Three-Dimensional Numeric Analysis Of Airflow Field In Diesel Engine

The quality of airflow field in cylinder of diesel engine will effect to the combustion process and further to dynamical performance,fuel economy and emission performance.Therefor,diesel engine researchers pay special attention to the research all the time.Because there is multidimensional,multicomponent,complex and transient process in airflow inside the cylinder of diesel engine,it is difficult to monitor overall airflow condition in cylinder.With the improvement of computer power and development of computational fluid dynamics,many scholars devote to researching fluid flow and heat transfer in diesel with the method of CFD.In this paper,a 280mm diameter cylinder model of a locomotive diesel engine was set up.Based on this model,temperature field,velocity field and pressure field in the cylinder was simulated by numerical methods under different parameter.The simulation was based on continuity equation, momentum equation and energy equations in fluid dynamics;k-εtwo-equation turbulence model was used to simulate turbulence flow in cylinder.Finite volume method was used to discretize the computed area;Upwind differencing scheme was used in the numerical computation,and SIMPLE algorithm was adopted to couple the velocity and pressure in flow field.Because intake and exhaust valves as well as piston are in a state of movement when diesel engine was working, moving mesh conservation equations was used in the simulation.To analysis air flow in cylinder in detail;the simulation was done in different strokes of the diesel engine.Besides that,the distribution of gas speed,temperature and pressure in cylinder were simulated with different running speed,different valve timing and different modular construction of MPC system.The calculation results shows:the intake swirl is formed from the outside to the inside,small to big,while the big swirl is eccentricity;the exhaust swirl is formed from the flow whirl which generated by valve resistance,and the maximum velocity of the flow focus away from the vent;the speed of the diesel engine has great influence on the flows characteristics in-cylinder.The average temperature,average pressure and turbulent kinetic energy at high engine running speed are higher than that at low engine running speed,and there are many differences in changing trend.The simulation result also shows that at different running speed the diesel engine should be used different gas exchange timing,and the best valve timing could be found in the numerical analysis method.The contraction ratioφand included angleθof structure parameter about MPC have great influence on IC-Engine performance.The contraction ratio is in the direct ratio to the kinetic energy efficiency;and the flow loss inverses proportion to included angleθ.There is minimum flow loss whenθis equal to 45°.The backflow in upper main pipe and secondary flow along circle are the main factor of energy loss in MPC,while the latter has greater effect.The flow of brance pipe has sustained influence on lower main pipe.