Numerical Simulation And Optimization Of In-cylinder Combustion Of Opposed Piston Two Stroke Engine

The piston engine is small in size,high in power density,and simple in structure,making it ideal for small and medium-sized unmanned aerial vehicl.The opposed piston two stroke engine is a type of piston engine.Compared with the four-stroke engine,this kind of engines' power density is higher.And due to the configuration of the opposed piston,there is no cylinder head structure.The structure of the engine is further simplified and reduced,which is very suitable for application on the UAV.In this paper,the combustion process of opposed piston two-stroke engine is studied and optimized.Based on the prototype test data provided by Beijing Institute of Technology,this paper uses GT-POWER and AVL-FIRE to build the corresponding one-dimensional simulation model and three-dimensional computational fluid dynamics model.The boundary conditions of the three-dimensional simulation model are obtained by using the one-dimensional simulation model,and the simulation results and experimental data are fitted.According to the performance requirements of the unmanned aerial vehicle engine,some parameters of the prototype are optimized and adjusted,so that the adjusted engine parameters are more suitable for the UAV,and several parameters,such as injection hole parameters,injection cone angle,injection timing,are simulated and optimized.The changes of the nozzle parameters,the injection cone angle,the injection timing and the injection pressure of the opposed piston two-stroke engine are studied in this paper.When the number of injection holes is 4,the injection cone angle is 50°,the injection timing is 30° BTDC,and the injection pressure is 140 MPa,the combustion process of the engine is better,the average pressure in the cylinder and the early heat release rate are higher.Considering that the working process of the engine is affected by many kinds of parameters,a 7-factor 3-level orthogonal test table is established in this paper.By the method of orthogonal test design,the influence of 7 factors on the performance of the engine,i.e.the injection pressure,the injection temperature,the injection timing,the inlet pressure,the inlet temperature,the diameter of the injection hole and the number of the injection holes on each injection nozzle,is explored.The performance and emission of the engine are optimized by the method of the range and variance of the results.The pressure curve,the heat release rate curve and the distribution of NO and soot are analyzed.