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Thermodynamic Analysis of Supercritical Carbon Dioxide Cycle for Internal Combustion Engine Waste Heat Recovery

by Wan Yu 1,2, Qichao Gong 1,2, Dan Gao 1,2, Gang Wang 1,2,*, Huashan Su 1,2 and Xiang Li 1,2
1
Hubei Key Laboratory of Hydroelectric Machinery Design & Maintenance, China Three Gorges University, Yichang 443002, China
2
College of Mechanical & Power Engineering, China Three Gorges University, Yichang 443002, China
*
Author to whom correspondence should be addressed.
Processes 2020, 8(2), 216; https://doi.org/10.3390/pr8020216 (registering DOI)
Received: 17 December 2019 / Revised: 2 February 2020 / Accepted: 10 February 2020 / Published: 12 February 2020
(This article belongs to the Special Issue Advances in Supercritical Fluid Extraction)
Waste heat recovery of the internal combustion engine (ICE) has attracted much attention, and the supercritical carbon dioxide (S-CO2) cycle was considered as a promising technology. In this paper, a comparison of four S-CO2 cycles for waste heat recovery from the ICE was presented. Improving the exhaust heat recovery ratio and cycle thermal efficiency were significant to the net output power. A discussion about four different cycles with different design parameters was conducted, along with a thermodynamic performance. The results showed that choosing an appropriate inlet pressure of the compressor could achieve the maximum exhaust heat recovery ratio, and the pressure increased with the rising of the turbine inlet pressure and compressor inlet temperature. The maximum exhaust heat recovery ratio for recuperation and pre-compression of the S-CO2 cycle were achieved at 7.65 Mpa and 5.8 MPa, respectively. For the split-flow recompression cycle, thermal efficiency first increased with the increasing of the split ratio (SR), then decreased with a further increase of the SR, but the exhaust heat recovery ratio showed a sustained downward trend with the increase of the SR. For the split-flow expansion cycle, the optimal SR was 0.43 when the thermal efficiency and exhaust heat recovery ratio achieved the maximum. The highest recovery ratio was 24.75% for the split-flow expansion cycle when the total output power, which is the sum of the ICE power output and turbine mechanical power output, increased 15.3%. The thermal performance of the split-flow expansion cycle was the best compared to the other three cycles. View Full-Text
Keywords: supercritical; pressure; thermal efficiency; exhaust heat recovery ratio; split ratio supercritical; pressure; thermal efficiency; exhaust heat recovery ratio; split ratio
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Yu, W.; Gong, Q.; Gao, D.; Wang, G.; Su, H.; Li, X. Thermodynamic Analysis of Supercritical Carbon Dioxide Cycle for Internal Combustion Engine Waste Heat Recovery. Processes 2020, 8, 216.

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