The fuel then flows through the center passage of the plunger. During the remainder of the downstroke, the fuel flows through the lower port. This sudden release of pressure causes the fuel to hit the deflector (spill) with a high force. The deflector (spill) protects the housing nut of the fuel injector from erosion (wear) due to the force of the released fuel. During the return stroke (upstroke), the chamber inside the injector barrel is filled with fuel again.
The plunger can be turned by the rack while the plunger is being moved up and down by the rocker arm. The rack is engaged with the gear on the plunger. When the rack moves, the rack turns the plunger through the gear. The rotation of the plunger controls fuel injection timing and the fuel output of the fuel injector. The rotation of the plunger changes the relationship between the scrolls on the plunger and the ports in the barrel.
By changing this relationship, the length of the effective stroke can be increased or the length of the effective stroke can be decreased. Also, the timing of the fuel injection is changed.
When the rack is moved all the way inward against the fuel injector body, no fuel injection takes place during the downstroke of the plunger. This is the FUEL-OFF position. A small amount of outward rack movement is used as a movement of no fuel or OFF position for governing purposes. The distance of no fuel starts at the ALL THE WAY INWARD position of the rack. The distance of no fuel ends when the lower scroll opens the lower port and the upper scroll closes the upper port. Fuel rack movement in the fuel-on direction produces an interval in the plunger stroke when both ports are closed by the scrolls and fuel injection takes place. As the rack is moved farther in the fuel-on direction, the quantity of fuel during the fuel injection stroke increases until a maximum is available at full rack movement.
The scrolls on the plunger are used to establish the start of fuel injection. The scrolls are also used to set the amount of fuel per fuel injection stroke. The scrolls can change the start of fuel injection in relation to the engine's piston position. The scrolls can also change the length of the effective stroke in relation to the various engine loads. This is known as fuel injection with a variable beginning and a constant ending. The start of fuel injection will change with a decrease or an increase in fuel injection output according to the engine's needs.
During the fuel injection stroke, fuel passes from the barrel chamber through a valve assembly. The valve assembly has a spring-loaded needle valve with a cone-shaped end which operates against a seat. The angle of the valve is slightly larger than the angle of the seat in order to achieve line contact. The valve opens at approximately 38100 to 44700 kPa (5530 to 6485 psi). The fuel flows from the chamber inside the barrel through drilled passages and grooves in the spring cage. Then, the fuel flows through passages around the guide section of the valve to the valve chamber. Here, the fuel pressure lifts the needle valve off the needle valve's seat. The fuel now flows through the fuel injection nozzle. After the fuel flows through the fuel injection nozzle, the fuel flows outward through the orifices into the combustion chamber.
A flat check valve is used above the needle valve. The flat check valve is used to prevent the combustion gases from entering the fuel injector. The combustion gases are under high pressure. If the needle valve is held open by small foreign particles for a moment between fuel injection cycles, combustion gases can enter the fuel injector. If combustion gases enter the fuel injector, damage can occur. The fuel injector operates with the flat check valve until the foreign particle is purged from the fuel injector. After the foreign particle is purged from the fuel injector, normal operation resumes.
The fuel injection nozzle of the fuel injector extends a short distance below the cylinder head into the combustion chamber. The fuel injection nozzle has several small orifices that are spaced evenly around the outside diameter. The fuel injection nozzle sprays fuel into the combustion chamber. The top surface of the piston has a shaped crater. The design of the piston and the shape of the crater causes rotation of the air as the air comes through the inlet valves into the combustion chamber. This rotation of the air improves the fuel air mixture.