Electrical Injector on Common Rail System

Electrical injector is the most important and complicated component on common rail system. It injects the furl in high pressure common rail into combustor of diesel engine at the best injection timing, injection quantity and injection rate through controlling magnet valve of-off based on the signal sent by ECU. 

 

To realize concerted injection shape, injector requires reasonable optimal design. Volume of cabinet decides the sensitivity of needle valve during on. If volume of cabinet is over large, needle valve cannot cut off fuel after injection, resulting in bad fuel atomization. If volume of cabinet is too small, it cannot provide enough effective stroke to needle valve, increasing fluid resistance during injection. Therefore, volume of cabinet should be chosen according to the maximum injection quantity. 

 

Moreover, the minimum injection pressure of electrical injector depends on flow rate of hole of oil return and input and area of end face of control piston. After confirming structural dimension of oil return, inlet and cabinet, stability of needle for full on and the minimum injection process are also worked out, so as to the minimum injection quantity of injector. Reducing volume of cabinet can accelerate response rate of needle valve, reducing the impacts on injection quantity caused by fuel temperature. 

 

However, volume of cabinet cannot be reduced without limitation. It must ensure lift of needle valve on injector so that needle valve can be full on. Two metering holes decide the dynamic pressure inside cabinet, and decide motion law of needle valve further. Controlling discharge coefficient of the two metering holes can produce ideal injection characteristics. 

 

Due to extremely high injection pressure in common rail system, the sectional of office on injector is quite small. For example, the diameter of office of injector provided by BOSCH is 0.169mm×6. For such small office diameter while such high injection pressure, fuel flow is quite unstable. Spray cone angle of oil becomes larger and fuel atomization became better but penetration distance is shorter. Nevertheless, inlet vortex intensity and structure of combustor on diesel engine should be changed to ensure the best burning process.  

 

For magnet valve on electrical injector, common rail system requires it to have enough opening rate. Because of pilot injection is the best injection way to improve performance of diesel engine, response rate of magnet valve should be fast as much as possible.