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Technical analysis of high pressure common rail of diesel engine - high pressure injector

- Sep 10, 2018 -

Technical analysis of high pressure common rail of diesel engine - high pressure injector


The function of the injector is to control the opening and closing of the solenoid valve to inject the fuel into the combustion chamber with the best injection timing, quantity and rate according to the control signal of ECU.

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Physical diagram of high pressure common rail injector for diesel engine


The structure of the injector can be divided into three functional components: orifice nozzle, hydraulic servo system and solenoid valve.

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Anatomy of injector for high pressure common rail diesel engine

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Physical diagram of high pressure common rail injector for diesel engine

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Structure of High Pressure Common Rail Injector for Diesel Engine-Coil Power Off: Ball Valve Closing Control Cavity Pressure + Needle Valve Spring Pressure > Needle Valve Cavity Pressure

The fuel comes from the high-pressure oil circuit, flows to the nozzle through the channel, and flows to the control chamber through the throttle orifice. The control chamber is connected to the fuel circuit through a drain hole controlled by the solenoid valve.

When the orifice closes, the hydraulic pressure acting on the control piston of the needle valve exceeds its force on the pressure-bearing surface of the injector needle valve. As a result, the needle valve is forced to enter the valve seat and isolate the high-pressure passage from the combustion chamber.

When the solenoid valve of the injector is triggered and the hole is opened, the pressure in the control chamber decreases. As a result, the hydraulic pressure on the piston decreases. Once the hydraulic pressure drops below the pressure acting on the pressure surface of the needle valve of the injector, the needle valve is opened and the fuel is injected into the combustion chamber through the hole. This non-direct control of the nozzle needle valve uses a hydraulic pressure amplification system, because the force needed to quickly open the needle valve can not be directly generated by the solenoid valve, the so-called control function of opening the needle valve is through the solenoid valve to open the orifice to reduce the pressure in the control chamber, thereby opening the needle valve.

In addition, the fuel also produces leaks at the needle valve and control plunger, controls and leaks the amount of fuel, through the connection back to the fuel pipe, together with the high-pressure pump and pressure control valve back to the fuel tank.

Electronic controlled injector; static resistance: 230 milliohm;


Principle of High Pressure Common Rail Injector for Diesel Engine-Electromagnetic Valve on Power: Ball Valve Opening, Oil Drain Control Cavity Pressure of Drain Hole + Needle Valve Spring Pressure < Needle Valve Cavity Pressure

When the solenoid valve of the injector is not triggered, the small spring presses the ball valve of the electric drive to the release control hole and forms the common rail high pressure in the control cavity; similarly, the common rail high pressure is formed in the nozzle cavity, and the pressure of the common rail pressure on the control plunger end surface and the pressure of the nozzle spring are equal to the opening pressure of the high pressure fuel acting on the cone surface of the needle valve. Keep the needle valve closed.

Fuel injection start state: When the solenoid valve is triggered, the electric drive opens the oil outlet, and the fuel flows from the valve control chamber to the upper cavity (returning to the tank through the return pipeline), which reduces the pressure in the control chamber, reduces the force acting on the control plunger, and then the nozzle needle valve is opened and sprayed. The oil starts to spray.

Fuel injection end state: Once the solenoid valve is not triggered by power failure, the small spring force will make the solenoid valve drive down pressure, the ball valve will close the leak hole; after the leak hole closes, the fuel from the inlet hole into the control room to establish the oil pressure (this pressure is the rail pressure), the high pressure on the control plunger end surface, the rail pressure plus bullet. The spring force is greater than the pressure on the cone surface of the needle valve, so that the nozzle needle valve is closed.

Injection response = solenoid valve response + hydraulic system response should generally be 0.1 ms ~ 0.3 ms (injection rate control requirements)