RESEARCH ARTICLE Optimum composition ratios of multicomponent mixtures of organic Rankine cycle for engine waste heat recovery Min-Hsiung Yang 1 | Rong-Hua Yeh 2 1 Department of Naval Architecture and Ocean Engineering, National Kaohsiung University of Science and Technology, Taiwan, ROC 2 Department of Marine Engineering, National Kaohsiung University of Science and Technology, Taiwan, ROC Correspondence Rong-Hua Yeh, Department of Marine Engineering, National Kaohsiung University of Science and Technology, No. 142, Haijhuan Road, Nanzih District, Kaohsiung City 81157, Taiwan, ROC. Email: rhyeh@nkust.edu.tw Funding information Ministry of Science and Technology, Grant/Award Number: MOST 108-2221-E- 992 -024 -MY2 Summary With the temperature glide in saturation states, the mixture working fluids have the advantages in thermal energy conversion. In this study, through the investigation in optimum mass fractions of multicomponent mixture working fluids, the economic performance enhancement of the organic Rankine cycle system is obtained for recovering waste heat from engine. The zero ozone- depletion-potential and dry working fluids of R236fa, R245fa, and R1336mzz (Z) are selected as the components of multicomponent mixtures in the system. The net power output, heat transfer calculation, and apparatus cost evaluation are employed to evaluate the power cost of the organic Rankine cycle system. Parameters of temperatures of waste heat sources and efficiencies of expanders are taken into account. The comparisons of economic performances for single- component working fluid and multicomponent mixtures with optimum mass fractions are proposed. The results show that R245fa, having a levelized cost of energy, LCOE, of 8.75 × 10 -2 $/kW-h, performs the best for single-component working fluids, better than R236fa by 1.6% and R1336mzz(Z) by 8.3%. All the two-component mixtures are superior to their single-component working fluids in economic performance. Among the three two-component mixture working fluids, R1336mzz(Z)/R236fa has the lowest LCOE min , 8.57 × 10 -2 $/kW-h, followed by R236fa/R245fa and R245fa/R1336mzz(Z). In addition, R236fa/R245fa/R1336mzz(Z) mixture, which has a LCOE min of 8.47 × 10 -2 $/kW-h, economically outperforms all other working fluids and has a lower LCOE min than R236fa/R245fa by 1.7% and R245fa/R1336mzz(Z) by 2%. KEYWORDS composition ratio, economic performance, multicomponent mixture, organic rankine cycle, working fluid 1 | INTRODUCTION Lately, engine waste heat recovery (WHR) has attracted more and more attentions since it can both improve the thermal efficiencies of engines and help vehicles and ves- sels meet the worldwide restrictions of CO 2 emissions. For large diesel engines in merchant ships, the exhaust gas, cylinder cooling water, and scavenge air cooling water may serve as the waste heat sources. Owing to the low boiling temperature of working fluid, the organic Rankine cycle (ORC) system possesses a great potential in conversion of these waste heat energies into electricity. To recover the waste heat from the internal combustion engine, Vaja and Gambarotta 1 considered three different Received: 5 July 2019 Revised: 14 October 2019 Accepted: 17 October 2019 DOI: 10.1002/er.4977 Int J Energy Res. 2019;1–19. wileyonlinelibrary.com/journal/er © 2019 John Wiley & Sons, Ltd. 1