Research On Three-dimensional Flow Characteristics On The Port Of An Engine

Gas flow of the cylinder, gas velocity distribution,vortices and turbulence have great influence on combustion of the engine, and affect the performance of power, economy and emission, which is key to an engine performance design. Based on the macroscopic concept of empirical extrapolation method, the traditional design method needs repeated shakedown test, comparisons, semiempirical analysis to various kinds of "lumped" parameters and cut-and-try procedures,etc. Problems such as expensive, long cycle, low applicability and unobvious effect become increasingly evident. How to use the modern design theory and method to study gas flow characteristics in the engine is one of the challenging subjects now. Numerical simulation used to research flow characteristics of ports, not only can get the overall merit parameters, but also can get the microscopic information and provide important basis for port optimization design.Researched on 125 engine intake system,the three dimensional flow model is created in this paper.Through Fluent software,finite volume method and unstructured grid with local encryption technology were used.Flow characteristics of intake system and flow velocity,pressure and turbulent kinetic energy distribution were analyzed in this paper. The numerical results are in good agreement with the measurement in the test rig,which has proved the validation of numerical simulation model. Comparisons and analyses of flow characterists among different lifts,different grid models and different turbulent models are made. Some conclusions have been deduced that the accuracy of the calculation can not be evidently improved by increasing the grid units,while using RNG k-εturbulent model the flow of the largly curved streamline can be handled better and the results are preciser. Based on these results, the local optimization and simulation analysis of the intake port were made in this study and reversed flow in the inside of the bending segment was eliminated, which increased the minimum circulation area and lowered the intake resistance. As a result, the flow coefficient of the intake port was greatly increased. The research results is good for unsderstanding the law of air flow in cylinder of engine deeply, Which has provided powerful basis of intake system optimization and has an important theoretical and practical value.