Experimental Study On Compressed Air Braking Cycle Under Variable Inlet Pressure

Energy consumption and environmental pollution of traditional energy sources,such as fossil fuels,are the most concerned social problems in the world.On the automotive industry,the development of energy-saving and emission reduction technologies,alternative fuels and new energy power has gradually become the main direction of development.In addition,the frequent braking,starting and stopping of the vehicle in the urban condition,consume a lot of kinetic energy through the irreversible thermal process.In view of the problems above,this paper analyzes the energy recovery performance of the energy recovery system based on compressed air and supposed a technical scheme of double-stage energy storage.And then studied the braking process based on compressed air under variable inlet pressure of double stage energy storage system through experiment.The main work and conclusions are as follows:1.Thermodynamic study of compression braking cycle.Compression braking cycle mathematical model is established based on thermodynamic theory of variable quality,and select the IMEP(Indicated Mean Effective Pressure),recycled air mass per revolution,COP(Coefficient of Performance)and exergy conversion rate as four indicators to evaluate the braking effect and energy recovery capacity of compression braking cycle.The results show that:for single stage energy storage,the increase of the pressure of the air tank will greatly reduce the energy recovery efficiency of the compression cycle.Double stage energy storage compression braking cycle can enhance the performance of braking and energy recovery by providing variable-pressure inlet;2.The compressed air braking test bed with variable inlet pressure was built.Test bed can simulate the compression braking cycle with variable inlet pressure.During the test,optimization of charge valve opening timing is done firstly with the primary optimization goal to maximize the COP.The optimization results show that the optimal valve opening time is advanced with the increase of engine speed,the increase of inlet pressure and the decrease of gas tank pressure.3.The effects of intake pressure,air tank pressure and engine speed on the performance of compression braking cycle are studied through experiment.The analysis of the test data shows that recycled mass per revolution increased with the increase of engine speed;when the engine runs at a fixed speed,recycled mass per revolution is influenced by the inlet pressure and the gas tank pressure linearly;the ratio of air tank pressure and inlet pressure is an important factor influencing COP,and COP increased with the ratio decreases;based on the conclusion that COP varies with ratio of air tank pressure and inlet pressure,conclusion is as follow after mathematical deduction:when the air tank pressure is higher than 15bar,inlet pressure is higher than 7bar,ratio of gas tank pressure and the intake pressure is seen as an important factor affecting the exergy conversion rate.