| About one third of the total energy from fuel combustion in the vehicle engine is still wasted as exhaust gas,which not only aggravates the environmental problem,but causes the waste of fossil energy.Organic Rankine Cycle(ORC)technology can convert the exhaust heat energy from engines into mechanical energy or electrical power efficiently to improving the efficiency of engines,thus alleviating environmental pollution and energy shortages.The engine system with an ORC system has been a complex energy system whose subsystem is coupled and interacts with each other compared with the original engine.Compared to the simulation of the engine and the ORC system separately,modeling of the engine-ORC combined system(combined system)can simulate the operating state of the combined system and each component more accurately.Therefore,in order to explore the actual operating state of the engine and the ORC system under actual operating conditions,the engine-ORC combined system under variable working conditions is studied in this paper.Firstly,based on GT-Suite software,the integrated simulation model of the engine-ORC combined system is established,and the sensitivity analysis of the key operating parameters of the combined system is conducted.The synergistic changes between various parameters are investigated for the various engine conditions.The research shows that the injection timing has the highest main effect value for the net power output of the combined system,followed by the exhaust timing,and finally the expander speed and the pump speed.The latter two main effect values are equivalent,and when the four parameters cooperate,the net power output of the combined system increases first and then decreases.Therefore,there are optimal parameter ranges that maximize the net power output of the combined system under various operating conditions.It is necessary to conduct global optimization on the combined system for variaous operating conditions.To realize the cooperative work between the engine and the ORC system in the combined system,this paper builds a GT-Suite/Simulink co-simulation model.The parameters of the engine(exhaust timing,injection timing)and the operating parameters of ORC system(expander speed,pump speed)are selected as decision variables.Particle swarm optimization(PSO)is used to optimize the combined system globally.The net power output under full load condition and the fuel economy under partial load condition are improved.The optimization results showed that the net power output and BSFC of the combined system are improved under full load condition.The net power output can be increased by 3.24% and BSFC can be reduced by 3.13%.Under the partial load condition of the engine,the fuel economy of the combined system is improved,and the BSFC can be reduced by 5.71%.To obtain the energy saving potential of the ORC system under the driving condition of the vehicle,a dynamic model of the vehicle with the ORC waste heat recovery system is built in this paper to analyze the dynamic coupling effect between the ORC and the engine and the energy output characteristics of the ORC under different driving conditions.The analysis found that the average energy recovery efficiency of EUDC condition is 2.43%,and the instantaneous maximum is 11.98%,while the average energy recovery efficiency of UDDS condition is 1.66%,and the instantaneous maximum is 2.91%.The performance of energy recovery of the vehicle system with the ORC in the suburban working condition is better.In the more complicated urban road conditions,the performance of energy recovery is not significant,and fluctuates greatly.Therefore,using the ORC for energy recovery is more suitable for suburban and highway conditions. |
