Parametric optimization and heat transfer analysis of a dual loop ORC (organic Rankine cycle) system for CNG engine waste heat recovery

Yang, F., Zhang, H., Yu, Z. , Wang, E., Meng, F., Liu, H. and Wang, J. (2017) Parametric optimization and heat transfer analysis of a dual loop ORC (organic Rankine cycle) system for CNG engine waste heat recovery. Energy, 118, pp. 753-775. (doi: 10.1016/j.energy.2016.10.119)

Abstract

In this study, a dual loop ORC (organic Rankine cycle) system is adopted to recover exhaust energy, waste heat from the coolant system, and intercooler heat rejection of a six-cylinder CNG (compressed natural gas) engine. The thermodynamic, heat transfer, and optimization models for the dual loop ORC system are established. On the basis of the waste heat characteristics of the CNG engine over the whole operating range, a GA (genetic algorithm) is used to solve the Pareto solution for the thermodynamic and heat transfer performances to maximize net power output and minimize heat transfer area. Combined with optimization results, the optimal parameter regions of the dual loop ORC system are determined under various operating conditions. Then, the variation in the heat transfer area with the operating conditions of the CNG engine is analyzed. The results show that the optimal evaporation pressure and superheat degree of the HT (high temperature) cycle are mainly influenced by the operating conditions of the CNG engine. The optimal evaporation pressure and superheat degree of the HT cycle over the whole operating range are within 2.5–2.9 MPa and 0.43–12.35 K, respectively. The optimal condensation temperature of the HT cycle, evaporation and condensation temperatures of the LT (low temperature) cycle, and exhaust temperature at the outlet of evaporator 1 are kept nearly constant under various operating conditions of the CNG engine. The thermal efficiency of the dual loop ORC system is within the range of 8.79%–10.17%. The dual loop ORC system achieves the maximum net power output of 23.62 kW under the engine rated condition. In addition, the operating conditions of the CNG engine and the operating parameters of the dual loop ORC system significantly influence the heat transfer areas for each heat exchanger.

• Item Type: Articles
• Additional Information: This work was sponsored by the Projects of International Cooperation and Exchanges NSFC (Grant No. 51611130193), the National Natural Science Foundation of China (Grant No. 51376011), the Beijing Natural Science Foundation Program (Grant No. 3152005), the National Basic Research Program of China (973 Program) (Grant No. 2013CB228306), and the Scientific Research Key Program of Beijing Municipal Commission of Education (Grant No. KZ201410005003).
• Keywords: CNG engine, waste heat recovery, dual loop organic Rankine cycle, parametric optimization, heat transfer analysis.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Wang, Dr Enhua and Yu, Professor Zhibin
• Authors: Yang, F., Zhang, H., Yu, Z., Wang, E., Meng, F., Liu, H., and Wang, J.
• Subjects: T Technology > TJ Mechanical engineering and machinery
• College/School: College of Science and Engineering > School of Engineering > Systems Power and Energy
• Journal Name: Energy
• Publisher: Elsevier
• ISSN: 0360-5442
• Published Online: 02 November 2016
• Copyright Holders: Copyright © 2016 Elsevier Ltd.
• First Published: First published in Energy 118: 753-775
• Publisher Policy: Reproduced in accordance with the publisher copyright policy