| Intake and exhaust port are the key parts for the mobile engine .The helical intake port has great influence on diesel engine for air-fuel mixture formation , combustion and charge exchange .The contour of helical intake port is the most complicated .Therefore, the strict design requirements are needed .The flow characteristic of helical intake port has sensitively influence on diesel engine ,including economy performance ,dynamical performance and the level of injurant emission .Lately ,more and more requirememts for engine make the quality of the port to be improved.The design of port is depended on steady flow test to obtain swirl ratio and flow coefficient and use them to evaluate the performance of intake port. But these results can only token the macroscopical performance of the flow, it can't provide more information for the improvement of the port. The design depend on the designer's experiences. Using CFD to simulate the flow in helical port , it can achieve quantitative analysis and obtain the rule of pressure and velocity, obtain the influence of the structural parameter of port,valve and cylinder for the port design.The gas of the flow in port has high velocity. It can be considered compressible. The contour of the port is very complicated, it require more accurate computational grid. A numerical research has been adopted on the helical intake port for YC6108ZQ diesel engine with a CFD simulation tool FIRE who using finite volume method. The method can provide the design idea for the construction and improvement. At first the geometry modal of the helical modal is built. In order to ensure the precision of the contour of the helical port ,it can scan the sandy modal of the intake port using the three-dimensional coordinate scanner to obtain the figure of the sandy modal, it is called cloudy points. After amending using CATIA the geometry modal of the helical port has been obtained. The geometry modal is similar to practical intake port. The error is only within 0.2mm,it make for calculation.The important and difficulty question is the mesh of the computational modal. In practice the flow area in the engine has complicated outline ,it should ensure the consistent of computational area and practical area for the precision. The density and create of the computational modal are the key for the application of computational fluid dynamics in the practical work. According to these rules, the author mesh the computational modal. The max cell size is 0.015m,the number of whole intake port is about 560,000.The hex cells are most.Figure 1 mesh of intake port The computational area include not only intake port but also cylinder, as they have tight relation. The boundary condition should accord with the situation of the practical steady flow test. It considered the gas in the intake port as three-dimensional compressible gas. It provide the flow computational area with the pressure on inlet and outlet, but can't limit the size and the direction of the velocity on inlet and outlet boundary.The main computational work include:valve lift: 11.5mm,9.5mm,7.5mm,5.5mm,3.5mm,2mmpressure difference between inlet and outlet: 5.3kPa(550mmH2O)inlet temperature:293Kvalve lift: 11.5mm pressure difference between inlet and outlet: 5.3kPa(550mmH2O) inlet temperature:293K angle between two ports:45o(anticlockwise or clockwise)valve lift: 11.5mm pressure difference between inlet and outlet: 5.3kPa(550mm) inlet temperature:293K valve face angle: 45oThe main testing work include:1) steady flow test2) constant pressurepressure difference between inlet and outlet:5.3kPa;valve lift: 11.5mm,9.5mm,7.5mm,5.5mm,3.5mm,2mmThe conclusion are: It can get more detailed information about helical intake port, such as distributing of pressure,density,velocity,temperature,turbulence kinetic energy,viscosity by calculation at different valve lift. These rules can be used to design practical engine.Steady flow test validate the calculatio... |
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