The Design Of A Reverse-Loop Scavenging Free Piston Engine And Simulation Of The Gas Exchange Process

2-stroke free piston engine can be divided into single free piston engine,double free piston engine and opposed free piston engine, this dissertation main focus on the 2-storke single free piston one. The engine both has the simple structure and light weight of 2-stroke engine, and has VCR (variable compression ratio) of the free piston engine. The diesel engine's maximum power is decided by the fresh air amount that enters and stays in the cylinder, so as the most important part of a 2-stroke engine, gas exchange process direct influence the engine performance. At present, the experts have done much research on the free piston engine, and already designed out multiple generations prototype engines, but there is little research on simulating and improving the scavenging process of the 2-stroke single free piston engine,and that is the reason why this thesis make a study on it. The main content of this thesis is as follow.(1). Through collecting data of the free piston engine and combining the IC engine design principal theory, this thesis improves the existing E150 diesel engine,especial to the exhaust part.(2). Using 3D software of CATIA, this thesis simply model the improved engine, and then design some kind of scavenging ducts whose geometrical factors would influence the exhaust process.(3). By using CFDesign fluid simulation software, this thesis conducts a simulation analysis of the engine model which has been built. First it needs to load the 3D model into the simulation software and meshing it. According to finite volume method, some structures that need to be discredited would be meshing into tiny enough tetrahedral element to correspond with initial model. The parameters of the piston motion law are stetted depending on the fluid dynamics and the work principle of 2-stroke engine. As the scavenging process, it is set to the whole process start from the scavenging port is beginning to open until it totally closed again. And then this thesis does a research on the scavenging efficiency,kinetic energy at the state of agitation and the cylinder pressure when the piston at TDC of the 2-stroke single free piston engine through data and pictures, reaches some reasonable conclusions about the design, furthermore concludes the flow field design method, which could provide theoretical support for the practical design of single-cylinder engine and the analysis on its flow field.