An injector is one of the mechanical elements placed in the engine of a car acting as a fuel supply nozzle. The main function of the injector is to supply the most proper amount of fuel into the combustion chamber during the exact period. This function is directly related to the overall engine efficiency of the car. Accurate fuel injection is necessary to increase power and efficiency.
The injector consists of several parts, including needle, stopper, and armature. Also, the injector acts controlled by the Engine Control Unit (ECU). When the injector operates, the magnetic force generated by the solenoid coil lifts the armature and the needle from the closing position to the fully open position in the vertical direction. In the lifting motion, a horizontal force inevitably generates on the needle. The horizontal force is acting on a different position from the center of mass of the needle, so the needle produces the eccentricity and tilting motion during the lifting operation. This can result in wear between the needle and the armature, between the stopper and the inner surface of the injector, and in the ball area where the fuel is directly sprayed. This is also directly related to the efficiency of the injector, so the proper selection of the clearances of these parts can prevent the wear. In this study, the lubrication analysis is conducted to determine the optimum clearance of the parts having sliding motions inside the injector.
The height functions considering the dynamic behavior and relative velocity of all parts are derived. Using the derived height function, the pressure profiles are calculated for all lubrication surfaces from the Reynolds'' equations. Then, all the fluid reaction forces are calculated. The equations of motions applied to the calculated fluid reaction forces and external forces are finally solved to calculate the minimum film thickness between each part with the variation of the clearances. The optimum clearances are finally determined. The effect of the clearances on the behavior of the moving parts is presented and discussed.