Fuel Delivery Variation

Fig. 9 Fuel Delivery Variation:

The delivery is controlled by varying the effective stroke. This is done by the governor by means of the control rod, Fig. 9. The pressure chamber above the plunger is always connected to the chamber below the helix by means of the vertical groove in the plunger. The helix influences the fuel delivery. At bottom dead center fuel flows through the inlet port into the pump barrel. As the plunger rises, it closes the inlet port and forces the fuel through the delivery valve to the injection nozzle. At a specific point in the stroke the helix opens the inlet port in the barrel. The fuel in the pressure chamber now flows through the vertical groove, past the helix and through the inlet port in the barrel. This process is known as "spill" or port opening. After port opening the plunger no longer delivers any more fuel to the injection nozzle on its way to top dead center. The helix runs diagonally over the circumference of the pump plunger. The distance covered by the pump plunger until the moment of port opening depends on the position of the helix in relation to the inlet port. This position can be changed by turning the pump plunger.