船用柴油机与非共沸工质有机朗肯循环耦合工作机理研究

It is critical for marine diesel engine to recover waste heat by thermal power cycles to improve fuel efficiency and fulfil new energy efficiency standard. Improving energy efficiency under off-design conditions is a key point. Meanwhile, working fluids with high efficiency and good environmental properties are urgently required to be developed. Aiming at these two difficulties, this project proposes an Organic Rankine Cycle (ORC) system whose working fluid is a zeotropic mixture optimized by a multi-object algorithm based on the group-contribution method, the working mechanism of marine diesel engine-ORC combined system will be studied by theoretical analysis and experimental test: ① theoretical study of zeotropic mixtures by a multi-object mathematical model based on the group-contribution method, obtaining zeotropic working fluids with good thermodynamic and environmental properties and the match characteristics between the groups and waste heat sources over the entire engine’s operation regions; ② research of working mechanism of the combined system under various off-design conditions, analyzing the influences of adjusting working parameters of the top diesel cycle on the combined system efficiency; ③ exploration of the principle of composition shift of zeotropic mixtures within the entire operation regions and experimental validation, achieving optimal match of the composition of zeotropic working fluid with various waste heat sources over the entire engine’s operation region by fully utilizing the temperature sliding characteristics of zeotropic mixtures. Based on these studies, the systematic theory of marine diesel engine and bottoming ORC with zeotropic working fluid can be established ultimately. This research can improve the energy efficiency under off-design conditions effectively and can be used for any other heat sources with variable temperature or load. It can enrich and develop the theory of organic Rankine cycle and has important scientific significance and wide applicable value.

船用柴油机余热动力循环对提高燃料效率，满足更严格的能效标准至关重要。非设计点工况余热回收效率提高是关键，高效环保工质开发也亟待突破。针对以上难点，本项目提出基于基团贡献法优选的非共沸工质有机朗肯循环(ORC)，着重研究船用柴油机与ORC联合系统耦合工作机理，解决船用柴油机全工况范围余热高效回收问题。项目结合理论分析和试验测试开展：①基于基团贡献法的非共沸工质多目标优选理论研究，获得船用柴油机全工况范围高效环保工质及基团匹配特性；②非设计点工况联合系统的协同工作机理研究，分析船用柴油机工况调整对联合系统总能效影响机理；③非共沸工质最佳组分迁移规律研究与试验验证，利用非共沸工质温度滑移优势，实现全工况范围工质与热源的最佳匹配。最终建立船用柴油机与非共沸工质ORC的联合系统理论。本研究成果可有效提升非设计点工况余热回收效率，也可应用于其它热源或负荷变化场合，具有重要的科学意义和广泛的应用价值。

本项目采用理论计算和数值仿真及测试试验对船用柴油机与非共沸工质的有机朗肯循环(ORC)耦合系统的工质选择、底循环设计、联合系统工作特性和非共沸工质的组分迁移进行了深入的分析和研究。通过构建基于PC-SAFT的工质热物性计算模型，以硅氧烷和HFO/HFE类工质为对象分析了在过热区和两相区的物性计算精度，并预测了碳氢类工质的ORC系统性能，基于基团的分子设计方法，改进了PC-SAFT模型的工质设计算法，所得到的基于PC-SAFT的有机工质设计方法显著减少了新型环保工质设计算法的计算工作量；采用热经济性分析方法对比研究了ORC和Kalina循环及跨临界CO2循环的性能，并在考虑膨胀机工作特性基础上分析了非共沸工质ORC的非设计点工况工作特性，为工业余热利用的高效动力系统设计提供了有益的参考；随后，搭建了ORC系统与柴油机的联合动态仿真模型，设计了开环和闭环反馈控制策略，分析了在动态工况下联合系统的工作特性，进一步建立了千瓦级小功率ORC用轴流涡轮的设计和性能分析流程，为ORC系统在实际柴油机上的应用提供了有价值的技术方案；最后，在整个柴油机工况范围内，分析了非共沸工质组分与排气温度和环境温度的匹配特性，得到了非共沸工质的设计准则，为热源温度变化条件下非共沸工质ORC系统的设计和性能改善提供了重要的思路。课题组在柴油机余热回收利用相关方向发表的已标注基金号的国际期刊论文16篇，取得了一定的研究成果，基于本课题研究已出版专著2本，申请发明专利3项，其中1项已经授权。此外，依托本项目共培养2名博士生，8名硕士生。本课题从新的角度揭示了非共沸工质ORC与柴油机的耦合系统工作机理，进一步丰富了基于分子设计理论的有机工质设计方法，同时为ORC系统在柴油机余热回收上的应用提供了有益的参考。