Study On Scavenging And Starting Process Of Micro Free-piston Power Device

In recent years,micro-power devices have the advantages of small size and high output energy density,and their use of hydrocarbon fuel combustion to do work has attracted the attention of many scholars.In the early stage of this research group,the problems of flame quenching,HCCI ignition control and how to achieve low-temperature combustion were discussed.Based on this,corresponding numerical simulation and experimental research have been carried out,such as fuel mixing H₂/CO₂ to reduce the temperature in the device.Catalytic compression ignition method is used to analyze the uncatalyzed and catalyzed combustion characteristics and a visual test bench was built to carry out intake preheating and catalytic combustion tests.However,due to inadequate scavenging,problems such as low fuel utilization and unstable operating conditions can easily occur during the operation of the device.In response to these challenges,this thesis mainly studies the scavenging process and starting process of the micro free-piston power device.Two new device structures are designed to improve the scavenging efficiency and starting performance of the micro power device.On the basis of GAMBIT software,a grid model of single-cylinder compression ignition scavenging process was established and FLUENT was used to carry out numerical simulation research.The scavenging factors of the single-cylinder research mainly include the distance L between the intake and exhaust ports,the inclination angleα,the angleβ,and the diameter D_in,D_out.The calculation results show that when the distance between the intake and exhaust ducts increases,the scavenging efficiency first increases and then decreases.When L is 2 mm,the minimum scavenging ratio is 58.47%,and the scavenging quality in the cylinder is the best.When the intake port forms a certain angle with the axis,a vortex is generated in the micro-combustion chamber,and the combustion reaction is more complete.Whenαis 30°,the scavenging effect is the best.Whenβis 60°,the scavenging ratio is 36.98%,which is about 50%higher than the scavenging efficiency when the inclination angle of the intake and exhaust ducts is 90°.When the relative diameters of the intake and the exhaust port decreases,it is also beneficial to improve the scavenging efficiency of the power device.In the micro-combustion chamber with a diameter of 3mm,a stroke of 20 mm,an initial intake pressure of 0.1 MPa,an initial temperature of 300K,a piston speed of 22.8 m/s,and an effective compression distance of 10 mm,the distance L is 2 mm,the angleαis 30°,and the angleβis 60°,the diameter D_in is 0.5 mm,and the diameter D_out is 0.6 mm,the scavenging effect is the best.After that,a physical model of the starting process of the dual-cylinder micro free-piston power device was established,and the influence of constant force on the starting performance of the micro power device was analyzed through numerical calculation.The results show that when F is less than 0.03N,too small mixture pressure and inertial force make the piston unable to continue to reciprocate.When F is0.03N,the starting process of the miniature free piston power device is more stable,and the constant force is the critical force.A numerical simulation study was carried out for the double-cylinder starting and scavenging process.The results show that when the distance L is 2 mm,the angleαis 30°,the angleβis60°,the diameter D_in is 0.5 mm,and the diameter D_out is 0.6 mm,and the constant force is greater than0.12N,the micro power device can realize multiple cycles of operation.Compared with the dual-cylinder pure compression starting condition,the starting of the intake and exhaust device requires greater constant force.A large number of numerical simulation calculations in this thesis have enriched the research theory of the scavenging and starting process of the micro free piston power device.It has a certain reference value for the research of other types of micro power system reciprocating motion.It provides a rich theoretical basis for the prototype design of the micro-power device.