Research On Characteristics Of Piston Expander Based On Double Crank Mechanism

Among many energy storage technologies,compressed air energy storage technology is considered have great potential.The expander uses compressed air as the working medium to output mechanical work,which has an important influence on the performance of compressed air energy storage system.Compared with screw type,scroll type,free piston type,rolling piston type and other structural forms,reciprocating piston type expander has the advantages of mature technology,simple sealing,variety of working medium and low cost and is widely used.However,the working conditions of the expander,such as load and intake pressure,are uncertain and unstable,which affect the output characteristics of the expander.At the same time,the reciprocating piston expander has low efficiency and insufficient output power,which become the bottleneck problem restricting its development.According to this problem,this article is based on the basis of the research on the reciprocating piston expander,a multi-link variable piston expander expansion ratio,expansion machine was optimized by changing the way expansion ratio of the output characteristic,under different conditions can realize the maximum utilization of expander output mechanical work,this paper studies the main contents include:(1)Firstly,based on the work principle of reciprocating piston expander,the energy conversion process of reciprocating piston expander was studied,including thermodynamic exergy of compressed gas,ideal work output of expander,energy conversion rate,and calculation formula of geometric expansion ratio of reciprocating piston expander.On this basis,a method to change the expansion ratio of reciprocating piston expander by changing the clearance volume of cylinder is proposed.(2)Secondly,according to the energy equation,mass flow equation,state equation and motion equation to establish mathematical model,using MATLAB/Simulink to build simulation model.The experimental platform of reciprocating piston expander was built to verify the accuracy of the simulation model.The error range between the experimental data and the simulation data was controlled within ±5%,indicating the reliability of the simulation model,and the reasons for the error were analyzed.(3)Then,the MATLAB/Simulink model is used for simulation research.The variation law of gas pressure in cylinder and instantaneous torque of crankshaft in reciprocating piston expander was studied.The effects of inlet pressure and cylinder clearance volume on the performance of reciprocating piston expander are studied.The results show that the output power of the reciprocating piston expander increases with the increase of the intake pressure,and the efficiency decreases with the increase of the intake pressure.Reducing the clearance volume can increase the output power of reciprocating piston expander,and the efficiency of reciprocating piston expander should have different optimal clearance volume under certain intake pressure.(4)Finally,the piston expander with variable expansion ratio based on multi-link mechanism is proposed,its working principle is studied and its motion is analyzed,and the output characteristics of the piston expander with different clearance are obtained by using Solid Works and MATLAB co-simulation.The results show that the optimum clearance volume corresponds to the maximum efficiency under different intake pressures.When the intake pressure is fixed,the speed range corresponding to the maximum output power of the expander is different under different clearance volumes.It provides the basis for selecting the optimum expansion ratio of expander under different working conditions and provides reference for the design of new expander.