A Study Of Gap Flow In Micro Internal Combustion Swing Engine And Design Of Swing Arm

With the development of portable electronic devices, individual soldier combat systems and miniature unmanned aerial vehicle systems, miniaturization of the equipment is mainly controlled by the development of the power supply unit. Because of the advantages in energy density, power density and configuration, Micro Internal Combustion Swing Engine (MICSE) has become one of the greatest potential power supply unit for micro systems now. However, the leakage between swing arm and cylinder has a strong impact on engine efficiency, which restricts the improvement of the engine operation performance. On the issue of leakage in MICSE, macroscopic method was adopted to estimate leakage rate at present. However, this method introduces large error because micro-effects has appeared in practical engine. Therefore a more accurate kinetic method called Discrete Velocity Direction (DVD) model was adopted in this paper to simulate the gas flow in the gap in MICSE accurately, beyond that a reasonable gap size and sealing structure was designed to reduce gas leakage in the engine. This paper mainly contains the following aspects.DVD model was adopted to verify the model precision in Couette flow and Poiseuille flow between plates, the results were compared with that calculated from Linearized Boltzmann Equations (LBE) and Navier-Stokes Equations. The calculation results show that, from slip-flow regime to transition regime, velocity distribution, flow rate and shear force calculated by DVD model agree well with that by LBE method. In terms of computational accuracy especially in prediction of flow rate, DVD model is more accurate in the designed gap size, so more reliable data can be supplied to the engine operation.DVD model was adopted to simulate the gap flow between swing arm and cylinder. By controlling gap size and swing speed of the swing arm, velocity distribution and flow rate under different Knudsen number and wall velocity have been received. Through analyzing the results, a conclusion of the main way to control clearance leakage and velocity slip in the boundary under different scale can be reached. Gas composition and corresponding temperature in the cylinder under different operation condition were obtained by numerical modeling of the combustion process. According to the gap size in various conditions, Knudsen number can be determined, which can provide theoretical foundation and reference to reducing leakage in the gap.In order to reduce clearance leakage and improve system efficiency, this paper optimizing the structure of the swing arm in consideration of convenient machining. Several sealing grooves were machined in the swing arm, gas leakage was reduced as a result of pressure drop at the outlet through throttling process in the space between two adjacent grooves and eddy-dissipation process in the groove. By simulation of gas flow in the sealing structure, the influences of operation condition and dimension parameters of sealing structure on sealing effect can be obtained. The results show that, if dimension parameters of the sealing structure were fixed, the sealing effect is better in expansion process than compression process because of the difference in pressure ratio between these two processes; if the pressure ratio was fixed, the sealing effect enhances with sealing groove number, whereas groove depth, length and space between adjacent grooves have optimum design value, which was calculated under certain pressure ratio and gap...