| Along with the progress of the technology, the study on the character and movement rule of fluid is going more and more deeply. As the fluid is in the section with complex boundary figure, the measure for it is very hard. In addition, due to the limitation of physical model test, the experiment can only afford the parameter for whole flow, while the numerical simulation can offer the detailed information for correlative flow. Because of the strong points in numerical simulation, it has become an effective means for research of fluid-related machinery.FLUENT is one of business software that used to simulate the compressible fluid. With its application to the flow field of injector, we can get the total distribution of each fluid parameter. The computation with FLUENT is simple, fast and convenient and the precision is fine. It not only can simulate laminar flow and turbulence but also can simulate incompressible viscous flows and compressible flows, so it has great practicability.The three-dimensional numerical simulation for the compressible flow inside the nozzle tip was processed by using CFD (Computation Fluid Dynamic) FLUENT software. The study showed that there is less pressure loss in seal seat surface with 90°anger compared with 60°anger; as the inject pressure become higher, the discharge coefficient of the nozzle become smaller; the discharge coefficient would become larger if the fillet of nozzle applied, which will help to reduce the pressure lose caused by high inject pressure. The result of a strengthen high-speed diesel contains the nozzle of this product in more than 220 thousand km of the practical application indicates that the needle valve significantly reducing the rate of failure, and reliability of its work, a substantial increase in life.
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