Research On The Working Fluids Of Engine Exhaust Energy Recovery System

Exhaust Energy Recovery (EER) technology based on Rankine cycle (RC) forInternal Combustion (IC) engines has been proved to not just bring measurableadvantages for improving fuel consumption but also increase engine power output,further reducing CO2and other harmful exhaust emissions correspondingly, in thepaper, the relationship between physical property and cycle performance of pureworking fluid and mixed fluid has been studied respectively.With reference to the actual heat exchanger, the system model was established inMATLAB, with variable pinch point temperature difference (PPTD) method, therelationship of thermal physical property and cycle performance was calculated andanalyzed among28working fluids. Results show that the PPTD changes withdifferent evaporation pressures. With the pressure ranging from0.5to3.5MPa, thePPTD varies by in close to30℃. Therefore the PPTD change should be considered inthe calculation. Relatively, the fluid with a higher critical temperature has a lowercycle efficiency. An optimal region of the ratio of the evaporation temperature and thecritical temperature exists in which the fluids have higher efficiencies than others, andmoves towards right with the increase of evaporation pressure. The wet fluids havethe highest power output followed by the isentropic fluids, and the dry fluids producethe lowest one at the given condition.To analyze the relationship between cycle performance and the components massfraction, the first and second law thermodynamic cycle performance of six kind ofbinary mixtures, Propane/Ethane, Propane/Isobutane, Propane/Pentane, Propane/Butane, R32/R125, R141b/RC318, are studied. Results show that the cycle efficiencyfluctuates between those of the pure fluids and the exergy efficiency of mixtures isless than those of either pure components making up the mixtures. The evaporatorirreversible loss is less than those of either pure components, for example, the figureof the loss of Propane and Ethane is4.02kW and4.22kW, respectively, but when theymix with each other, the figure decreases significantly, fluctuating between3.67kWand3.88kW.According to the law of the critical temperature and pure working fluid, the groupcontribution method is used to replace the origin pure working fluid and its cycle efficiency is re-calculated. And the relationship between the evaporator irrreversibleloss and the critical pressure of the mixtures is analyzed. Results show that the CH,CH2, CH3are replaced with CF, CF2, CF3, and FCOCH3, CH3NH2, CH3NHF,CH2FNHF, CFHCF3are obtained. The new fluids with lower critical temperature alsohave higher cycle efficiency. The critical pressure and the evaporator irreversible lossvary with the change of the mass fraction of the components in the opposite. Theevaporator irreversible loss decreases monotonically in the monotonically increasingrange of the critical pressure.