Study On Performance Simulation And Cooperative Control Of Vehicle Engine-Organic Rankine Cycle System

At present,oil-fueled vehicle still occupies the main body,and its thermal efficiency is low,the energy loss through exhaust accounts for a large fraction of the total of fuel combustion.As a means of recovering the engine exhaust waste heat energy,organic Rankine cycle(O RC)technology can effectively improve the utilization ratio of energy and achieve energy-saving and emission reduction.But how to realize the coordinated work of the engine-ORC system and maximize the energy-saving potential of under road transient condition is a hot topic in this field.In this paper,a simulation model of the diesel engine-ORC system in the driving cycle is established by combining theoretical analysis,experimental research and simulation,and in order to optimize the energy-saving in the driving cycle,the research on the cooperative control strategy and its control is carried out,which provides a reference for the engineering application of ORC system for the engine exhaust waste heat recovery.Based on the engine test,the exhaust characteristics of the diesel engine in all operating conditions are studied,and the simulation model of the more realistic diesel engine is established.The results show that the exhaust waste heat energy is considerable,especially in the high rotation speed region where it is greater than the diesel engine output and its recovery potential is great,the proportion of the exhaust temperature reaching middle-high temperature is over 90 %,the energy quality is high,the large range of variation of the exhaust temperature,exhaust mass flow rate,exhaust waste heat energy and maximum available exhaust waste heat energy of the diesel engine,showing remarkable cascade characteristics,which determines that the exhaust waste heat energy has dynamic characteristics under road conditions.The simulation model of the diesel engine based on GT-POWER is closer to reality and its precision is higher.With the optimization objective of recovering the exhaust waste heat energy safely,stably,efficiently and economically,the structure,component type,working fluids and parameter matching of ORC system are determined.The results show that the simple ORC system is superior to ORC system with IHE in terms of thermodynamic and economic performance.According to the exhaust characteristics andconsidering the compact structure,the system components suc h as multistage centrifugal pump,the finned tube evaporator,single screw expander and plate heat condenser are selected.By studying the thermodynamic performance of 11 working fluids,the results show that the net power output,mass flow rate and exergy destruction rate of R420 a are better than that of other working fluids.According to the working characteristics of the components,the simplification of the structure and the optimization of the thermodynamic performance,the parameters matching range is determined.Based on the component structure and test data of O RC system,the simulation model of ORC system is established,and then the diesel engine-ORC system is established.Based on the test and simulation,the control para meters and their range are determined to reduce BSFC effectively.The multi-ways calibration analysis shows that the simulation models of ORC system and the diesel engine-ORC system can meet the requirements.The test and simulation analysis of four parameters of the diesel engine show that the common rail pressure can be used as a control parameter,and there is an optimal value in the whole operating range,so that the diesel engine output,torque and BSFC remain basically unchanged,and to maximize the e xhaust temperature.DOE analysis on the rotation speed of pump and expander shows that the net power output and parameters matching established requirements of the diesel engine-ORC system can be met at the maximum limit when the pump rotation speed changes within the allowable range and the expander rotation speed is fixed at 900 r /min.According to the technical parameters,the simulation model of the diesel vehicle including the diesel engine-ORC system in NEDC driving cycle is built.Based on the simulation analysis,the working mode of ORC system is divided,and a cooperative control strategy is proposed.The simulation analysis shows that the parameters change periodically during EC E driving cycle,and when the vehicle reaches the maximum speed or near the maximum,the parameters reach the maximum value during UDC driving cycle.During ECE driving cycle,the exhaust temperature of the evaporator outlet does not reach the safe temperature of the exhaust acid dew point,and the net power output of the ORC system is greater than zero only in about 40% of the time.Based on the dynamic characteristics and stable operating conditions the diesel engine-ORC system,the working mode of O RC system is divided into four kinds: stop,start,idle and work to ensure the stable operation,then the coordinated control strategy is proposed.A collaborative control model of the diesel engine-ORC system is developed based on the design of GT-SUITE/SIMULINK co-simulation platform and cooperative control method,the performance of the diesel engine-ORC system under the collaborative control and the original diesel engine in driving cycle is compared and analyzed,and the application conditions of the ORC system in vehicles are proposed.The results show that,in driving cycle,the average net power output of ORC system is 0.135 k W,the maximum net power raising and the average net power raising of the diesel engine-ORC system are 0.552 k W and 0.133 k W,respectively,and the average improvement extent of BSFC is 9.01%.