		System components - Fuel injector
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Combustion

Fuel injector

The task of the fuel injectors is to inject the fuel into the relevant cylinder at high pressure. The injection timing point and the injection period, and therefore the injection quantity, are determined by the following factors:

Actuation duration of piezoceramic element
Nozzle needle opening/closing rate
Needle lift
Nozzle geometry with 7-hole nozzle module (model 211)
Nozzle geometry with 8-hole nozzle module (models 164 and 251)

Fuel return line with fuel injector

1 Restrictor in T-fitting

60/1 Actuator module

60/4 Coupler module

60/7 Valve group

60/10 Nozzle module

60/13 Fuel return line

60/14 Connection bushing

60/15 High pressure line connection

Y76 Fuel injector

Injector leak-off fuel/diverted fuel quantity

Fuel injector starting Position

Engine OFF
The injection system is full of fuel, but is unpressurized (atmospheric pressure). The valve spring of the valve group holds the valve pin, the nozzle spring and the nozzle needle closed. Injection does not take place.

Engine ON
The fuel rail pressure produced by the high pressure pump is present via the fuel rail at the injector, and therefore at the nozzle needle, and via the feed restrictor in the control chamber. The nozzle needle remains closed due to the pressure. Injection does not take place.

Fuel injector start position

50/1 Valve pin

50/2 Outlet restrictor

50/3 Control chamber

50/4 Feed restrictor

50/5 Bypass

50/6 Nozzle needle

50/7 Nozzle spring

Fuel injector function

Needle opens
When the piezo actuator is energized, it becomes longer, presses on the valve pin via the coupler module and closes off the bypass. The outlet restrictor causes the pressure in the control chamber to drop, the nozzle needle opens and injection commences. The opening speed of the nozzle needle is defined by the ratio between the cross sections of the outlet and feed restrictors. The diverted fuel quantity travels via the fuel return line back to the tank. The injection period and injection quantity are determined by holding the actuation voltage

Needle closes
The piezo actuator is discharged and becomes shorter. The valve pin opens the bypass and closes off the control chamber. Via the outlet restrictor, the feed restrictor and the bypass, the pressure in the control chamber rises to the level of the fuel rail pressure and the nozzle needle closes. Injection is complete. The application of fuel rail pressure to the control chamber via the feed restrictor, the outlet restrictor and the bypass simultaneously causes the needle to close particularly quickly.