organic Rankine Cycle (ORC)-based waste-heat recovery system represents an important technological pathway toward decarbonization in the maritime industry. This study focuses on the design and optimization of a multi-heat-source Organic Rankine Cycle (MHSORC) power generation system specifically developed for large marine diesel engines, which simultaneously utilizes exhaust gas, cylinder jacket water, and scavenging air as heat sources. Unified thermodynamic, economic, and environmental models are constructed to evaluate the coupled performance of the system.Eight low GWP working fluids are assessed, and a multi-objective optimization is performed to balance efficiency, cost, and environmental impact. The optimal design point is subsequently identified using a decision-making algorithm. The results indicate that, for the MHSORC, higher evaporating temperatures and lower condensing temperatures improve system performance, and the heat-source temperature exerts a direct and substantial influence on that performance. Among the candidate fluids, R601 exhibits the best overall performance, whereas R1234ze performs the worst. With R601 as the working fluid, the MHSORC achieves an exergy efficiency of 41.69%, a LCOE of 0.0495 $/kWh, and greenhouse gas emissions of 0.8019 kt of CO2,eq.