BOSCH Fuel Injection - Diesel Type: Description
A fuel pump, which is driven by the injection pump, draws fuel from fuel tank. After passing through a pre-filter, fuel is forced through a main filter into suction chamber of injection pump. An overflow valve mounted to end section of injection pump suction chamber maintains permanent pressure on fuel in suction chamber which is supplied by fuel pump. At a minimum pressure of 11.7 psi (0.8 atm), surplus fuel at end of suction chamber flows back into fuel tank via overflow valve. In any case, fuel pump will deliver more fuel than is necessary for injection into engine in order to prevent bubble formation and to ensure that suction chamber is filled with pressurized fuel.
Plungers of four injection pump elements force fuel, contained in vacuum chamber, through injection pump pressure valves into injection lines, and from there to injection nozzles. Through injection nozzle, which operate at spray pressure ratings of 161.7 to 176.4 psi (11.0 to 12.0 atm), fuel reaches pre-chambers and finally, main combustion chamber of diesel.
Fuel leaking from injection nozzles is returned to fuel tank via a leakage line and fuel return line.
Control of amount of fuel injected is dependent upon position of accelerator pedal, and upon engine load and speed, and is affected by a governor (mounted to rear of injection pump).