Utilization Of Diesel Exhaust Waste Heat Based On Organic Rankine Cycle System

Internal combustion engine is an important power component of oil consumption,and more than 50% of fuel energy is lost through engine cooling and exhaust heat.Exhaust heat accounts for a large proportion of high grade,effective use of this part of the energy can effectively improve the efficiency of internal combustion engine,reduce the emission of pollutants.Organic Rankine Cycle is widely regarded as an effective technology for recovering exhaust heat due to its advantages of simple structure,low maintenance cost and high reliability.In this paper,the performance of pure working fluid and mixed working fluid exhaust waste heat ORC system was studied from the aspects of thermodynamic simulation of ORC system and steady-state performance test of ORC system by combining theory with experiment.The experimental datas of diesel engine exhaust temperature,flow rate and ratio of exhaust components were taken as heat source input parameters,through modeling and analysis of key components of ORC system,the MATLAB software was used to program each component of the system,and 8 pure working fluids were selected to evaluate the system performance of each working medium with different performance evaluation indexes.It was found that under the condition of safe and stable operation of the system,the higher the critical temperature of the working fluid,the better the comprehensive performance of the ORC system.The non-combustible working fluids with better comprehensive performance and a certain difference in boiling point were selected to form four binary working fluids: R1233zd(E)/R1234ze(E),R1233zd(E)/R227 ea,R245fa/R1234ze(E),R245fa/R227 ea.The temperature slippages of the mixed working fluids with four different mass ratios were analyzed,and the working fluids with the maximum slippage mass ratio were selected to analyze the performance of the exhaust ORC system.The results show that the mixed working fluid with higher unit heat absorption was more beneficial to recovery of middle and high temperature waste heat.Using the existing ORC system test-bed in the laboratory,experiments were carried out with R245 fa,R227ea and R245fa/R227 ea with different concentration ratios as working fluids,and the influences of key parameters such as evaporation temperature,heat source temperature and working fluid flow rates on each evaluation index of the system were analyzed.Experiments show that when the working fluid flow was constant,the heat source temperature should not be too high,but in order to ensure that the system can have a larger stability range and a higher work capacity under a certain heat source temperature,the heat source temperature of pure working fluid should be near the critical temperature of working fluid,and the heat source temperature of mixed working fluid system should be slightly higher than the critical temperature.The evaporation temperature was the key parameter of the system for any mixed working fluid and pure working fluid.When the heat source temperature was constant,the increase of working fluid flow makes the optimal evaporation temperature shift to the low temperature zone When the mass ratio of R227 ea in the mixed working fluid was 0.5 and the heat source temperature was 130℃,the flow rate of working fluid was from 350L/h to 550L/h,and the optimal evaporation temperature decreased from 100℃ to 70℃.In order to achieve better comprehensive performance of the system,the evaporation temperature can be appropriately reduced at a higher working fluid flow rate.When the heat source temperature and the working fluid flow rate were constant,the evaporation bubble point and condensation bubble point were selected as the evaporation temperature and condensation temperature base point respectively.Without considering the influence caused by condensation temperature deviation,the performance parameters of different mixed working fluids were better than pure working fluid R227 ea,but worse than pure working fluid R245 fa.In addition,under the condition of controllable condensation conditions,the ORC system with lower condensation temperature had better thermal performance and economy.