Thermal Cycle Optimization And Operation Control Of Engine Waste Heat Recovery System

China has a large consumer of fossil energy,The car ownership has increased significantly,resulting in a sharp increase in energy consumption.This trend is still growing.The energy taken from the exhaust of automobile engines accounts for about 40% of the heat released by fuel combustion.Therefore,the recovery of waste heat from automobile engines is an important way to improve engine efficiency.In recent years,various thermal cycles have been used to recover engine waste heat to obtain benefits,which can further improve the efficiency of power systems by about 10%-15% and reduce energy consumption.Among these waste heat recovery to improve engine efficiency,Rankine cycle is one of the most widely used methods of waste heat recovery.According to the characteristics of automobile engine waste heat,this paper selects water as the working medium,and conducts research on how to avoid the phenomenon that the wet fluid will cause liquid collision to the expander and realize the control of the waste heat recovery system.According to the needs of engine waste heat recovery system,this paper designs a data collection and control system.The data acquisition system includes temperature,pressure,liquid level and other parameter measurements.With STM32F103 series MCU as the main control chip,AD7793 is used to collect the analog signal of the sensor.Using ADR43 X series chips to provide a reliable voltage reference for the AD conversion chip,the system can measure multiple analog signals.Through the collected analog signals,ULN2003 is used to control the operating state of the multi-way solenoid valve,and the DA conversion chip TLC5615 is used to control the pump speed of the MCU and the needs of the automotive waste heat recovery system.How to realize the operation control of the waste heat recovery system,analyze the working principle of Rankine cycle,determine the control object,realize the evaporator pressure control by controlling the speed of the working fluid pump,cooperate with Rankine cycle structure to achieve superheat stability control and improve the efficiency of the circulation system.Due to the time-varying,non-linear,and large lag characteristics of the evaporator-working fluid pump system,as well as many interference factors in the external environment.the integrator has hysteresis.Excessive integration will cause system oscillation.To solve this situation,use Integral separation PID control algorithm with dead zone realizes system stability control.Finally,the experimental data analysis of the system.First,test and adjust the hardware circuit.After completing the data collection and analysis,it is found that the exhaust temperature of the car engine is 400-800 ?,and the waste heat recovery system using water as the working medium can achieve better superheat control,indicating that this system Reliable performance,able to complete the operation of waste heat recovery system.Under this experimental condition,it was found that the output power and cycle efficiency of thesystem showed a trend of increasing first and then decreasing as the speed increased,and there was a maximum output power and cycle efficiency.