Numerical Simulation Study Of The Dual-opposed Diesel Engine’s Gas Exchange Process

The dual-opposed two-stroke diesel engine with simple configuration has acharacteristic of higher power density, its unique uniflow scavenging structure cansignificantly improve the scavenging efficiency, which can lead to better engine performance.This paper, based on the flow characteristics of the Dual-opposed Two-stroke Diesel Engine’sbreathing process, creates a three-dimensional transient flow simulation model. AVL-FIREsoftware was used to conduct the numerical simulation calculation, and then discussed theventilation process affecting factors with three different engine speeds of3600rpm(ratedspeed),2500rpm (maximum torque speed) and1600rpm(lower speed).Firstly, build the three-dimensional solid model of the intake and exhaust ports as wellas the cylinder and combustion chamber in Pro/e software, save this model as a*stl formatsurface file. Secondly, import the*stl file into FIRE’s pre-processor to create volumemesh.Two top surfaces of the intake and exhaust piston and the cylinder line consist of the gasvolume, namely computational domain. As the computational domain changing with thevarying crank angle during gas exchange process, a moving mesh is needed to perform theinstantaneous calculation. The moving mesh is generated based upon the previous step createdvolume mesh by use of FIRE’s move mesh generation tool FAME Engine. Finally, in theSolver Steering File (SSF), setup the boundary conditions, initial conditions, governingequations and other parameters such as the convergence criteria, etc. Among them, the intakeand exhaust piston top surface is set to movement border. The air inlet is set to total pressureboundary, and exhaust outlet to static pressure boundary. After all of the solution parametersis completed, use FIRE v2008to start the calculation.Data processing and analysis of the calculation result have been done in the IMPRESS post-processing program. Analyzing of the air inflow, residual gas in cylinder, pressure andturbulence field of the flow in the ventilation system at173degCA with the exhaust port fullyopened,253degCA with the exhaust port closed and268degCA with the intake port fullyclosed shows that the designed intake and exhaust ports with specified constructure argumentin the engine has a better breathing performance at lower engine speed. A uniflow scavengingway can help to avoid getting the fresh charge and exhaust gas mixed with each other, whicheffectively improves the breathing quality of the dual-opposed two-stroke engine. Thethree-dimensional numerical simulation method in this paper, provides guidence forimproving ventilation quality of the double-opposed two-stroke engine.