Numerical Simulation For Cavitation Flow In High-Pressure Fuel Injector

Along with the increasing requirements of diesel's power performance and emission quality,the growing development of the electronically controlled fuel injection technology and the rising improvement of the injection pressure,the cavitation phenomenon in the high-pressure nozzle has drawn wide concern.Cavitation has a significant effect on the performance of diesel engine.On the one hand,cutting down the effective flow area of nozzle orifice,it decreases the fuel quantity.On the other hand,it promotes the combustion of injection fuel and reduces the formation of soot by increasing the spray cone angle and atomization level.In the electronically controlled fuel injection system,the cavitation level is mainly determined by the structure of injector nozzle and the control law of needle valve.Worked on the cavitation flow characteristics by employing the the numerical method,used to discuss the influence of the structure of injector grooves and the control law of needle valve(the injection pulse and response speed of needle valve),this paper proposed a injector nozzle with grooves in the tip of needle valve,and this paper could make some contribution for control and optimization of cavitation,and provide important theoretical basis for high-pressure nozzle's design and structural optimization.Firstly,based on the method of RANS,this paper established the mathematical-physical model,which was applied in the calculation of nozzle internal cavitation flow.And then,This model is verified by the cavitation flow test of Winklhofer.The results showed that the model established can capture the internal orifice cavitation flow phenomena and flow parameters well,and the model can be used to do further study on the phenomenon of cavitation flow in high-pressure nozzle.Secondly,simulating the 3D transient flow process inside diesel injection nozzle and comparing the internal characteristics with common nozzle,the influence of grooves on cavitation flow in large fuel injection pulse width was analyzed.And the result showed that the initial cavitation of nozzle orifice strengthens in the degree,the cavitation bubble of nozzle combustion chamber increases and the decreased fuel quantity of injection caused by cavitation reduces by laser-making the grooves.According to the works above,to research the effects of groove structural parameters,this paper gave a further study on nozzle cavitation flow characteristics of different depth,number and inclination angle.It presented that in the particular control law of needle valve the positive impact is significant under the structure of depth 0.005 mm,inclination angle 0° and single groove.Finally,the influence mechanism of groove structure on cavitation flow was discussed under different control laws of needle valve,and the coupling effect of needle valve control laws and groove structure on the key parameters of cavitation flow was analyzed in this paper.The result shows that changing the injection pulse width and response speed of needle valve makes different impacts of groove on cavitation flow;under the small injection pulse width,the response speed of needle valve has a great effect on the inside nozzle cavitation flow,while the influence of groove structure can be neglected;under the medium injection pulse width,the influence of response speed of needle valve and groove structure is almost equal;under the large injection pulse width,the groove structure has a evident effect on initial cavitation and atomization,and the response speed of needle valve has a considerable influence on fuel injection quantity.