Study On Space Regeneration Characteristics Of Organic Rankine Cycle

The utilization of fuel in automotive internal combustion engines is low.A large amount of heat energy dissipates to the atmosphere through exhaust gas.Recovery of waste heat of exhaust gas has the potential to improve vehicle thermal efficiency,and organic rankine cycle(ORC)system is considered to be one of the most advantageous technologies for automobile exhaust heat recovery.In order to improve the performance of ORC system,a new space regenerative ORC(NRORC)system is proposed in this paper.The system has the advantages of complete work and simple structure.This paper puts forward a technical route with space regeneration as the core,aiming at recovering the sensible and latent heat of low-pressure superheated working fluid,and defines a scheme for recovering the waste heat of diesel engine exhaust gas with NRORC system as the research focus.In this paper,the structure and operation principle of ORC system,preheated organic rankine cycle(PORC)system and NRORC system are introduced in detail,and the thermodynamic analysis of the main thermodynamic processes of the above three systems is carried out.The theoretical feasibility of using preheating and space regeneration to improve the performance of ORC system is verified.The effects of evaporation pressure and evaporation temperature on the performance of ORC system and its components are investigated.The effects of operating conditions of 6DL diesel engine on the performance of ORC system are also studied.The results show that increasing evaporation pressure can obviously improve the performance of ORC system and its components.Evaporation temperature has little effect on the performance of ORC system and its components.However,when the heat transfer rate is constant,the mass flow of working fluid required by ORC system can be reduced by increasing evaporation temperature.The performance of ORC system is better under medium and large load conditions,but worse under low load conditions.Under the conditions of A25 and C100,the engine power recovery rate of ORC system is the worst and the best,which are 6.67% and 14.78% respectively.Based on the school-enterprise cooperation project,the ORC prototype system is built,which consists of combustion system,heat exchange system,working fluid loop system,cooling system,load system,data acquisition and display system.The operation principle of ORC prototype system and the selection and parameters of its components are introduced.The effects of evaporation pressure,mass flow rate of working fluid,types of working fluid and operating conditions of diesel engine on the performance of NRORC system are studied by simulation.The results show that the performance of NRORC system can be improved by increasing the evaporation pressure.When the evaporation pressure is increased from 20 bar to 36 bar,the net output power,thermal efficiency,exergy efficiency and engine power recovery efficiency of NRORC system are increased by 2.6kW,2.39%,5.48% and 1.44% respectively.The net output power and thermal efficiency of the NRORC system are 18.58 kW and 17.04% when the mass flow rate of working fluid is 1740 kg/h,which are 0.053 kW and 0.05% less than the maximum net output power and thermal efficiency,but the mass flow rate of working fluid is reduced by 140 kg/h at the maximum value.Compared with R245 ca,R134a and R152 a as working fluids,the NRORC system using R245 fa as working fluids has the best performance.The net output power of NRORC system is positively correlated with the temperature and mass flow rate of diesel exhaust.The thermal efficiency of NRORC system is not affected significantly by the operating conditions,the exergy efficiency decreases with the increase of the temperature difference between the inlet and outlet of the evaporator,and the engine power recovery efficiency decreases with the increase of the engine thermal efficiency.The performances of ORC,PORC and NRORC systems under different operating conditions are compared and analyzed.The results show that the thermal process of space regeneration can improve the performance of ORC system more effectively than that of preheating,taking B75 as an example,the net output power,thermal efficiency,exergy efficiency and engine power recovery efficiency of PORC system are 7.39%,1.14%,2.6%,0.69% higher than that of ORC system,the net output power,thermal efficiency,exergy efficiency and engine power recovery efficiency of NRORC system are 35.82%,5.18%,11.6%,3.11% higher than that of ORC system.Compared with ORC and PORC systems,NRORC system require the least mass flow of working fluid per unit work output.Under B75 condition,the mechanism of using preheating and space regeneration to improve the performance of ORC system is explored.The results show that during the cooling process,the heat emitted rate by ORC,PORC and NRORC systems is 88.8 kW,82.77 kW and 80.05 kW.PORC system recovers 13.7kW of heat in the preheating process and NRORC system recovers 24.8 kW of heat in the space regeneration process.Thermodynamic process of preheating can only recover the sensible heat of low-pressure superheated working fluid,while the space regeneration can recover the sensible and latent heat of low-pressure superheated working fluid.