Research On Sealing Performance Of Plunger In High Pressure Common Rail Fuel Injector

The plunger matching parts is a key component in injector,whose function is to control the opening and closing of the needle valve and maintain the high pressure of the control chamber.Therefore,it is very important to ensure the good sealing performance of the plunger matching parts.Due to the poor operating conditions,the plunger matching parts would not maintain the coaxial state.As a result,it is necessary to analyze the seal leakage characteristics of the plunger matching parts under different conditions and understand its leakage principle.The thesis takes the high pressure common rail injector as the research object,analyzes the characteristics of the plunger clearance oil film,then studies the seal leakage mechanism.On the basis of the Navier-Stokes equation,according to the working principle of the plunger pair,the pressure field model suitable for the oil film of the plunger pair clearance can be established.By geometric calculation,the thickness distribution of the oil film in the plunger's clearance is obtained.It is found that the larger the plunger tilt angle is,the more uneven the oil film pressure distribution is,and the larger the thickness of the inlet oil film is,the easier it is to generate the dynamic pressure support effect.Because there is a circumferential pressure gradient,the plunger clearance fuel has a circumferential flow.By solving the Reynolds equation,the velocity distribution of the clearance oil film flow field is obtained,and the plunger clearance leakage model considering the dynamic lubrication is established.The leakage rate decreases when the plunger is tilted.When the tilt angle is 0.013°,the leakage rate is reduced by 6.6% compared with the coaxial state.Considering that the plunger is tilted,the leakage rate is approximately proportional to the inlet pressure and is proportional to the plunger movement speed.Considering the viscous effect of the fuel,the viscosity at the outlet of the plunger is 7.6 mPa·s.When considering the viscous pressure effect at 160 MPa,78% of the leakage rate of the viscous effect is not taken into account,so the leakage rate is reduced.To analyze the influence of structural parameters of plungers on leakage and calculate the speed distribution and leakage rate of the plunger at different relative eccentricity.The increase of the relative eccentricity gives rise to the greater the maximum fuel flow rate and the leakage rate.When the relative eccentricity increases from 0.3 to 0.7,the leakage rate increases by 36%.The influence of pressure change in the plunger control chamber on the leakage is calculated,and the larger the inlet hole diameter is,the lower the pressure in the plunger chamber is,leading to the greater the leakage rate,and the plunger leakage rate is directly proportional to the control chamber pressure.When the plunger and plunger sleeve are coaxial,the heat-fluid-solid coupling model of the plunger matching parts is established.Regardless of the power lubrication,the plunger matching parts is optimized by using the ANASYS Workbench.The optimization effect of the two types of enhanced holes and equalization groove on the plunger clearance was analyzed.The results show that the two optimization measures reduce the plunger deformation to some extent and enhanced holes with taper have better optimization effect.We designed a test bench measuring plunger leakage to compare experiment data with the calculation results.The actual leakage was reduced by 12% relative to the calculated value the reason was the reciprocating movement of the plunger.After measuring the leakage rate of the plunger with enhanced holes,and it was verified that the enhanced holes with taper have a good optimization effect that the leakage rate is 0.0769 mL/s under 160 MPa,a decrease of 10%.