Research On Fuel Injection And Leakage Characteristics Of Common Rail Injector

This paper takes BOSCH CRI2.0 injector as the object,which is applied in a small and medium power engine,to study on the variation law of injection characteristics and leakage characteristics of common rail injector.Firstly,according to the structural characteristics of common rail injector,this paper analyses the principle of its operation,and redesigns the test combining with the shortcomings of previous studies,which can only make indirect qualitative measurements for injector couples and is unable to obtain actual leakage of needle valve and control plunger.The fuel injection quantity under different pulse width and different rail pressure is measured on high pressure common rail fuel injection platform.The leakage characteristics test realizes the independent measurement of plunger and needle valve occasional static leakage and the total dynamic leakage measurement.Secondly,through reasonable hypothesis,the simulation model of common rail injector is built in one-dimensional hydraulic fluid software AMESim,and the model is verified by the test results.The results show that the simulation and experiment has high precision in the study of fuel injection characteristics.The overall trend is the same in the study of leakage characteristics,but there is a greate error between the experimental value and the simulation value.And we also analyz the relationship between rail pressure,pulse width and injection quantity and leakage.Then based on the simulation model of the injector,we choose the evaluation index of fuel injection characteristics and study serval parameters such as the diameter of the oil inlet hole,the diameter of the oil outlet hole,control chamber volume,orifice diameter,and valve spring preload influence on the injection characteristics.Combine with annular leakage formula,we take the leakage rate and the maximum leakage rate as indicators and analyze the influence of structural parameters on the leakage characteristics.Finally,considering that the fuel injection and leakage of common rail injector are not independent,and there is a certain coupling and mutual influence between them.So we use the method of orthogonal array design and select injector accessory clearance,control chamber inlet,outlet hole diameter,valve spring preload,control plunger diameter as five improtant factors,which are divided into four levels respectively in this paper.This parameters are optimal designed for increasing fuel injection rate in single cycle of injector and reducing the static and dynamic leakage rate.The results show that the neddle valve maximum static and dynamic leakage rates is reduced by 40.68% and 38.54% respectively,the control plunger maximum static and dynamic leakage rate of the plunger is reduced by 42.4% and 38.53% respectively.