Operation strategy of a multi-mode Organic Rankine cycle system for waste heat recovery from engine cooling water

Engine cooling water contains a large amount of waste heat. Waste heat recovery (WHR) is a necessary way to improve the efficiency of engine. But too high or too low cooling water temperatures affect engine emissions and performance. To combine efficient WHR and rational use of waste heat from engine cooling water under variable engine operating conditions, this study proposed a parallel dual expander organic Rankine cycle (ORC) system that can operate in multiple modes. To exploit its advantages, the system characteristics were explored and a system operation strategy was developed through experimental studies. The regulations of the system operation were summarised through extensive experiments exploring system performance. Four system operation modes were developed based on these regulations. The four modes are applied to different heat sources to meet heat exchange requirements while operating efficiently. Finally, the feasibility of this operating strategy was verified by experiments under 16 sets different heat sources. Results show that the ORC-WHR system and operating strategy can effectively adapt to the heat source variation. The parallel operation of the dual expanders can broaden the applicable heat source conditions by 120%. This study provides the basis for the practical application of this system.

Automated summary

Engine cooling water contains waste heat, and waste heat recovery (WHR) is essential for improving engine efficiency. However, extreme cooling water temperatures can negatively impact engine emissions and performance. This study proposes a parallel dual expander organic Rankine cycle (ORC) system that can operate in multiple modes to efficiently recover and utilize waste heat from engine cooling water under varying conditions. Through experimental studies, the system characteristics and operation strategy were explored, and four operation modes were developed based on extensive performance experiments. The feasibility of this operating strategy was verified through experiments with 16 different heat sources, demonstrating effective adaptation to heat source variation and the ability to expand applicable conditions by 120%. This study provides a foundation for the practical application of the ORC-WHR system.