Design And Simulation Study On Combined Harvester Diesel Engine Waste Heat Recovery System

With the continuous improvement of agricultural mechanization and mechanical harvesting rate,the rate of grain harvesting is getting faster and faster.Since about 20% of the grain harvested is high water-bearing grain,a large amount of grain in China is sprouted and mildewy every year because it is not dry enough.On the other hand,the energy converted into mechanical energy in the diesel engine of combine harvester only accounts for about one third of the total energy,and the thermal energy of coolant and exhaust accounts for about 60% of the total energy,so there is a large amount of energy waste.In view of the above two problems,this paper designs a waste heat recovery system to recover the heat energy from diesel engine coolant and exhaust.The recovered heat energy is used to dry the crops after threshing on the combine harvester,so as to solve the problem of grain mildew and energy waste of diesel engine.Firstly,the energy and structure characteristics of DongFeng 2000 combine harvester are analyzed and the waste heat recovery system of diesel engine is designed according to the characteristics of energy and structure.CATIA is used to establish a three-dimensional solid model of waste heat recovery system,and the installation location and connection relationship of equipment in the system are determined.Secondly,according to the initial data to complete the heat exchanger,three-way valve,fan,fluid pipeline and other waste heat recovery equipment parameters calculation and type selection design.Then,the mathematical models of heat exchanger?,heat exchanger?,three-way valve and controller are established.Simulation model is established based on the mathematical model,and the heat exchanger simulation model is verified and the temperature change characteristic is simulated.Thirdly,the method combining model simulation and Z-N engineering setting is used to preliminarily determine the control parameters of PID controller,and the simulation model of waste heat recovery system is established.According to the simulation model,the simulation comparison shows that the PI controller has the best control effect and the Check Step Response Characteristics optimization module is used to optimize the parameters of the controller.After the optimization,the overshoot of the air outlet temperature for heat exchange is almost zero,and the time of temperature stabilization to the set value is shortened by about 60%.Finally,the simulation model is used to analyze the heat transfer performance and control performance of the waste heat recovery system.When the temperature of coolant changes dynamically,the controller can quickly adjust the valve opening to keep the temperature of air stable,and the system has strong control performance and stability,which verifies the feasibility of waste heat recovery system.