Thermodynamic feasibility and system-level performance assessment of integrated scavenge-air cooling and waste-heat-driven absorption refrigeration for marine engines

This study investigates the thermodynamic feasibility and system-level performance of integrating a waste-heat-driven lithium bromide–water (LiBr–H 2 O) absorption refrigeration system with dynamic scavenge-air cooling (SAC) on an LNG carrier. A one-dimensional thermal–fluid model is developed to represent the coupled interactions between engine operation, ambient conditions, and cooling subsystems under both steady-state and transient voyage scenarios. The model accounts for load-dependent variations in absorption refrigeration capacity and incorporates cooling-capacity constraints under realistic operating conditions. Optimal scavenge-air temperatures are determined across a wide range of load–humidity combinations using manufacturer-based correlations, and system performance is evaluated under representative climatic conditions and real voyage data. Results indicate that steady-state fuel savings range from 0.07% to 0.66%, depending on engine load and the ambient conditions. Under transient voyage operation, total fuel savings decreased to approximately 0.1% due to dynamic thermal constraints and variations in cooling availability. When surplus absorption refrigeration capacity is utilized to offset onboard HVAC demand, the equivalent fuel-saving potential increases to 0.2–0.5%, primarily governed by engine load distribution, ambient conditions, and the utilization of available cooling capacity. The analysis further shows that cooling capacity exceeds system demand for a substantial portion of the voyage, indicating underutilization of available thermal resources. A first-order economic assessment indicates that, under current conditions, the economic viability of the system is limited, with estimated payback periods exceeding typical vessel lifetimes. Overall, the results suggest that while the integrated SAC–ARS system provides measurable thermodynamic benefits, its performance remains modest and strongly dependent on operating conditions and system utilization. This work provides a physics-based framework for feasibility assessment and highlights key considerations for future optimization and practical evaluation.