Research On Flow Performance Of Injector Control Valve Of High-pressure Common Rail System Based On Test Verification

The delayed hydraulic response within the injectors of the common rail system affects the in-cylinder combustion performance of diesel engines.The flow performance of the control valve is one of the factors affecting the injector hydraulic response,while the main factors affecting the flow performance of the control valve are cavitation and its structural parameters.Due to the high-pressure difference between the import and export and its narrow structural features at the throttle,the transient movement of the ball valve will inevitably lead to cavitation in the control valve,seriously affecting its flow performance.Cavitation may also induce cavitation on the surface of the ball valve and its sealing surface and cause vibration,noise,affecting the safe and stable operation of the control valve.The diameter deviation of the control valve outlet orifice,which acts as a pressure relief channel during opening,has an extremely important influence on the flow performance.Due to the current cavitation and outlet throttle diameter deviation on the control valve flow performance of the law of less research,so the control valve cavitation suppression and outlet throttle tolerance design lack of the corresponding theoretical basis,making the control valve flow performance is difficult to ensure.This paper uses experimental probing,numerical simulation and theoretical analysis to analyze the influence law of system operating parameters and control valve structure parameters on injector hydraulic response characteristics.The cavitation flow characteristics and flow performance within the control valve are systematically studied,the mathematical expressions for the effect of the deviation of the outlet throttle diameter on the flow performance of the control valve at different rail pressures are obtained,the mechanism of the initial flow area around the ball valve and the cavitation strength on the flow performance of the control valve is studied,and the flow performance of the control valve is improved.The main research work and the innovative results achieved are as follows:In the study of the influence law of the system operating parameters and control valve structure parameters on the injector hydraulic response characteristics,the AMESim software was applied to establish a simulation model of the working process of the high-pressure common rail system.The calculation results of the model match with the test of the injection performance test system.The results show that the simulation model of the high-pressure common rail system established in this paper has a high degree of accuracy and can be used to study the influence law of the hydraulic response characteristics of the high-pressure common rail system.Based on the above model,the influence of the system operating parameters(rail pressure and control pulse width)and control valve structure parameters(inlet throttle,outlet throttle and ball valve lift)on the injector hydraulic response was analysed and the optimal selection range for each parameter was determined.In the study of cavitation flow characteristics and flow performance in control valves,the influence of the transient cavitation process on the hydraulic characteristics and flow performance of control valves has been elucidated,revealing the mechanism by which cavitation and control valve backflow characteristics are generated.The results of the study show that the area between the ball valve and its sealing seat surface is the main area where cavitation occurs,which is consistent with the control valve cavitation damage detection test results.As the generation of cavitation reduces the pressure in the area,fuel reflux occurs at the control valve outlet when the average gas phase volume fraction reaches a maximum,however fuel reflux inhibits the development of cavitation.Cavitation is effective in reducing the hydraulic shock to the ball valve and sealing surface,but can inhibit the flow performance of the control valve.This is due to the bubbles created by the cavitation phenomenon relieving the ball valve and sealing seat surface from fuel impact,but the gas phase can impede the flow rate of the liquid phase within the control valve,thus reducing the pressure relief rate of the control valve and reducing its flow performance.The reduced pressure drop in the control chamber in the presence of cavitation compared to the absence of cavitation is one of the reasons for the hydraulic delay in the opening process of the injector.In the study of the influence of the outlet throttle diameter deviation on the flow performance of the control valve,clarified the outlet throttle diameter deviation on the control valve cavitation characteristics and flow performance of the influence of the law,fitting the different rail pressure under the outlet throttle diameter deviation on the flow performance of the control valve mathematical expressions.The results of the study show that as the outlet throttle diameter increases,the outlet throttle pressure relief rate(average mass flow rate)increases and the control valve flow capacity increases;However,the consequent increase in the volume of the vapor in the valve(cavitation)inhibits the flow capacity,although its effect is minor.As the rail pressure increases,the influence of the outlet throttle diameter deviation on its flow performance increases.Based on this,a fitting function is proposed to calculate the effect of the deviation of the outlet throttle diameter on the flow performance at different rail pressures.As bench test verification is not currently possible,the results are verified in this paper using a one-dimensional model.In the study of the influence of the initial flow area around the ball valve and cavitation strength on the flow performance of the control valve,the mechanism of the initial flow area around the ball valve and cavitation strength on the flow performance of the control valve is revealed,and the method of controlling the cavitation flow and flow performance by a stepped briquette structure is proposed.The results of the study show that the reduction in cavitation intensity further increases the fuel flow rate,which in turn decreases the pressure,thus exacerbating the cavitation phenomenon,and these changes form a cyclical process.The stepped pressure block structure further inhibits the increase in the low-pressure area between the ball valve and its sealing surface,reducing the occurrence of cavitation and providing the control valve with better resistance to cavitation,thus improving the flow performance of the control valve.The reduction of the initial flow area around the ball valve effectively inhibits the increase in cavitation caused by the increase in rail pressure.