Engine Operation 30 UENR0623-02 The ECM determines the quantity, timing, and pressure of the fuel in order to be injected into the fuel injector. The injector nozzle and control piston volume are continuously connected to the fuel manifold (rail) through the high-pressure fuel line. The nozzle needle is controlled by the control piston, which in turn is controlled by the pressure in the control piston volume. The injector contains a solenoid valve that controls the spill flow from the control piston volume. The control piston volume has an inlet throttle and an outlet throttle.
The sizing of the throttles determines the rate of pressure decay in the control volume and hence the rate of nozzle opening. By opening the solenoid valve, fuel flows out of the control volume lowering its internal pressure which allows nozzle pressure to lift the needle and control piston, this enables injection to occur. The ECM uses input from the sensors on the engine. These sensors include the speed/timing sensors and the pressure sensors. The ECM controls the timing and the flow of fuel by actuating the injector solenoid. The amount of fuel is injected is a function of fuel pressure in the fuel manifold and the duration of the signal to the injector solenoid.
The ECM controls the fuel pressure by increasing or decreasing the flow of fuel from the fuel injection pump. To end injection, the solenoid valve is closed. Closing the solenoid valve blocks off the control volume outlet orifice which causes the control volume pressure to increase. By increasing control volume pressure, this forces the control piston, and needle, back down until the needle reseats in the nozzle. The injection process ends. Fuel Injectors The needle valve has a close fit with the inside of the nozzle. This makes a positive seal for the valve. The electronic unit injectors can be instructed to inject fuel multiple times during the combustion process.
A close pilot injection occurs before the main injection. The close pilot injection helps to reduce NOx and noise. The main injection period helps to increase the torque of the engine. The after injection period helps to reduce the amount of smoke that is produced. Fuel Manifold Illustration 24 g02493878 Typical example (1) Electrical connections (2) Bolt (3) Clamp (4) Combustion washer (5) O-ring (6) Fuel inlet The fuel injectors contain no serviceable parts apart from the O-ring seal and the combustion washer. The clamp and setscrew are serviced separately. Illustration 25 g02493879 Typical example