Dynamic Performance Comparison of CO2 Mixture Transcritical Power Cycle Systems with Variable Configurations for Engine Waste Heat Recovery

Rui Wang,Hua Tian,Xuan Wang,Yan Gao,Gequn Shu,Jing Zhang,Xingyan Bian

doi:10.3390/en13010032

Abstract

Carbon dioxide transcritical power cycle (CTPC) is suitable for engine waste heat recovery owing to its advantages, such as compact construction and high decomposition temperature. In addition, the addition of refrigerant can further improve the performance of pure carbon dioxide (CO2). Because there are limited studies considering the dynamic performance of CTPC systems with CO2 mixture as the working fluid (CMTPC), let alone the dynamic performance comparison of different structures of the CMTPC system, the object of the current work was to compare the dynamic performance, including the off-design performance and dynamic response speed, of four kinds of CMTPC systems, as well as their sensitivity to system input parameters. The dynamic models of four CMTPC systems were established and validated against experimental data, which includes basic CMTPC (B-CMTPC), CMTPC with a preheater (P-CMTPC), CMTPC with a recuperator (R-CMTPC), and CMTPC with both a recuperator and preheater (PR-CMTPC). Based on the dynamic models, the off-design performance and dynamic response speed of four CMTPC systems were compared by changing the engine load. The fluctuation amplitude and response time of a R-CTPC system are the maximum under off-design conditions. Moreover, the sensitivity analysis demonstrates that different output parameters of four CMTPC systems have differing sensitivity to input parameters. It is necessary to pay attention to the more sensitive input parameters under the specific working condition to avoid system damage or unsafe operation.

Highlights

Improving engine efficiency and reducing engine emissions are crucial to alleviating the energy crisis and environmental pollution [1], because more than 50% of the total energy in the engine is usually wasted by low temperature jacket water (60–85 ◦ C) and high temperature exhaust (200–900 ◦ C) [2].Waste heat recovery (WHR) technology is regarded as a potential way to improve engine efficiency and reduce oil consumption
Wang et al [23] studied a dual loop organic Rankine cycle (ORC) coupled with a light-duty diesel engine and the results showed that the maximum thermal efficiency of the engine can be increased by
The results reveal the dynamic performance different performance of the WHR systems under engine driving conditions is quite different from of that under system structures, which would be helpful for controller design and architecture selection

Summary

Introduction

Improving engine efficiency and reducing engine emissions are crucial to alleviating the energy crisis and environmental pollution [1], because more than 50% of the total energy in the engine is usually wasted by low temperature jacket water (60–85 ◦ C) and high temperature exhaust (200–900 ◦ C) [2]. Waste heat recovery (WHR) technology is regarded as a potential way to improve engine efficiency and reduce oil consumption. The reasons lie in their low cost and relatively high conversion efficiency compared with other technologies, such as thermoelectric generation. Some researches concentrated on exploring suitable fluids [6,7,8], and carbon dioxide (CO2 ) is regarded as a potential candidate [9]. The reasons lie in three aspects: Firstly, Energies 2020, 13, 32; doi:10.3390/en13010032 www.mdpi.com/journal/energies

Methods

Results

Conclusion