Performance Analysis Of CO₂ Based Mixtures Transcritical Rankine Cycle（TRC） For Engine’s Waste Heat Recovery（WHR）

Generally,in the internal combustion engine（ICE）only 35%-45% can be converted into useful mechanical body of work from the total combustion energy.The rest part will be dissipated into the environment through exhaust gas and engine coolant,this cause the great loss of energy.Therefore,energy saving and emission reduction of engine are tremendous importance to improve the energy crisis and environmental pollution.Due to most advancement in technology,ICE will continue to governing source of power in the near future of life.The waste heat recovery of engine is one of the most effective technologies to recognize the energy saving and emission reduction.The exhaust gas and engine coolant of ICEs show the great prospective in WHR because of its high temperature and grade.So the CO₂ Transcritical Rankine cycle has reasonable and significant developing for the waste heat recovery of engine.In this field the CO₂ TRC has a better versatility and great prospective for engine’s WHR.However,to solve problems of high pressure,stringent condensation condition requirement and low efficiency of CO₂ TRC,this study initially explored and the use of feasibility for CO₂ mixed working fluid instead of pure CO₂ TRC for engine’s WHR.In order to improvement of thermal and economical achievement of TRC pure CO₂ there some GWP organic fluids R123,R161,R32,R1234yf,R22,R1234ze,R132a and R152a have been selected in this study whose mass fraction taken 50% to blend into CO₂ TRC.This study extensively explored above CO₂ mixed working fluid.Based on the improvement of process performance,condensation conditions and operating pressure,the theoretical exploration with simulation carried out to select the most suitable CO₂ mixtures for TRC.To analysis the performance of CO₂ mixtures based TRC first need to calculate of basic physical properties of CO₂ mixtures by the use of first and second primary thermodynamic principles.Theoretical investigation has studied by software with experimental data calculation and Peng-Robinson equation applied to calculate properties such as enthalpy,entropy,critical temperature and critical pressure with less than 3%error found in results.In this study preheater and regenerator TRC waste heat recovery system basic structure used to implement theoretical exploration and research with different CO₂ mixed working fluids.The influences of different CO₂ mixtures and operating parameters on the cycle performance were studied.On the basis of net power,thermal efficiency,exergy efficiency,electricity production cost it was found that when the condensing temperature is greater than 40℃,the net output work of the CO₂/R161（0.30/0.70）cycle is the largest but for CO₂/R32（0.3/0.7） it was higher when less than 40℃.When the condensation temperature was set at 21℃,the working pressure of CO₂/R161（0.30/0.70） and CO₂/R32（0.3/0.7） in TRC was reduced by 15.3% and 22.6%,the maximum net output power of the system is increased by 11.8% and 15.6% respectively,as compared to CO₂TRC.Finally,this paper conducted an experimental study on the mixture of R134a and CO₂ as the working medium.The experimental results showed that the addition of the mixture in CO₂ can indeed increase the output work of the system,reduce the maximum operating pressure and improve the condensation temperature of the system.