Injector(S), Fuel: Operation
The injector receives a single high pressure supply which, once inside the injector, is distributed in two distinct flows. One mainly supplies the nozzle and the other controls the pressure rod. Both of these flows also contribute to the lubrication of the injector's moving parts, thanks to consistent seepage present in an injection system that operates at such a high pressure. There is also recirculation, which is necessary to dissipate the diesel used to operate the pilot valve for channeling the seepage. The temperature of the diesel recirculated by the injector can reach very high levels 100 °C (212 °F). The recirculation systems must therefore be equipped with pipes that can withstand these temperatures. In order to better understand its operation, the injector may be considered as comprising two parts:
- 1. The actuator/nozzle, comprising the jet and pressure rod-pin assembly.
- 2. The control solenoid, comprising the solenoid and valve.
The volume inside the pilot valve and immediately above the actuator is known as the control capacity, and carries out a vital role in the operation of the injector. It is permanently supplied with diesel via a "Z" port (inlet) (4). The diesel flows out from this reservoir through a second "A" port (outlet) (2), whose opening is controlled by the control solenoid valve. The diesel contained in the control reservoir exerts a pressure that can be modulated and which acts upon the upper surface of the pressure rod, whose area is Ac; the force acting on this area therefore depends on the pressure within the control volume.
The actuator/nozzle comprises a jet with 7 openings at the end, for the output of diesel, and a pressure rod-pin assembly. The jet is supplied with pressurized diesel when the pressure rod-pin assembly is in the raised position. This is raised by an imbalance between the opposing forces acting on the assembly. There are three forces acting on the pressure rod-pin system:
- Spring force Fe exerted in the closing direction and created by the spring which acts on the pin; this force guarantees the seal of the nozzle when the line pressure drops to zero, avoiding the formation of drops of fuel in the cylinder.
- Force Fc which also acts in the closing direction; this is caused by the pressure of the diesel present in the control volume. This pressure acts on the upper area of the pressure rod.
- Force Fa exerted in the opening direction, created by the pressure of the fuel present in the supply volume and acting on the area of the circular crown marked out on the outside by the sliding diameter of the pin in the jet and on the inside by the sealing diameter of the conical housing.
The equilibrium of the pressure rod-pin assembly depends on the balance between these three forces; when the injector is not energized, the pressures in the supply and control volumes are identical and equal to the line pressure provided by the rail. In this condition: Fc + Fe > Fa.