Simulation And Optimization Of Opposed Piston Two-stroke Engine Ventilation System For UAV

The Opposed Piston 2 Stroke(OP2S)internal combustion engine is a piston type internal combustion engine.Due to its special opposed piston structure,the engine structure is smaller,the self-balancing is better,the operation is more stable,the noise is lower,and the utility model is more suitable for UAV.The ventilation process of the OP2 S internal combustion engine is an important factor affecting the efficiency and emissions of the internal combustion engine.Based on the existing OP2 S internal combustion engine structure and the original experimental data,the GT-POWER is used to establish the corresponding simulation model of the whole machine performance.The key parameters of the internal combustion engine are modified to be applied to the drone.The influence of the inlet and outlet width coefficients and the intake pressure on the ventilation process and the performance of the internal combustion engine is analyzed.The results show that when the crankcase pressure ratio is 1.6,and the inlet and exhaust width coefficients are all 0.7,high ventilation efficiency can be obtained at different altitudes,and the higher the gas-to-gas ratio and the good capture rate,the overall ventilation process is optimal,and the simulation results will provide a boundary for the AVL-FIRE 3D simulation.At the same time,the paper proposes a full hexahedral mesh model based on AVL-FIRE.In order to ensure the accuracy of the simulation results,the grid spatial density and time step are analyzed and optimized,and the simulation results of the final model are compared with GT-POWER machine performance simulation for comparison and mutual verification.In order to further study the ventilation process of the OP2 S internal combustion engine,a plurality of sets of intake ports of different inclination angles are provided.Then,based on CFD simulation,the velocity field distribution,mass fraction of O2 and CO2,and the change of turbulent kinetic energy in the cylinder during different airing dip angles are analyzed.The results show that the intake inclination angle will affect the velocity field,the mass distribution of O2 and CO2,and the turbulent kinetic energy of the airflow during the ventilation process.The inclination of the intake air has two obvious effects on the ventilation process.One is to reduce the area of the dead zone of ventilation,the second is to extend the ventilation process;too large intake inclination angle will lead to poor ventilation in the area near the cylinder axis.The best comprehensive ventilation effect is obtained when the intake inclination angle is 20°,the highest burst pressure is increased by 6.6% and the cumulative heat release is increased by 7.6% compared to no intake inclination angle.