Dynamic behavior of Rankine cycle system for waste heat recovery of heavy duty diesel engines under driving cycle
Dynamic behavior of Rankine cycle system for waste heat recovery of heavy duty diesel engines under driving cycle
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DOI：
10.1016/j.apenergy.2013.05.071
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发表时间：
2013-12
期刊：
影响因子：
11.2
通讯作者：
H. Xie;Can Yang
中科院分区：
文献类型：
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作者：
H. Xie;Can Yang
RCS（朗肯循环系统）用于从发动机中回收WHE（废热）已被认为是实现更高效率的最有潜力的方法之一。然而，如何在行驶工况下保持RCS的良好性能是一个巨大的挑战。本文试图揭示和解释其在道路上的低效率。提前分析了RCS在行驶工况下的工作过程。然后，定义了四种基本工作模式，包括启动模式、涡轮转动模式、电源模式和保护模式。然后，建立了RCS模型，并在此基础上讨论了RCS在实际行驶工况下的运行性能。结果表明，在额定工作点，道路RCS-E（朗肯循环系统效率）低至3.63%，不到设计RCS-E（7.77%）的一半。尽管汽态波动是不可避免的，但在行驶循环过程中操作模式的切换导致了道路上的低效率。进一步研究表明，工作流体、设计过热度和蒸发压力对膨胀机安全温度及其安全裕度的影响是决定工作模式切换的主要因素。最后，深入研究了工质、设计过热度和蒸发压力对工作模式切换和RC（朗肯循环）效率的影响。研究表明，干流体和等熵流体由于其饱和蒸汽特性，其液滴形成的概率较小，因此优于湿流体。蒸汽参数对RCT-E（朗肯循环热效率）和工作模式切换的影响相反。因此，为了优化RCS，最好在追求RCT-E最大的同时，充分考虑减少工作模式切换。
The RCS (Rankine cycle system) used to recover the WHE (waste heat energy) from engines has been regarded as one of the most potential ways of achieving higher efficiency. However, it is of great challenge to keep the RCS still in good performance under driving cycle. This paper tries to reveal and explain its on-road inefficiency.The operating process of the RCS under driving cycle was analyzed in advance. Afterwards, four basic operating modes were defined, including startup mode, turbine turning mode, power mode and protection mode. Then, a RCS model was established and operating performances of the RCS under an actual driving cycle were discussed based on this model. The results indicate that the on-road RCS-E (Rankine cycle system efficiency) is as low as 3.63%, which is less than half of the design RCS-E (7.77%) at the rated operating point. Despite the inevitable vapor state fluctuation, it is the operating mode switching during the driving cycle that leads to the on-road inefficiency. Further investigations indicate that the expander safety temperature and its safety margin affected by the working fluids, designed superheat degree and evaporating pressure are the main factors determining the operating mode switching. Finally, the effects of the working fluids, designed superheat degree and evaporating pressure on the operating mode switching and RC (Rankine cycle) efficiencies were profoundly investigated. The study shows that the dry and isentropic fluids are superior to the wet ones due to their less probabilities of droplets formation as a consequence of their saturated vapor characteristics. The effects of the vapor parameters on the RCT-E (Rankine cycle thermal efficiency) and operating mode switching are opposite. Therefore, in order to optimize the RCS, it would be better to take full consideration in reducing the operating mode switching, while pursuing the maximum RCT-E.