In the present work, an investigation is carried out for the assessment of the energy efficiency improvement, which can be achieved with the employment of a supercritical CO₂ power cycle operating in conjunction with a marine Diesel engine. The focus is directed towards the appropriate design of the CO₂ cycle, which recovers heat from three distinct waste heat sources exhibiting different temperature levels (exhaust gas, compressed scavenge air and jacket cooling water), and contributes to the propulsion load in order for the total fuel consumption to be minimized. Engineering optimization problems, based on the superstructure optimization concept, are formulated and solved, in order for the optimal configuration of the CO₂ cycle and the thermodynamic states of the working fluid to be specified. For this purpose, several possible alternatives regarding the CO₂ cycle are examined, and a CO₂ cycle configuration resulting to improved performance of the overall system is proposed as an outcome of the optimization algorithms application. The implications of size limitations of several of the heat exchangers included in the CO₂ cycle and their effects on the performance of the overall system are also assessed. The results indicate that, in comparison with a standalone operating marine Diesel engine, an efficiency enhancement in a range approximately between 6.6% and 7.25% is attainable with the best performing CO₂ cycle configuration, according to the heat exchangers size limitations that may be imposed in a practical implementation of the proposed solution. Although applied for the case of a marine Diesel engine, the findings and results of the present study can also be relevant to other applications as well, in which a heavy duty turbocharged Diesel engine is used.

在目前的工作中，对能效改进的评估进行了一项调查，这可以通过使用超临界 CO ₂动力循环与船用柴油机一起运行来实现。重点针对 CO ₂循环的适当设计，该循环从表现出不同温度水平的三种不同废热源（废气、压缩扫气和夹套冷却水）回收热量，并有助于推进载荷，以便将总油耗降至最低。基于上部结构优化概念的工程优化问题被制定和解决，以便优化配置 CO ₂要指定的工作流体的循环和热力学状态。为此，研究了关于 CO ₂循环的几种可能的替代方案，并且作为优化算法应用的结果提出了导致整个系统性能提高的 CO ₂循环配置。还评估了包括在 CO ₂循环中的几个热交换器的尺寸限制的影响及其对整个系统性能的影响。结果表明，与独立运行的船用柴油发动机相比，使用性能最佳的 CO ₂可将效率提高约 6.6% 至 7.25%循环配置，根据在建议的解决方案的实际实施中可能施加的热交换器尺寸限制。虽然适用于船用柴油发动机的情况，但本研究的发现和结果也适用于其他应用，其中使用了重型涡轮增压柴油发动机。