Abstract: The movement of needle valve in the common rail injector determines the injection and atomization effect directly. The movement rule of needle valve in the common rail injector is important to improve the structure of injector and the atomization effect. A high-pressure common rail injector simulation system was built, and a calculation model was established for optimizing the flow coefficients in two stages of cavitation and non-cavitation at the oil inlet and outlet holes of high pressure common rail injector and in the ball valve area. The movement characteristics of needle valve in the common rail injector are studied through theoretical analysis and experiments. The results show that the opening process of needle valve can be divided into two stages: slow opening stage and fast opening stage. Two opening stages of needle valve are due to the transfer of the throttled position. However, the needle valve is mainly influenced by the throttled position, so the closure of the needle valve is a single-stage. Rail pressure has an effect on the second fast opening stage, but not on the slow opening stage or the closing process. The opening process speeds up with the rise of the rail pressure. When the rail pressure reaches to a certain value, the fast opening stage of needle valve remains unchanged. Key

Key words: powermachineryengineering, dieselengine, commonrailinjector, needlelift, hydraulicprocess