Investigation On Cavitation Flow Characteristics Of Control Valve For High Pressure Common Rail Injector

High pressure common rail injector,which connects fuel supply and combustion,is a key component of high pressure common rail fuel system,and has become a complex and precise control fluid mechanical parts.The development of high-pressure common rail injector puts forward higher requirements for the improvement of ultra-high pressure injection,precision and response.As the core control part of the control valve,the complexity of its hydraulic process is more prominent.Therefore,it is of great practical significance to study the mechanism and control of cavitation flow in injector control valve of high pressure common rail system.In this paper,the cavitation characteristics in the control valve of high pressure common rail injector are numerically studied by means of computational fluid dynamics,which provides theoretical support for the design and development of a new type of high pressure common rail injector.Firstly,aiming at the internal flow and cavitation characteristics of high pressure common rail injector control valve,a three-dimensional two-phase flow cavitation numerical model of diesel engine injector control valve under high pressure was established based on time averaged Reynolds stress method,combined with single bubble dynamic cavitation model and mixed homogeneous two-phase flow model.The dynamic grid layer technology is used to simulate the opening and closing motion of the ball valve during the injection process of the common rail system,and the transient cavitation characteristics of the internal control oil circuit of the control valve are studied.With the help of the verified one-dimensional model,the accuracy of the three-dimensional simulation results of the control valve internal flow is verified.The results show that the data of the two models are in good agreement,and the three-dimensional cavitation model of the control valve can better capture the generation and development of internal cavitation morphology.Secondly,the influence of pressure and ball valve lift on the internal flow of control valve was studied,and the influence of common rail pressure on the average flow rate,mass flow rate and cavitation volume fraction in the control valve was explored.By co MParing the distribution of velocity and cavitation volume fraction in the control valve,the effects of transient unsteady process pressure and multiple injection interval on transient cavitation characteristics were studied.The results show that when the inlet pressure reaches 70 MPa or above in steady flow,the cavitation in the control valve is completely developed and is no longer affected by the pressure.The initial position of cavitation in the control valve is limited by the throttle position of the control valve.In the transient process,higher pressure will lead to faster cavitation development,and shorter multiple injection interval will make the cavitation generated in the previous process not completely disappear and continue to increase,which is not conducive to the stability of injector control.Finally,the influence of some structural parameters of the control valve on the transient flow and cavitation characteristics is studied.The mechanism of the shape of the outlet orifice and the inlet fillet on the flow in the orifice under transient conditions is explored.The influence mechanism of the valve seat structure on the cavitation at the sealing surface of the ball valve is studied by changing the valve seat angle.The results show that the oil outlet orifice with gradual contraction and inlet fillet transition can be effectively weakened The cavitation in the hole and the increase of the valve seat angle are not conducive to inhibit the development of cavitation in the control valve.